A low pressure system deepened rapidly over the Atlantic just off the Carolina coast during the day on 01 April 2020. GOES-East water vapor imagery and RAP surface analysis provide a great visualization of the strengthening low as it progressed east away from the coast (Fig 1). Dry/warming descending air (warm colors) is evident wrapping around the low from the south, while ascending/cooling air (including deep moist convection) is obvious further east, north, and west of the low.
Figure 1: 01 April 2020 GOES-East 6.2 um Water Vapor Imagery and RAP MSLP analysis. Higher res
As the low strengthened, very gusty winds developed at the surface, prompting the issuance of a Hurricane Force Wind Warning by the NWS. HRRR model analyses indicate widespread wind gusts in excess of 50 knots wrapping around the southern and eastern portion of the low (Fig 2).
Figure 2: 01 April 2020 HRRR surface wind gust analysis. Higher res
GOES-East low-level DMWs, while not abundant nearest the center of circulation where cloud streets developed and winds were likely strongest, did produce several wind vectors over 50 knots near the low center, indicating strong flow just above the surface.
Figure 3: 01 April 2020 GOES-East 0.64 um VIS, 600 mb – SFC DMWs. Higher res
METOP-B ASCAT observed surface winds in excess of 50 knots wrapping around the western portion of the low between 1500 and 1600 UTC (Fig 4a). Later between 1800 and 1900 UTC, AMSR2 measured surface wind speeds between 50-60 knots on the western portion of the low, and 40-50 knots wrapping around the southern quadrant, between 18-19 UTC (Fig 4b).
Figure 4a: 01 April 2020 METOP-B ASCAT surface wind speed. Higher resFigure 4b: 01 April 2020 AMSR2 surface wind speed (knots). Higher res
An area of clearing was present adjacent to deep moist convection near the low center during the morning hours after sunrise. GOES-East visible (0.64 um) imagery captured rough seas (white caps) and associated/implied sea spray under the clear skies, confirming gusty winds reaching the surface during that period (Fig 5). The white caps/sea spray is diagnosed by regions of higher reflectance compared to nearby calmer seas. A modified gray-scale colortable is utilized in order to best highlight the white cap/lofted sea spray signature.
Figure 5: 01 April 2020 GOES-East 0.64 um VIS. Higher res
A zoomed in feature following animation provides an alternative means for viewing the evolution of the white caps through the morning (Fig 6). The phenomenon is most prolific extending south and east from the region of thunderstorms in the center of the scene.
The longer wavelength 0.865 um imagery provides better contrast for detecting the white caps (compared to clear sky calmer seas) given less influence of atmospheric aerosols compared to at the shorter wavelengths (Fig 7). However, spatial resolution is degraded by 4x compared to the 0.64 um channel with ABI, reducing clarity of the feature.
Figure 7: 01 April 2020 GOES-East 0.856 um VIS. Higher res
The white caps can be diagnosed in the snow-cloud RGB as regions of bright blue (Fig 8).
Finally, the milky appearance of the white caps was easily apparent in the Geocolor (true color) imagery (Fig 9).
Figure 9: 01 April 2020 GOES-East Geocolor imagery. Higher res
A longer feature following animation shows white caps and sea spray continued along the southern portion of the low center into the afternoon and early evening hours (Fig 10).
A remarkable shortwave trough brought widespread strong to severe thunderstorms to the Mississippi River Valley region during the day/evening of 28 March 2020.
GOES-East 6.2 um water vapor imagery with RAP field overlays provides an excellent view of the synoptic setup and evolution during this event (Fig 1). Features such as the positions of the low and upper level jet core as depicted in model analyses (such as the RAP here) are confirmed/corrected through analysis of the water vapor imagery.
Figure 1: 27-29 March 2020 GOES-East 6.2 um water vapor imagery, glm FED, RAP MSLP (dotted white contour), 500 mb height (solid white contour), and 130 knot 300 mb jet (yellow contour). Higher res
Focusing in on the Midwest, convection developed along a dryline and warm front, with thunderstorms eventually producing large hail and tornadoes. The GOES-East Split Window Difference (SWD) and Infrared Window Combo imagery (available on the STOR) captures the evolution of the dry air north and east around the southeast portion of the deepening cyclone, and convective initiation along it’s leading edge (Fig 2). The GOES imagery provides better horizontal spatial and temporal resolution when compared to surface observations and surface analyses (hourly RAP surface equivalent potential temperature shown here). The simple gray scale color table of the SWD shows relatively dry low-level air as darker gray, with relatively moist regions lighter gray. An overlay of IR window is provided for cold brightness temperatures (clouds) as non-gray colors). The dry air is diagnosed surging northeast through eastern Kansas into northern Missouri and southern Iowa. Convection develops along the dryline, as diagnosed in the SWD imagery, across Iowa.
Figure 2: 28 March 2020 GOES-East split window difference (gray scale), IR window for cold BTs (non-gray color scale), RAP surface equivalent potential temperature (white contours), RAP surface wind field. Higher res
While the GOES-East TPW derived product also captured the punch of drier air northward and dryline boundary evolution (at lower spatial res), the CAPE product only ever shows values less than 500 j/kg (Figs 3 and 4). This is lower than what was observed by radiosondes and what was computed by model analyses and the SPC mesoanalysis.
Figure 3: 28 March 2020 GOES-East VIS, TPW. Higher resFigure 4: 28 March 2020 GOES-East VIS, CAPE. Higher res
One-minute imagery from GOES-East was available across the region during this event. Day Cloud Phase Distinction 1-min imagery showed deepening cumulus clouds along the dryline, with a transition from cyan to green indicating glaciation and imminent convective initiation (Fig 5). Continued vertical growth and transition to yellow and red colors indicates further glaciation and cooling of cloud tops, and that convective initiation has occurred. Shortly thereafter, the first lightning flashes occurred with these storms per GLM FED data. FED values then increase quickly leading up to the first reported tornado. All of this is apparent in real-time given the very low latency (<1-min) of the 1-min imagery.
Figure 5: 28 March 2020 GOES-East 1-min Day cloud Phase Distinction RGB, GLM FED, Tornado LSR symbol. Higher res
Polar passes from SNPP (x2) and NOAA-20 meant three VIIRS images within about a 1.5 hour timeframe. This imagery provided higher spatial detail in the cloud field as convection began to initiate along the dryline. Day Cloud Phase Distinction RGB imagery created from the VIIRS 375 m I bands allows for the diagnosis of highly detailed glaciation trends in the cloud field (Fig 6).
Figure 6a: 1812 UTC 28 March 2020 I-Band VIIRS Day Cloud Phase Distinction RGB. Higher resFigure 6b: 1903 UTC 28 March 2020 I-Band VIIRS Day Cloud Phase Distinction RGB. Higher resFigure 6c: 1954 UTC 28 March 2020 I-Band VIIRS Day Cloud Phase Distinction RGB. Higher res.
Further south, strong thunderstorms developed within the broader cloud shield over northeast Arkansas, with one storm producing a tornado that caused damage and injuries across Jonesboro, AR. GOES-East 1-min visible imagery with GLM semi-transparent overlay shows increasing visible texture through the broad cirrus shield as the storm approaches Jonesboro from the southwest (Fig 7). FED values increase quickly as well just prior to/during the development of a tornado, with MRMS low-level rotation tracks confirming significant rotation as the storm advanced through the town.
Figure 7: 28 March 2020 GOES-East 0.64 um VIS, GLM FED, MRMS 60-min LL rotation track. Transparency of FED decreases slightly with increasing FED from near 100% at the lowest values to around 70% at the highest values. Higher res
Low clouds quickly expanded across the central high plains during the overnight hours of 25-26 March 2020 as low-level easterly upslope flow associated with a surface lee trough drove moisture into the region (Fig. 1). GOES-East Nighttime Microphysics RGB imagery highlighted the westward expansion of low clouds (cyan) through the evening, along with the evolution of other cloud layers such as high cirrus clouds (red or black), and mid level clouds (green and dark yellow). This RGB was modified slightly to account for the colder airmass (reduce warm end of the blue IR component).
The animation transitions to the Day Cloud Phase Distinction RGB after sunrise to allow for continued cloud classification. The transition procedure can be found on the STOR VLAB page. The clouds still appear as cyan, with high level cirrus clouds shades of yellow and red, surface snow is green, and bare ground dark blue. This RGB was also modified slightly to account for the colder airmass (reduce warm end of red IR component) and low light conditions (reduce high end of VIS and NIR components). The low clouds progressively erode during the morning, and completely dissipate by early afternoon.
Figure 1: 26 March 2020 GOES-East Nighttime Microphysics RGB to Day Cloud Phase Distinction RGB Transition Imagery over the central High Plains. Better res
A widespread sea stratus event evolved across the Gulf of Alaska and into adjacent inner channels from 3/15 – 3/16 as broad high pressure established itself over the region above favorable low level moisture. Forecasters at the NWS WFO Juneau office noted their use of GOES and VIIRS imagery together to aid in tracking the evolution of low clouds during this event, along with an associated drizzle threat at the surface beneath the stratus.
GOES-West full disk water vapor imagery revealed an omega block setup over the Gulf of Alaska, with low pressure on either side of the Gulf of Alaska high pressure (Fig 1).
Figure 1: 15-16 March 2020 GOES-West 6.2 um water vapor imagery. Higher res
Both GOES-17 imagery and VIIRS imagery were used by forecasters in decisions of whether or not to include lower CIGs/VIS conditions in the 18Z TAFs. These decisions impacted local pilots whose ability to fly depended on the extent of the lower cloud bases. Forecasters also used GOES and VIIRS imagery in combination with other datasets to provide DSS to core partners regarding low cloud evolution. For example, Forest Service called the office inquiring about if and when the low clouds were going to lift in a certain area as they needed to take a helicopter to a mountain top to service infrastructure. Forecasters were able to give them some guidance on if it would lift and what the ceiling could be if it did by using a combination of area cameras, recent trends in satellite data, and model data.
Analysis of GOES-West full disk Nighttime Microphysics RGB imagery at night transitioning to Day Cloud Phase distinction RGB imagery during the day on the 16th reveals the wide swath of low cloud cover over the Gulf, and expansion of clouds east into the inner channels (Fig 2). The IR components to the RGBs were modified slightly to account for the cooler airmass (lower the warm end by 10-20 C). At nadir, the ABI bands in the nighttime RGB have 2 km spatial resolution, while the Day RGB components have 0.5, 1, and 2 km resolutions. However, at the latitude of the Gulf of Alaska, pixel size is approximately 3-4x larger.
Figure 2: 15-16 March 2020 GOES-West Nighttime Microphysics RGB transition to Day Cloud Phase Distinction RGB Imagery. Higher res
Overnight 375 m I band VIIRS fog difference (11.4 um minus 3.7 um) imagery provides a much higher resolution (spatially) of the low clouds, with three subsequent passes showing expansion of the low clouds east into the inner channels (Fig 3). Cloud edges and smaller scale cloud features are more easily diagnosed in the more detailed VIIRS imagery compared to GOES. During this 1.5 hour period of time, low stratus spread around PAGS and into PASI and PAGN weather observation sites. Recall the VIIRS I bands (0.64 um, 0.86 um, 1.6 um, 3.7 um, 11.4 um) and associated multispectral products provide the highest resolution (375 m), while the M bands and associated products provide a lower 750 m.
Figure 3: 16 March 2020 SNPP and NOAA-20 VIIRS 375 m I Bands 11.4 um minus 3.7 um nighttime fog difference imagery. Dark gray – low clouds, moderate gray – clear sky, light gray – high clouds. Higher res
Day cloud Phase Distinction RGB imagery from VIIRS provides a similar higher resolution look at the extent of the low clouds during the day (Fig 4). Localized low cloud cover is diagnosed spreading south over PAPG during this 1.5 hour time frame. This RGB utilizes three I bands, so provides 375 m resolution.
Figure 4: 16 March 2020 SNPP and NOAA-20 VIIRS 375 m I Bands Day Cloud Phase Distinction RGB (11.4 um, 0.6 um, 1.6 um). Cyan – low clouds, yellow/red – high clouds, green – snow on ground – very dark blue – surface water. Higher res
Forecasters specifically noted the value of the periodic high resolution and low parallax VIIRS imagery for this type of event in order to get a better representation of cloud type. In AWIPS, they will view the GOES imagery with VIIRS overlaid, taking advantage of the strengths of both data sources.
Bill Line (NESDIS and CIRA) and Aaron Jacobs (NWS WFO Juneau)
A Kona Low established itself west of Kauai on 16 Mar 2020, driving anomalously high levels of tropical moisture (TPW of 1.5″ to 2.0″) into the region. GOES-West full disk water vapor imagery showed the tightly wrapped low set up west of the Hawaiian Islands and only slowly moving east from late on the 15th through the 16th (Fig 1).
Figure 1: 16 Mar 2020 GOES-West Water Vapor Imagery with GFS 500 mb height contours. Higher Res
The Advected Layer PW product combines temperature and moisture information from multiple polar-orbiting satellites to provide a 4D structure of moisture in the atmosphere. In this case, the blended product shows deep moisture from the tropics wrapping around the low and over Hawaii in all layers (Fig 2).
Figure 2: 15-16 Mar 2020 CIRA Advected Layer PW product. Higher Res
The increased moisture and forcing associated with the low resulted in the development of persistent showers thunderstorms over/near the islands during the previous evening through the day. These storms produced heavy rain and gusty winds, leading to the issuance of a Flash Flood Watch for the state, a Flash Flood Warning for the island of Kauai, and multiple Special Marine Warnings for gusty winds.
The development and evolution of deep convection near the islands around the sunrise period is shown in an IR to VIS/IR Sandwich transition loop (Fig 3). Prior to sunrise, the animation shows IR alone, while after sunrise, the animation includes the high texture of the VIS in combination with the IR. The most impressive convection is diagnosed developing near and northeast of Kauai.
Figure 3: 16 Mar 2020 GOES-West IR imagery to VIS/IR Sandwich transition. Higher Res
Visible imagery combined with semi-transparent GLM after sunrise reveals periodic lightning flashes associated with the convection, but with relatively low density (Fig 4). Surface obs indicated measured peak wind gusts of 38 knots associated with these thunderstorms. Hawaii is in the southwest corner of the GOES-West PACUS sector, meaning 5-min imagery is always available over the islands.
Figure 4: 16 Mar 2020 GOES-West Visible imagery with GLM FED overlay. Higher Res
Substituting visible imagery for the Day Cloud Phase Distinction RGB provides more insight into cloud makeup with this event (Fig 5). It provides a contrast between low liquid clouds (cyan) and high ice clouds (red and yellow), with convective cores (textured red/yellow) still apparent due to the contribution of texture from the 500 m VIS.
Figure 5: 16 Mar 2020 GOES-West Day Cloud Phase Distinction RGB imagery with GLM FED overlay. Higher Res
The Kona Low remained in place west of Hawaii on the 17th, continuing to drive moisture northward and resulting in persistant thunderstorm activity over and near the state. Given the continued thunderstorm flash flood threat, WFO Honolulu requested and was granted a long-duration (36 hours) GOES-West meso sector (2) to provide 1-min satellite imagery over the region. Ninety-minutes of 1-minute visible imagery from the morning of the 17th, with semi-transparent GLM FED overlay, shows the most robust thunderstorm activity developing south of the islands (Fig 6). The very high temporal resolution imagery with very low latency provides forecasters a valuable tool for diagnosing newly developing updrafts and tracking their evolution, particularly over the ocean far from radar coverage.
Figure 6: 17 March 2020 GOES-West 1-min VIS and 5-min GLM FED accumulation (updating every 1-minute). Higher res
The Kona Low stuck around west of Hawaii through Thursday night, when it finally lifted to the northeast and exited the region as a broad upper trough/closed low approached from the west. Hourly GOES-West Water Vapor imagery from Sunday morning thorough Friday morning shows the evolution of the upper low and associated lightning activity (GLM FED) through the week (Fig 7). The continued flux of tropical moisture and development of convection near/over Hawaii is apparent in the imagery. As the late week trough approaches from the west, the Kona low lifts northeast within the increasing southwesterly flow.
Figure 7: 15 – 20 March 2020 GOES-West 6.2 um hourly water vapor imagery and 5-min GLM FED. Higher res
A potent upper level low pressure system traversed across northern Africa on 12 March 2020, causing the development of strong winds at the surface. Water Vapor imagery from EUMETSAT Meteosat-8 shows the compact low advancing east across Egypt on the 12th, with gravity waves emanating southward across bordering countries (Fig 1).
Figure 1: 12 March 2020 EUMETSAT Meteosat-8 6.2 um water vapor imagery. Higher res
The windy conditions at the surface resulted in a broad area of blowing dust across much of the northern half of the continent. The EUMETSAT Meteosat-8 satellite captured the lofted dust as it was carried south and west away from the low and over a long distance. The thick layer of lofted dust was captured well in both the 0.6 um VIS (Fig 2) and 10.8 um IR Window (Fig 3) single-band imagery.
Figure 2: 12 March 2020 EUMETSAT Meteosat-8 0.6 um visible imagery. Dust is represented by relatively higher reflectance values, or lighter gray values compared to the bare surface. Higher resFigure 3: 12 March 2020 EUMETSAT Meteosat-8 10.8 um IR imagery. Dust is represented by the cooler brightness temperatures, or lighter gray values compared to the bare surface. Higher res
Combining multiple bands to make multispectral imagery allowed for similar detection of dust across Africa. The dust was diagnosed in the split window difference and IR Window image combo, Geocolor, and Dust RGB imagery.
Figure 4: 12 March 2020 EUMETSAT Meteosat-8 10.8 minus 12.0 um split window difference imagery. Negative values, or darker grays and blacks, represent lofted dust. Colors are cold IR brightness temperatures, or clouds. Higher resFigure 5: 12 March 2020 EUMETSAT Meteosat-8 Geocolor imagery from CIRA. Higher resFigure 6: 12 March 2020 EUMETSAT Meteosat-8 Dust RGB imagery. Dust is represented by the varying shades of Magenta across the scene. Higher res
A closer look at region of optically thick blowing dust across Sudan is provided in Figure 7.
Figure 7: 12 March 2020 EUMETSAT Meteosat-8 0.6 um visible imagery (zoomed in to Sudan). Dust is represented by relatively higher reflectance values, or lighter gray values compared to the bare surface. Higher res
In this FDTD GOES Applications Webinar, the Huntsville NWS office discussed the history of total lightning data usage at the HUN NWS Office, and described the usage of GLM data during a couple of recent severe weather cases. On December 16, 2019, the GLM data were used to diagnose severe convection in a moderately unstable environment. On January 11, 2020, GLM data factored heavily into warning decisions for severe convection, including tornado warnings, when their primary radar (KHTX) failed.
Slide from March 11, 2020 FDTD webinar.
Below is an example of how GLM data were used in messaging during one of the events:
“Once the storms entered Marshall county, we really started to see an uptick in lightning activity, the strongest that we had seen that day. So we got on the radio and social media, and said, ‘we are really confident this storm is rapidly intensifying, something can happen here, … people in the path really need to be taking shelter right now.'”
FDTD Satellite Applications Webinars are peer-to-peer learning; staff from WFOs, National Centers, CWSUs, RFCs lead the presentations. The presentations are short (less than 30 minutes) and recorded for on-demand viewing.
March 2020 started off rather windy and unstable in the Northern Plains leading to convection during a month that still sees predominately wintertime stratiform precipitation. There were several instances of showers producing lightning, graupel/snow, and convectively forced severe wind gusts in addition to synoptically driven high winds. Designating convective cells that may be more impactful than others in the cool season (late fall, winter, and early spring) can be difficult using remote sensing instruments like satellite and radar due to their shallow heights and relatively warm cloud tops. Satellite appearance of shallow convection tends to be unimpressive in the infrared using default color schemes made for taller, colder cloud topped warm season convection. Also, due to the shallow depth of the cloud layer, radar can easily overshoot this layer composed of what tends to be marginal returns. Lastly, lightning activity tends to be much lower than that in the warm season, if present at all.
But there are some ways to make subtle features of shallow convection more easily tracked by adjusting the satellite display. Let’s explore..
Figure 1: 04 Mar 2020 GOES-East Day Snow-Fog RGB. Full res
First let’s take a look at an event on March 4, 2020, that produced several convectively induced high wind gusts at times exceeding 75 mph. The Day Snow-Fog RGB has proven useful in monitoring wintertime precipitation, mainly because of its use of near-infrared bands to help delineate snow cover, bare ground, and cloud top microphysical composition. It is also well known that using RGB’s capable of tracking cloud features while color sorting aforementioned properties (looking at you Day Cloud Phase Distinction RGB) can be quite useful for tracking forcing mechanisms, areas of potential convective initiation, and stage in convective life cycle.
Figure 1 shows convective clouds moving through eastern Montana into the Dakotas and northern Wyoming. Convection is already ongoing in the start of the loop with a line of showers attached to a cold front extending from near Great Falls to Glasgow, Montana. The cold front can be tracked on satellite propagating south and east undercutting additional convection in the “warm sector” ahead of the front. Ahead of the front are additional clusters of growing cumulus clouds as the convective temperature was reached, aided by ample insolation over a snow free surface beneath a relatively cool column of air (focus of cloud growth probably had some influence from differential heating and convergence augmented by variations in terrain). These cumulus clouds initially exhibit a highly textured, bubble-like appearance with whiter coloring indicating non-glaciated clouds. They very quickly become bright pink while maintaining their texture signaling glaciation of clouds through ascent. Finally they turn from cumulonimbus to stratocirrus losing texture, acquire more purple coloring, and move west to east in broader upper flow as parcels detrain from their initial paths of low level ascent, thus indicating the majority of additional ascent is likely over. The ability to track these mesoscale forcing mechanisms and stages in storm growth can be important to forecasters as this may give lead time to potential initiation or advection of impactful convection, as well as convective decay.
Figure 2: 04 Mar 2020 4 Panel: Top Left: GOES-East Day Cloud Phase Distinction RGB (adjusted red component)+ surface observations + severe thunderstorm warnings. Top Right: GOES-East Band 13 (adjusted range and color scheme). Bottom Left: GOES-East GLM (adjusted range) + severe thunderstorm warning + significant weather advisories. Bottom Right: MRMS isothermal reflectivity at -20 C. Full res.
Now let’s focus on the tristate region of the Dakotas and Montana, an area where several severe wind gusts were measured. Using Rapid City’s observed sounding as representative of the environment, this area was primed to transfer not only cloud layer winds of around 50 kt towards the surface, but any evaporation of descending precipitation cores may help accelerate these winds from aloft towards the surface (DCAPE ~700 J/kg, inverted V sounding).
We can utilize procedures meant for tracking severe convection in the warm season while making some minor adjustments to help gear towards a cool season environment. Figure 2 is an example of one such procedure. The range of the Day Cloud Phase Distinction RGB’s red component (10.3 um, Band 13, “Clean IR”) was edited from [Min: 7.5, Max: -53.5] to [Min: -10, Max -70] in an effort to desaturate red coloring by shifting this thermal sensing band towards the colder, better representing the temperatures typical in the cool season. Convective evolution is represented by a transition of colors from cyan to green to yellow/red as clouds glaciate and then cool. The inclusion of the visible spectrum within the Day Cloud Phase Distinction RGB also gave clues on storm development featuring more turbulent cloud texture near the upshear side of continually developing anvils, indicative of sustained updrafts reaching their equilibrium level. A separate, standalone look at Band 13 offered a way to track coldest cloud tops, although adjustments were also made here shortening the range from [Min: 55.0, Max: -109.0] to [Min: 0, Max -70] while making all values warmer than -25 C transparent. This allowed robust convection to be more easily tracked in an area of poor radar coverage with more red colored tops corresponding to relatively taller, stronger updrafts. One particular cluster of showers moved through Glendive, MT, with its AWOS measuring a 47 kt (54 mph) wind gust 18:56 UTC followed by Dickinson, ND, reporting 66 kt (76 mph) wind gust 19:56 UTC. This cluster exhibited relatively rapid cloud top cooling around 40 minutes prior to reaching Glendive and another prior to reaching Dickinson. Lastly, lightning activity can be analogous to updraft strength. Adjustments to the GLM FED appearance were made to shorten the default range of 1-260 to 1-20 helping draw out meager lightning rates. While overall lightning activity was low (as can be typical in cool season convection in the Northern Plains), this adjustment did help bring attention to cells that had relatively high activity compared to neighboring cells. One cell that stands out emanates from the same cluster that moved through Glendive and Dickinson but on its southern flank. Looking at MRMS isothermal reflectivity at -20C, the cell holding highest lightning activity has reflectivity exceeding 40 dBZ. All of these signals, upstream reported severe wind gusts, and our knowledge of the thermodynamic and kinematic environment can steer the forecaster into thinking this particular cell is strong and chances of producing severe downdraft wind gusts are high. This prompted NWS Bismarck’s to issue its earliest severe thunderstorm warning with an eventual 81 mph wind gust being reported at a mesonet site in Hettinger County, North Dakota.
Honorable mentions:
Figure 3: 03 Mar 2020 4 Panel: Top Left: GOES-East Nighttime Microphysics RGB. Top Right: GOES-East Band 13. Bottom Left: GOES-East GLM (adjusted range) + ENTLN lightning products. Bottom Right: MRMS isothermal reflectivity at -20 C. Full res.
A lightning-producing cell precipitating rain, snow, and graupel formed west of Bismarck, North Dakota, moving southeast into northeast South Dakota, during the evening of March 3, 2020. Using a similar procedure as displayed before, Figure 3 shows relatively rapid cooling of an expanding cloud top/anvil as noted in Band 13 (default color scheme shown). Values exceeding 35 dBZ in MRMS isothermal reflectivity at -20 C correlated nicely with the appearance of sensed lightning by GLM and ground based networks.
Figure 4: 03 Mar 2020 GOES-East Day Snow-Fog RGB (adjusted red and green components) + 0.5 degree reflectivity. Full res.
A graupel/snow depositing shower moved through Fargo, North Dakota, near sunrise March 3, 2020. This along with other showers left a trail of accumulated graupel/snow apparent on the Day Snow-Fog RGB (Figure 4). This is seen as more orange shaded streaks atop the background darker red coloring of the older snowpack. The shower moved through the Fargo-Moorhead metro right as sunlight was becoming available. Thus, it was beneficial to adjust the near infrared components of the RGB to account for little visible light to work with. This helped brighten the image revealing the metro was right on the edge of new accumulation (which lined up nicely with radar).
Figure 5: 03 Mar 2020 GOES-East Day Snow-Fog RGB (adjusted red and green components). Full res.
Later in the day, clouds peeled away revealing additional showers had deposited new frozen precip accumulation throughout eastern North Dakota into northwest Minnesota (Figure 5).
The main takeaway of this post is to encourage forecasters to become more comfortable with adjusting satellite products to help draw out convective features. Such adjustments may be especially necessary during the cool season. That’s not to say just blindly make adjustments, rather forecasters need to understand what is being adjusted and how that would affect the appearance and meaning of edited products. After determining an environment is possible for impactful convection, forecasters should think about adjusting satellite display to make subtle convective features typical in the cool season more easily tracked.
A hyperactive period of intense, extratropical cyclone development unfolded last month across the North Atlantic. A series of four winter storms, each generating hurricane force winds, developed in rapid succession. No minimum central pressure records were broken, but all four storms underwent rapid cyclogenesis or bombogenesis. One of the storms, Storm Dennis (named by the UK Met Office), attained the second lowest pressure reading behind Storm Braer in 1993. Three of these four cyclones managed to achieve remarkable pressures in the 920-930 mb range.
Below is a table summarizing what we know about each of these four storms.
Next, we describe each system using a combination of satellite and surface analyses.
The first storm, which we are calling the “Greenland Bomb,” deepened explosively to 930 mb by February 8. In the surface analysis below, the storm – designated as a hurricane-force low – is located just east of the tip of Greenland. The extreme cyclonic wind field helped propel the next storm in the series, shown over Newfoundland as a 966 mb low, into Europe.
Atlantic Surface Analysis from NOAA NWS Ocean Prediction Center valid for 8 February 2020 at 00 UTC.
The low reached the British Isles as a 945 mb storm, causing widespread flooding and wind damage. It was named Storm Ciara by the UK Met Office, and is shown on the synoptic surface chart below.
Atlantic Surface Analysis from NOAA NWS Ocean Prediction Center valid for 9 February 2020 at 12 UTC.
On 12 February 2020, a third storm was brewing in the North Atlantic Ocean that was forecast to rapidly intensify into an strong extratropical cyclone that would develop hurricane-force winds. The system’s pressure dropped from 1005 mb on 12 February at 00 UTC to 962 mb on 13 February at 00 UTC, a 43 mb decrease in pressure in just 24 hours that classified this system as a bomb cyclone. We are referring to this third cyclone as the “Iceland Bomb.”
GOES-16 Airmass RGB imagery of the Iceland Bomb for 12 February 2020 at 1430 UTC.
Stratospheric air intrusions are a known contributor to rapid intensification of extratropical cyclones via the advection of potential vorticity from the stratosphere into the troposphere. In the case of the Iceland Bomb, there was a strong signal of stratospheric air in the troposphere seen in GOES-16 Airmass RGB imagery, indicated by deep red/magenta in the dry slot of the cyclone.
GOES-16 Airmass RGB imagery of the active wave pattern across the North Atlantic on 12 February 2020 at 1510 UTC.
The wave pattern across the North Atlantic was extremely active, as seen in the Airmass RGB imagery above and Atlantic surface analysis below. A storm force low preceded the Iceland Bomb, and Storm Dennis closely following.
Atlantic Surface Analysis from NOAA NWS Ocean Prediction Center valid for 12 February 2020 at 18 UTC.
In the image below, the RGB imagery of the Iceland Bomb does a remarkable job of delineating “textbook” conveyor belts, or the basic 3D circulation branches of a wintertime, marine cyclone. The dry conveyor belt descends from the stratosphere into the southwestern quadrant of the storm. The warm conveyor belt – with its moisture-laden, high cloud shield originating in the warm sector – stands out in stark contrast to the cold conveyor belt. The cold conveyor belt undercuts the warm conveyor belt from the east, wrapping into the comma-head of low and middle layer clouds.
GOES-16 Airmass RGB imagery of the Iceland Bomb with annotated conveyor belt structure on 13 February 2020 at 00 UTC.
The Iceland Bomb deepened further as it moved across the Atlantic and reached its minimum central pressure of 929 mb on 14 February at 06 UTC. Hurricane-force winds were sustained for 48 hours by this extratropical cyclone, slamming Iceland with winds of historic strength and producing phenomenal wave heights up to 64 ft. Although terrain enhanced, the highest wind gust recorded in Iceland was 159 mph in Hafnarfjall.
GOES-16 Airmass RGB imagery of the Iceland Bomb on 13 February 2020 at 1630 UTC
Almost like dejavu, another cyclone closely followed the Iceland Bomb. The low pressure system, which would eventually receive the name of Storm Dennis, originated in the same location as the Iceland Bomb and took nearly the same path. The system deepened from 996 mb on 13 February at 12 UTC to 956 mb on 14 February at 12 UTC, a 40 mb drop in 24 hours, classifying this system as another bomb cyclone.
Atlantic Surface Analysis from NOAA NWS Ocean Prediction Center valid on 14 February 2020 at 00 UTC.
Unlike the Iceland Bomb, this cyclone moved a little more to the east, impacting Ireland and the United Kingdom with intense hurricane-force winds. A wind gust of 118 mph was recorded in the Scottish Highlands, and a gust of 107 mph was recorded in Brocken, Germany, the strongest gust recorded outside of the United Kingdom (WNEP).
Other impacts included intense waves with heights up to 52 ft, severe flooding produced by prolonged intense rainfall, and structural damage caused by falling trees. All of this occurred just a week after the region was hit by storm Ciara, which exacerbated the impacts.
GOES-16 Airmass RGB imagery of Storm Dennis and the Iceland Bomb on 14 February 2020 at 1810 UTC.
Rapid intensification of Storm Dennis was aided by a stratospheric air intrusion that originated in a trough located over the eastern United States that can be seen in the Airmass RGB imagery above. Deep red/majenta coloring indicates dry upper levels and high ozone concentrations associated with stratospheric air in the troposphere. Orange coloring indicates potential vorticity in the Airmass RGB product, and it trails all the way from the trough towards Europe, feeding into storm Dennis. Also pictured above is a massive atmospheric river stretching across the entire North Atlantic that provided ample moisture for the development of Storm Dennis.
Atlantic Surface Analysis from NOAA NWS Ocean Prediction Center valid for 15 February 2020 at 12 UTC.
The low pressure centers from the Iceland Bomb and Storm Dennis met up just south of Iceland where they did a Fujiwara dance, rotating around each other and then merging into one low pressure center. The dance can be seen in the Atlantic surface analysis above and the Airmass RGB imagery below. The Fujiwara effect is most commonly observed when two tropical cyclones pass close to one another. The combined system continued to move northeastward and dissipated by 18 February at 00 UTC.
GOES-16 Airmass RGB imagery of the Iceland Bomb and Storm Dennis doing a Fujiwara dance on 15 February 2020 at 0530 UTC.
Broader Perspectives Of The Hyperactive Storm Period
Having bomb cyclones in February is not unusual, as the peak season for these events in the North Atlantic and North Pacific is September through April, but having FOUR bomb cyclones in rapid succession of this intensity is unique.
This winter has featured a persistent, strongly positive arctic oscillation (AO) index, as shown below. Such a strong, positive index is driven by intense low pressure over the polar North Atlantic and high pressure ridging in the subtropical Atlantic.
Arctic Oscillation Index observations and GFS forecasts for winter 2019-2020.
The extreme pressure difference or gradient, in turn, has ratcheted up the intensity of the zonally-oriented polar jet stream coursing across the Atlantic Basin – at times reaching 240 mph. The dynamics of such an intense jet are a key reason for the sequence of very intense North Atlantic cyclones.
GFS forecast 250 mb heights and wind speeds valid for 15 February 2020 at 00 UTC.
When one compares this winter’s East Coast snow activity (thus far, one of the least snowiest winters on record for portions of the Mid Atlantic), with the winter of 2009-2010 (record-breaking seasonal snowfall), the contrast in persistent North Atlantic Oscillation phase is striking (image below). Since early December, nor’easters have failed to materialize along the typical breeding ground of Cape Hatteras.
North Atlantic Oscillation indexes for winter 2009-2010 and 2019-2020.
The intensity of the Iceland Bomb and Storm Dennis was aided by a massive atmospheric river spanning the entire width of the Atlantic Ocean. The atmospheric river funneled moisture from the tropical Caribbean all the way to Europe, following along a 5,000 mile long surface cold front and an intense upper air jet, which aided Dennis in producing an impressive 6.2 inches of rain over 48 hours in Cray Reservoir in South Wales as well as high rain totals across the region (WNEP).
Shown below is the integrated water vapor (IVP) product at 12 UTC on 16 February, showing extensive plume of Caribbean moisture entering into the large circulation of Storm Dennis (top panel). Also below, the Atlantic surface analysis the day prior illustrates the lengthy cold front, bisecting the entire Atlantic basin, that helped concentrate this atmospheric river.
GFS integrated water vapor, 850 mb winds, and sea level pressure valid for 16 February 2020 at 12 UTC.
Atlantic Surface Analysis from NOAA NWS Ocean Prediction Center valid for 15 February 2020 at 12 UTC.
This stormy period will be remembered for the incredible low pressures, verified hurricane-force winds (using ASCAT), and significant wave activity. The North Atlantic has remained stormy in early March, but pressures have been higher, though hurricane-force wind events continue.
Thank you for reading!
Deirdre Dolan (U. of MD-College Park), Jeffrey Halverson (U. of MD-Baltimore County), and Michael Folmer (NWS/NCEP/OPC)
The 4 March 2020 FDTD Satellite Applications Webinar was a tag-team discussion of a high profile snow squall event in PA/NY led by Dave Radell (SOO at New York City, NY) and Mike Jurewicz (SOO at State College, PA). In this webinar Mike and Dave shared several tips and tricks for fellow forecasters who may face this type of phenomenon in their own offices in the future. Here is one example of how satellite data was used to give a more complete picture as the event unfolded:
“A product that’s gaining a lot of popularity is the Day Cloud Phase, it’s an RGB product […] I would highly recommend the RGB product not only for these snow squall scenarios but for convection in general. […] although you get some idea in the traditional visible of the cloud enhancements, it really jumps out at you on the RGB loop. As these cloud features are growing taller and you’re getting more glaciation at the higher levels. With the ingredients that go into the RGB loop you can see that red and orange tint so it really jumps out at you nicely what the developing convective features are versus the lighter blue shading which is the flatter more laminar stratocumulus features. Again it could be another clue as to what really are the features of interest.”
“These snow squalls can be pretty robust convection in the winter time but in the grand scheme they’re fairly shallow features so you’re going to have issues with radar overshooting. But if you can combine your radar analysis with satellite you can get a more complete picture of how things are evolving.”
FDTD Satellite Applications Webinars are peer-to-peer learning; staff from WFOs, National Centers, CWSUs, RFCs lead the presentations. The presentations are short (less than 30 minutes) and recorded for on-demand viewing.
