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.

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.

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.

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.

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).

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.

Bill Line, NESDIS and CIRA

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.

Bill Line, NESDIS and CIRA

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).

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.

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.

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.

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).

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).

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.

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.

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.

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.

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.

Bill Line, NESDIS and CIRA