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Monitoring the Remnants of Ian from GOES-16

Posted by Kevin Thiel (CIWRO) on 10/03/2022
Posted in: G16-CH07_3.9_SWIR, G16-CH13_10.3_IR-Clean, Nighttime Microphysics RGB, SPC. Leave a comment

On Saturday October 1st the remnants of Hurricane Ian were moving northward through the Mid-Atlantic region, after making a second U.S. landfall the previous day in South Carolina. Overnight, the SPC was monitoring the final stages of Ian’s extra-tropical transition with a marginal threat for severe weather in the coastal North Carolina/Virginia region.

One forecaster on shift that night was monitoring the remnants from the perspective of GOES-16, and noted how various ABI products could be used to examine cloud layers and types in this dynamic environment.

CH7 shortwave and CH13/15 longwave IR shows mainly the cooler cloud tops associated with high-level clouds. Low-level clouds can be inferred by the warmer temps (CH7) or weaker grey features in CH13/15. However, the NtM [Nighttime Microphysics] RGB composite satellite data neatly contrasts colder, high-level clouds (western PA westward and in a warm conveyer belt over the Atlantic) from the lower but cool clouds (North Carolina into Virginia) and the very low, warm clouds (southeast Pennsylvania into New Jersey and Delaware). Though buoyancy is scant and severe is not expected in this area, the NtM RGB composite’s ability to contrast cloud types in this event demonstrates potential to identify important cloud features related to severe weather.

SPC Forecaster Comment

When overlaid with the RAP mesoanalysis field at 500 mb, the Channel-13 (Clean Longwave IR) and Channel-7 (Shortwave IR) bands from the ABI reveal the higher, cooler cloud tops north of the low into Pennsylvania. The warm conveyor belt over the Atlantic coast can be seen in the 500 mb RAP mesoanalysis with enhanced southerly winds east of low, and from the ABI infrared imagery with a lack of high clouds due to upper level subsidence.

Channel 13 (clean longwave IR) imagery of Ian’s remnants from the perspective of GOES-16. Overlaid with 500 mb RAP mesoanalysis data.
Channel 7(shortwave IR) imagery of Ian’s remnants from the perspective of GOES-16. Overlaid with 500 mb RAP mesoanalysis data.

While these bands individually can be used to point out these features, the forecaster notes that the Nighttime Microphysics RGB allows them to more readily identify and monitor these cloud features from the tropical cyclone remnants at night. This is driven by the RGB’s ability to combine information from multiple ABI bands (7, 13, and 15) to provide qualitative information for forecasters regarding cloud types and heights.

Nighttime Microphysics RGB imagery of Ian’s remnants from the perspective of GOES-16. Overlaid with 500 mb RAP mesoanalysis data.

Kevin Thiel, OU CIWRO

Forecasting on the Margins…Using ABI Imagery during Nighttime Mesoanalysis at the SPC

Posted by Kevin Thiel (CIWRO) on 09/08/2022
Posted in: Nighttime Microphysics RGB, SPC, Water Vapor Imagery. Leave a comment

During the early morning hours of September 7th, 2022, the SPC convective outlook issued at 1200 Z featured two upgraded areas from the previous outlook at 0500 Z (see image gallery below). Today we will focus on the upgrade from ‘Thunderstorm’ to ‘Marginal’ in southeast Texas and southwest Louisiana.

The question is..what caused the upgrade? The SPC Convective Outlook discussion from 0500 Z mentions thunderstorm activity in the area from a weak shortwave trough, but with little shear and poor lapse rates limiting thunderstorm severity potential. The Outlook from 1200 Z reveals that a mesoscale disturbance was moving into this area from the northeast, and modifying the mesoscale environment that would coincide with thunderstorms later in the day.

   …Southeast TX and southwest LA…

A minor mid-level impulse evident in water vapor imagery over the Ark-La-Tex should gradually move south-southwest into south TX by this evening. A pocket of relatively cooler mid-level temperatures and steeper lapse rates attendant to this impulse should support a plume of moderate to large MLCAPE of 1500-3000 J/kg. While deep-layer shear will be modest and generally offset west of the greater instability/buoyancy, isolated marginally severe hail and strong to localized severe wind gusts will be possible as scattered thunderstorms occur this afternoon.

SPC Day 1 Convective Outlook, 7 September 2022 (12Z)

Water vapory imagery shows the location of the mesoscale disturbance as it moves from southern Missouri into eastern Texas and western Louisiana, and begins to even initiate morning convection.

GOES-16 Upper Level Water Vapor Imagery (Channel 8) from 0300 Z to 1300 Z on 7 September 2022. Note the increased water vapor and cyclonic motion associated with the mid-level impulse identified in the 12Z SPC convective outlook discussion.

The SPC Mesoanalysis at 1400 Z reveals increased mid-level lapse rates and ML-CAPE moving southwest into the Marginal hazard area during the morning hours, driven by the mid-level impulse.

One potential failure mode in this scenario would be early morning cloud cover, which would keep the ML-CIN in place and limit thunderstorm development. High clouds from Hurricane Kay in the eastern Pacific are one potential source. In this scenario however, the SPC forecaster used the Nighttime Microphysics RGB to examine the locations of cloud layers before visible satellite imagery became available during the day. The following quote from the SPC forecaster on shift highlights this application.

Deep convection over the Ark-La-Tex. Patchy low clouds to the southwest of this into south-central TX beneath high-level cirrus loosely associated with TC Kay off southern Baja CA. Mainly cloud-free in between across southeast TX to southwest LA indicative of nearly full insolation this morning for the newly added MRGL in the 13Z outlook. Helpful to “see” before visible satellite imagery becomes available.

SPC Forecaster Comment
GOES-16 Nighttime Microphysics RGB product over central Texas from 0300 Z to 1300 Z on 7 September 2022. Note the initiating convection coinciding with the mesoscale disturbance, the cumulus clouds over central Texas, and the high clouds from Hurricane Kay in the eastern Pacific over southern Texas.

Kevin Thiel, OU CIWRO

Oklahoma Supercells at Sunset from GOES-16

Posted by Kevin Thiel (CIWRO) on 04/26/2022
Posted in: Day Cloud Phase Distinction RGB, G16-CH13_10.3_IR-Clean, GLM, RGB, SPC, Tornado. Leave a comment

Supercells were expected to initiate along a dryline in west-central Oklahoma during Saturday evening on April 23rd. The Storm Prediction Center had issued a slight risk of severe storms in their 1630 Z (1:30 PM CDT) outlook, with the risk tornadoes (5%), damaging hail (15%), and damaging wind (15%). Thunderstorms initiated around 2200 Z (5:00 PM CDT) as shown from the Day Cloud Phase Distinction RGB animation below. As the sun began to set near the end of the animation, decreasing contributions from the green (Channel 2, visible) and blue (Channel 5, near-IR) bands created a shift to more red colors in the imagery (Channel 13, clean-IR).

Animation of the Day Cloud Phase Distinction RGB from 2130 to 2300 Z (4:30-6:00 PM CDT).

An SPC Mesoscale Discussion and Tornado Watch, along with NWS Norman Public Information Graphics show the transition from the initial SPC Convective Outlook to the warnings that would later be issued that evening. (Images below in chronological order)

As convection matured into supercells after sundown, satellite imagery became confined to the infrared bands (Channels 7-16), with Clean-IR imagery most often used. Additionally, rapidly updating (1 minute) lightning data from the GLM Flash Extent Density product can provide information about thunderstorm trends between NEXRAD full-volume scans (4-5 minute updates). At night, the GOES-16 GLM detection efficiency often exceeds 90% across the south-central United States.

Intensification of two supercells and tightening of their low level mesocyclones, southwest of Oklahoma City and southwest of Stillwater, as indicated by radar prompted the NWS Norman office to issue tornado warnings for both storms. The Tornado Warning for the Stillwater supercell was issued at 2359 Z (6:59 PM CDT), and the Tornado Warning for the Oklahoma City supercell was issued at 0003 Z (7:03 PM CDT).

5-minute ABI and GLM data from 2330 to 0030 Z (6:30 – 7:30 PM CDT)
Left: GLM Flash Extent Density (5 minute total) overlaid on the ABI Clean-IR band.
Right: ABI Clean-IR Band.

The animation above is from 2330 Z to 0030 Z (5 minute intervals), and shows how both storms intensified from the perspective of the GLM FED and ABI Clean-IR products. Deep overshooting tops were observed from the ABI along with notable increases in GLM flash rates. In this scenario satellite information may have provided a ‘heads-up’ on which storms to monitor, along with additional confirmation of trends observed from NEXRAD.

One-minute data was observed from the GOES-East Mesoscale Domain for both products (below). In this scenario NWS Norman also had access to the Terminal Doppler Weather Radar at the Oklahoma City Airport (TOKC), providing 1-minute radar reflectivity and doppler velocity data within the vicinity of the airport. For the supercell near Oklahoma City, this may make a forecaster less reliant on one-minute satellite data when making warning decisions. However, for the storm southwest of Stillwater no TDWR data was available. The rapid increase in lightning flash rates identified by the GLM FED product for this storm can provide additional verification for an NWS forecaster that the updraft was intensifying, and tightening of the low level mesocyclone prior to tornadogenesis may be imminent.

1-minute data from the GOES-East ABI (Clean-IR) and GLM (FED) within the mesoscale domain. Imagery is from 2350 – 0010 Z (6:50-7:10 PM CDT) (Click animation to view at full size)

Kevin Thiel (OU CIWRO)

Dense Fog in Ohio Viewed from the Nighttime Microphysics RGB

Posted by Kevin Thiel (CIWRO) on 04/22/2022
Posted in: Nighttime Microphysics RGB, RGB. Leave a comment

During the early morning hours of April 22nd, fog began to form across southern Ohio, West Virginia, and Pennsylvania. In anticipation of the fog, the NWS Weather Forecast Office in Wilmington OH issued a Dense Fog Advisory for a portion of their forecast area.

Latest guidance increases confidence in development of areas of dense fog late tonight. Based on this, have hoisted Dense Fog Advisory south of Interstate 71.

NWS ILN, AFD Issued at 0133 UTC (9:33 EDT)

Confirmation of the dense fog can be observed via satellite from the Nighttime Microphysics RGB starting around 0500 Z (1:00 AM EDT), with greater contributions from the Green Band (10.3 um – 3.9 um band difference) and minor contributions from the Blue Band (10.3 um band). The stationary, more faint, and highly localized appearance of the fog stands in contrast to the low level clouds in southwest Pennsylvania and central West Virginia, which often have a similar color due to similarities in their composition. Additionally the movement of cirrus and stratocumulus clouds into the area, from precipitation over Indiana, did obscure the extent of the fog in western Ohio by 1000 Z (6:00 AM EDT). This is one limitation of the product, as skies have to be fairly clear in order to properly identify fog.

Based on surface observations and imagery from the Nighttime Microphysics RGB, it was apparent by 0830 Z (4:30 AM EDT) that the dense fog was expanding north of Interstate 71. This confirms NWS Wilmington expanding the Dense Fog Advisory north into the Cincinnati and Dayton metro areas, prior to the increase of traffic during the morning rush. In this case the combination of surface observations and the Nighttime Microphysics RGB can provide confirmation of developing fog and its spread overnight for the Dense Fog Advisory. Using satellite RGBs in tandem with other observations can help maximize situational awareness, especially when satellite data cannot be relied on exclusively as shown in this example.

The fog is becoming dense in many locations across northern KY, southern Ohio, and southeast Indiana. Have expanded the dense fog advisory north to about I-70.

NWS ILN, AFD Issued at 0831 Z (4:31 AM EDT).

Kevin Thiel (OU CIWRO)