The toggle above compares a CONUS Sector visible image (0.64 µm) over the Caribbean (at 1732 UTC) with a 1730 UTC Full Disk Legacy Atmospheric Profile (LAP) Derived Stability Lifted Index field.  (A “Veggie” Band 03 0.86 µm image, here, means that coastlines need not be drawn in because of the outstanding land/sea contrast at the wavelength).  The LAP Derived Stability Lifted Index shows modestly stable air southwest of the island of Jamaica;  the blue enhancement suggests positive lifted indices (stable air) vs. the yellow regions north and south where values range from -1 to -2.  Visible imagery over the stable region does show fewer clouds than to the north and south.  Does that help you believe the small variations in stability?

Suomi NPP Overflew the region shortly before 1800 UTC, and NUCAPS soundings that are produced using data from the CrIS (Cross-Track Infared Sounder) and ATMS (Advanced Technology Microwave Sounder) on Suomi NPP are available at the points shown above. Points indicated in green show where both the Infrared and Microwave retrievals successfully completed, and the animation below shows NUCAPS Soundings (at 18.66ºN, 18.20ºN, 17.74ºN, 17.28ºN, 16.82ºN and 16.36ºN) that bisect the region diagnosed as stable by the LAP Lifted Index.  Note that the NUCAPS sounding with the smallest MU Parcel CAPE, at 17.28ºN, is in the middle of the GOES-16-diagnosed stable region.

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After a strong arctic cold front plunged southward across the US, the Gulf of Mexico, and then southern Mexico during the previous two days (surface analyses), GOES-17 (GOES-West) and GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) revealed the hazy plume of dust-laden Tehuano gap wind flow as it emerged from the southern coast of Mexico and spread southwestward across the Gulf of Tehuantepec and the Pacific Ocean on 05 March 2019. An image of the topography of southeastern Mexico shows the location of Chivela Pass, through which these gap winds flow. Along the Gulf of Mexico coast, surface winds gusted to 30 knots and higher after the cold front moved through Minatitlán/Coatzacoalcos International Airport (station identifier MMMT); off the Pacific coast, a ship in the Gulf of Tehuantepec reported a sustained wind speed of 30 knots at 12 UTC.

The GOES-16 Aerosol Optical Depth product (below) showed lightly enhanced AOD values toward the outer edges of the swath of Tehuano winds. Note the gap in the product during the afternoon hours, when large amounts of sun glint were present.

The GOES-16 Dust Detection product (below) did portray Low to Medium-Confidence areas of dust within the gap wind flow.

An overpass of the Suomi NPP satellite after 19 UTC provided numerous NUCAPS sounding profiles both within and outside of the perimeter of the Tehuano winds (below).

A comparison between a dry NUCAPS sounding (Point D) where the gap winds were first exiting the coast over the Gulf of Tehuantepec and a more “undisturbed” moist sounding (Point M) northwest of the gap wind flow is shown below. The dry air of the Tehuano wind flow was very shallow, but its presence could be seen in differences between the marine boundary layer dew point profile and the resulting height of the Lifting Condensation Level (LCL).

A NOAA-20 VIIRS True Color Red-Green-Blue (RGB) image viewed using RealEarth (below) also showed the hazy signature of dust-laden air.

===== 06 March Update =====

GOES-16 Shortwave Infrared (3.9 µm) images with overlays of Metop-A ASCAT winds around 0338 UTC (above) and 1607 UTC (below) revealed a secondary surge of Tehuano winds on 06 March. The highest wind speed at 0338 UTC was 44 knots, with 38 knots being measured at 1607 UTC.

GOES-16 Shortwave Infrared images (below) were useful to monitor the spread of cooler water (shades of yellow) as the strong surface winds induced upwelling — especially since the resulting strong gradient in water temperatures was falsely interpreted as cloud by the GOES-16 Sea Surface Temperature product.

GOES-17 and GOES-16 Visible images (below) showed how the swath of Tehuano winds had spread out toward the south and southwest compared to the previous day.

In contrast to the previous day, the GOES-16 Dust Detection product (below) showed a larger coverage of dust on 06 March — with significantly more Medium Confidence areas.

A Suomi NPP VIIRS True Color RGB image at 1930 UTC (below) showed the hazy corridor of Tehuano winds bracketed by rope clouds.

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The planned change for Mesoscale Domain Sector #2, noted here, has occurred as scheduled on 5 March at 1500 UTC. The toggle above shows Mesoscale Domain Sector Two at 1459 and 1500 UTC on 5 March 2019.

The image below (courtesy Mat Gunshor, CIMSS) shows the default locations for all scanned sectors. The Full Disk is scanned every 5, 10 or 15 minutes (for Modes 4, 6 and 3, respectively; currently Mode 3 is the default). The PACUS (Pacific Ocean/US) domain, shown in the dashed line, is scanned every 5 minutes. The two Mesoscale sectors are scanned every minute in Modes 3 and 6; default locations are shown, one over the western United States (Mesoscale Domain Sector 1) and one over Alaska (Mesoscale Domain Sector 2), but these can be positioned anywhere over the Globe.

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An outbreak of severe thunderstorms occurred during the afternoon hours of 03 March 2019, which produced large hail, damaging winds and tornadoes (SPC storm reports). 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed the development of numerous thunderstorms along and ahead of an advancing cold front (surface analyses); many of those storms exhibited well-defined overshooting tops. Tornado track summaries for Alabama and Georgia are available from NWS Birmingham and NWS Atlanta.

The corresponding GOES-16 “Clean” Infrared Window (10.3 µm) images are shown below. Cloud-top infrared brightness temperatures cooled to around -70ºC (darker black enhancement) with many of the stronger storms — judging from rawinsonde data from Birmingham, Alabama (at 12 UTC) and Peachtree City, Georgia (at 18 UTC), this roughly corresponded to an air parcel rising significantly past the tropopause to an altitude of at least 15 km.

An area which included western Lee County (located in far eastern Alabama, adjacent to the Georgia border) was highlighted by a SPC MCD that was issued at 1900 UTC. Beginning about an hour later, 2 large tornadoes producing EF2 to EF4 damage moved across southern Lee County — initially beginning around 2000 UTC, then again beginning around 2050 UTC — and the formation of prominent overshooting tops was evident in GOES-16 Visible and Infrared imagery (below). Station identifier KAUO in Lee County is the Auburn-Opelika Airport. (side note: later, around 2204 UTC, the Weedon Field Airport KEUF METAR site to the south of Lee County was directly hit by a separate EF2 tornado, and rendered inoperative)

In a plot of the GOES-16 “Clean” Infrared Window coldest brightness temperature for the EF4-tornado storm’s overshooting top as it moved from Macon/Lee Counties in Alabama to Muscogee/Harris/Talbot Counties in Georgia (below), 3 distinct periods of cooling/warming occurred — with the warming indicative of a temporary collapse of the overshooting top pulse. The first (and largest-magnitude) cold/warm pulse (-70.3ºC to -65.6ºC) occurred from 1953-1959 UTC — just prior to the beginning of the Beauregard-Smiths Station EF4 Tornado at 2000 UTC. A second cold/warm pulse (-70.8ºC to -66.9ºC) occurred from 2006-2012 UTC, with a third (-70.0ºC to -66.0ºC) from 2015-2022 UTC. At 2029 UTC the long-track tornado then crossed into Muscogee County in Georgia, producing EF3 damage.

The NOAA/CIMSS ProbSevere product (below) displayed a high tornado probability for the cells that approached Lee County, as discussed by the Hazardous Weather Testbed. The ProbSevere model incorporates GOES-derived Normalized vertical growth rate and Cloud-top glaciation rate as 2 of its predictors.

A comparison of Aqua MODIS Visible (0.65 µm) and Infrared Window (11.0 µm) images along with the Total Precipitable Water derived product at 1836 UTC (below) showed that a few large thunderstorms had begun to develop by that time; TPW values were as high as 43 mm (1.7 inches) over far southwestern Georgia.

An overpass of the Suomi NPP satellite around 1850 UTC provided NUCAPS soundings in non-cloudy areas (above). One of the Good quality (green) NUCAPS soundings in the pre-storm environment was located over southwestern Georgia (circled in magenta) — it showed a Most Unstable CAPE value of 1264 J/kg, with a Lifted Index value of -4 (below).

The GOES-16 All Sky CAPE product (below) showed a trend of destabilization across southern Alabama and southern Georgia during the 5 hours leading up to the fatal tornadoes in Lee County AL.

===== 05 March Update =====

A toggle between before/after (24 February / 05 March 2019) Terra MODIS True Color and False Color Red-Green-Blue (RGB) images from the MODIS Today site (above) showed subtle evidence of portions of a tornado damage path — presumably that of the EF4 tornado that began in/near Lee County, Alabama and ended in far western Georgia. Click an additional time on the image to view at full magnification.

Sentinel-2 True Color images (below) provided a higher-resolution view of the tornado damage path. Imagery courtesy of Sentinel Hub.

The path of the #tornado that hit #Alabama last March 3 is clearly visible from images of #Sentinel2 ?. pic.twitter.com/GLatHrIQ5r

— Annamaria Luongo (@annamaria_84) March 7, 2019

34 tornadoes have been confirmed across Alabama, the Florida panhandle, Georgia and South Carolina from the Sunday March 3, 2019 outbreak. One tornado tracked for nearly 69 miles across AL (EF-4) into GA (EF-3). There were 1 EF-4, 1 EF-3, 7 EF-2, 19 EF-1 and 6 EF-0 tornadoes. pic.twitter.com/qjSQV5poKw

— NWS Eastern Region (@NWSEastern) March 6, 2019

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