GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images with plots of hourly surface weather type (above) showed the broad areal coverage of precipitation across Virginia and North Carolina during the nighttime and morning hours on 28 January 2021. Storm total snowfall and peak wind gusts associated with this event are listed here. Note that snow was even observed along the outer banks of North Carolina (although accumulations there were minimal).

After sunrise, the resulting northwest-to-southeast oriented swath of snow cover was revealed on GOES-16 “Red” Visible (0.64 µm), Day Snow-Fog RGB (snow = darker shades of red) and Day Cloud Phase Distinction RGB (snow=brighter shades of green) images (below).

A toggle between Suomi NPP VIIRS True Color and False Color images at 1732 UTC is shown below. Snow cover appears as shades of cyan in the False Color image.

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A tornado struck the Tallahassee, FL, airport at 1643 UTC on 27 January 2021 (SPC Storm Report).  The animation above shows ProbSevere (version 2) fields (from this site) in the hour leading up to tornadogenesis.  The animation demonstrates how ProbTor values can be used to identify for closer scrutiny a particular radar object:  the radar object that ultimately caused a tornado showed greater ProbTor values (than surrounding identified radar objects) in the hour leading up to tornadogenesis. In addition, ProbTor values ramped up quickly just prior to tornadogenesis as low-level azimuthal shear jumped.

One time series below compares ProbWind, ProbHail and ProbTor for the radar object (#15080) that produced the tornado; for this event, ProbWind and ProbTor values were comparable until a ramp-up in ProbTor values before the tornado occurred. The second time series shows the various components of ProbTor for radar object 15080 (both time series courtesy John Cintineo, SSEC/CIMSS).  Note in particular that this storm was not a lightning-producer.  Much of ProbTor’s variability was determined by changes in low-level azimuthal shear.

Lead time with ProbTor in this example was not exceptional.  However, its elevated values in the hour leading up to the tornado could have provided better situational awareness, and perhaps enhanced confidence in warning issuance for this well-warned event.

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Unfortunately, the default Mesoscale Domain Sectors were positioned too far north to cover the Florida Panhandle — but 5-minute CONUS Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) depicted a west-to-east oriented line of thunderstorms across the northern portion of the Panhandle; a trend of cooling cloud-top infrared brightness temperatures was seen as the convection began to produce the tornado.

There was an overpass of the Terra satellite about 19 minutes before the start of the tornado event, at 1618 UTC — 1-km resolution MODIS Visible (0.64 µm) and Infrared Window (11.0 µm) images are shown below.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.35 um) images (above) displayed the large supercell moving northeastward across Alabama several hours after sunset on 25 January 2021. This thunderstorm eventually produced an EF3 tornado just north of Birmingham (KBHM) beginning at 0440 UTC.

A slightly closer view of GOES-16 Infrared images that include plots of surface reports is shown below. Dew point values feeding northeastward into the thunderstorms were in the middle 60s F.

The coldest infrared brightness temperatures exhibited by the pulsing overshooting tops were -66ºC (darker shades of black) — which appeared to be the temperature that would be attained by a Most Unstable air parcel reaching the Maximum Parcel Level (MU MPL) as analyzed on a plot of 00 UTC rawinsonde data from Birmingham (below).

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As an anomalously-deep 500 hPa low began to move inland over Southern California during the 23 January – 24 January 2021 period, GOES-17 (GOES-West)  Air Mass RGB images (above) showed a compact Potential Vorticity (PV) anomaly approaching the coast — and the RAP40 model indicated that the “dynamic tropopause” (defined here as the pressure of the PV1.5 surface) was descending to the 675 hPa pressure level at 18 UTC.

A west-to-east oriented cross section of RAP40 model fields along Line A-A’ (below) depicted the descending dynamic tropopause at 19 UTC.

GOES-17 Mid-level Water Vapor (6.9 µm) images (below) showed the increasing reports of rain and snow that resulted as the PV Anomaly moved inland and provided additional forcing for ascent. Near the coast, thunderstorms were reported at Fulton and Long Beach around 03 UTC. Storm total precipitation amounts included rainfall of 1.40 inch and snowfall of 12-18 inches.

GOES-17 Water Vapor images at 2301 UTC and 0246 UTC (below) revealed sporadic lightning activity (indicated by small clusters of GLM Groups).

===== 24 January Update =====

On the following day, as clouds began to clear the areal extent of resulting fresh snow cover (darker shades of red) was seen in GOES-17 Day Snow-Fog RGB images (above). Even parts of the high desert — north and east of the mountain ranges — received some snowfall (for example, 2-3 inches were reported at Hesperia).

Suomi NPP VIIRS True Color RGB and False Color RGB images (below) showed the snow cover (shades of cyan) at 2036 UTC.

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