1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) images (above) showed Atlantic Tropical Depression Three as it intensified to become Tropical Storm Bret at 2100 UTC on 19 June 2023. Overshooting tops exhibited infrared brightness temperature values as cold as -79ºC.

Bret was in a favorable environment for continued intensification, as shown by low values of deep-layer wind shear from the CIMSS Tropical Cyclones site (below) — and the storm was moving over relatively warm water (Sea Surface Temperature).

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GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) + Fire Power (a component of the GOES Fire Detection and Characterization Algorithm FDCA), Shortwave Infrared (3.9 µm), Day Land Cloud Fire RGB and Fire Temperature RGB images (above) showed thermal signatures and pyrocumulus pulses associated with the Pulp Road Fire in far southeastern North Carolina on 16 June 2023. Beginning at 1646 UTC, the fire occasionally exhibited 3.9 µm brightness temperatures of 137.71ºC (the saturation temperature of the GOES-16 ABI Band 7 detectors) — and Fire Power values exceeded 2300 MW at times. The fire rapidly grew in size from 2,500 acres at 1300 UTC on 16 June to 11,500 acres at 0000 UTC on 17 June.

A toggle between VIIRS Infrared Window (11.45 µm), Shortwave Infrared (3.74 µm), True Color RGB and False Color RGB images from Suomi-NPP (valid at 1747 UTC) and NOAA-20 (valid at 1819 UTC) (below) revealed that the fire produced a pyrocumulonimbus (pyroCb) cloud, which exhibited anvil-top 11.45 µm brightness temperature values of -40ºC and colder (shades of blue). Data used to create the VIIRS imagery were downloaded and processed by the SSEC/CIMSS Direct Broadcast ground station.

To the best of our knowledge, this is the first documented case of a pyroCb in the State of North Carolina.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) with/without an overlay of GLM Flash Extent Density (above) showed the development of a thunderstorm that produced the fatal EF3-rated tornado that moved through Perryton, Texas (located about 4 miles southwest of airport identifier KPYX) from 2206-2217 UTC on 15 June 2023. A modest amount of lightning activity was associated with these storms. Prior to convective initiation in the far northern Texas Panhandle, orphan anvil pulses were evident south of Perryton (indicating that convective inhibition was diminishing across that area).

The corresponding GOES-16 “Clean” Infrared Window (10.3 µm) and Cloud Top Temperature derived product images are shown below; just prior to the tornado, the coldest 10.3 µm infrared brightness temperature and Cloud Top Temperature values were -73.41ºC and -76.92ºC, respectively, at 2158 UTC (note that the coldest temperature for this infrared color enhancement was adjusted to be -95ºC).

In a toggle between GOES-16 Visible and Infrared images at 2158 UTC (below), the apparent location of the thunderstorm’s cold overshooting top was over the Oklahoma Panhandle — but taking parallax into account, the actual location of that overshooting top would have been about 20 km (12 miles) to the southeast (closer to Perryton).

GOES-16 Lifted Index (LI) and Convective Available Potential Energy (CAPE) derived products (below) showed that the thunderstorms were approaching a N-S oriented corridor of instability (as was also discussed in this blog post). The most unstable LI values within that corridor were around -10ºC, with CAPE values around 2500 J/kg.

GOES-16 Total Precipitable Water (TPW) derived product images (below) indicated that an axis of moisture was also in place within the corridor of instability. Peak TPW values were around 1.3 inches.

GOES-16 Visible and Infrared images (below) include time-matched (+/- 3 minutes) plots of SPC Storm Reports.

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The Storm Prediction Center predicted a moderate risk of severe weather (link) over the southern Plains of the US on 15 June 2023. The animation above shows surface-based CAPE derived from 4-km WRF model output. This model incorporates information from Polar Hyperspectral Soundings via the Fusion process. Model CAPE fields are overlain by NOAA/CIMSS ProbSevere (version 3) polygons from 1700-2000 UTC. There is good agreement for those times between the gradient of the CAPE fields and the location of the ProbSevere polygons that show were severe weather is most likely. The 2100 UTC image of surface-based CAPE is also shown. Where do you think the polygons will be at 2100 UTC? That is shown below. These model fields can help with situational awareness in the near-term. (Model output is available at this link).

A particular benefit of the PHS model output fields shown above is that they are high-resolution, that information is available in cloudy and clear regions and that the forecast provides short-term (that is, 0-9 hour) guidance. Other satellite-based stability products are available of course. The two-panel below shows PHS output and GOES-16 Derived Stability Index estimates of CAPE. The character and gradients of the fields are very similar — but the Level-2 GOES estimate is created only in regions of clear skies. A direct (toggled) comparison of the fields at 1900 UTC is here. The comparison between the real-time GOES estimates and the 5-h model field suggests that the model evolution is just a bit slow.

NOAA-20 overflew the eastern part of this domain at around 1900 UTC, and gridded NUCAPS fields of temperature and moisture were used to diagnose the stability. That is shown below. As with the PHS-enhanced WRF model output, NUCAPS fields give information in clear and cloudy regions. The horizontal resolution of NUCAPS data, however, is around 50 km; the display of tight gradients is a challenge.

The toggle below shows Sounding Availability points (Green Points: infrared retrieval converged to a solution; Yellow Points: microwave retrieval converged to a solution; Red Points: neither infrared nor microwave retrieval converged), the Total Totals index, and the lapse rate from 700-500 mb. The Total Totals index suggests the strongest instability over western Oklahoma, a region with steep 700-500 mb lapse rates.

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The PHSnMWnABI model output (and Probsevere Version 3) were both evaluated at SPC’s Hazardous Weather Testbed within the past month. Blog Posts from the forecasters that describe how these products can be used are here. SPC storm reports for this day are shown below. They do align with satellite estimates of CAPE.

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