1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) widespread showed thunderstorms that produced tornadoes (resulting in a number of fatalities), large hail (up to 3.5 inches in diameter in Oklahoma) and damaging winds as high as 78 mph in Kansas (SPC Storm Reports) across the southern and central Plains during the daytime hours on 25 May 2024. Pulses of overshooting tops were apparent in the Visible imagery.

In the corresponding 1-minute GOES-16 “Clean” Infrared Window (10.3 µm) images (below), the coldest overshooting top infrared brightness temperatures were in the -70 to -79ºC range (shades of black to white).

In a closer view of a deadly supercell thunderstorm that was moving across North Texas, 1-miinute GOES-16 Infrared images (below) showed pulses of overshooting tops exhibiting cloud-top infrared brightness temperatures of -80ºC or colder (violet pixels) as it produced tornadoes (one of which produced fatalities at Valley View, Texas around 0346 UTC), hail to 3.00″ in diameter and damaging winds to 70 mph.

In addition, a closer view of another deadly tornado-producing supercell thunderstorm (below) similarly showed numerous pulses of overshooting tops as it moved across northeast Oklahoma (including the communities of Claremore and Pryor) and continued across northwest Arkansas (where it produced several more fatalities).

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One focus on day 4 of HWT in Norman was the North Platte, Nebraska (WFO LBF) County Warning Area (CWA) over western Nebraska. This was near a gradient in the Storm Prediction Center Convective Outlook that had an enhanced risk over central Nebraska and a Slight risk over western Nebraska. The first concern was when would convective initiation occur? The 1600 UTC PHS model run had convective initiating at 2000 UTC and building from then on.

The distribution of moisture modeled in the MUCAPE field above was very similar to the Split Window Difference field (here, from this link).

The PHS model runs hourly. The data above shows the 2000 UTC forecast from 1600 UTC (that is, a 4-hour forecast). The 3-h forecast valid at 2000 UTC (from the PHS run at 1700 UTC) did not include initiation until after 2000 UTC. Compare the two fields below, 3-h and 4-h forecasts for 2000 UTC and 2100 UTC from 1600 UTC and 1700 UTC, respectively.

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PHS Model Forecasts are available at this website. HRRR model forecasts are available here (and elsewhere). The following six figures compare the forecasts for 2200 UTC in forecasts initialized at 1600, 1700, 1800, 1900, 2000 and 2100 UTC, that is 6-h, 5-h, 4-h, 3-h, 2-h and 1-h forecasts. (Click here for an animation of the forecasts; For views of what was occurring between 2000 and 2220 UTC on 23 May, click here for the North Platte WFO and here for the Aberdeen WFO). The WRF model with assimilated PHS data showed stronger convection forming earlier, closer to the actual time of convective initiation, than was predicted by the HRRR model that does not include PHS information.

The image below also shows HRRR model output (initialized without any Polar Hyperspectral Sounding information) as available at this website. The forecast was too slow in initiating convection over Nebraska.

The stepped animations below show the hourly GOES-East Day Cloud Phase Distinction RGB over the northern High Plains from 2000-2300 UTC on 23 May, and the GOES-East Day Cloud Phase Distinction RGB overlain with the PHS forecasts of Composite Reflectivity at 2100, 2200 and 2300 UTC on 23 May. Strong convective growth is apparent in both fields. Severe weather was reported in both the North Platte and Aberdeen CWAs from this convection (SPC Storm Reports).

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The AMSR-2 89-GHz brightness temperature image above (courtesy Brandon Aydlett, WFO GUM), from 1628 UTC on 22 May 2024 (downloaded at the Guam National Weather Service Direct Broadcast antenna and processed with CSPP software) shows curved convective bands around the center of Invest 93W in the western Pacific between Guam and the Philippines. Processed wind speeds from this overpass (not shown, but also available at the forecast office in Guam) showed maximum winds near 20 knots. Why is this data important? It allows forecasters on Guam information on a developing system, one that is in between ASCAT overpasses (see below), for better analysis, awareness and decision-making.

By 0000 UTC on 24 May 2024, below, this tropical disturbance was approaching the Phillippines. Small values of vertical wind shear and warm water temperatures will help it to organize; terrain over the Phillippines will interfere with any organization. For more information on this system, refer to the CIMSS Tropical Weather Website, the Joint Typhoon Warning Center, the JMA/Tokyo RSMC, and Pagasa in the Phillippines.

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Many thanks to Brandon Aydlett, Science and Observations Officer at WFO GUM for forwarding along the GCOM-W1 and ASCAT images!

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The San Angelo TX forecast office (WFO SJT) was an area of focus during HWT at SPC on 22 May. This blog posts includes observations about how the model performed (other observations on PHS performance are in the HWT Blog here). The animation above shows updraft velocity at 500mb over the course of the afternoon. Strong convection developed during this time over the San Angelo WFO County Warning Area. What did the radar show? The animation below, from 1744 to 2054 UTC, shows a splitting cell within the white box after about 2000 UTC. Does the modeled convection above show a similar splitting behavior? An argument for yes can be made, although It’s hard to tell for certain given the 1-hour time step (A note on the timing of the convection: on 22 May 2024, all of the Convection-Allowing Models — CAMs — were late in developing convection). GOES-16 imagery below also shows the storm split.

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I also compared instability values on this day, both from the RAP-40km model run, from PHS, and from GOES-16. Those are shown in the toggle below. Note the PHS CAPE minimum under the strong convection over north-central Texas that is shown in the plot with GOES-16 CAPE that is clear-sky only. Overall, there is good agreement in the distribution of CAPEs

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One thing that struck my eye in the 850-mb dewpoint field from PHS, shown below, was the notch of drying over southwest Texas, mostly west of WFO SJT. There’s fair agreement between that modeled dry air at 850 mb and the plotted surface dewpoints.

The GOES-16 Split Window Difference field for the same time shows a similar notch of dry air (that pinches off by 2300 UTC). In the enhancement used below, the dry air over west Texas is darker, the moist air over WFO SJT is lighter. Convection that develops as the dry slot pinches off shows as black in the enhancement below, and is also apparent in the GOES-16 visible imagery shown above.

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HWT continues through Thursday 23 May 2024 in Norman. There is more information on this storm at the Satellite Liaison Blog.

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