The Storm Prediction Center has deemed 6 May 2024 as a day with a High Risk of severe weather over the central/south-central Plains:

...SUMMARY...
   A regional outbreak of severe weather with multiple intense (EF3+),
   long-tracked tornadoes, as well as very large hail and severe
   thunderstorm gusts, is expected over parts of the south-central
   Plains from this afternoon through evening.

By 2100 UTC, strong convection had developed from South Dakota southward to western Oklahoma, as shown in the radar animation below (source).

The Polar Hyperspectral Model (PHS) includes as its assimilated input Fusion Data, i.e., ABI “retrievals” that are matched to the latest observations from Low Earth Orbit (LEO) Hyperspectral Soundings. The ABI retrievals thus have the great spatio-temporal resolution of ABI data and the excellent spectral resolution of the LEO Sounders. The result is a better description of the initial moisture distribution in the model. How is this performing today? Imagery below was taken from the model website here; once there click on Forecast Plots and then on the calendar to the correct day. The toggle below compares the 6-h forecast and the 3-h forecast of the PHS-influenced model (a 4-km WRF simulation). A series of Supercellular-like storms arcs from Nebraska southward to Kansas, with strong storms in northwestern South Dakota as well. Compare the toggle below to the one from a 3-km HRRR simulation that has not been influenced by PHS data. The HRRR simulation shows weaker convection.

The toggle below compares the 3-h forecasts (valid at 2100 UTC) of 3-km HRRR (no PHS data) with the 4-km WRF (with PHS data). (Here is a similar comparison of 6-h forecasts valid at 2100 UTC) The PHS data has lead to a more accurate simulation of the convective strength over Nebraska, Kansas and South Dakota.

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PHS scientists have created maps that combine where the High Shear and High Instability regions into one ‘Vortex Prediction’ image, shown below for 1700 UTC (and available at this website). This image below shows hourly forecasts valid at 1700 UTC, from forecasts initialized from 1100 – 1500 UTC on 6 May 2024. At 1700 UTC, the consistently-forecast most favorable environment for strong convection is over western Nebraska. That region is very close to the location of the first tornado touchdown of the day, shown below in SPC storm reports from 1830 UTC. (Imagery below courtesy Bill Smith Sr and Anthony DiNorscia, Hampton University).

Note that the HRRR simulation (left, below) has no similar signal as the WRF simulation with assimilated PHS data.

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At the request of Pacific Region Headquarters, the LightningCast domain centered on American Samoa has increased. At 1840 UTC, the domain roughly doubled, as shown in the two screen shots below from the RealEarth site. The Red Box captures the size of the previous domain; note that at 1900 UTC the contours extend from 160^oW westward to the dateline. The north-south domain size has also increased. The 1940 UTC image at the bottom of this post includes the new domain.

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Users will note that contours that touch the dateline in RealEarth will be drawn incorrectly (as shown here). This is being investigated. The AWIPS screen-capture, below, courtesy Eric Jacobsen, NWS/PRH, shows the display in AWIPS.

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5-minute CONUS Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed narrow tendrils of river valley fog — along a portion of the Mississippi River and a few of its tributaries in Wisconsin, Minnesota and Iowa — which dissipated after sunrise on 05 May 2024.

In southwest Wisconsin, the GOES-16 Marginal Visual Flight Rules (MVFR) Fog Probability derived product (above) correctly displayed an area of increased MVFR Probabillty just north of KCMY-KVOK beginning at 0801 UTC — and at 0901 UTC the visibility at the METAR site located within that region of higher probability dropped to 1/4 mile with fog. At 1101 UTC, surface reports at 2 sites in southwest Wisconsin reported Freezing Fog, with visibility as low as Zero to 1/4 mile. While the MVFR product did display low to medium probability values for some of the more pronounced areas of river valley fog, many of the fog features were too narrow to be resolved by the 2-km resolution Infrared data from GOES.

The GOES-16 Low Cloud Thickness derived product (below) indicated that most of the fog and low stratus across the region was only 500-800 ft thick — with some of the more pronounced areas of river valley fog exhibiting values of 1000-1200 ft.

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EUMETSAT Meteosat-9 Infrared Window (10.8 µm) images (above) showed Cyclone Hidaya as it intensified from a Tropical Storm (at 1200 UTC on 02 May) to Category 1 Hurricane intensity at 0000 UTC on 03 May 2024 (advisory | discussion). JTWC later noted that Hidaya had become the most intense tropical cyclone on record for this region, peaking at 80 kt (discussion).

A DMSP-18 SSMIS Microwave (85 GHz) image at 0024 UTC on 03 May, from the CIMSS Tropical Cyclones site (below) revealed a well-defined eye and surrounding eyewall structure.

Cyclone Hidaya had been moving across warm water and through an environment of fairly low deep-layer wind shear (below), two factors which were favorable for intensification.

An overpass of RCM-3 provided Synthetic Aperture Radar (SAR) imagery (source) at 1531 UTC on 02 May (below) — the maximum sensed wind speed was 74.94 kt in the SE quadrant of the eyewall.

However, an overpass of RCM-3 at 1539 UTC on 03 May (below) sensed a maximum velocity of 92.29 kt in the NE quadrant.

===== 04 May Update =====

Although Hidaya weakened to Tropical Storm intensity at 0000 UTC on 04 May (track), Meteosat-9 Infrared images (above) showed that a few brief convective bursts occurred as the tropical cyclone was approaching the coast of Tanzania. Hidaya made landfall by about 0300 UTC on 04 May (near Mafia Island), while still at Tropical Storm intensity.

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