Snow fell across the Rockies and High Plains while severe storms and flooding struck the Central and Southern U.S. as May got off to an active start. From 06 to 07 May 2024, a potent low pressure system slowly trekked from Wyoming to South Dakota, reaching a minimum pressure of 980 mb at 1200 UTC 07 May 2024. NWS Weather Prediction Center (WPC) Meteorologist David Roth noted that Rapid City, SD, recorded a minimum pressure of 982.7 mb, breaking the previous May record of 983.7 mb recorded on 18 May 1893. Records in Rapid City date back to 1889. GOES-East Airmass RGB imagery from 1200 UTC 06 May 2024 to 1200 UTC 07 May 2024 showed the intensifying extratropical cyclone slowly pivoting to the east in an environment with high levels of potential vorticity, noted by the dark oranges and reds. In the animation you can also see storms explode along a dry line across the Central and Southern Plains during the afternoon and evening of 06 May 2024, including in Oklahoma where the NWS Storm Prediction Center had issued a High Risk for severe storms.
Figure 1: GOES-East Airmass RGB imagery shows a powerful low pressure moving from Wyoming to South Dakota from 1200 UTC 06 May to 1200 UTC 07 May 2024. Credit: NESDIS/STAR
The storm system brought late-season snow to the central and northern Rockies as well as the Black Hills. At ~1900 UTC 08 May 2024, GOES-East Day-Snow-Fog RGB imagery showed snow cover depicted by the bright red color across the Intermountain West with ice and water clouds moving overhead (pink and gray colors).
Figure 2: GOES-East Day-Snow-Fog RGB imagery at ~1900 UTC 08 May 2024 with fresh snow cover and traversing clouds across the Intermountain West. This animation was created in AWIPS, and display files can be shared on request.
On 08 May 2024, the main threat for severe storms shifted to the east, targeting eastern Oklahoma and Texas through the Tennessee Valley and Southeast. GOES-East Visible imagery (Band 2) overlaid with NOAA-20 NUCAPS showed plenty of soundings available at 1540 UTC 08 May 2024 across the Central U.S., with more reliable data noted by green dots and yellow dots on the edge of cloud cover. The circled yellow dot was the location of choice to examine a Skew-T plot as storms fired to the west in Missouri. The Skew-T sounding’s associated Mixed Layer (ML) CAPE parameter had a value over 1400 J/kg. Shortly after this sounding, the WPC issued a Mesoscale Precipitation Discussion (MPD) at 1735 UTC May 2024. From WPC in the early PM of 5/08: “The mesoscale environment in the vicinity of these storms is characterized by an ML CAPE gradient of 1000-2500 J/kg, PWATs of 1.2-1.4 inches (already near the 90th percentile, per SPC sounding climatology), and effective bulk shear of 50-70 kts.” The ML CAPE values from NUCAPS and in the text of the MPD matched well.
Figure 3: NOAA-20 NUCAPS Sounding location of choice, circled, overlaid with GOES-East Visible (Band 2) imagery valid at 1540 UTC 08 May 2024. This image was exported from AWIPS.
Figure 4: NOAA-20 NUCAPS Skew-T and associated parameters at the sounding location with the ML CAPE value highlighted. This image was exported from AWIPS.
Figure 5: GOES-East GeoColor RGB imagery used in the WPC MPD over eastern Missouri and southern Illinois during the afternoon of 08 May 2024.
By 1900 UTC 08 May 2024, a wide swath of convection stretched from northeast Oklahoma to North Carolina, marked in the GOES-East Day Cloud Phase Distinction RGB by bright yellows, indicating high, thick, glaciating clouds. GOES-East Geostationary Lightning Mapper Flash Extent Density (FED) imagery at the same time also detected lightning, with more intense storms noted by yellows, oranges, and reds where the FED values were higher.
Figure 6: GOES-East Cloud Phase Distinction RGB imagery with storms stretching from Oklahoma to North Carolina at ~1900 UTC 08 May 2024. This animation was created in AWIPS, and display files can be shared on request.
Figure 7: GOES-East GLM FED with lightning accompanying most of the convection at ~1900 UTC 08 May 2024. This animation was created in AWIPS, and display files can be shared on request.
By 09 May 2024, areas east of the higher elevations in Montana received anywhere from ~3.5-7.5″ of rain, which according to David Roth, leads to a weekly precipitation anomaly of over 600 percent. Meanwhile, snowfall amounts in western South Dakota reached a foot-and-a-half. From NWS WPC in the late AM of 5/09: “…Selected preliminary Storm Total Snowfall in inches where the event has ended………SOUTH DAKOTA…O’NEIL PASS 18.0…Selected preliminary Storm Total Rainfall in inches where theevent has ended……MONTANA…RW-ROCKY BOY 1 E 7.30 “.
NOAA-21 NUCAPS are now available in the NUCAPS Sounding Availability menu option in AWIPS.
Chris Smith, CISESS GOES-R Satellite Liaison for NWS WPC/OPC
