Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun May 04 2025 08:31:16 FOUS30 KWBC 040831 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 431 AM EDT Sun May 4 2025 Day 1 Valid 12Z Sun May 04 2025 - 12Z Mon May 05 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE HIGH PLAINS ADJACENT TO THE SOUTHERN ROCKIES... New Mexico... There is a slight risk of excessive rainfall over portions of eastern New Mexico as south to southeasterly flow draws moisture into the region as height falls begin in response to shortwave energy approaches. The 04/00Z suite of numerical guidance develops heavy rainfall developing in the diurnal activity that then=20 persists over the southern High Plains well into late tonight/early Monday morning. Precipitable water anomaly values reaches 2 sigma=20 over this area by 00Z Monday..with the 04/00Z HREF mean suggests=20 some repeating threats for 1"/hr rates across the Slight area with=20 potential for 2-3" over much of the area. The eastern portion of=20 the Marginal risk area was largely left unchanged...but the western portion of the area was trimmed to minimize overlap with heavy=20 snow areas (especially over the San Juan mountains). Great Basin... While the probability of excessive rainfall is likely non-zero given the showery nature of precipitation given the upper trough=20 and cold mid- level temperatures aloft...the amount of rain=20 shouldn't be a problem unless it all falls in under an hour. Individual thunderstorms may result in briefly heavy rates...but thinking is that the thunderstorms will be embedded=20 within a broader field of showers circulating around the main upper low. This should help mitigate the overall threat of flooding. Midwest to Northeast... The slow moving closed low embedded within a broader upper trough continues to make its way eastward across the Ohio Valley today and tonight. Deepest moisture of 1.25 to 1.5 inches will be eventually be shunted off the Mid- Atlantic coast today but still stream in=20 over New York back and then drawn back through northern Ohio. The=20 Marginal Risk is maintained with only nudges to the western/northern periphery of the Marginal risk area based on the latest QPF.=20 Bann Day 2 Valid 12Z Mon May 05 2025 - 12Z Tue May 06 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN HIGH PLAINS... Texas into New Mexico... A closed upper low over the Desert Southwest will continue to meander eastward on Monday. Confidence remains in a focused area=20 for repeating heavy rainfall south from the TX Panhandle to the NM border where a Slight Risk remains without many changes...with main activity occurring once again around the time of maximum daytime heating and then persisting into or through the night. The suite=20 of 04/00Z numerical guidance still shows the magnitude of=20 precipitable water values to exceed 2 sigma by 00Z Tuesday with the 1.25" precipitable water line reaching the Caprock. The 12Z QPF=20 consensus is for 2-4" over a sizable area just south of the TX=20 Panhandle...with locally higher amounts embedded in the broader QPF area. Mojave Desert through Southern Utah... Numerous showers with embedded daytime and evening thunderstorms is still expected as upper low continues to meander over Arizona as=20 it begins to fill. Moisture is still anomalous for this time of=20 year...being some 2 to 3 standardized anomalies above climatology=20 for early May...but concern would be greater for excessive rainfall if the actual values of precipitable water values were greater and intense rainfall rates would be sustained for a longer duration.=20 As a result...the risk of excessive rainfall appears to be non-zero but not enough to warrant a Marginal risk area based on=20 coordination with local offices. Northern Mid-Atlantic into southern New England... Closed low will continue to meanders across portions of the Upper=20 OH Valley through Monday night. Continued onshore flow brings the=20 threat for repeating locally heavy rain over the northern Mid-=20 Atlantic into southern New England which will have seen some heavy=20 rain between now and then. A Marginal Risk is maintained. Bann Day 3 Valid 12Z Tue May 06 2025 - 12Z Wed May 07 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN MISSISSIPPI VALLEY/CENTRAL GULF COAST REGION... Showers and thunderstorms capable of producing intense rainfall rates and heavy/excessive rainfall will become more numerous=20=20 on Tuesday as height falls make their way out across Texas and as the parent upper low ejects out over the Southern Plains. With increasing flow off the Gulf drawing deeper moisture on- shore....the convection should become increasingly efficient=20 rainfall makers.especially over portions of Louisiana and=20 Mississippi. There is still some differences in where models place=20 the heaviest rainfall...with the GFS and Canadian favoring a faster solution while the EC/UK favoring the axis from eastern Texas into northern Louisiana. This forecast cycle nudged the Moderate risk=20 area a bit eastward but not as far east as the GFS/Canadian. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6dTVjEEkBIyndyMa9Gh5Zi_Ce7BxVBqHlgPlVou7vCQS= Y9Ykfz-I1t8Lkkkl0R4tBCGHFHdwFp-6sNEj9-aOP5VZSDA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6dTVjEEkBIyndyMa9Gh5Zi_Ce7BxVBqHlgPlVou7vCQS= Y9Ykfz-I1t8Lkkkl0R4tBCGHFHdwFp-6sNEj9-aOjeHnvSo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6dTVjEEkBIyndyMa9Gh5Zi_Ce7BxVBqHlgPlVou7vCQS= Y9Ykfz-I1t8Lkkkl0R4tBCGHFHdwFp-6sNEj9-aOX1u4wL8$=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .