Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat May 03 2025 15:59:56 FOUS30 KWBC 031559 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1159 AM EDT Sat May 3 2025 Day 1 Valid 16Z Sat May 03 2025 - 12Z Sun May 04 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE EASTERN U.S. AND THE SACRAMENTO MOUNTAINS OF NEW MEXICO... 16Z Update...=20 An upper-level low is forming over the mid-Mississippi region and=20 becomes cutoff over Kentucky tonight as the jet focuses over=20 eastern Canada. Low level flow is drawing Gulf moisture through and ahead of the system from the Gulf Coast up through the Eastern=20 Seaboard. Several focus areas for thunderstorms are expected=20 through tonight in the broad area which covered by a contiguous=20 Marginal Risk.=20 Ohio Valley to Gulf Coast...=20 Locally heavy activity has developed ahead of a surface low over=20 western TN with scattered storms south ahead of the advancing cold=20 front through MS and north along a stalled boundary that extends to the upper Ohio Valley. This activity may pivot over eastern=20 KY/southern OH through the middle afternoon while activity over AL=20 to the Gulf Coast should be more progressive.=20 Carolinas, Central Appalachians and Mid-Atlantic...=20 Lee trough development over the Piedmont in the Carolinas later=20 this afternoon will allow potentially training activity in deep=20 SSWly flow there well into the evening, so the Marginal Risk was=20 expanded east a bit over SC/NC. This activity lifts north through the central Appalachians into this evening with localized flash flood threats. Later tonight the activity shifts east with some training potential, so the Marginal was maintained east through the Baltimore/Washington urban centers. Northeast... The northern end of the moisture plume converges on a frontal zone over Upstate NY and central New England through this afternoon=20 bringing potential for excessive rain despite strong deep layer=20 flow. The Marginal Risk was expanded north into central New=20 England. A second round of development is expected farther south=20 this evening in the Hudson Valley and southern New England which=20 was already covered by a Marginal.=20 New Mexico...=20 Afternoon convection over the Sacramento Mtns brings a threat for=20 runoff issues from burn scars into this evening, so the Marginal=20 Risk is maintained. Jackson Day 2 Valid 12Z Sun May 04 2025 - 12Z Mon May 05 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE EASTERN UNITED STATES AND SOUTHERN ROCKIES AND ADJACENT HIGH PLAINS... The risk of excessive rainfall persists across parts of the Mid- Atlantic and Southeast US as a slow moving closed low embedded within a broader upper trough continues to make its way eastward. Deepest moisture of 1.25 to 1.5 inches will be eventually be shunted off- shore late in the period. Until then...isolated downpours are possible with spaghetti plots of 2 and 3-inches of rain in 24 hours mainly being produced by models with the ARW core...but enough members from the NMM core and from the GEFS to warrant a Marginal. The western boundary of the Marginal was trimmed compared with the previous outlook given the models being more progressive with the surface cold front and the push of drier air being brought in behind the front. There is also a Marginal Risk area over parts of New Mexico again as moisture continue to spread northward and westward from the Gulf. After 00Z...the flow aloft between the westerly subtropical jet and a jet streak and low- and mid-levels become increasingly diffluent with height falls beginning ahead of an approaching closed low from the west. This...along with moisture and a low level boundary already in place...should support late day and evening storms that may produce locally heavy rainfall rates. Bann Day 3 Valid 12Z Mon May 05 2025 - 12Z Tue May 06 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE HIGH PLAINS ADJACENT TO THE SOUTHERN ROCKIES... Shortwave energy rotating around the periphery of an upper low making its way over the Southwest US will trigger late day thunderstorms on Monday over parts of West Texas that grow upscale in terms of both coverage and rainfall amounts through much of Monday night/early Tuesday morning. A feed of low level moisture being forced upslope ahead of the approaching shortwave will help fuel the potential for downpours and locally heavy rainfall amounts leading to the potential of flash flooding. QPF from the operational models have maximum amounts of rainfall in the 2.5 to 3.8 inches...which tended to be supported by the SREF and GEFS spaghetti plots and by machine learning first guess EROs. Felt a Slight Risk area covers the potential for time being. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4p0s8cSHTpSumRt7ojK4BgBep2S_TTZtjWBnuprwC1FC= p8nEN7RAnMHrVSpT9rD1r1O7Fgb7ruOuDKIIuSyorAdLLsk$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4p0s8cSHTpSumRt7ojK4BgBep2S_TTZtjWBnuprwC1FC= p8nEN7RAnMHrVSpT9rD1r1O7Fgb7ruOuDKIIuSyom7ZqxxU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4p0s8cSHTpSumRt7ojK4BgBep2S_TTZtjWBnuprwC1FC= p8nEN7RAnMHrVSpT9rD1r1O7Fgb7ruOuDKIIuSyoqwom3do$=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) .