Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat May 03 2025 20:37:22 FOUS30 KWBC 032037 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 437 PM 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... An upper-level low is forming over the mid-Mississippi region and becomes cutoff over Kentucky tonight as the jet focuses over eastern Canada. Low level flow is drawing Gulf moisture through and ahead of the system from the Gulf Coast up through the Eastern Seaboard. Several focus areas for thunderstorms are expected through tonight in the broad area which covered by a contiguous Marginal Risk. Ohio Valley to Gulf Coast... Locally heavy activity has developed ahead of a surface low over western TN with scattered storms south ahead of the advancing cold front through MS and north along a stalled boundary that extends to the upper Ohio Valley. This activity may pivot over eastern KY/southern OH through the middle afternoon while activity over AL to the Gulf Coast should be more progressive. Carolinas, Central Appalachians and Mid-Atlantic... Lee trough development over the Piedmont in the Carolinas later this afternoon will allow potentially training activity in deep SSWly flow there well into the evening, so the Marginal Risk was 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 bringing potential for excessive rain despite strong deep layer flow. The Marginal Risk was expanded north into central New England. A second round of development is expected farther south this evening in the Hudson Valley and southern New England which was already covered by a Marginal. New Mexico... Afternoon convection over the Sacramento Mtns brings a threat for runoff issues from burn scars into this evening, so the Marginal Risk is maintained. Jackson Day 2 Valid 12Z Sun May 04 2025 - 12Z Mon May 05 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE EASTERN UNITED STATES AND SOUTHERN ROCKIES AND ADJACENT HIGH PLAINS... 21Z Update... New Mexico... A Slight Risk has been raised for portions of eastern NM based on a notable increase in QPF from the 12Z guidance consensus. SWly flow over TX brings robust Gulf moisture up through the southern Rockies and adjacent High Plains as a closed low develops and stalls over the Sonoran Desert. Heavy rain develops in the diurnal activity that then persists over the southern High Plains well into Sunday night as the low stalls. The PW anomaly reaches 2 sigma over this area by 00Z Monday. The 12Z HREF mean suggests some repeating threats for 1"/hr rates through this Slight area with potential for 2-3" over much of the area. The Marginal risk was expanded to the lower flanks of the San Juans based on updated QPF and FFG. Great Basin... Sunday is the second day for the Great Basin under the upper trough. With PW anomalies of 2-3 sigma over normal with instability and fairly light deep layer flow should allow some repeating activity over Nevada and the Mojave Desert where a Marginal Risk is raised. Midwest to Northeast... The slow moving closed low embedded within a broader upper trough continues to make its way eastward Sunday. Deepest moisture of 1.25 to 1.5 inches will be eventually be shunted off the Mid- Atlantic coast Sunday afternoon, but still stream in over NY back through northern Ohio. The Marginal Risk is maintained with an expansion over the Detroit metro given 12Z QPF consensus along with lower FFG. Jackson Day 3 Valid 12Z Mon May 05 2025 - 12Z Tue May 06 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF WEST TEXAS... Texas into New Mexico... The upper low drifts east over southern AZ Monday, causing a minor shift east in downstream rainfall compared to Sunday. Confidence remains in a focused area for repeating heavy rain south from the TX Panhandle to the NM border where a Slight Risk remains (it was expanded a bit west through the NM border). A bit of a lull in QPF is expected Monday morning, but diurnal increases expected in the afternoon that then persist into or through the night. The PW anomaly is forecast to exceed 2 sigma by 00Z Tuesday with the 1.25" PW line reaching the Caprock. The 12Z QPF consensus is for 2-4" over a sizable area just south of the TX Panhandle. Mojave Desert through Southern Utah... The broadening upper low over AZ aids instability over the Mojave Desert through northern AZ and southern/central UT where a Marginal Risk is raised for Monday. Continued light deep layer flow and PW anomalies of 2-3 sigma should allow slow moving, heavy thunderstorms over this area which includes the Slot Canyons of southern UT. Northern Mid-Atlantic into southern New England... Closed low meanders to the Upper OH Valley Monday night. Continued onshore flow brings the threat for repeating locally heavy rain over the northern Mid-Atlantic into southern New England which will have seen some heavy rain between now and then. A Marginal Risk is maintained. Jackson Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_5_IjFrWArYNhKbX3d93uvm_ogG1W_rlPbutYb2tCOlu= bLJ34v2McXYld19HY3hd9DHe8vfDxoLlDJDqxymVInWs2FU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_5_IjFrWArYNhKbX3d93uvm_ogG1W_rlPbutYb2tCOlu= bLJ34v2McXYld19HY3hd9DHe8vfDxoLlDJDqxymVEdCWK2M$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_5_IjFrWArYNhKbX3d93uvm_ogG1W_rlPbutYb2tCOlu= bLJ34v2McXYld19HY3hd9DHe8vfDxoLlDJDqxymV3TXyul0$=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. 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