Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Sep 12 2023 20:14:23 FOUS30 KWBC 122014 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 413 PM EDT Tue Sep 12 2023 Day 1 Valid 16Z Tue Sep 12 2023 - 12Z Wed Sep 13 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NEW MEXICO INTO EASTERN ARIZONA... ....Southwest to the southern High Plains... Expanded Slight Risk a bit north in New Mexico based on 12Z HREF CAMs consensus for areas with lower flash flood guidance. Marginal Risk expanded a bit north into Colorado based on 12Z HREF CAMs consensus. Active, quasi-zonal southern stream with embedded shortwave energy traversing w-e across the area will continue to support numerous showers and thunderstorms, particularly during the peak heating hours this afternoon. Meanwhile, a subtle (70-90kt) yet persistent upper jet streak along the OK-TX Panhandles into the northern Red River Valley will favor a boost in deep-layer ascent through this evening across east-central AZ into central and southern portions of NM (including the Albuquerque area). This is where we have delineated the Slight Risk in the Day 1 ERO, and while instability will remain marginal given the degree of cloud cover (MUCAPEs generally under 1000 J/Kg), PW and 850-700 moisture flux anomalies will be fairly robust within the Slight Risk area (around 2 standard deviations above normal). The latest (00Z) HREF shows probabilities of QPF exceeding 2.00" peaking between 30-50% within the Slight Risk area during the Day 1 period. Elsewhere, the concentration of heavier rainfall is expected to be more isolated-scattered per the model consensus, and as such the flash flood threat is expected to be more limited/localized (i.e. Marginal Risk). ....Carolinas, Appalachians, into the Northeast... Expanded Marginal Risk through south-central Appalachians and central North Carolina Amplifying upper trough over the Upper Midwest/western Great Lakes will pinwheel east into the OH Valley and eastern Great Lakes by 12Z Wednesday. Pre-trough/pre-frontal activity has developed over the upper Ohio Valley which will continue to expand east through tonight. The front is fairly progressive, and the PW anomaly peaks at about one standard deviation above normal by 06Z tonight, but SWly deep layer mean flow is parallel to this boundary so there is a threat for some repeating, locally heavy activity, warranting the Marginal Risk expansion, especially where there is lower FFG from recent rains. This activity further intensifies tomorrow over the Northeast where there is a Slight Risk. Jackson/Hurley Day 2 Valid 12Z Wed Sep 13 2023 - 12Z Thu Sep 14 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS AND NORTHEAST... ....Southwest and Four Corners Region into the Southern Plains... An impulse currently over NV shifts ESE across the southern Rockies Wednesday morning with organized activity in the southern High Plains/Caprock spreading through north-central TX where moisture has been building over the past couple days in flow off the western Gulf. 12Z CAM guidance focuses heavy rain a bit farther south/west which is where the Slight Risk in northeast NM into central Texas was shifted. This Slight Risk area is coincident with the +1.5 sigma PW anomaly. ....Upper Texas Coast... Continued onshore flow from the northwest Gulf of Mexico brings PWs above 2" and the approaching impulse should allow evening/overnight heavy convective development along the northern half of the Texas Coast into southwest LA. Decent model agreement from the 12Z HREF CAMs warrants an introduction of a Marginal Risk here despite the area being in exceptional drought due to sensitive urban areas and particularly heavy rates expected. ....Mid-Atlantic into Eastern New York and through New England... An upper low over the Upper Great Lakes this afternoon opens into a trough that takes on a negative tilt over eastern Ontario/Quebec Wednesday night. Strengthening deep-layer forcing ahead of the low/trough will get a boost from a southerly 80-100kt upper jet streak on the eastern flank and support more widespread, organized convection developing late tonight ahead of the advancing cold front. This cold front is progged to be a bit more progressive and the extent of high PW (over 1.75") is generally limited to south/central New England, so the Slight Risk was trimmed a bit from the west, limited to southern VT/central NH, but also expanded a bit east in Mass/RI which are more sensitive after heavy rains yesterday. Jackson Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-964snp_6KyId5j2y7ZbqHx3L5gnMFsi16tt-nia40ty= JAmlIuHPv94ItW-j7V-kU_32_RWZ8Z0bt99Frn92OdNiPoc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-964snp_6KyId5j2y7ZbqHx3L5gnMFsi16tt-nia40ty= JAmlIuHPv94ItW-j7V-kU_32_RWZ8Z0bt99Frn92Uy3O1BA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-964snp_6KyId5j2y7ZbqHx3L5gnMFsi16tt-nia40ty= JAmlIuHPv94ItW-j7V-kU_32_RWZ8Z0bt99Frn92hRqoR8s$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .