Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jan 03 2023 20:29:36 FOUS30 KWBC 032029 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 328 PM EST Tue Jan 03 2023 Day 1 Valid 16Z Tue Jan 03 2023 - 12Z Wed Jan 04 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN ALABAMA AND SOUTHWEST GA... ....16z update... Our day 1 moderate risk area was expanded into portions of southwestern Alabama to mainly account for ongoing convective trends emanating from parts of southern Mississippi. In coordination with local offices, the marginal risk area was expanded into portions of western and central Pennsylvania. The HREF mean signal for continued rainfall until at least this evening, anomalous PWATs between +3 to +4 standard deviations from the mean, and reasonably high 1-2" exceedance probablities for the 24 hour period ending at 12z support at least some sort of risk for these areas. Additionally, the slight risk over portions of the Southeast was expanded north into parts of southern Kentucky to account for increased 24hr exceedance probablities, modest HREF 1hr precip signals hovering around 0.25/hr and multiple rounds of rainfall through tonight. ....Previous discussion... ....Central Gulf Coast to the lower Ohio Valley and southern Appalachians... Moist, southerly flow ahead of a deep low lifting out of the central Plains will continue to interact with strong upper forcing to support a broken line of convection extending from the lower Ohio back into the lower Mississippi Valley early today. PWs around 1.5 inches, coincident with a 40-50 kt low level jet will continue to interact with strong ascent afforded by a coupled upper jet to support storms with potentially heavy rainfall this morning. Storms are expected to advance through the Tennessee Valley into the southern Appalachians during the day, with locally heavy amounts expected. Meanwhile farther to the south, increasing instability, ample moisture and mid level energy moving through the broader scale trough are expected to enhance the potential for developing storms across the central Gulf Coast states during the afternoon. Intense rates along with potential training are expected to contribute to the threat for heavy amounts. These initial storms are expected to lift out to the northeast during the evening. However, another surge of deep moisture supported by an amplifying upstream trough is forecast to generate another round of convection and potential heavy amounts along the system's advancing cold front. While there is still some uncertainty, the majority the 00Z HREF guidance, excluding the ARW, showed the greatest threat for heavy amounts centered across southern Alabama into southwest Georgia. A Moderate Risk was introduced across this area, highlighting high neighborhood probabilities for accumulations of 3 inches or more during the period. Kebede/Pereira=20=20=20 Day 2 Valid 12Z Wed Jan 04 2023 - 12Z Thu Jan 05 2023 ....THERE IS MODERATE RISK FOR EXCESSIVE RAINFALL ALONG NORTHERN AND CENTRAL CALIFORNIA COAST... ....2030 update... No changes were made to the moderate risk area. Minor changes were made to the slight and marginal risk areas to encompass some canyons and mountain passes along the Sierra/southern Cascades. The latest guidance is in reasonable agreement with the overnight suite regarding qpf, rain rates, the low level jet and PWATs. Elsewhere, a marginal risk of excessive rainfall was introduced over portions of the central Appalachians and the Carolina piedmont. ....Previous Discussion... ....California... A deepening upper low is forecast to move across the eastern Pacific toward the Northern California and Oregon coasts on Wednesday. This will direct a long fetch of deep moisture into California, fueling widespread heavy precipitation, including heavy rain, along the coast and the interior valleys.=20 Precipitation is expected to begin with the arrival of a well-defined warm front on Wednesday, which by itself may produce locally heavy amounts across the region. However, the heaviest amounts are expected to unfold later in the day and continuing into the overnight as the trailing cold front and coinciding plume of copious moisture moves onshore. Strong onshore flow along with favorable upper jet forcing will help contribute to heavy precipitation. Widespread accumulations of 2 to 4 inches are expected across northern and central California, with localized heavier totals in the favored terrain. This includes much of the northern and central California coast from the Redwood Coast south through Monterey Bay, where rainfall totals are most likely.=20 Given the wet antecedent soil conditions produced by recent heavy rains and the likelihood for additional heavy amounts, a Moderate Risk was introduced this period, indicating that numerous flash floods and runoff concerns are likely across this area. Kebede/Pereira 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!7O8Te-Z0_BBB10Vl_ZXk-bm_TQm70t9Q3MSlU9lX6-L6= lZFhYvhl27qcgPcrIhoOfozoLdJ7-hAOVGcrCzh-h9qRfi8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7O8Te-Z0_BBB10Vl_ZXk-bm_TQm70t9Q3MSlU9lX6-L6= lZFhYvhl27qcgPcrIhoOfozoLdJ7-hAOVGcrCzh-etsHEPQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7O8Te-Z0_BBB10Vl_ZXk-bm_TQm70t9Q3MSlU9lX6-L6= lZFhYvhl27qcgPcrIhoOfozoLdJ7-hAOVGcrCzh-hsdrOxg$=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) .