Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 02 2023 16:10:14 FOUS30 KWBC 021610 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1109 AM EST Mon Jan 02 2023 Day 1 Valid 16Z Mon Jan 02 2023 - 12Z Tue Jan 03 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE LOWER MISSISSIPPI AND LOWER OHIO VALLEYS... 1600Z Update... A Moderate Risk of excessive rainfall has been introduced with this update for areas of central to northeast AR, far southeast MO including the Bootheel, and into adjacent areas of far southern IL and western KY based on the latest trends from the 12Z HREF guidance. A very strong and confluent low-level jet (50 to 60+ kts) developing ahead of the strong upper trough/closed low ejecting east out of the Four Corners region will be facilitating the pooling of very anomalous moisture for this time of the year across much of the Arklatex, Lower MS Valley and the Lower OH Valley by later today and especially heading into the overnight time period. PWs are forecast to rise to 1.5+ inches across much of this region with 850/700 mb moisture flux anomalies reaching 3 to 5+ standard deviations above the mean. This will all be coinciding with at least a loosely coupled upper-jet structure for enhanced divergence aloft and an axis of locally moderate instability (MUCAPE values of 1000 to 1500+ J/kg), although even greater instability parameters will be noted farther south over the Lower MS Valley closer to the Gulf Coast. Based on the current observational data and latest HREF guidance, the expectation is for a regional outbreak of well-organized convection with areas of repeating/training supercell convective and ultimately a QLCS evolution from late this afternoon into the overnight hours. Rainfall rates are likely to reach 1 to 2+ inches/hour, and some storm total amounts in and around the Moderate Risk area may reach 3 to 6 inches given the concerns for multiple rounds of convection. A regional threat of flash flooding appears likely given the setup. Orrison Previous discussion... ....Eastern Texas and Oklahoma to the lower Ohio Valley... A deep closed low/upper trough will continue to move eastward from the Southwest-Four Corners Region into the Rockies/High Plains today. Deep southerly flow ahead of the advancing system will transport a plume of copious moisture from the western Gulf of Mexico across the region. Guidance continues to show PWs in excess of 1.5 inches along the axis of strongest inflow. This moisture along with increasing instability is expected to interact with an area of strong ascent afforded in part by favorable upper jet forcing. This will support widespread thunderstorm development during the afternoon ahead of an advancing cold front. Intense rainfall rates are likely to develop, with cell mergers and training convection likely to support heavy amounts within the outlook area. Neighborhood probabilities from the 00Z HREF suggest the potential for widespread amounts of 2-3 inches within the Slight Risk area. Overall, the new Day 1 outlook area remained similar to the previous Day 2, with a small northeastward adjustment into the lower Ohio Valley that reflects the 00Z model trends. Pereira Day 2 Valid 12Z Tue Jan 03 2023 - 12Z Wed Jan 04 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE GULF COAST AND THE TENNESSEE VALLEY TO SOUTHERN APPALACHIANS... ....Central Gulf Coast to the southern Appalachians and the Tennessee and Ohio Valleys... The upper low moving into the central Plains on Monday night will continue its pivot to the northeast, tracking into the upper Midwest on Tuesday as shortwave energy to its south amplifies the trough over the south-central U.S. Ongoing convection from the Day 1 period is expected to continue into at least the early part of Day 2. Although guidance indicates diminishing moisture at this point, instability and strong forcing may be sufficient to maintain the threat for intense rainfall rates and heavy accumulations from the lower Ohio Valley back to southwestern Louisiana and far southeastern Texas Tuesday morning. Some storms may continue farther east through the morning and then reintensify during the afternoon/evening across the Tennessee Valley into the southern Appalachians. Then as the amplifying upper trough continues to move east, some models indicate that increasing upper forcing and another surge of deeper moisture may prouce an additional round of storms bolstering the threat for heavy accumulations across portions of the Tennessee Valley into the southern Appalachians. Farther to the south, convection is expected to become better organized during the day across the central Gulf Coast states, with energy embedded within the trough supporting development from Louisiana into Mississippi and Alabama. Models present a fair amount of spread with how convection will evolve and their placement of heavier amounts. Global guidance, including the ECMWF and the UKMET, remain much more tied to the coast, while some of mesoscale guidance, including the Canadian Regional, focus heavier amounts well to the north along with some of the better forcing. With limited confidence, maintained continuity with the Slight Risk still along portions the Gulf Coast from southern Alabama to the Florida Panhandle, but also extended it farther north to include more southern Alabama with this issuance.=20=20 Pereira Day 3 Valid 12Z Wed Jan 04 2023 - 12Z Thu Jan 05 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CALIFORNIA... ....California... There remains a strong signal for another atmospheric river event with heavy precipitation, including heavy rains, developing across a large portion of California this period. Models show a deep closed low advancing eastward across the eastern Pacific this period, with deep southwesterly flow directing a plume of deep moisture into California on Wednesday. Precipitation is expected to arrive with the system's associated warm front on Wednesday.=20 Precipitation will then likely intensify late Wednesday into the overnight as the trailing cold front and accompanying plume of deep moisture move inland. Widespread accumulations of 2-4 inches, with heavier amounts in the favored terrain, is expected along much of the coast, with heavy rains also expected inland across northern parts of the central valleys and the Sierra foothills. Given the wet antecedent conditions, these rains are expected to produce additional runoff concerns. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7H76UuCz2ieKhZknQFQf3mttFFarLmFuFDcnBsoxS2XE= U68JnsmHBcvuPUrpTCPjhZ5fTe2Kc1CUIS-Op21F5awPiBM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7H76UuCz2ieKhZknQFQf3mttFFarLmFuFDcnBsoxS2XE= U68JnsmHBcvuPUrpTCPjhZ5fTe2Kc1CUIS-Op21FMYizh9U$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7H76UuCz2ieKhZknQFQf3mttFFarLmFuFDcnBsoxS2XE= U68JnsmHBcvuPUrpTCPjhZ5fTe2Kc1CUIS-Op21FUk1ViPQ$=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) .