Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jan 19 2024 08:11:30 FOUS30 KWBC 190811 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 310 AM EST Fri Jan 19 2024 Day 1 Valid 12Z Fri Jan 19 2024 - 12Z Sat Jan 20 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Pereira Day 2 Valid 12Z Sat Jan 20 2024 - 12Z Sun Jan 21 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NORTHERN CALIFORNIA AND SOUTHWEST OREGON... Guidance has remained consistently wet now over the past few runs across portions of northern California and southwestern Oregon.=20 Precipitation is expected to develop across much of the region prior to Day 2 as a negatively-tilted mid-to-upper level trough and its associated frontal band move into the region Friday night. The models have been consistent in showing a weakening IVT plume as it moves onshore late Friday into early Saturday. However, westerly flow south of the parent low is expected to tap a secondary surge of deeper moisture and direct into the region as it lifts northeast along the northern California to southern Oregon coasts on Saturday. This moisture along with sufficient large-scale lift is expected to support an increase in rainfall rates with moderate to heavy amounts expected beginning Saturday morning. The general consensus of the deterministic models over past few runs suggests amounts of 1-3 inches, with locally heavier accumulations are likely across the region, with the heaviest amounts most likely in the upslope regions of the coastal ranges and the northern Sierra and southern Shasta foothills. HREF probabilities suggest that much of this may occur in the first 12 hours, showing high neighborhood probabilities for accumulations of 2 inches or more from 12Z Sat - 00Z Sun across parts of the area. Given the wet antecedent conditions and the move in the models toward a wetter solution, opted to upgrade this area to a Slight Risk.=20=20=20 Pereira Day 3 Valid 12Z Sun Jan 21 2024 - 12Z Mon Jan 22 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF NORTHERN CALIFORNIA... ....California and southwest Oregon... An unsettled period is forecast to continue with widespread precipitation and the potential for locally heavy amounts continuing as a broad upper trough with a series of embedded shortwaves moves across the region. Given what is significant model QPF spread, confidence in the details is limited, however opted to maintain a Slight Risk across an area similar to Day 2, where some models indicate the redevelopment of heavier rates ahead of an amplifying shortwave approaching Northern California early Monday. In contrast to Day 2, the overall model QPF trend has been lighter. Should this trend continue, the Slight Risk may be removed at some point. However, given the potential for at least locally heavy amounts across the same area where heavy accumulations are expected to occur in the prior period, opted to maintain the Slight Risk for now. .....Southern and central Texas... As a broad upper trough moves across the Southwest into the southern Rockies and High Plains, southerly low level inflow is expected to increase across southern to eastern Texas. PWs are forecast to increase to 1.25-1.5 along a 40-50 kt low level jet extending from the northwestern Gulf of Mexico through eastern Texas. This moisture, interacting with increasing ascent afforded in part by favorable upper jet forcing, will support the development of moderate to heavy rainfall across portions of southern to central Texas. While several models indicate heavy amounts, they differ on the magnitude and location. And while they show ample moisture and lift, rainfall rates may be limited by the lack of instability apart from South Texas and along the Gulf Coast. Therefore, opted to maintain the Marginal Risk. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7L1VuHMxe7rGV-m6aBY8wGYE4LlN2PDHAWiTtQoNzEWz= nPUZy1lmBl4DB3T5kG1NF3VMla5IRE2Lx9EtcKgwyBPXyVc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7L1VuHMxe7rGV-m6aBY8wGYE4LlN2PDHAWiTtQoNzEWz= nPUZy1lmBl4DB3T5kG1NF3VMla5IRE2Lx9EtcKgwQpZHHrM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7L1VuHMxe7rGV-m6aBY8wGYE4LlN2PDHAWiTtQoNzEWz= nPUZy1lmBl4DB3T5kG1NF3VMla5IRE2Lx9EtcKgwZRTPBHY$=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) .