Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jan 31 2024 08:11:55 FOUS30 KWBC 310811 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 311 AM EST Wed Jan 31 2024 Day 1 Valid 12Z Wed Jan 31 2024 - 12Z Thu Feb 01 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS FAR SOUTHWEST OREGON AND PARTS OF NORTHWEST AND WESTERN CALIFORNIA, INCLUDING THE COASTAL RANGES, MUCH OF THE SACRAMENTO VALLEY, BAY AREA, AND CENTRAL CALIFORNIA COAST... The Day 1 Slight and Marginal areas were largely unchanged from yesterday's Day 2 outlook. Deep/occluded cyclone currently centered well off the OR coast will meander slowly eastward over the next couple of days, though remain offshore through Friday. Meanwhile, a robust NW-SE oriented upper level jet streak (130-150kt at 250 mb) will help drag the longwave trough farther south into southern CA by Thursday. Strong deep-layer synoptic scale support will move into the outlook areas within an expanding area of increased difluence aloft, as both the upper level divergence and south-to-north transport of low-mid layer subtropical moisture become enhanced within the left-exit region of the aforementioned upper jet streak. Robust 850 mb S-SW flow today will be around 5 standard deviations above normal for late Jan per the 00Z GEFS and SREF, peaking between 50-60kts long the coast. Meanwhile, 850-700 mb moisture flux anomalies are expected to reach +4 to +5 standard deviations this morning as the 1.00-1.25" PW plume skirts the CA coast. During the afternoon and overnight, low-mid layer moisture flux anomalies are expected to scale back a bit (closer to +3-3.5 standard deviations above normal) as the AR drops south into the Central CA Coast. The strength and duration of the IVT anomaly equates to a moderate AR based on the CW3E AR Scale per both the GEFS and ECMWF ensemble means, with peak IVT magnitudes of 600-800+ kg/m/s. However the relatively swift duration of the AR should limit the coverage of short-term runoff impacts across the outlook area, along with the weakening magnitude of the AR with time (especially late Wed-Wed night) as it becomes more dislodged from the cutoff low to the north. The latest CSU GEFS-based first-guess fields, particularly the UFVS-verified version, continue to support the continuation of the Slight Risk that was noted in yesterday's Day 2 ERO. The forward progression of the system and a lack of instability along/ahead of the front both continue to be limiting factors with regards to the magnitude of the flood threat. Nonetheless, strong convergence along the southward shifting cold front combined with favorable upper jet dynamics will likely support some embedded convective elements and locally intense rainfall rates within the rain shield . The 00Z HREF neighborhood probabilities of hourly rainfall exceeding 0.75" through 12Z Thursday are 30%+ over a good portion of the Slight Risk area. Thus it seems likely that some heavier rates will transpire, and so even with a progressive system do expect to see some flooding impacts. The greatest coverage/magnitude of impacts (urban and small stream flooding, rock/landslides) still appear to be over northern CA where 3-5" (locally higher) rainfall is expected, but some impacts are likely further down the coast as well within the favored terrain and where any higher rates materialize. Hurley/Chenard Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7B2ml44it-YLQzntwM1VK8Jic4-dc0xMoHFxkA5BfZz3= c-3xLF64sFNLKUWkjuSlMSKwM9RcImD7nqfBcmUDIyD-TQM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7B2ml44it-YLQzntwM1VK8Jic4-dc0xMoHFxkA5BfZz3= c-3xLF64sFNLKUWkjuSlMSKwM9RcImD7nqfBcmUDgOQQWVw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7B2ml44it-YLQzntwM1VK8Jic4-dc0xMoHFxkA5BfZz3= c-3xLF64sFNLKUWkjuSlMSKwM9RcImD7nqfBcmUDxnAJ15E$=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) .