Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Mar 28 2024 08:17:28 FOUS30 KWBC 280817 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 417 AM EDT Thu Mar 28 2024 Day 1 Valid 12Z Thu Mar 28 2024 - 12Z Fri Mar 29 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF EASTERN NORTH CAROLINA AND SOUTHEASTERN VIRGINIA... ....Eastern North Carolina - Southeastern Virginia... An upper trough moving over the lower Mississippi Valley and northern Gulf will begin to assume a negative tilt as it moves into the Southeast today. Right-entrance region upper jet forcing will=20 support a deepening low that will track north along the Southeast=20 to the southern Mid-Atlantic coast later this morning. This will support continued southwest to northeast training showers and=20 thunderstorms into the afternoon, with additional heavy rainfall=20 amounts expected over the region. Although instability will be=20 limited, strong forcing interacting with sufficient moisture (PWs=20 1.25-1.5 inches) will be enough to support rainfall rates up 1=20 inch/hour and accumulations 1-3 inches. HREF neighborhood=20 probabilities indicate that additional totals of 2 inches or more=20 are likely within the Slight Risk area. These amounts on top of=20 wet antecedent conditions can be expected to cause additional=20 runoff concerns.=20 ....New England... As the previously noted low develops and approaches from the south, a slow-moving front will provide the focus for deepening moisture and soaking rains across much of coastal New England. Overall, models have remained consistent in showing a long stripe of 1-3 inch amounts extending from eastern Connecticut to DownEast Maine. Rainfall rates will be limited by a lack instability, likely=20 topping out near 0.25 inch/hour. However, given the recent rainfall and saturated soils, there remain some runoff concerns, promoting=20 the continuation of a Marginal Risk.=20 Pereira Day 2 Valid 12Z Fri Mar 29 2024 - 12Z Sat Mar 30 2024 .....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHERN CALIFORNIA... A well-defined shortwave diving west of a closed low centered west of Vancouver Island is expected to support the development of a=20 closed low further south that will drop south along the northern=20 California coast Friday into Saturday. Models continue to advertise an anomalously deep system for this time of year, with 500 mb=20 heights dropping 1-3 standard deviations below normal across much=20 of California this period. Deep southwesterly flow ahead of the low will support increasing IVTs, with the highest values dropping=20 south along the coast from Monterey Bay into the Transverse Ranges. A Slight Risk was maintained over Santa Barbara and Ventura=20 counties, where the models continue to show a decent signal for=20 locally heavy amounts in the favored terrain. The consensus of the=20 deterministic guidance shows amounts of 1-3 inches in the region,=20 with locally heavier amounts possible by 12Z Saturday. There is=20 also some signal for locally heavy amounts further to the north=20 along the immediate coast, indicating the Slight Risk area may need to be drawn further to north into central California. But for now, maintained a broad Marginal Risk that covers much of central=20 California from the coast into the Sierra foothills. .....DownEast Maine... Rain developing across the region on Day 1 is expected to carry over into early Friday with an additional 1-2 inches of rain expected before precipitation changes over snow and diminishes behind of the departing low. As on Day 1, a lack of instability will limit rainfall rates and the potential for flash flooding.=20 However, areal flooding will remain a concern given the saturated=20 soils. Pereira Day 3 Valid 12Z Sat Mar 30 2024 - 12Z Sun Mar 31 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHERN CALIFORNIA.. As an anomalously deep low continues to drop south, excessive=20 rainfall concerns developing on Day 2 are expected to continue and=20 expand further south across portions of southern California this period. Increasing IVTs associated with a well-defined frontal=20 boundary will push across southern California on Saturday, with=20 PWs reaching 0.75-1 inch (2-3 standard deviations above normal). A=20 Slight Risk remains in place from the Transverse into the=20 Peninsular Ranges, where areal average amounts of 1-3 inches are=20 expected. Moisture spreading east of the mountains will support widespread precipitation, with locally heavy amounts possible into the lower Colorado Basin, where a Marginal Risk was maintained for portions of southern Nevada and western Arizona. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7wrDRFMw5Mb9Ll6D75hTt6bfBxOU9lbZujODVdDyMqkd= hn9yJszqXRNUwQnXqzTOK55fDTWvCLeNVkZtKdYtmV17Vrw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7wrDRFMw5Mb9Ll6D75hTt6bfBxOU9lbZujODVdDyMqkd= hn9yJszqXRNUwQnXqzTOK55fDTWvCLeNVkZtKdYt5CoBvk4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7wrDRFMw5Mb9Ll6D75hTt6bfBxOU9lbZujODVdDyMqkd= hn9yJszqXRNUwQnXqzTOK55fDTWvCLeNVkZtKdYtHoSLYGM$=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. 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