Subj : HVYRAIN: Excessive Rainfall Discussion...corrected To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Mar 28 2024 20:14:11 FOUS30 KWBC 282013 CCA QPFERD Excessive Rainfall Discussion...CORRECTED NWS Weather Prediction Center College Park MD 413 PM EDT Thu Mar 28 2024 Day 1 Valid 2007Z Thu Mar 28 2024 - 12Z Fri Mar 29 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHEAST U.S.... ....New England... A Slight Risk of excessive rainfall remains over portions of New=20 England through tonight. Satellite imagery showed another region of cooling cloud tops upstream from the area as of late this=20 morning...so any respite from rainfall overnight and early this=20 morning should be short-lived. The expectation is that neither=20 rainfall rates nor rainfall amounts will be blockbuster in=20 magnitude and that most places would be handled under most=20 circumstances (as suggested by the 12Z HREF neighborhood=20 probabilities showing less than 5 percent risk of 1-/3-/6-hour QPF=20 exceeding respective Flash Flood Guidance). But discussions with=20 the National Water Center and offices in the area indicate that the amount of water added by melting and compaction of the snowpack=20 may be enough for more than isolated problems with runoff in areas=20 of poor drainage. 12Z HREF guidance shows better coverage of=20 rainfall along and near the coastal regions of New England with=20 nearly 1.5 inches of additional rainfall. ....Eastern Carolinas... As the threat for heavy rainfall in and near eastern NC is ending, the risk areas for these region were eliminated in this special update. Bann/Roth 08Z Excessive Rainfall Discussion... ....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 topping out near 0.25 inch/hour. However, given the recent rainfall and saturated soils, there remain some runoff concerns, promoting the continuation of a Marginal Risk. 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... 20Z Excessive Rainfall Discussion... Few changes were needed with models continuing to bring a closed low southward along the northern California coast on Friday night/Saturday morning. Higher rainfall rates look to approach the central and southern coast of California late Friday night or very early Saturday morning. The previous outlook had that covered and only minor adjustments were made based on the 12Z suite of model guidance and WPC QPF. Likewise...made minor adjustments to the northern extent of the Marginal Risk area in Maine given the latest spaghetti plots of higher QPF. In addition...there should be a change in precipitation type from rain to snow as cold advection sweeps across Maine which will help mitigate excessive rainfall concerns. Bann 08Z Excessive Rainfall Discussion... A well-defined shortwave diving west of a closed low centered west of Vancouver Island is expected to support the development of a closed low further south that will drop south along the northern California coast Friday into Saturday. Models continue to advertise an anomalously deep system for this time of year, with 500 mb heights dropping 1-3 standard deviations below normal across much of California this period. Deep southwesterly flow ahead of the low will support increasing IVTs, with the highest values dropping south along the coast from Monterey Bay into the Transverse Ranges. A Slight Risk was maintained over Santa Barbara and Ventura counties, where the models continue to show a decent signal for locally heavy amounts in the favored terrain. The consensus of the deterministic guidance shows amounts of 1-3 inches in the region, with locally heavier amounts possible by 12Z Saturday. There is also some signal for locally heavy amounts further to the north 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 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. However, areal flooding will remain a concern given the saturated 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.. 20Z Excessive Rainfall Discussion... Consistent model and ensemble QPF across southern California and with WPC QPF meant little need for more than minor adjustments to the previously issued Slight Risk across portions of southern California and the eastward extension of the Marginal risk into portions of southern Nevada and western Arizona. Bann 08Z Excessive Rainfall Discussion... As an anomalously deep low continues to drop south, excessive rainfall concerns developing on Day 2 are expected to continue and expand further south across portions of southern California this period. Increasing IVTs associated with a well-defined frontal boundary will push across southern California on Saturday, with PWs reaching 0.75-1 inch (2-3 standard deviations above normal). A Slight Risk remains in place from the Transverse into the Peninsular Ranges, where areal average amounts of 1-3 inches are 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!_OBZbJ0ht-2lkiQUn1G_XW1Jsph34xdLORONRAjOqRiG= 9EesDDG0QGf4rDrr23eWg_EhlrLPPmpgkYzlc0xe8RgbriI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_OBZbJ0ht-2lkiQUn1G_XW1Jsph34xdLORONRAjOqRiG= 9EesDDG0QGf4rDrr23eWg_EhlrLPPmpgkYzlc0xepjv4pTs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_OBZbJ0ht-2lkiQUn1G_XW1Jsph34xdLORONRAjOqRiG= 9EesDDG0QGf4rDrr23eWg_EhlrLPPmpgkYzlc0xeS1MpV24$=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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