Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Mar 13 2023 20:18:42 FOUS30 KWBC 132018 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 417 PM EDT Mon Mar 13 2023 Day 1 Valid 16Z Mon Mar 13 2023 - 12Z Tue Mar 14 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHERN CALIFORNIA AND EXTREME SOUTHWESTERN OREGON... ....Southwestern Oregon and Northern California... 16Z update... The environmental setup along with the forecast model solutions remain on track for several inches of rain to impact Oregon and California. The latest guidance continue to support 2 to 5 inch areal averages across the region. The inherited Risk areas remain warranted and were broadened to the north and east to reflect the latest QPF trends. Campbell Organized, heavier precipitation is expected to develop across the region later today as a well-defined shortwave moves south of a weakening low centered east of British Columbia. Southwesterly flow along the associated cold front will focus deeper moisture across southwestern Oregon and Northern California. This moisture along with favorable upper forcing is likely to support periods of moderate to locally heavy precipitation that may to continue into the overnight before the onshore flow is disrupted briefly by another shortwave approaching Northern California. While not expected to be an extreme event, significant amounts are likely over the next 24-hrs, with the HREF showing high probabilities for accumulations of 3 inches or more within the area highlighted by a Moderate Risk. This includes the coastal ranges, the southern Cascades, and the northern Sierra Foothills. For most areas, snow levels will be around 5500-6500 ft early on before dipping lower across southwestern Oregon into far northwestern California as the front moves into the region and stalls. This additional rain, combined with snowmelt, and wet soils are likely to contribute to short-term runoff concerns during this period. ....Coastal New Jersey, New York, and Connecticut... 16Z update... The Marginal Risk area remains in good order across the coastal Northeast, as it covers where the best potential will be for periods of moderate to heavy rainfall. Campbell A powerful coastal storm is forecast to move along the Northeast Coast this evening and through the overnight, with heavy rain expected along the coastal region. This rain may accentuate flooding concerns along the coast, promoted by what are forecast to be strong easterly winds on the north side of the system. Pereira Day 2 Valid 12Z Tue Mar 14 2023 - 12Z Wed Mar 15 2023 ....THERE IS A HIGH RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF SOUTHERN CALIFORNIA AND THE SOUTHERN SIERRAS... ....California... 21Z update... The environment will be very favorable for prolonged, terrain-enhanced rainfall along the central and southern coastline and the Sierra foothills. The global guidance and a majority of the hi-res guidance hammer this part of the state with 3 to 6+ inches of rain, some occurring over areas still dealing with the high stream flows of the previous, not so distant AR event. Higher dew points are expected to infiltrate the region which will help prime the snowpack for melting and possibly expedited by the heavy rain, thus increasing the threat for rapid runoff and the areal coverage of flooding. Campbell Another strong storm is expected to impact a large portion of the state this period, including heavy to excessive rains from the central to the southern coast, and along the Sierra Foothills.=20 Models show a shortwave trough off of the Northern California Coast Tuesday morning. This system is expected to amplify as it approaches the coast and interacts with a trough to the north.=20 This will tap a long-fetch of deep moisture, with strong southwesterly winds ahead of the trough spreading moisture inland across the state on Tuesday. PWs are forecast to surge to 4-5 standard deviations above normal on Tuesday along an axis of 40+kt low level inflow centered across Central into Southern California. This anomalous moisture, coupled with strong forcing is likely to produce widespread heavy amounts, especially for the upslope regions in the coastal ranges and the Sierra. Within the Moderate Risk area, rainfall accumulations of 3-6 inches, with locally heavier amounts are expected. In addition to channeling copious moisture, the deep southwesterly winds will push snow levels higher across the region on Tuesday, promoting snowmelt and the threat for runoff concerns. Pereira Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9LBH9g7BUYyg3Q1nblRntTHlVTI6xJf4GGnIntYHiDHh= Q9rFd1o9BdUrmaqZF1MkIbMs7J69iMUYnrS4NHh-JIdgvqM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9LBH9g7BUYyg3Q1nblRntTHlVTI6xJf4GGnIntYHiDHh= Q9rFd1o9BdUrmaqZF1MkIbMs7J69iMUYnrS4NHh-d_Bj1fo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9LBH9g7BUYyg3Q1nblRntTHlVTI6xJf4GGnIntYHiDHh= Q9rFd1o9BdUrmaqZF1MkIbMs7J69iMUYnrS4NHh-C8C7EHY$=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) .