Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 21 2022 02:58:14 FOUS30 KWBC 210258 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 957 PM EST Tue Dec 20 2022 Day 1 Valid 0255Z Wed Dec 21 2022 - 12Z Wed Dec 21 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 Roth Day 2 Valid 12Z Wed Dec 21 2022 - 12Z Thu Dec 22 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Otto Day 3 Valid 12Z Thu Dec 22 2022 - 12Z Fri Dec 23 2022 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE MID-ATLANTIC INTO SOUTHERN PORTIONS OF THE NORTHEAST... Coastal North Carolina... Areas of heavy rain are expected to be ongoing from the South Carolina coast into southern North Carolina coast Thursday morning. A surface low will track northward along the Southeast coast through Thursday evening with a narrow warm sector east of the frontal wave. Across the Coastal Plain, precipitable water values of 1.2-1.6 inches and MUCAPE of 500-1500 J/kg are expected along with increasing upper level support through 00Z Friday with increasing diffluence and left exit region divergence related to a subtropical jet streak translating offshore of the Southeast. Progressive cell motions and sandy soils/marsh are limiting factors for runoff concerns but brief training of heavy rain allowing hourly rainfall totals of 2 or more inches will be possible. The latest model consensus is for 24 hour maximum rainfall of 2-4 inches centered on the North Carolina coast, but the 12Z FV3 and 06Z GEM_regional supported 6+ inches on or just offshore of the North Carolina coast. The Marginal Risk was maintained from continuity but any issues that occur will likely be confined to urban areas. =20 Appalachians/Northern Mid-Atlantic into southern New England... While minor timing and placement differences exist in the latest model guidance, there is agreement that a mid-upper level trough will strengthen and become a powerful closed low as it approaches the Ohio Valley from Thursday into Friday morning. As this occurs, increasing upper level diffluence and divergence is expected to develop over the northern Mid-Atlantic and southern New England Thursday evening and overnight. Increasing low level moisture transport will overspread the East Coast with standardized precipitable water anomalies of +1.5 to +2.5 forecast by the 12Z GFS to stretch from the Mid-Atlantic into southern New England during the forecast period. While 1+ inch precipitable water values are not forecast by the model consensus to penetrate very far inland and weak instability (less than 500 J/kg MUCAPE for the northern Mid-Atlantic into the Northeast) should limit hourly rainfall totals to the 0.5 to 1.0 inch range, 1 to 2 inch rainfall totals in a 6 hour period and 24 hour totals of 2 to 4 inches will remain possible. Cold to frozen soil temperatures and snow cover for northwestern portions of Marginal Risk area were considerations for a targeted Slight Risk, covering northeastern Pennsylvania, southern Upstate New York and northern New Jersey. However, after collaboration with the affected WFOs, there was agreement to hold off on anything higher than a Marginal Risk at this time. Consideration to adding a small Slight can be given with future forecast cycles if model output becomes more aggressive. Otto Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_nk7-mLETn64VqXyIC5tZjzbzMf5bCkdfUcP9ksPBBly= NvxB6EwH73HRELy26EEVQqHIC5CmTbX3fmFPBVcYCJb9dGc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_nk7-mLETn64VqXyIC5tZjzbzMf5bCkdfUcP9ksPBBly= NvxB6EwH73HRELy26EEVQqHIC5CmTbX3fmFPBVcYkFtCciM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_nk7-mLETn64VqXyIC5tZjzbzMf5bCkdfUcP9ksPBBly= NvxB6EwH73HRELy26EEVQqHIC5CmTbX3fmFPBVcYAlbY_9g$=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) .