Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 21 2022 08:17:50 FOUS30 KWBC 210817 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 316 AM EST Wed Dec 21 2022 Day 1 Valid 12Z Wed Dec 21 2022 - 12Z Thu Dec 22 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 Roth Day 2 Valid 12Z Thu Dec 22 2022 - 12Z Fri Dec 23 2022 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF MIDDLE AND UPPER EASTERN SEABOARD...=20 =20 Coastal North Carolina...=20 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=20 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 diffluence and divergence related to a subtropical jet streak translating offshore of the Southeast. Some 850 hPa frontogenesis exists over the Outer Banks. While convection should achieve some level of organization, progressive cell motions and sandy soils/marsh are limiting factors for runoff concerns but brief training (or cell mergers) of thunderstorms would allow hourly rainfall totals to rise to 1-2" (00z HREF shows a good signal for 1"+ per hour) with local amounts of 2-4" being possible. The Marginal Risk was maintained from continuity; any issues that occur will likely be confined to urban areas.=20 =20=20 =20 Appalachians/Northern Mid-Atlantic into southern New England...=20 An upper level trough will strengthen and become a powerful closed low aloft as it approaches the Ohio Valley from Thursday into Friday morning. As this occurs, increasing upper level diffluence/divergence is expected to develop over the northern Mid-Atlantic and southern New England Thursday evening and overnight. Increasing warmth and moisture flux 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. Two periods of overlapping low- to mid-level frontogenesis are expected both early on and then as the sharp cold front/possible frontogenetic squall line moves through the southern and central Appalachians into the Piedmont. =20 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), the saturated column and expected frontogenesis should make up for this shortcoming. Hourly rainfall totals to a maximum of ~1" are expected with local amounts of 2-4" remaining possible. Cold to frozen soil temperatures and snow cover over northeastern Pennsylvania, southern Upstate New York and far northern New Jersey could lead to a small area of Slight Risk-type impacts.=20 The size of the region this would cover is considered too small to be depicted in a probabilistic outlook.=20 =20 Roth 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!-VhbUC9x39ble8DRv7mFf8u5heM3bjatwSGu5f6rgtBt= F8F6dsiLA7kKhqQWA8-0as413_Yr2jZWv-Rh9fPFvYLgdcg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-VhbUC9x39ble8DRv7mFf8u5heM3bjatwSGu5f6rgtBt= F8F6dsiLA7kKhqQWA8-0as413_Yr2jZWv-Rh9fPF6l7eDZA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-VhbUC9x39ble8DRv7mFf8u5heM3bjatwSGu5f6rgtBt= F8F6dsiLA7kKhqQWA8-0as413_Yr2jZWv-Rh9fPF9qDDQ8c$=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) .