Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Apr 21 2023 19:05:07 FOUS30 KWBC 211905 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 304 PM EDT Fri Apr 21 2023 Day 1 Valid 16Z Fri Apr 21 2023 - 12Z Sat Apr 22 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR MUCH OF THE LOWER MISSISSIPPI AND OHIO RIVER VALLEYS... The Marginal Risk was affirmed per 12Z HREF QPF/exceedance probabilities as well as FFG with some trimming. The cold front will continue pushing through areas with Gulf-moisture content and instability, producing locally heavy rainfall particularly this afternoon. Strong southwesterly deep-layer flow will continue to be nearly parallel to the approaching frontal boundary, keeping a risk for repeating activity. Jackson Day 2 Valid 12Z Sat Apr 22 2023 - 12Z Sun Apr 23 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR A PORTION OF CENTRAL TEXAS... ....Central Texas... Low pressure developing over west Texas and a high pressure ridge extending to the Upper Texas Gulf coast Friday night allows return flow and western Gulf moisture to stream over central Texas Saturday. PW values rise to 1.25" over central Texas by Saturday evening (more than 1 sigma above normal) which is when convective activity should begin. Westerly deep-layer flow could allow some repeating activity as the storms shift east, producing localized maxima of a few inches of rain. Portions of this area received heavy rainfall last night, which raises susceptibility for repeat flash flooding and warrants a Marginal Risk for portions of central Texas. ....Mid-Atlantic... An eastward moving cold front reaches the Eastern Seaboard on Saturday with the upper level trough becoming more negatively tilted. With limited instability, a progressive nature to activity, and higher FFGs from recent dryness, the excessive rain outlook remains below 5%. Jackson Day 3 Valid 12Z Sun Apr 23 2023 - 12Z Mon Apr 24 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL AND SOUTHEAST TEXAS AND NEW ENGLAND... ....New England... A progressive cold front shifts off the Mid-Atlantic coast Saturday night, but coastal low development over the northern Mid-Atlantic and the presence of a blocking ridge over Atlantic Canada causes a slowing of the rainfall north of this low across New England. 12Z guidance retains a risk for 1 to 2 inch rainfall focused along the NH/southern ME coast, so the Marginal Risk remains with just a little trim for areas such as northern New Hampshire. A better sense of rain rates will come into better focus with the arrival of CAM guidance over the next day. ....South Texas... Continued low level return flow off the western Gulf will reinforce ample moisture while westerly deep-layer flow will allow thunderstorms to potentially repeat as they progress to the middle Texas coast Sunday night. The Marginal Risk was hemmed a bit based on a southerly trend in 12Z guidance (away from Houston which remains in the Marginal for now) and to focus the risk area north of the South Texas Sand Sheet. Should Saturday activity raise prospects of more repetition of heavy rain in the central Texas area or CAM guidance come in with slower moving convection, a targeted Slight Risk upgrade is possible. Jackson Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8yDyz8umwC9GBJoVyczfrNBGZ1pto7Niy-LA51hfRKZi= WWnG3bC7EF0HbvMSHyq9TWDEusV7sGZtAHVNtExoTRCxZ7s$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8yDyz8umwC9GBJoVyczfrNBGZ1pto7Niy-LA51hfRKZi= WWnG3bC7EF0HbvMSHyq9TWDEusV7sGZtAHVNtExoc3Zd0gA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8yDyz8umwC9GBJoVyczfrNBGZ1pto7Niy-LA51hfRKZi= WWnG3bC7EF0HbvMSHyq9TWDEusV7sGZtAHVNtExoVnrScGg$=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) .