Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Apr 21 2023 08:13:21 FOUS30 KWBC 210813 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 412 AM EDT Fri Apr 21 2023 Day 1 Valid 12Z 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... A strong front and attendant squall line are tracking across coastal TX, LA and up the MS and OH rivers into IL and IN. With time, the line is becoming more progressive, so it's increased speed of movement is consequently resulting in diminishing chances of flash flooding associated therewith. Much of the 00Z CAMS guidance shows that while new areas of storms are likely to develop during the day behind the main line moving across the area as of the time of this writing, in addition to minimal overlap, the newly developed storms are not expected to be as strong or as widespread as the current line. Thus, any flash flooding will be limited to those isolated instances where the strongest storms in the second line overlap with where the heaviest rain fell with the first line. Otherwise, FFGs throughout the Marginal Risk area are high, with soil moisture at or below normal, with more below normal soil moisture further north into northern KY and OH, per NASA Sport imagery. Regardless, the second round of storms is most likely over MS, and is expected to be moving at similar fast speeds as the first line, limiting the threat there as well. Considering all of those above factors, and in coordination with MEG/Memphis, TN and LIX/New Orleans, LA forecast offices, the inherited Slight Risk area was downgraded to a Marginal Risk with this update.=20 Wegman Day 2 Valid 12Z Sat Apr 22 2023 - 12Z Sun Apr 23 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. As the front over the Midwest Friday pushes east on Saturday, a shortwave trough in the upper levels will shift the upper level trough more negatively tilted with time. This energy will continue to support a progressive front that traverses the Mid-Atlantic towards the east through the day. Instability will be limited, peaking around 1,500 J/kg over eastern NC, but barely making 300 J/kg from DC north. In NC and southeastern VA, FFGs remain high, and the guidance continues to struggle on where any local maxima of rainfall will set up, with most favoring a mostly uniform area of 1.25 to 1.75 inches of rain from NC through NY. Since the upper levels will still be moving, favoring storms that will be moving along at a decent clip, the threat for flash flooding is very low all up and down the mid-Atlantic. In coordination with the AKQ/Wakefield, VA and MHX/Morehead City, NC forecast offices, the Marginal Risk area for those regions was downgraded to a risk-free day nationwide on Saturday. Wegman 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!4qiQt0kaEh-pElMHtTRtxab4VBCgHF3l9fOZlxl-Ei00= 5otBV6Q9WVuUDEe38aN74jrbJZQz3APCR-AJRzD5U1szrIQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4qiQt0kaEh-pElMHtTRtxab4VBCgHF3l9fOZlxl-Ei00= 5otBV6Q9WVuUDEe38aN74jrbJZQz3APCR-AJRzD5sqRmKL0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4qiQt0kaEh-pElMHtTRtxab4VBCgHF3l9fOZlxl-Ei00= 5otBV6Q9WVuUDEe38aN74jrbJZQz3APCR-AJRzD50VLC7Qo$=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) .