Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Thu Apr 20 2023 18:55:00 FOUS30 KWBC 202018 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 417 PM EDT Thu Apr 20 2023 Day 1 Valid 16Z Thu Apr 20 2023 - 12Z Fri Apr 21 2023 ......THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF EASTERN TEXAS TO THE MID-SOUTH... Deep-layer Gulf moisture streams up across eastern Texas through the Midwest ahead of a cold front pushing southeast from the Great Plains. PW values of 1.75 inches (1.5 to 2 sigma) will spread over central/eastern Texas and across Arkansas by this afternoon. The southwesterly deep-layer flow will be nearly parallel to the frontal boundary which means repeating and backbuilding storms and localized extreme rainfall. 12Z HREF consensus is for 1 to 4 inches from east-central Texas to the Upper Texas Coast/Southwest Louisiana, across Arkansas and far southeast Missouri with localized maxima of 5 to 7 inches near the convergence of the Gulf-sourced plume and pre-frontal activity over east-central Texas up through central Arkansas. The Slight Risk area was expanded a bit more into central Texas where HREF EAS QPF is maximized, meaning where the most HREF members have overlap of several inches. The Marginal Risk was expanded south through Corpus Christi in this west Gulf plume of moisture. Further north, amounts around 1 inch or less are expected north of the mid-Mississippi Valley, though FFG will remain lower there due to recent rains (and snowmelt in WI), keeping an elevated threat for flooding concerns. Jackson Day 2 Valid 12Z Fri Apr 21 2023 - 12Z Sat Apr 22 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR A PORTION OF THE LOWER MISSISSIPPI RIVER VALLEY... Organized pre-cold frontal convection should be ongoing and near the central Gulf Coast around 12Z Friday as it continues tracking east or southeast. Deep Gulf-sourced moisture will continue to be drawn northward ahead of the front to fuel showers and thunderstorms with increasing confidence that the strongest moisture convergence will be over southern Louisiana where PWs reaching 2 inches are 2 sigma above normal. Flow in southern Louisiana will also be a little less than farther north. However, areas in the Mid-South will have deep-layer flow more parallel to the approaching cold front bringing a risk for repeating activity over western Tennessee/northwest Mississippi. There was consideration of focusing the Slight Risk area farther north over the Mid-South and removing the southern portion in Louisiana. However, uncertainty on the progression of the overnight activity seen in the 18Z HRRR and NAMnest warranted keeping the full Slight Risk area where there is potential for 2 to 4 inches. Farther north, greater progression allows the Marginal Risk to be shifted east over more of Ohio and Kentucky where there is a risk for 1 to 2 inches. Jackson Day 3 Valid 12Z Sat Apr 22 2023 - 12Z Sun Apr 23 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN MID-ATLANTIC... A plume of sub-tropical moisture spreading up the Eastern Seaboard on Saturday is focused fairly well over the southern Mid-Atlantic. While most global guidance brings a general risk of 1 to 2 inches to much of the Mid-Atlantic, the 12Z Canadian runs do focus QPF in excess of 2 inches near the existing Marginal Risk in southeast Virginia and Northeast North Carolina. Therefore, the Marginal Risk was maintained with a bit of an expansion over the relatively more flood prone Hampton Roads metro. Fairly dry antecedent conditions may allow this risk area to be dropped on subsequent shifts should the heavy rain focus become less certain. Jackson $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .