Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Apr 19 2023 20:17:21 FOUS30 KWBC 192017 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 416 PM EDT Wed Apr 19 2023 Day 1 Valid 16Z Wed Apr 19 2023 - 12Z Thu Apr 20 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR AN EASTERN PORTION OF THE CENTRAL PLAINS... Round 1 of activity continues over WI this afternoon ahead of an impulse over MN/IA with locally heavy rain generally moving out of the areas with snowpack. A stronger impulse currently over CO shifts over the central Plains this evening, riding a cold front currently pushing south over western KS that will stall this afternoon. Round 2 of activity is ahead this cold front over the eastern portions of the Central Plains (southeast Neb/northeast KS) this evening with initiation after 00Z. One or two rounds of activity occurs over this area spreading into southwest IA/northwest MO before expanding southwest to northeast through the night from eastern Kansas through Wisconsin. PW of 1.25" is 2 sigma above normal. A Slight Risk area has been raised for far southeast Neb/northeast KS/southwest IA and far northwest MO. The new 12Z HREF still depicts a risk for rainfall rates over 1"/hr. While KS/Neb/IA/MO will have the most instability this evening, antecedent conditions are also favorable for flash flooding in Wisconsin due to added snowmelt from the recent winter storm over the western half of the state. Thus if FFG is able to be exceeded, we could realize some lower end flood impacts, especially over any more susceptible areas. The Marginal Risk area was expanded west a bit for activity over southeast Neb and trimmed on the eastern end per 12Z CAM trends. Jackson Day 2 Valid 12Z Thu Apr 20 2023 - 12Z Fri Apr 21 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF NORTHEAST TEXAS TO THE MID-SOUTH... Deep-layer Gulf moisture streams up across Texas until a cold frontal passage early Friday. PW values of 1.75 inches (1.5 to 2 sigma) will spread over central/eastern Texas through Arkansas and the Mid-South by Thursday afternoon ahead of the frontal boundary as it approaches. Continued southwesterly deep layer flow will be nearly parallel to the front, bringing the risk for repeating and backbuilding storms. 12Z consensus for areal averages of 1 to 3.5 inches from the Heart of Texas (The I-35 corridor between Austin and Dallas) to southeast Missouri with amounts generally an inch or less for the Upper Mississippi Valley and Great Lakes, though FFG will remain lower there due to recent rains (and snowmelt in WI), thus keeping an elevated threat for flooding concerns. The Slight Risk area was expanded a bit more, further southwest into central Texas and northeast into southern Illinois. The southern bounds of the Marginal Risk ares was also expanded south and eastward to include the Houston metro and farther into western Louisiana to account for convergent activity with otherwise progressive prefrontal thunderstorm lines. Jackson Day 3 Valid 12Z Fri Apr 21 2023 - 12Z Sat Apr 22 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FROM THE LOUISIANA COAST THROUGH THE MID-SOUTH... The key excessive rainfall concern for the Friday is the timing and progression of the pre-cold frontal thunderstorms pushing through east Texas into Louisiana late Thursday night. Early CAM guidance from the 12Z NAMNest/FV3LAM and now the 18Z HRRR indicate more progressive prefrontal activity that may clear some of southwest Louisiana by 12Z Friday. Opted to make some adjustment to account for this more progressive scenario, and more adjustment to the Slight and Marginal Risk areas may be needed pending further CAM output with the 00Z HREF tonight. Ahead of this front, deep layer Gulf moisture will continue to fuel showers and thunderstorms with the strongest moisture convergences aligning from southern Louisiana to western Tennessee with perhaps the best repeating threats along the western Gulf Coast early Friday and near the Mississippi Delta later in the day. 12Z consensus is for 2 to 3 inches QPF in either of these areas and for portions of the Lower Mississippi Valley between. A Slight Risk was trimmed a bit on the west side near the Texas/Louisiana border and maintained from western Tennessee to Louisiana. The Marginal Risk was trimmed a bit in eastern Texas and expanded east a bit over the Ohio valley for greater frontal progression. Jackson Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!94YVgdMLB_4Y8v_VZ6rGfF5-nUQJ2NjbaeM7Br80_9q_= _GnHd1W5mSO1MJB0X0fhdkC7TsSyqQsigcbhRHoiZ0caNTw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!94YVgdMLB_4Y8v_VZ6rGfF5-nUQJ2NjbaeM7Br80_9q_= _GnHd1W5mSO1MJB0X0fhdkC7TsSyqQsigcbhRHoiDQE5dvA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!94YVgdMLB_4Y8v_VZ6rGfF5-nUQJ2NjbaeM7Br80_9q_= _GnHd1W5mSO1MJB0X0fhdkC7TsSyqQsigcbhRHoidat6HKY$=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) .