Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Apr 19 2023 01:01:11 FOUS30 KWBC 190101 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 900 PM EDT Tue Apr 18 2023 Day 1 Valid 01Z Wed Apr 19 2023 - 12Z Wed Apr 19 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHERN MINNESOTA INTO NORTHEAST IOWA... Opted to introduce a small Marginal risk over portions of southern MN into northeast IA with this update. This is for the expected elevated convection that should impact the area after 06z tonight. Looks like a pretty good setup for elevated convection...with decent instability rooted above a strong low level inversion, a mid level shortwave approaching the area, and strong upper level diffluence. It seems like these purely elevated convective events can sometimes over perform model guidance. Of all the CAMs the 3km NAM typically handles these type of events best, with the HRRR generally the worst. Thus not too surprising to see the 3km NAM on the wetter side of the model spread, and the HRRR one of the drier models. This fits with past experiences, with something closer to the wetter NAM usually better in these scenarios. So while the 3km NAM may be a bit too aggressive, do think we could end up with some totals over 1.5", with much of that falling in a few hours. Thus both 1 and 3 hr FFG could be approached and/or locally exceeded across portions of this area later tonight. The more saturated soil conditions and anomalous streamflows are generally just north of this area...but even this region is seeing generally near to above average values. Thus if FFG is able to be exceeded, we could realize some lower end flood impacts, especially over any more susceptible areas. Chenard Day 2 Valid 12Z Wed Apr 19 2023 - 12Z Thu Apr 20 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM THE CENTRAL PLAINS TO THE UPPER MISSISSIPPI VALLEY... Showers and thunderstorms are expected to develop ahead of a cold front over eastern portions of the Central Plains early Wednesday evening before expanding southwest to northeast through the night from eastern Kansas through Wisconsin. Higher QPF is forecast to setup over eastern Kansas through southern Iowa where there is better alignment of deep layer flow with the slow moving cold front with instability (CAPE values of 1000-1500 J/kg). There is a risk for rainfall rates over 1"/hr per the 12Z HREF. While KS will have the most instability, antecedent conditions are most favorable for flash flooding in Wisconsin due to added snowmelt from the recent winter storm over the western half of the state. Furthermore, some rainfall is expected tonight over southeast Neb and IA which could aid preconditioning. The Marginal Risk was refined just a bit from eastern Kansas through Wisconsin based on the 12Z model consensus. Jackson Day 3 Valid 12Z Thu Apr 20 2023 - 12Z Fri Apr 21 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FROM NORTHEAST TEXAS TO THE MID-SOUTH... Gulf moisture will continue to advect northward and pool ahead of a cold front pushing southeast from the central Plains. PW values of 1 to 1.75 inches (1.5 to 2 sigma) will in place ahead of the frontal boundary as it approaches the Mid-South and eastern Texas Thursday afternoon. Continued southwesterly deep layer flow, which will be nearly parallel to the front will be conducive for storms repeating with some backbuilding of convection. Based on the 12Z guidance consensus, the Slight Risk area was maintained/focused a bit from northeast Texas to the Mid-Mississippi Valley where areal averages of 1 to 3 inches are forecast. QPF across the Upper Mississippi Valley/Great Lakes region are closer to the 1 inch range, but FFG will remain lower due to recent rains (and snowmelt in the Upper Midwest), thus keeping an elevated threat for flooding concerns. The Marginal Risk continues to span from eastern Texas to the Upper Peninsula of Michigan. Jackson Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_pjqXjEPhWTu9m-NRM54WYpA6X_KlIG7A8zr-mBgJik0= TLWEwpOlQWM6gAKW0r8eo3l7hIEQKGGUqUiLcvLxEFIlyx8$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_pjqXjEPhWTu9m-NRM54WYpA6X_KlIG7A8zr-mBgJik0= TLWEwpOlQWM6gAKW0r8eo3l7hIEQKGGUqUiLcvLxNiOhDtE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_pjqXjEPhWTu9m-NRM54WYpA6X_KlIG7A8zr-mBgJik0= TLWEwpOlQWM6gAKW0r8eo3l7hIEQKGGUqUiLcvLxVwvNxmY$=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) .