Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Feb 27 2024 08:01:06 FOUS30 KWBC 270801 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 300 AM EST Tue Feb 27 2024 Day 1 Valid 12Z Tue Feb 27 2024 - 12Z Wed Feb 28 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE OHIO AND MID-MISSISSIPPI VALLEYS AND THE CENTRAL APPALACHIANS... Two main features to note via WV satellite; digging shortwave trough over the northern Rockies will continue to propagate to the southeast, eventually shifting east, then northeast by the end of the forecast cycle. Out ahead of the mean trough out west, a fast moving vort max will motion out of the mid-Mississippi Valley overnight and push through the Mid-Atlantic and Northeast U.S by morning, exiting out of the picture by the afternoon hours. These two disturbances will be the primary rain makers for the eastern half of the CONUS Tuesday into Wednesday morning. The bigger impact will be from the former of the two disturbances as the shortwave progression out of the Rockies into the plains will begin to ramp up the convective pattern east of the Mississippi. Broad difluent flow ahead of the shortwave trough will allow for greater large scale forcing to take shape within a priming environment thanks to boundary layer flow out of the south ushering warm, moist air poleward from the Gulf. Increasing instability axis in-of the Tennessee and Ohio Valleys will be setup for the incoming shortwave trough as theta-E fields signal a strong meridional push of low-level moisture with sights on areas as far north as the Great Lakes by later this afternoon. A surface low will spawn within the central Midwest with a triple-point depiction fairly consistent on deterministic guidance, especially as it matures heading into northern IL. By late afternoon, scattered showers and storms will fire within the warm sector and quickly move to the northeast as the steering flow is fairly progressive through the period. Locally heavy rain can be found within any of these convective cells, but the forward motion of the showers/storms will likely mitigate the flash flood threat to a low-end probability when coupled with the expected rates (0.5-1"/hr based off latest HREF neighborhood probability fields). As we step forward into Tuesday evening through the overnight time frame, more showers and storms will organize into a tight linear segment just out ahead of a swift-moving cold front plowing eastward out of the Mississippi Valley with greater coverage downstream over the central Appalachians up through western PA thanks to increasing difluent pattern pivoting eastward with the progression of the mean trough. QPF forecast shows local maximums within the confines of central and southern OH into the previously stated zones, mainly due to greater convective clustering as cells merge over time after their initiation over places further west. Some hi-res deterministic are being fairly liberal with their QPF footprint indicating some local 1.5-2" totals within the confines of the Alleghanies in western PA, back into southern OH thanks to the organized convective pattern. Elevated PWAT indices approaching 2-3 deviations above normal would constitute an environment favorable for locally heavy rain, and with the topographic elements coming into play within those areas, that is where the best opportunity for localized flooding concerns is anticipated. The saving grace is the progressive propagation of the system as a whole which will limit a larger scale event and keep this closer to a Marginal Risk which has been the forecast for the past several cycles, and will be maintained in this forecast package. The main adjustments were related to the latest QPF footprint of the CAMs and alignment with the favorable instability fields which will drive the rates and convective regime necessary for flooding to occur. Kleebauer=20 Day 2 The Day 2 outlook will be updated by 0830Z. 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!7peZXw6g09ykxdItSG_6Jfrgq15YVWCM2KPHW_eO0HOJ= cO2FRgqA3yo4CwqbIhzrk-9ALsn9VAfkZWKun8vI8_WC1Vo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7peZXw6g09ykxdItSG_6Jfrgq15YVWCM2KPHW_eO0HOJ= cO2FRgqA3yo4CwqbIhzrk-9ALsn9VAfkZWKun8vI_DACeaM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7peZXw6g09ykxdItSG_6Jfrgq15YVWCM2KPHW_eO0HOJ= cO2FRgqA3yo4CwqbIhzrk-9ALsn9VAfkZWKun8vIv8dKCz0$=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) .