Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Apr 18 2024 15:43:00 FOUS30 KWBC 181542 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1142 AM EDT Thu Apr 18 2024 Day 1 Valid 16Z Thu Apr 18 2024 - 12Z Fri Apr 19 2024 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS, MISSISSIPPI VALLEY, AND WESTERN OHIO VALLEY... ....16Z Update... Areal coverage of the inherited MRGL risk was expanded to account for the latest trends in guidance and radar/sat evolution this morning. Surface low is currently located over southern KS with expected northeastward motion through the period. A stationary boundary located over the northern Ozarks and points east will be a focal point for convection later this afternoon and evening with a shortwave dipping southeast into the Mid-Mississippi Valley. A secondary area of focus is unfolding over southern AR into northern LA as a weak shortwave ejects eastward out of TX and induces some modest large scale ascent within an increasingly unstable environment over the Deep South.=20 Recent radar and IR satellite have indicated a quick growth of=20 convection across the aforementioned area with radar estimates of=20 rates approaching 2.5-3"/hr over far northeastern LA. This was a=20 newer trend within the latest CAMs with persistence into the=20 afternoon as the convection moves to the northeast in time (See MPD #0161 for more information). The primary area of interest will=20 include that AR/LA border near the Mississippi River, eventually=20 propagating into north-central MS this afternoon and dissipating=20 prior to evening as the mid-level impulse degrades and we lose the=20 upper forcing mechanism. This was still enough to warrant a push=20 south of the MRGL risk with 1 and 3-hr FFG markers running right=20 around the proposed rates of 2-3"/hr within those cells in=20 question, backed up by 12z HREF probabilities of 20-30% potential=20 for at least 2"/hr possible and 40-50% for at least 2"/3-hrs.=20 Further north, the trend with the convective pattern over MO into the Mid-Mississippi Valley has been fairly consistent the past several deterministic runs and is in lock step with ML algorithms signaling a primary QPF maximum within the confines of eastern MO, southern IL, into far western KY. This was no different within=20 this mornings CAMs and aligns perfectly with the current SPC D1=20 Outlook of a widespread Slight and Enhanced risk co-located within=20 the northern extent of the MRGL risk area. An upgrade was=20 entertained, but the progressive nature any convection was a=20 deterrent for the update. It still bears watching as any storm=20 that gets rooted at the surface along the stationary front could=20 induce training potential that isn't being picked up by the latest=20 CAMs. For now, maintained continuity based on the HREF blended mean QPF and lower end probabilities for exceeding 2"/hr within the hi- res ensemble (10-15% maximum).=20 There are no changes within Texas as surface based convection will develop over central TX within an area of prime instability. Coverage is not expected to be widespread and primary interest will likely be one or two stronger storms that will produce some locally heavy rainfall over the northern Hill Country to about the I-35 corridor. Probabilities of at least 3" of total rainfall area generally 10-15% within central TX with a bullseye of 20-30% over the Hill Country between Brady and Junction.=20 Kleebauer Day 2 Valid 12Z Fri Apr 19 2024 - 12Z Sat Apr 20 2024 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE TEXAS BIG BEND AND WEST TEXAS AND FOR PARTS OF THE RED RIVER... The cold front will continue to press southward through the Southern Plains and Lower Mississippi Valley before slowing/stalling. A dryline will also be present from the Oklahoma Panhandle to the Big Bend area. Convection is expected to be along and south of the front over the Southern/Central Plains and Lower Mississippi Valley with the higher QPF near/east of the dryline in west-central Texas. The consensus for the area over the Texas Big Bend up through the Edwards Plateau has grown within this suite of guidance with the environment primed for higher end convective development from the Lower Trans Pecos, eastward into the Rio Grande and adjacent Edwards Plateau. Ensemble probabilities remain on the lower end, however they are within the 10-20% range for totals exceeding 2" which would be sufficient for localized flood concerns within the terrain focused over the area. The timing differences remain across the Red River and southern Oklahoma with the front into that area with the convergence pattern expected towards the back end of the forecast period with a higher potential for flash flooding. A Marginal Risk area spans the Big Bend area northeast into the Edwards Plateau and Concho Valley. Another Marginal Risk area covers portions of southern Oklahoma, northeast Texas and western Arkansas. Campbell/Kleebauer Day 3 Valid 12Z Sat Apr 20 2024 - 12Z Sun Apr 21 2024 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR EASTERN TEXAS, NORTHWEST Louisiana, SOUTHWEST ARKANSAS AND EXTREME SOUTHERN OKLAHOMA... The front will remain stalled across the South meanwhile moisture will steadily increase. Precipitable water values of 1 to 1.5 inches (upwards of 2.5 sigma) will be in place across much of the Southern Plains and Lower Mississippi Valley also where there will be very strong mid-level ascent. This environment will be very conducive for widespread heavy rainfall. The highest QPF will focus over central and eastern Texas where areal averages of 2 to 4 inches will be common - a Slight Risk area covers much of this part of region. Isolated higher amounts will possible, particularly for locations east/northeast of the Hill Country. A Marginal Risk area spans from western Texas to eastern Mississippi. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6XaPmZFXHzSp73z8ixBoBk7o0Lvmb4D9mfrjhOPn8HhO= 1htA9jIrbqR42r4NViDl_h2ekKTbtkW81EeLBbgAFWdTIho$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6XaPmZFXHzSp73z8ixBoBk7o0Lvmb4D9mfrjhOPn8HhO= 1htA9jIrbqR42r4NViDl_h2ekKTbtkW81EeLBbgA-szLtS0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6XaPmZFXHzSp73z8ixBoBk7o0Lvmb4D9mfrjhOPn8HhO= 1htA9jIrbqR42r4NViDl_h2ekKTbtkW81EeLBbgAt3JnyI4$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .