Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Feb 14 2023 01:00:28 FOUS30 KWBC 140100 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 759 PM EST Mon Feb 13 2023 Day 1 Valid 01Z Tue Feb 14 2023 - 12Z Tue Feb 14 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill Day 2 Valid 12Z Tue Feb 14 2023 - 12Z Wed Feb 15 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 3 Valid 12Z Wed Feb 15 2023 - 12Z Thu Feb 16 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, TENNESSEE VALLEY, AND LOWER OHIO VALLEY... Heavy showers and thunderstorms are expected to develop and expand in coverage Wednesday night through Thursday morning across portions of the lower MS Valley, TN Valley and lower OH Valley. This will be in response to the ejection of a strong shortwave trough from the Four Corners region that will cross the central Plains by early Thursday while driving deepening low pressure from the Red River Valley toward the lower OH Valley. The 12Z guidance shows some notable timing differences with the speed at which the energy ejects out, and this plays a role ultimately with how much convective organization can be attained in the overnight period going through 12Z/Thursday along with corresponding rainfall totals. The NAM and GFS are on the fast side of the guidance, especially at the surface, and tend to support more energy arriving in the lower OH Valley by the end of the period versus the non-NCEP guidance which has more energy/forcing focused back over the lower MS Valley. Unfortunately, the ensemble means are in even greater disagreement with the 12Z GEFS mean outpacing the deterministic GFS, whereas the 00Z ECENS mean is more aligned with the slower ECMWF/CMC camp. The 12Z UKMET is the slowest and is a bit of an outlier. Taking a consensus of the guidance weighted toward 12Z ECMWF/00Z ECENS/12Z GEM cluster would support deepening low pressure at least approaching southeast MO or southern IL by 12Z/Thursday and this is expected to result in a strong low-level jet reaching on the order of 40 to 50+ kts across the lower MS Valley and nosing toward adjacent areas of the Mid-South. This will drive enhanced moisture transport from the Gulf of Mexico up north into the vicinity of a rather strong front draped across the region which will be attempting to lift northeast as a warm front ahead of the low center. Strengthening right-entrance region upper-jet dynamics, robust isentropic ascent, and the arrival of elevated instability with MUCAPE values of 500 to 1000+ J/kg should at least a relatively strong outbreak of convection near and to the north of the frontal boundary Wednesday evening and expanding in coverage heading into early Thursday with sufficient shear to drive several broken clusters of organized convection. PWs increasing to 1.5 to 1.75 inches locally, coupled with the robust low-level jet and improving instability parameters should favor convective cells attaining rainfall rates of 1 to 2 inches/hour at least locally. However, one of the uncertainties with the forecast overall will be forward propagation of the convection which may be sufficient to cut down on the total rainfall potential. Nevertheless, there may be some episodic instances of repeating cell activity as convection organizes Wednesday night and becomes better aligned with the deeper layer southwest flow aloft. Some spotty 2 to 3+ inch rainfall amounts cannot be ruled out, and thus there should be at least an isolated threat for some flash flooding. For now, given the rather significant mass field differences seen with the models today with respect to timing of the energy late in the period, and convective propagation uncertainties, a Marginal Risk of excessive rainfall will be maintained. However, an upgrade to a Slight Risk may need to be considered with later forecast cycles. Orrison Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6L0cRmVbUF8TimUSYFLegz8S6epp63sOhWkSQFzGZ2s9= L7eVqYjw2HcG7NPAMO-wMhiLMOF30FgSLdyYeuAm4yI9SGQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6L0cRmVbUF8TimUSYFLegz8S6epp63sOhWkSQFzGZ2s9= L7eVqYjw2HcG7NPAMO-wMhiLMOF30FgSLdyYeuAmSKsgHmA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6L0cRmVbUF8TimUSYFLegz8S6epp63sOhWkSQFzGZ2s9= L7eVqYjw2HcG7NPAMO-wMhiLMOF30FgSLdyYeuAmGKKgCZQ$=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) .