Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 08 2022 00:18:23 FOUS30 KWBC 080018 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 717 PM EST Wed Dec 07 2022 Day 1 Valid 01Z Thu Dec 08 2022 - 12Z Thu Dec 08 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF THE SOUTHERN PLAINS EAST TO THE TENNESSEE VALLEY... Frontal boundary draped east/west across portions of the S. Plains toward the S. Appalachians will continue to be the focus for showers and thunderstorms. This activity is along an axis of higher moisture with the latest blended TPW product showing PWs of 1.3" to near 1.5", and should continue for a few more hours before dissipating as energy focuses back to the west. Until then, hourly totals between 0.5-1" are likely and this may cause localized flooding due mainly to the recent heavier rainfall that has now pushed soil saturation in the top 40 cm layer above 80 percent (NASA SPoRT) and resulted in lower FFGs. Further west across the S. Plains, shortwave energy lifting out of western Texas will create favorable forcing for ascent to produce a round of showers and elevated thunderstorms through early Thursday morning. Slightly anomalous moisture characterized by PWs approaching 1.5" will work with fairly limited instability (MUCAPE under 500 J/kg) for isolated heavy periods of rainfall. Most recent hi-res guidance and 18Z HREF show isolated signals for 1"+ hourly totals between 06Z-12Z across central Oklahoma, northwest Arkansas, and southwest Missouri and some repeating rounds will be possible given the favorable parallel mean flow to storm motions. However, the overall dryness in the soils and progressive movement of the showers/storms should limit any flash flood potential to just isolated instances. Taylor Day 2 Valid 12Z Thu Dec 08 2022 - 12Z Fri Dec 09 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 3 Valid 12Z Fri Dec 09 2022 - 12Z Sat Dec 10 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE COAST AND COASTAL RANGES IN NORTHWEST CALIFORNIA... 2030Z Excessive Rainfall Discussion... The only change made to the on-going outlook was to remove the Oregon portion of the Marginal Risk area and keep it in northern California where the models show better on-shore flow into the terrain as shortwave energy embedded aids in the re-amplification of a longwave trough along the west coast. The strength of the onshore flow allows for anomalous low- to mid-level moisture flux with modest elevated CAPE...so previous thinking that there could be isolated rainfall rates that results in flooding (with burn-scars being the most vulnerable) remains on track. Bann 0830Z Excessive Rainfall Discussion... Another vigorous upper level jet streak and associated shortwave energy dropping off the Pacific NW coast will allow the longwave trough to re-amplify toward the end of day 3 (Friday night), with robust exit region upper level forcing (DPVA/upper level difluence and strengthening low-mid level moisture transport) working into the outlook area. While not a classic AR setup given the broad central Pacific ridge and mid/upper level trajectories advecting down from the northern Pacific instead of the subtropical regions (limiting the TPW potential), the strength of the onshore flow (sw/ssw 45-55 kts at 850mb along the coast after 00Z Sat) will average between 4 and 5 standard deviations above normal per the GEFS and SREF. The anomalous degree of the low-mid layer moisture flux, with PWs between 0.75-1.00" and marginal elevated CAPEs of ~200-400 J/Kg, will likely result in isolated areas of 0.50+ inch/hr and/or 1.5+ inch/3hr rainfall rates west of the more elevated terrain where the precip will fall as snow. These rates may lead to isolated areas of rapid inundation, especially over burn scars. As a result, a Marginal Risk was included in the Day 3 ERO across these areas in southwest OR and northwest CA. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7bQavs3oPLw9yIFCb96KUXMa-21fRz_DUiASCORQOqSJ= FgbYHmZacpjVsiu7YCeMSTec1ivICqcis8pYl7EbBTKy_bg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7bQavs3oPLw9yIFCb96KUXMa-21fRz_DUiASCORQOqSJ= FgbYHmZacpjVsiu7YCeMSTec1ivICqcis8pYl7EbNPpXPx4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7bQavs3oPLw9yIFCb96KUXMa-21fRz_DUiASCORQOqSJ= FgbYHmZacpjVsiu7YCeMSTec1ivICqcis8pYl7Ebn879kZY$=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) .