Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Nov 05 2022 20:01:27 FOUS30 KWBC 052001 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Sat Nov 05 2022 Day 1 Valid 16Z Sat Nov 05 2022 - 12Z Sun Nov 06 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....Central Gulf Coast... A long-lived line of pre-frontal showers and thunderstorms continues to advance gradually off to the east across the Gulf Coast states as a deep layer trough continues to pivot northeastward across the Midwest. In time heading through the afternoon hours, the stronger upper support that was helping to sustain the convective threat from overnight and through this morning will begin to pull away and become detached from any conducive downstream thermodynamic environment for sustainable convection. The airmass downstream out ahead of the current activity is quite stable and this should favor a continued weakening trend of the shower and thunderstorm activity over the next several hours. These is a very modest nose of weak instability still lurking near southern MS and southern AL, and the 12Z HREF guidance suggests perhaps enough convective vigor for some spotty 1 to 2 inch rainfall amounts going through mid-afternoon across these areas and mainly along the immediate coast. Aside from some highly isolated urban runoff considerations in the near-term, flash flooding is not expected. Thus, the Marginal Risk area has been dropped with this update. Orrison Day 2 Valid 12Z Sun Nov 06 2022 - 12Z Mon Nov 07 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS COASTAL OREGON AND NORTHWESTERN CALIFORNIA... ....Coastal OR and Northwest CA... Generally no changes to the previous thinking. The Marginal Risk area is maintained for the coastal ranges of central to southwest OR and down into northwest CA for this period. A deep upper trough will be evolving along the West Coast Sunday through Sunday night as a strong vertically stacked low drops south just offshore of the Pacific Northwest. Shortwave energy rounding the base of the upper trough coupled with a southward advancing cold front and moist onshore flow will help to focus an axis of stronger forcing and moisture convergence for a band of heavy showers to gradually drop southward down across the orographically favored. As the height falls with the upper trough arrive, snow levels will be gradually dropping, and should lower from about 3500 feet early Sunday down to 2500 feet Sunday night. Rainfall totals of 1 to 3 inches are still expected, but any runoff concerns are expected to be highly localized. ....Blue Ridge of Western NC... A rather narrow axis of heavy showers may impact the eastern slopes of the Blue Ridge over western NC Sunday morning as a small-scale channel of stronger moisture convergence works northward up along the terrain. There will be the eastward advance of weakening shortwave energy (related to the current upper trough over the MS Valley) that will be crossing the region too, and that coupled with a modest instability footprint (MUCAPE values of 500+ j/kg) may help provide an additional catalyst for this narrow axis of rather low-topped convection to materialize. It will be quite moist with PWs running a solid 2+ standard deviations above normal, and so there will be an elevated degree of warm rain processes in play with this set-up. Some localized 1 to 3 inch rainfall amounts will be possible with this axis of showers that sets up and potentially trains over the same area. The 12Z HREF guidance does show some low-end probabilities of there being some FFG exceedance in the 12Z to 18Z time frame, so there will be a non-zero threat of some runoff problems. Some consideration was given to introducing a Marginal Risk, but the given the small-scale and highly uncertain nature of the convective evolution, it was kept out for the time being. Orrison Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_ZJmlUeeL9t3PnhK8y-aIKPUgujkOTLTbTUObujdwsyN= _fmtCp-uPDatRH7NmNC2D6hkU6V2QEB3PxqwhlBpppOKlMc$=20=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_ZJmlUeeL9t3PnhK8y-aIKPUgujkOTLTbTUObujdwsyN= _fmtCp-uPDatRH7NmNC2D6hkU6V2QEB3PxqwhlBpVElSyFM$=20=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_ZJmlUeeL9t3PnhK8y-aIKPUgujkOTLTbTUObujdwsyN= _fmtCp-uPDatRH7NmNC2D6hkU6V2QEB3PxqwhlBp_jt8F_E$=20=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) .