Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Nov 06 2022 00:21:28 FOUS30 KWBC 060021 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 820 PM EDT Sat Nov 05 2022 Day 1 Valid 01Z Sun Nov 06 2022 - 12Z Sun Nov 06 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Pereira 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 Valid 12Z Mon Nov 07 2022 - 12Z Tue Nov 08 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS THE TRANSVERSE RANGES OF SOUTHERN CALIFORNIA... ....Southern California... A deep upper trough will be situated along the West Coast early Monday with a strong closed low noted just offshore of the Pacific Northwest. Robust shortwave/jet energy will be rounding into the base of the upper trough and encroaching on the coastal ranges of southern CA later Monday and into early Tuesday while coinciding with the gradual southeast advance of a cold front. The latest guidance suggests a channel of rather concentrated moisture in the low to mid-levels of the column and there will be a favorably orthogonal orientation of the deeper layer flow relative to the terrain. The PWs are forecast to be about 1.5 to 2+ standard deviations above normal along the front. The expectation is for at least some broken bands of heavy showers to impact the Los Angeles basin and especially the Transverse Ranges for the latter part the period. There is expected to be as much as a 30 to 40 kt low-level jet advancing into the windward slopes of the terrain, and will help to enhance the rainfall rates. Some spotty 1 to 2+ inch rainfall amounts are expected, and this may result in some runoff problems with at least an isolated flash flooding concern around the more sensitive burn scar locations. A Marginal Risk of excessive rainfall has been introduced as a result. Orrison Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-JvkMN_5fHbOkgzOJ9CaIHPpc9Rjld3j7aeaeje16Xef= c5qOfGymQeOyzjHG4kH6OTnRK9qwaP52Es4YTc6svInN5-Y$=20=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-JvkMN_5fHbOkgzOJ9CaIHPpc9Rjld3j7aeaeje16Xef= c5qOfGymQeOyzjHG4kH6OTnRK9qwaP52Es4YTc6sZRA0IUg$=20=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-JvkMN_5fHbOkgzOJ9CaIHPpc9Rjld3j7aeaeje16Xef= c5qOfGymQeOyzjHG4kH6OTnRK9qwaP52Es4YTc6spV1EdMs$=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) .