Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Fri Jan 26 2024 08:55:00 FOUS30 KWBC 260825 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 325 AM EST Fri Jan 26 2024 Day 1 Valid 12Z Fri Jan 26 2024 - 12Z Sat Jan 27 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL GULF COAST AND SOUTHEAST, AS WELL AS FOR FAR SOUTHWEST OREGON AND NORTHWESTERN CALIFORNIA... ....Central Gulf Coast and Southeast... The inherited Slight Risk has been shifted west a bit again this cycle, owing to the trends in the new 00z HREF guidance. The focus for heavy rainfall will occur in the vicinity of a lingering frontal boundary, which is expected to be rejuvenated by the progression of an upper low moving east across the Southern Plains. While the forecast largely calls for localized totals of 1-2" across the Slight Risk area, there is some potential for localized amounts of 2-3". These higher totals are most favored across the western half of the Slight (from much of LA northward through western MS and far southeastern AR), with the majority of the rainfall occurring late in the forecast period (after 00z) when the upper low begins to approach the region. Rainfall rates of 1"/hr or less are expected early in the day (which could result in an inch or so in accumulations locally) before 1-2"/hr rates become more common later in the evening and overnight. While soils have had some opportunity to recover from the recent heavy rainfall, FFGs remain somewhat suppressed and generally range from 2-3". Therefore any instances of renewed flash flooding are expected to remain isolated to widely scattered. ....Oklahoma and surrounding portions of North Texas and southern Kansas... The forecast remains little changed over the southern plains, as an upper low developing over the lee of the southern Rockies will slide eastward with large scale ascent providing a blossoming precip field over North TX and much of OK. Rates will be on the lower end overall, but some localized 1"/hr potential is possible given the favorable upper level dynamics with forecast soundings over OK indicative of elevated convective potential with deep saturation through the column. This could result in localized totals around 2" in a short period, nearing 3-hr FFGs. ....Pacific Northwest... An atmospheric river is forecast to spread inland across the Pacific Northwest coast on Friday, likely resulting in 1-3" localized totals along the coastal areas from northwest CA into OR. The area over southwestern OR and northwest CA has the best chance for localized 3" exceedance (where an inherited Slight Risk was maintained). The bulk of the precipitation is expected late in the forecast period (with the bulk after 00z). Churchill/Kleebauer Day 2 Valid 12Z Sat Jan 27 2024 - 12Z Sun Jan 28 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN APPALACHIANS AND ADJACENT PORTIONS OF THE MID-ATLANTIC... ....Southeast and Mid-Atlantic... An upper low/shortwave trough will slowly progress eastward on Saturday from the Southern Plains into the OH/TN Valleys. A relatively weak surface low pressure system is forecast to form over the Southeast in response to this feature, tracking along/near a frontal zone draped/dammed across the southern Appalachians into the Mid-Atlantic. Although forecast soundings depict little to no elevated instability, the combination of vorticity advection, moderate warm air advection, and upslope flow along the terrain could support some convective elements and localized rainfall rates to around 1"/hr. Guidance is in good agreement suggesting 1-3" totals (which also corresponds with the WPC QPF), and the best chance for these totals is in the vicinity of the southern Appalachians and adjacent portions of the Mid-Atlantic (i.e. western NC/SC/VA). An inherited Slight Risk was maintained and expanded west a bit given the forecast. A broader Marginal Risk surrounds the area, extending into much of the Southeast (where lingering rainfall and flooding may be ongoing early in the period) and northeast into much of the Mid-Atlantic (where rates are expected to be more tame with totals of around an inch through 12z Sunday). ....Pacific Northwest... An inherited Marginal Risk was maintained for portions of the CA/OR/WA coasts with impacts from the aforementioned atmospheric river continuing into Saturday. The risk area highlights where guidance (and the WPC QPF) calls for an additional 1-3", and subsequent targeted upgrades are possible with the addition of more hi-res model guidance later today. Churchill Day 3 Valid 12Z Sun Jan 28 2024 - 12Z Mon Jan 29 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHWESTERN WASHINGTON STATE... An inherited Marginal Risk was maintained for lingering rainfall from a waning atmospheric river across the far northwestern portion of WA state. An additional 1-2" locally are possible here after 3-6" of forecast rainfall on Days 1 and 2. Longer duration flooding impacts are more likely over the area, but an isolated instance or two of more rapid onset flooding cannot be ruled out. Churchill $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .