Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Sat Jan 27 2024 09:47:00 FOUS30 KWBC 270833 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 332 AM EST Sat Jan 27 2024 Day 1 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. An associated (relatively weak) surface low pressure system over Southeast will track along/near a frontal zone draped/dammed across the southern Appalachians into the Mid-Atlantic today, bringing two distinct rounds of moderate to heavy rainfall to the Slight Risk area. 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. CAM guidance remains in good agreement, suggesting localized 1-3" totals the vicinity of the southern Appalachians and adjacent portions of the Mid-Atlantic (i.e. western NC/SC/VA) along and south of the terrain. An inherited Slight Risk was maintained and expanded a bit northeast into more of VA and far southern WV. A broader Marginal Risk surrounds the area, extending into much of the Southeast (where the primary round of heavier rainfall with rates of 1-2"/hr will occur early in the period, prior to midday) and northeast into much of the Mid-Atlantic (where rates are expected to be more tame with totals of an inch or less 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 today The risk area highlights where the hi-res 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. Rates are generally expected to remain below 0.5"/hr, which will cause most impacts to be due to longer duration flooding, but the threat for brief periods of higher rates necessitates the inclusion of a Marginal Risk. Churchill Day 2 Valid 12Z Sun Jan 28 2024 - 12Z Mon Jan 29 2024 THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS LESS THAN 5 PERCENT Churchill Day 3 Valid 12Z Mon Jan 29 2024 - 12Z Tue Jan 30 2024 THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS LESS THAN 5 PERCENT Churchill $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .