Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 12 2024 01:06:14 FOUS30 KWBC 120106 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 806 PM EST Wed Dec 11 2024 Day 1 Valid 01Z Thu Dec 12 2024 - 12Z Thu Dec 12 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN LONG=20 ISLAND UP THROUGH NORTHERN MAINE... Primary adjustment for the 01Z update was to shift the western extent of the previous outlook areas further east across the Northeast and remove the Mid-Atlantic, which is now post-frontal. Deep moisture (PWs 1.25-1.5 inches) and strong ascent ahead of an=20 approaching, negatively-tilted shortwave will contine to support=20 periods of the moderate to heavy rain across portions of Long=20 Island and New England this evening into the overnight. This rain=20 is expected to move east along with the advancing cold front=20 overnight. However, some areas, especially from eastern Long Island northward through eastern New England into northern Maine, may see an additional 1-2 inches before the rain ends. Limited instability is expected to keep rates in check, however given the wet soil=20 conditions throughout the region and snow melt across portions of=20 northern New England, these amounts may cause localized runoff=20 concerns. Pereira Day 2 Valid 12Z Thu Dec 12 2024 - 12Z Fri Dec 13 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Chenard Day 3 Valid 12Z Fri Dec 13 2024 - 12Z Sat Dec 14 2024 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHWEST CALIFORNIA AND SOUTHWESTERN OREGON... 20z Update: Forecast still looks on track. The latest model guidance expands the higher QPF a bit further south across coastal northern CA, and thus the Marginal risk was expanded in this direction. Generally expecting 1-3" of rain over the Marginal risk area through 12z Sat, with localized amounts of 3-4" within the most orographically favored terrain within the south to southwesterly low level flow. Chenard ....Previous Discussion below... Fairly robust disturbance over the Pacific will translate southeastward towards the North-Central CA coast by the end of the week with a persistent IVT pulse oriented southwest to northeast into the coastal plain over the course of the forecast period leading to waves of moderate precipitation to impact areas north of the Bay area. Current progs indicate precip totals on the order of 2-4" with locally higher embedded within the coastal ranges spanning north of Santa Rosa. Current rates anticipated to be modest with upwards of 0.5-0.75"/hr at peak intensity lending to a lower end threat for flash flooding, however totals are significant enough to warrant a low-end threshold MRGL, mainly for the coastal urban areas of Northwest CA up through Southwestern OR where totals will be on the order of 2-4", especially into the windward areas of the Klamath Range. MRGL was generally maintained from previous forecast with only some minor modifications to align with the latest guidance. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_f1dHYJrtJ9b0h3z5nh_GPcEkWGAqK4YTFU4_sJ0cfFR= CfRs3A2CVNvGsXdlmrYdhh6vQ0ooblY1Mfx1sP0lwZM9e9o$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_f1dHYJrtJ9b0h3z5nh_GPcEkWGAqK4YTFU4_sJ0cfFR= CfRs3A2CVNvGsXdlmrYdhh6vQ0ooblY1Mfx1sP0lX1FiwSQ$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_f1dHYJrtJ9b0h3z5nh_GPcEkWGAqK4YTFU4_sJ0cfFR= CfRs3A2CVNvGsXdlmrYdhh6vQ0ooblY1Mfx1sP0lIuTYtY4$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .