Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Nov 12 2022 08:07:37 FOUS30 KWBC 120807 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 306 AM EST Sat Nov 12 2022 Day 1 Valid 12Z Sat Nov 12 2022 - 12Z Sun Nov 13 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL PORTIONS OF NORTHERN NEW ENGLAND... Moderate to locally heavy rainfall is likely to be ongoing by the start of the day 1 period as precipitation rides along a potent cold front and nearby deepening surface low as it swings into northern Maine. Recent rainfall from the previous day may prime the soils as upwards of 1" per hour rates pass over the area, while also moving eastward at a decent clip. Very anomalous PWATs above 1.5" and +4 standard deviations above the climatological mean (per the 00z GEFS) will provide an environment more than capable of producing efficient rainfall rates within the line of showers. The limiting factor from a flash flood perspective is the speed at which the line of showers will be moving, exiting New Hampshire by 16z and Maine by 19z. Thus, the Marginal Risk was maintained and only expanded a bit southward in order to capture current radar and HIRES CAM guidance trends around the very beginning of the forecast period. Snell Day 2 Valid 12Z Sun Nov 13 2022 - 12Z Mon Nov 14 2022 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Snell Day 3 Valid 12Z Mon Nov 14 2022 - 12Z Tue Nov 15 2022 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS THE UPPER TEXAS COAST AND CENTRAL GULF COAST... By the day 3 timeframe, return flow out of the western Gulf of Mexico ahead of an approaching vigorous shortwave over the southern Plains will set the stage for potentially excessive rainfall extending from the Upper Texas Coast to southern Louisiana and eventually southern Mississippi and Alabama by the evening hours. PWATs over 1.5" and dew points into the 60s are forecast to push just inland with the help of a slow-moving warm front and 50 kt low-level jet. This moisture source will be short-lived and struggle to push well inland as a fast moving cold front kicks the convection eastward Monday night. The best intersection of instability, moisture, and shear along the warm front is likely to be near far southwestern Louisiana. So it is likely that is area will be monitored for a potential upgrade. Current QPF depicts widespread 1-3" rainfall amounts are possible within much of the Marginal Risk area and could reach locally higher. However, there remains some notable north-south spread regarding the axis of heaviest rain, with some guidance (00z ECMWF) actually keeping the heaviest rain just offshore. Urban areas are most at risk given the naturally lower threshold for flash floods and ponding water over impervious surfaces. Otherwise, FFG remains relatively high across this part of the country and was an additional factor for not elevating the risk area to a SLGT. Elevated convection is likely farther north into the Lower Mississippi Valley as well, where 1" rainfall totals could be realized, but should remain under FFG. Snell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7fX3VK653NgiKjDL7PgeOmBoWcnqs56nLH1zgeOc1e1w= Wc2kyROncqSZXjGg9KvXIuz5j7XoVl6aU5Z3EZVPuhjUk4M$=20=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7fX3VK653NgiKjDL7PgeOmBoWcnqs56nLH1zgeOc1e1w= Wc2kyROncqSZXjGg9KvXIuz5j7XoVl6aU5Z3EZVPiYFmFNI$=20=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7fX3VK653NgiKjDL7PgeOmBoWcnqs56nLH1zgeOc1e1w= Wc2kyROncqSZXjGg9KvXIuz5j7XoVl6aU5Z3EZVPiaHXVb8$=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) .