Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jan 06 2024 20:24:58 FOUS30 KWBC 062024 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 324 PM EST Sat Jan 06 2024 Day 1 Valid 16Z Sat Jan 06 2024 - 12Z Sun Jan 07 2024 ....16Z Excessive Rainfall Discussion... No big changes were needed to the previously issued Marginal Risk area. Neighborhood probabilities from the 12Z HREF still point to some low-end risk of rainfall exceeding flash flood guidance...moreso in the 3- and 6-hour time frames later in the afternoon and evening across parts of the Mid-Atlantic and points northeast. Spaghetti plots of the SREF/GEFS QPF showed better chance for 2+ inch amounts being confined in the immediate vicinity of the coast and an inch or more along the urban corridor. So the QPF signal itself remained meager...but felt the Marginal risk area still captures the essence of isolated ponding and run off problems in urban areas and areas of poor drainage (especially in areas that received locally heavy rainfall during the previous week or two).=20 Bann ....0830Z Excessive Rainfall Discussion... A pair of mid-level shortwaves should allow for diffluence aloft near the East Coast. Inflow of 50-60 kts at 850 hPa from the southeast is expected off the Atlantic. Low- to mid-level frontogenesis is likely to do the heavy lifting as instability will be quite low -- at or below 250 J/kg -- which should be able to yield hourly rain totals of 0.5"+ at times, an idea supported by the 00z HREF. The signal for heavy rainfall exists, but the guidance is not overly strong with the QPF signal as the system overall should remain progressive. Portions of this region experienced heavy rainfall within the past week, with pockets receiving 300%+ of their average weekly rainfall for this time of the year, which is the main reason the Marginal Risk area has been kept from continuity. Overall, thought there was just enough there for the Marginal Risk to carry forward, but some adjustments were made based on newly available guidance QPF-wise and to better account for the precipitation type expected with a little bit of overlap into the expected snow area (in case the guidance edges farther northwest on the expected rain/snow line as the system moves through general southwest flow aloft downstream of a more significant deep cyclone).=20 =20=20 Roth=20 Day 2 Valid 12Z Sun Jan 07 2024 - 12Z Mon Jan 08 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent.=20 =20 Bann Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-e1ukq7PflgYuKhIsuaZK94uFXfZ45gJRjvoVy6CLIAJ= aAdJ1wrMO0XAHS-Ixt_KasfqLPVtUAnw-5vaCdVoBahECQE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-e1ukq7PflgYuKhIsuaZK94uFXfZ45gJRjvoVy6CLIAJ= aAdJ1wrMO0XAHS-Ixt_KasfqLPVtUAnw-5vaCdVo-FvXtd8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-e1ukq7PflgYuKhIsuaZK94uFXfZ45gJRjvoVy6CLIAJ= aAdJ1wrMO0XAHS-Ixt_KasfqLPVtUAnw-5vaCdVoYQLR0Xk$=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) .