Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jan 06 2024 00:43:14 FOUS30 KWBC 060043 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 742 PM EST Fri Jan 05 2024 Day 1 Valid 01Z Sat Jan 06 2024 - 12Z Sat Jan 06 2024 ....FLORIDA PANHANDLE... Continued to trim the western extent of the Marginal risk with this update, with the risk now confined to portions of the FL Panhandle. The threat of flash flooding remains low, with minimal FFG exceedance in the 18z HREF. However some heavier convective cells will likely make it onshore over the FL Panhandle tonight, with 3"+ HREF neighborhood probabilities getting over 40% and recent HRRR runs depicting localized 3" amounts as well. Thus despite the threat being low, opted to maintain the Marginal risk, as can not rule out an isolated flash flood concern over any flood-sensitive urban and poor-drainage areas.=20=20=20 Chenard Day 2 Valid 12Z Sat Jan 06 2024 - 12Z Sun Jan 07 2024 In and near the Mid-Atlantic...=20 2030 Excessive Rainfall Discussion... The system making its way eastward along the Gulf coast on Day 1 turns and starts heading north/northeastward early on Day 2....spreading an expanding shield of precipitation along the East coast. Models still depict strong low-level inflow off the Atlantic and diffluent flow aloft that looks to support moderate to locally heavy rainfall rates...but the overall instability looks to be pretty meager. The QPF amounts looks to be similar to the previous set of guidance so no major changes needed.=20 Bann 0830Z Excessive Rainfall Discussion... A pair of mid-level shortwaves should allow for diffluence aloft near the East Coast. Inflow of ~50 kts at 850 hPa 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. 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 continues to edge northwest on the expected rain/snow line as the system moves through general southwest flow aloft downstream of a more significant deep cyclone). The Carolinas were removed from the risk area as the 850 hPa inflow looks increasingly parallel to their coastline/less onshore as the best moisture is nearby, which is more likely to keep convection more tied to the Gulf Stream offshore. =20 Roth Day 3 Valid 12Z Sun Jan 07 2024 - 12Z Mon Jan 08 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8PHVom5sxjUtlAe7c5tAKrtJ4Tqs33dmemPw6EzwSOvI= Xv78Yi1OTOYX5O3RkPQREKT9vUUwJaWwQYxxKwsuYjCmXAo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8PHVom5sxjUtlAe7c5tAKrtJ4Tqs33dmemPw6EzwSOvI= Xv78Yi1OTOYX5O3RkPQREKT9vUUwJaWwQYxxKwsu8sEWPl8$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8PHVom5sxjUtlAe7c5tAKrtJ4Tqs33dmemPw6EzwSOvI= Xv78Yi1OTOYX5O3RkPQREKT9vUUwJaWwQYxxKwsu4pg2geM$=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) .