Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Apr 07 2025 00:43:29 FOUS30 KWBC 070043 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 843 PM EDT Sun Apr 6 2025 Day 1 Valid 01Z Mon Apr 07 2025 - 12Z Mon Apr 07 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHEASTERN UNITED STATES... Training convection continues this evening across portions of the=20 central Gulf Coast producing areas of flash flooding. With plenty=20 of upstream instability and persistent, slow moving,=20 convergence...this axis of training convection should continue=20 for at least several more hours. The axis of convection will=20 slowly make eastward progress, while also likely expanding off to=20 the northeast with time. This convection will be capable of hourly=20 rainfall as high as 2-3"...with a swath of total rainfall amounts=20 of 3-5", locally as high as 5-8". This axis will likely stretch=20 from southern AL into portions of the far western FL Panhandle and=20 possibly west central GA. Rainfall rates and magnitudes will likely be high enough for scattered to numerous instances of flash=20 flooding along this training corridor...some of which could be=20 locally considerable in nature.=20 Recent HRRR runs are likely too fast in moving this convection off to the northeast. Recent radar and satellite trends continue to=20 show upstream development offshore, which will continue to feed=20 inland. Thus additional rainfall amounts may be higher than what=20 the 23z HRRR indicates. A secondary uptick in shower activity=20 should occur late tonight into Monday morning along the front. By=20 this time instability near the front should be lower, and thus=20 expecting weaker rainfall rates. Nonetheless rainfall rates of 0.5" to 1" per hour could move back over areas saturated from this=20 evenings rainfall resulting in areas of continued or renewed flash=20 flooding. A Moderate risk remains justified across portions of=20 southern AL into the far western FL Panhandle and portions of west=20 central GA. Across portions of the Carolinas into Virginia showers and embedded heavier convective elements are expected to expand in coverage overnight. Additional rainfall of 1-3" is expected, which should not result in widespread impacts...however localized instances of flash flooding can not be ruled out. Chenard Day 2 Valid 12Z Mon Apr 07 2025 - 12Z Tue Apr 08 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST US ON MONDAY... 19Z Update: Upon examination of the 12Z model and CAM guidance suite, the inherited Marginal Risk area was expanded a little to the north to include the greater Richmond, VA metro area and all of Hampton Roads, and a modest extension to the west to include the foothills of the southern Appalachians. The ARW has a slower exit of some of the heavier rainfall through midday Monday, with the potential for some 1-2 inch totals along and just northwest of the Interstate 85 corridor. There may also be a second area of enhanced rainfall across the coastal plain of North Carolina and extending into southeast Virginia where higher PWs and instability will exist ahead of the cold front, mainly south of Interstate 64. Depending on how much convective training occurs, some instances of 2-3+ inch totals will be possible on Monday before things taper off Monday evening, with some lingering lighter rains after sunset and ending overnight. One of the mitigating factors here is recent dry weather and higher flash flood guidance, so the threshold of flooding is higher and therefore this precludes the need for any Slight Risk areas at this time. Hamrick ....Previous Discussion... Overall...the ongoing forecast remained on track and only some minor adjustments were needed to account for a few pieces of guidance which still favored a slower solution and, consequently, higher rainfall amounts over a somewhat larger territory than in the previous outlook. Still think that any lingering moderate to heavy rainfall will continue to shift eastward on Monday as the large scale flow pattern remains progressive. Current model QPF generally remained in the 1.5 inch to 2.5 inch range with isolated higher totals possible from far northern Florida northward into the eastern portions of the Carolinas. The plume of 1.75+ inch precipitable water values slowly decreases with time before being shunted entirely off the Carolina coast Monday evening (and across the central Florida peninsula late Monday night/early Tuesday morning. Until that happens...moisture transport of deeper moisture remains favorable to support a low- end risk of excessive rainfall (especially in regions of poor drainage), Bann Day 3 Valid 12Z Tue Apr 08 2025 - 12Z Wed Apr 09 2025 A much needed return to drier weather comes by Tuesday morning and the cold front will be offshore, except for the Florida Peninsula, where it should exit by Tuesday evening. There may be a few heavier showers and storms that develop over South Florida, and any localized slow moving cells may result in some ponding of water in poor drainage areas, but not enough of a concern to merit any risk areas at this time. Most rainfall amounts should be under an inch. Hamrick Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!46mr09eigiz1aT9h6Pf7TVRCXChIwAMuVBB2iu_aQ2gG= bApMtoAS0l_t6djzYZeO_TB3foDTkb_-uHn1HpZB-0LCjaI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!46mr09eigiz1aT9h6Pf7TVRCXChIwAMuVBB2iu_aQ2gG= bApMtoAS0l_t6djzYZeO_TB3foDTkb_-uHn1HpZBaLMlhKs$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!46mr09eigiz1aT9h6Pf7TVRCXChIwAMuVBB2iu_aQ2gG= bApMtoAS0l_t6djzYZeO_TB3foDTkb_-uHn1HpZBVNGwT_g$=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) .