Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 11 2024 15:59:58 FOUS30 KWBC 111559 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1159 AM EDT Thu Jul 11 2024 Day 1 Valid 16Z Thu Jul 11 2024 - 12Z Fri Jul 12 2024 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR SOUTHEAST VIRGINIA AND EASTERN CAROLINAS... ....16Z Update Summary... SLGT risk across the Carolinas into Southern Virginia was expanded to the west to align with the current Flood Watch collaborations with some of the local WFOs. A new MRGL risk was added to the Southeast FL coast to account for a local sea breeze enhancement within the urban corridor extending from just north of Fort Lauderdale down through the Miami Metro. The remainder of the MRGL risk areas across Maine, the Midwest, and Southwestern U.S were maintained given spatial continuity in scattered QPF signatures within their respective synoptic/mesoscale evolutions. Kleebauer ....Coastal Mid Atlantic... ....16Z Update... A sheared axis of heavy rainfall is currently bisecting a portion of the Eastern Carolinas with local rainfall rates exceeding 2"/hr in some of the pulse cells along the stalled frontal boundary. Recent radar/satellite trends indicate a formidable pulse=20 convective environment with totals along and east of NC11 and US13=20 producing totals of 3-6" in some portions of the above zone. The axis of precip will be reluctant to move as the cells will remain anchored to the boundary over the course of the afternoon which could lead to some totals exceeding 8" within the course of impact. There will be a decay in the current evolution after 21z, but not before a thin band of heavy rain will induce flash flooding concerns for several more hours. The SLGT risk was maintained with a higher end SLGT located within that small corridor where rainfall will continue.=20 Energy from the leading edge of a disturbance approaching from the southeast off the Atlantic will redevelop multiple bands of convective rainfall later this evening through tomorrow morning with a general expanse to the northwest overnight. Some of those cells could produce enhanced rainfall with rates exceeding 2"/hr, especially over Southern and Southeastern VA down into Eastern NC. The current HREF QPF footprint outlined the secondary convective bands very well with a QPF maximum situated over portions of Southern VA with the northern extent reaching Southern MD, extending down into to the NC/VA border. As a result, the SLGT was also expanded a bit to the north with the accompanying MRGL also being spread further northwest to account for the trends.=20 Kleebauer ....Previous Discussion... Stalled frontal boundary will bisect portions of the Eastern Seaboard with elevated PWATs mirroring the alignment of the front to points east. Local environment will be primed for convective potential, but will have some assistance in upper level support as a meandering wave off the Southeast coast lifts northwest on the western fringe of the ridge in the Atlantic, acting as a beneficial forcing mechanism to enhance regional rainfall potential. The best chance will lie from the Southern Delmarva through the Virginia Tidewater down into the Eastern Carolinas. Latest HREF probabilities are fairly aggressive in their signature for local totals between 2-5" as neighborhood probs for 2-3" totals are running between 60-90% with an area of 5" probabilities between 50-70% across Eastern North Carolina. This area has been very dry as of late, and is well reflected within the FFG indices present for 1/3/6 hour markers. Isolated to scattered urbanized flooding and/or flash ponding possible for 2-4 inches/hour rates as per the latest HREF mean hourly QPF output. A Slight Risk was raised for the North Carolina coast and a very small potion of southeast Virginia and northeast South Carolina. A Marginal Risk spans from South Carolina to southern New Jersey. Kleebauer/Campbell ....Northern Maine... ....16Z Update... Remnant moisture and trailing mid-level energy behind Beryl's circulation will keep the threat of convection across Northern and Central ME for at least the next 3-6 hrs before fully escaping into the Canadian Maritimes. Probability fields are not as enthused as yesterday for significant totals, but antecedent conditions along with any convective focus could cause some localized flood concerns in-of the terrain up to the Canadian border near Caribou. The threat was sufficient enough to maintain continuity, especially with the elevated moisture presence still lingering across the northern tier.=20 Kleebauer ....Previous Discussion... Lingering convective threat across Northern Maine could induce some local flash flood concerns, mainly for northern and Downeast Maine. The latest guidance continues to signal the highest QPF across Downeast Maine where the highest PWAT anomalies remain leading to some deterministic output indicating 1-2" of rainfall within the first 3-6 hours. The Marginal Risk was kept for this issuance, but may be considered for removal is convection dissipates sooner than forecast. ....Midwest... ....16Z Update... There are no changes necessary to the previous MRGL risk across the Midwest as scattered thunderstorms within a much lower FFG footprint across the region thanks to impacts from Beryl will create a localized threat for flash flooding as a shortwave trough traverses overhead. Kleebauer ....Previous Discussion... Trailing shortwave trough pivoting southeast around the backside of the mean trough over the Great Lakes and Ohio Valley will strengthen as it moves across Iowa into Illinois by tomorrow afternoon with large scale forcing increasing across the Central Midwest and adjacent Mid-Mississippi Valley. Convection is expected to fire up across Illinois, Missouri and Indiana and within these storms some will be stronger and capable to producing hourly rates of 1 to 2 inches/hour. Much of the region was soaked by Beryl as is passed through and soils have not fully recovered. Antecedent moisture in the top layer of the soils is well-defined with NASA SPoRT moisture percentiles relaying the 0-10cm layer running between 75-90% leading to higher runoff capabilities. Given the sensitive nature of soils and the potential for a few inches, a Marginal Risk for excessive rainfall was maintained for this period. Kleebauer/Campbell=20 ....Southwest... ....16Z Update... No changes to the previous forecast as the Monsoonal pattern and forecasted QPF within zones of higher impact (Burn scars) remains on track. Kleebauer ....Previous Discussion... The persistent monsoonal pattern will continue to support highly isolated convection with the primary areas of interest being the burn scars in New Mexico and small urban threat of towns within complex terrain across Southeast Arizona through much of New Mexico. A Marginal Risk remains in effect for southeast Arizona and a majority of New Mexico. Campbell ....Southeast Florida... Sheared axis of convection is currently positioned off the east coast of FL with accompanying energy slowly migrating southwest towards the Southeast coast of FL. Sea breeze will propagate inland, but will be met with the west coast sea breeze to initiate a strong convergence signal in-of of the urban corridor along the Southeast FL coast. This will include areas like Fort Lauderdale down to the Miami Metro with some guidance fairly bullish in their QPF representation. Totals of 2-4" with locally upwards of 6" will be plausible as the environment remains conducive for heavy rainfall given the forecast sounding signatures of tall, skinny CAPE, SBCAPE around 2500-3000 J/kg, and a steering pattern focused parallel to the coastline. This type of setup has historical precedence in being a sneakier flash flood setup and the addition of a MRGL risk was in agreement with the Miami WFO.=20 Kleebauer Day 2 Valid 12Z Fri Jul 12 2024 - 12Z Sat Jul 13 2024 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL OVER PORTIONS OF THE MID-ATLANTIC AND THE CAROLINAS... A second round of slow moving convection is expected near the stalled frontal boundary. The greater impacts of scattered instances of flash ponding and flooding be primarily be focused over urbanized areas and areas that see repeat heavy rains from the period prior. The ridge will assist the convection spreading rains further inland. It's possible the northern extent of the Slight Risk could be scaled back given some small trends in lower QPF focused north of the Virginia Tidewater. Trends in that stretch of the coast will be monitored with future updates. The Eastern Carolinas will remain the primary target for heavier rainfall with some areas in the two day period potentially receiving over 5 inches from the evolving event. The Slight Risk spans from northeast South Carolina to southern New Jersey and the Marginal stretches from South Carolina to southern New Hampshire. Campbell Wanted to also make mention of monitoring the progression and convective evolution within a migrating inverted trough axis through South Texas into the Rio Grande. Current ensemble forecast is relatively tame within the realm of QPF, however the environment is more than favorable for higher convective impacts, including heavy rain within the Rio Grande and points just inland. First Guess fields do pinpoint a small MRGL located within the corridor from Eagle Pass down through Laredo, so perhaps if guidance ramps up the QPF signal in future updates, there could be a targeted Marginal Risk area added to the central RGV. Kleebauer Day 3 Valid 12Z Sat Jul 13 2024 - 12Z Sun Jul 14 2024 ....THERE ARE MARGINAL RISKS IN THE SOUTHWEST AND ACROSS NORTH DAKOTA AND MINNESOTA... be dropping south from ....Southwest... There will be a resurgence of monsoonal flow back into the Southwest. Diurnal heating will help fire up convection during the afternoon and evening hours with the potential for higher rainfall fall rates. Maintained the Marginal Risk area for much of Arizona, northwest New Mexico and southwest Colorado for this period. ....North Dakota and Minnesota... A shortwave trough will be tracking east across Canada and will send a surface cold front south-southeast through the Canadian Prairie and into the northern tier U.S.. Showers and thunderstorms are expected to form along and ahead of this feature which will predominately focus over North Dakota and northern Minnesota during this period. This part of the country has been above/well- above normal on moisture for the past few months and remain sensitive to additional rainfall. A Marginal Risk is in effect for eastern North Dakota and northern Minnesota. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9gqBrKmvQTlPSyD_a9yd_XzBI7lAwy7ngCfgWHlFIrc5= 44-tsRzlaxujIbndUuQgvpNyybO-MQeZ9QaEQJbf3Kkmr7Q$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9gqBrKmvQTlPSyD_a9yd_XzBI7lAwy7ngCfgWHlFIrc5= 44-tsRzlaxujIbndUuQgvpNyybO-MQeZ9QaEQJbfvVftNwY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9gqBrKmvQTlPSyD_a9yd_XzBI7lAwy7ngCfgWHlFIrc5= 44-tsRzlaxujIbndUuQgvpNyybO-MQeZ9QaEQJbfek4tgGM$=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) .