Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 10 2024 15:45:29 FOUS30 KWBC 101545 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1145 AM EDT Wed Jul 10 2024 Day 1 Valid 16Z Wed Jul 10 2024 - 12Z Thu Jul 11 2024 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF UPSTATE NEW YORK THROUGH MUCH OF VERMONT AND NORTHERN NEW HAMPSHIRE... ....16Z Update... Minor adjustments were made to the MDT risk with an expansion to cover the northeast coast off Lake Ontario near Watertown/Fort Drum, and took the risk area to the Canadian border. The 10 and=20 100 year ARI exceedance probabilities off the 12z HREF were very=20 impressive across much of North Country through Northern VT with=20 >50% 10 year ARI exceedance signatures and 30-50% centered over the Adirondacks. Totals between 2-4" are very likely for a large portions of Upstate NY through Northern VT/NH with maxima around 6" still expected. Further to the southwest over MI, a targeted heavy rain threat across Southeast MI will linger through 18z before moving out into the neighboring Ontario Province as the remnant circulation from Beryl continues to progress northeast. The risk areas over the Ohio Valley and MI were adjusted to conform to current radar trends and forecasted precip next 4 hrs.=20 There were no changes necessary over the Southwest U.S, mainly in NM where scattered convection will exacerbate flash flood threats within the multitude of burn scars present from the Sacramentos up through the north-central part of the state. Rates will top between 1-1.5"/hr at peak intensity in the strongest cells, more than capable of causing issues within any burn scars and smaller towns within the complex terrain.=20 Scattered heavy thunderstorms continue to impact the Central Gulf=20 coast with rates reaching upwards of 2-3"/hr in stronger pulses.=20 FFGs are sufficiently very high and the threat for flash flooding=20 will be highly localized, mainly to the southern edge of New=20 Orleans over to Biloxi. The threat will diminish across the area=20 after 00z so have maintained the targeted MRGL for continuity=20 purposes given the current radar depiction.=20 ....Northeast... Remnant moisture and mid-level energy from Beryl will translate northeastward out the Ohio Valley and Great Lakes creating a heightened threat for widespread heavy rain and flash flooding across Southeast Michigan through New York and Central/Northern New England. At the surface, a warm front will bisect much of New York through Central New England, marked very well by a sharp theta-E gradient. This will be a focal point for convection prior to the main circulation moving overhead, as well as the axis of where the highest PWATs will be confined during the unfolding of the synoptic scale event. Low- level instability will be highest within the confines of the warm front and points south with the best upper level forcing likely along and north of the boundary creating a dynamic scenario with a zone of highest heavy rain potential where all three characteristics overlap. The highest heavy rain prospects lay within the Adirondacks and points east into north-central Vermont and New Hampshire, including the Green and White Mountains in the respective states. 12z HREF EAS probabilities were much more aggressive in the signals for at least 2" and 3" across the aforementioned areas with a 50-80% probability for at least 2" within the Adirondacks to just south of the Champlain Valley, a strong signal for higher totals given the necessary overlap of CAMs to exhibit such a larger probability. Historically, when an EAS signal is above 70%, the expectation for widespread coverage of that value of rain or more is very certain and regardless a higher risk consideration if the areal FFG indices allow. HREF EAS for 3" managed to come in more aggressive with a large coverage of 25-40% with the highest=20 potential across the Adirondacks and northern Mohawk Valley=20 characterized by a targeted 45-50% signature. This is right within the inflection of where the warm front is forecast to reside,=20 creating a zone of higher confidence for heavy rainfall.=20 Heavy rain will be possible all the way into Maine where the elevated PWAT anomalies between +2 to +3 standard deviations will be recognized leading to a higher end SLGT risk residing from Southeast Michigan all the way into western and central Maine. Totals of 2-4" are anticipated with local maxima to 6" plausible within the above areas in the Moderate Risk. 1-3" will be possible as far south as central and northeastern PA up through the NY Capital District due to convection developing along and ahead of the trailing cold front moving through the area tomorrow afternoon and evening. Kleebauer ....Previous Discussion... ....Central Rockies and portions of the Southwest... A Slight Risk for excessive rainfall remains in effect across the higher terrain of central New Mexico. During this period monsoonal moisture and diurnal heating will maintain convection across portions of the Central and Southern Rockies and southwest New Mexico. Some of the highest forecast QPF is expected to focus in the vicinity of the Sacramento Mountains where there have been a few recent wildfires. he burn scar complex (Blue-2, South Fork, Salt and McBride) are highly sensitive to rainfall and can easily lead to flooding and debris flows, especially with the 0.25 to 1 inch QPF that is forecast. ....Central Gulf Coast... Training convection expected to continue along the stalled frontal boundary. Very high FFGs within the area highlighted by a Marginal Risk which will limit flash flooding to very isolated and mainly within larger urban zones like New Orleans and towns based in the southeastern Parishes. Given the limited threat, should the convection shift further south offshore there may be the need to downgrade in future updates. Campbell Day 2 Valid 12Z Thu Jul 11 2024 - 12Z Fri Jul 12 2024 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE NORTHEAST THROUGH THE MID ATLANTIC, AS WELL AS THE SOUTHWEST U.S... ....East Coast... Much of the remnant moisture and ascent from Beryl will be out of the region however additional rainfall of upwards of 1 to 1.5 inches will be possible across New England, mainly during the morning hours. Further south, the trailing cold front will be the focus for convective potential with the highest risk of flash flooding aligning within the Del-Mar-Va Coastal Plain down through the eastern Carolinas. An upper level disturbance of the Atlantic will approach the region and enhance upper forcing and moisture as it moves closer to the Carolina coast. Meanwhile, a area of convergence in proximity to a slow-moving surface front will help trigger the development of widespread convection. The deep layer of moisture over this region will help bolster rainfall and with the expected training of cells, 2 to 4 inches may spread over the Mid- Atlantic. Should the guidance persist with this set up and/or trend up with amounts, there may be the need to upgrade Risk level. Kleebauer/Campbell ....Southwest... The persistent monsoonal pattern of diurnal convection will maintain an elevated threat for localized heavy rainfall and flash flooding concerns. Local totals of up to 1" signal a lower-end threat, however it remains within the Marginal Risk threshold. Campbell Day 3 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 NORTH CAROLINA... The training of thunderstorms capable of producing several inches of rain will continue through this period. Rain from the day 2 period will have helped to raise soil saturation along the Mid- Atlantic and Carolina region thus lowering FFG. Most of the guidance is suggesting additional amounts of 1 to 3 inches from South Carolina to southern New Jersey with a couple showing local maximums up to 5 inches along this corridor. A Slight Risk was maintained for this part of the East Coast. A Marginal Risk spans from South Carolina northward to southern New hampshire. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6Edmqy7cF1UN7hE1yp0kYnbnZo3lnnexAi3ijFQxgl5g= D76WQ3x7f6kMetQNXimW9wvCZpY1VfsGwMcZbkuq9PBI_qc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6Edmqy7cF1UN7hE1yp0kYnbnZo3lnnexAi3ijFQxgl5g= D76WQ3x7f6kMetQNXimW9wvCZpY1VfsGwMcZbkuqzgqni38$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6Edmqy7cF1UN7hE1yp0kYnbnZo3lnnexAi3ijFQxgl5g= D76WQ3x7f6kMetQNXimW9wvCZpY1VfsGwMcZbkuqUDIhlQo$=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) .