251 FOUS30 KWBC 012023 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 423 PM EDT Tue Jul 1 2025 Day 1 Valid 16Z Tue Jul 01 2025 - 12Z Wed Jul 02 2025 ..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER NORTHERN PORTIONS OF THE MID-ATLANTIC REGION... ...Northeast through Ohio Valley... 16Z Update: The threat for the Mid Atlantic remains locked in for the D1 with the MDT risk maintained over the previous areas, but allowed for an expansion on the northeast flank to encompass all of the Philadelphia metro, including adjacent areas of Southern NJ. 12z KIAD sounding has come in with a robust 2.07" PWAT, a daily record for 7/1. The wet bulb zero height is also a daily record indicating a particularly deep warm-cloud layer situated within the lower troposphere. This type of environment along with a well- defined tall, skinny CAPE signature is representative of a strong prospect for not only heavy rainfall, but significant rate driven rain cores (2-3+"/hr) that can efficiently drop several inches of rain in a short span of time. The area encompassing the Central Mid Atlantic has a variety of factors for enhancing the potential (urbanization, antecedent moist grounds), but enhanced rates increase the threat by a respectable margin and historically points to a higher flash flood threat in both coverage and magnitude for a period. Recent CAMs are very much depicting several small QPF maxima littered over the Mid Atlantic with the highest signals positioned over Northern VA up through the MD Piedmont and points east-northeast. The alignment of the heavier QPF situated over Southeast PA into Northern DE and Southern NJ is likely in part to a targeted convective initiation and training point within a narrow sheared surface trough situated over the region as noted via the latest visible sat channels. The assessment this morning only provided greater credence to the threat with the previous discussion still well in-play in the overall outline of an elevated risk for flash flooding. Given some of the latest trends within the QPF and mesoscale evolution this morning, the MDT risk expansion through more of Southeast PA into Southern and Central NJ was generated. Higher end SLGT risk is now forecast across much of WV as locally heavy rainfall with potential for up to 2-2.5"/hr rates will likely cause problems within the complex terrain as funneling effects tend to exacerbate any convective threat in the state. This threat extends into far Southwest PA with focus around the periphery of an advancing MCV currently migrating through Southern OH. Kleebauer ..Previous Discussion.. Per collaboration with WFOs CTP, PHI, and LWX, we have included a Moderate Risk to the Day 1 ERO across parts of the northern Mid Atlantic Region to include NoVa and the DC-Balt metro regions, northern DE and into southeast PA. Longwave upper trough over the Upper Great Lakes/Midwest early this morning will pivot eastward Tue-Tue night, pushing east of the Appalachians Wed morning. Embedded within the longwave trough is a shortwave, currently along the IA/IL/MO tri- state area, which will track across the OH Valley later this afternoon and across the Mid Atlantic later this evening and overnight. This shortwave should enhance the broad- scale across the Mid Atlantic region (especially), while low-level frontogenesis also gets a boost south of the 90-100kt upper jet streak in the lee of the large-scale trough. 0-6km bulk shear values increasing to 25+ kts within the inherited broad Slight Risk area (30-40+ knots over the northern Mid Atlantic into the Northeast) will support the formation of widespread/multi-cluster line segments ahead of the upper trough/surface cold front during peak diurnal instability hours this afternoon into the evening. MUCAPEs peak between 2000-3000 J/Kg, while TPWs remain around 2 standard deviations above normal for early July (between 2.00-2.25" within the non-convective environment across much of the Mid Atlantic into southern New England). The concern over the Slight and especially Moderate Risk areas will be with upwind propagation and cell training, as the pre-frontal southwesterly low-level flow (20-25 kts at 850 mb becomes nearly parallel and of similar magnitude as the mean 850-300 mb flow. 00Z HREF and RRFS probabilities of 24hr QPF exceeding 3" climb above 60% within much of the Moderate Risk area (highest with the RRFS), while probs exceeding 5" within the 24hr period reach 40-60% in spots per the RRFS (though 20-25% tops per the HREF). Given the favorable thermodynamic profile (high CAPE/PW environment) along with the broad-scale forcing, anticipate areas of 2 to 3+ inch/hr rainfall rates this afternoon and evening. The Moderate Risk area also encompasses areas recently hit by heavier rainfall, evidenced by the lower FFGs (in some areas, 1 hr FFGs 1.00" or less). This includes areas SE PA including the Middletown/Lancaster/Lebanon/Redding areas that received 4-7" of rain on Monday. Hurley ...West Texas into New Mexico... 16Z Update: The current SLGT risk was generally maintained with only a minor expansion to the east to include more of the Western Rolling Plains adjacent to the Concho Valley. Quasi-stationary front will be the focal point later this afternoon and evening with typical diurnal heat flux providing greater buoyancy with the regional environment allowing for several thunderstorms to develop in proxy to the boundary. 12z KMAF sounding was right up against the daily record for PWATs and well beyond the 90th percentile for the date meaning the environment is ripe for locally heavy precip potential once the convective regime initiates. 12z HREF probs are robust for both the neighborhood >2" indicator and the >1" EAS field which notes a "bullseye" of up to 50% located over parts of the Upper Trans Pecos into the adjacent Guadalupe Mtns. The other area of concern will lie within that quasi-stationary front with a elevated signature for >2" situated from the NM/TX border, east across the Northern Permian Basin. Enhanced hourly rates will be the primary threat for the period with 1-2"/hr rates very likely in any strong convective cores. Look for scattered flash flood signals within the above zones with the greatest threat positioned over Southeast NM and adjacent TX Caprock as noted in the QPF/prob fields. Kleebauer ..Previous Discussion.. Farther south/west along the stalled frontal boundary...convection is expected to be develop within a region of decent CAPE and precipitable water values in excess of 2 standard deviations above climatology. This area will also benefit from weak upper level vorticity/shear axis within the broad-scale ridge, with tropical moisture feeding in per the low-mid layer southeasterly flow. 850-700 mb moisture transport is pretty solid across the outlook areas, but especially within the Slight Risk region across parts of West TX into southeast NM where the 850-700 mb moisture flux standardized anomalies peak between 3-4 standard deviations above normal per the 00Z SREF and GEFS. Given the relatively healthy low-level flow compared to the overall weaker mean flow, areas of heavy, possibly excessive rainfall are anticipated, especially within the Slight Risk area, considering the uptick in upwind propagation and thus chances for cell training. Hurley ...South Texas... 16Z Update: Only minor adjustments necessary for the SLGT risk across Deep South TX as the previous forecast remains on track. Little deviation in the prob fields from overnight allowed for a continuation of the SLGT risk with emphasis on greatest threat likely over the Lower RGV, including the cities of Brownsville and McAllen. Kleebauer ..Previous Discussion.. An influx of abnormally high TPW from the remnants of Tropical Cyclone Barry (2.2 to 2.4", which is close to 3 standard deviations above normal for early July) will combine with a modestly unstable environment (MUCAPEs increasing to 1500-2500 J/Kg) in producing very heavy short-term rainfall rates later this afternoon/evening and potentially later into the overnight period. Both the HREF and RRFS ensembles show high probabilities (>50%) of 3+ inch rainfall, with 30-40% probs of exceeding 5 inches. Therefore expect more than a localized risk of flash flooding (i.e. Slight vs Marginal) across portions of South Texas from Corpus Christi south through Brownsville and the RGV. Hurley Day 2 Valid 12Z Wed Jul 02 2025 - 12Z Thu Jul 03 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHEAST VIRGINIA AND NORTHEAST NORTH CAROLINA, WESTERN FLORIDA COAST, AND THE SOUTHWESTERN U.S... ...Lower Mid Atlantic and Southeast... 20Z Update: The combination of elevated moisture on the order of +1 to +2 deviation PWATs, relevant buoyancy, modest shear, and the progression of a cold front from the northwest will aid in sufficient convergence in-of the VA Tidewater down through Eastern NC on Wednesday. PWATs encroaching 2.2-2.4" across the above region will setup an environment capable of not only heavy rainfall, but efficient warm rain processes that should maximize QPF in any convective cores that materialize. 12z CAMs continue to depict forecast soundings over the Southeast Mid Atlantic coast that exhibit textbook tall, skinny CAPE signatures with a deep moisture layer sampled from the surface to tropopause. 12z HREF neighborhood probs for >3" were running between 70-90% over the area extending from Williamsburg, VA down through Morehead City, NC with >5" probs hovering between 25-40% with a bullseye of 50-60% over the Hampton Roads area of Southeast VA. These signals are indicative of locally heavy rainfall likely with an areal average of 1-2", at the very least within the ensemble means. This allowed for a general maintenance of the SLGT risk inherited with some minor expansions to cover for the latest HREF blended mean QPF footprint. Scattered heavy convection will also be forecast away from the above area with the main threat likely more urbanized flash flood concerns within any heavier cells as the environment is ripe for locally heavy rainfall from the Central Gulf coast to points north and northeast. ...Southwest... 20Z Update: Synoptic progression across the Southwestern CONUS coupled with a deep, moist advection pattern further inland from the southeast will lead to widespread convective development across West TX, extending westward through the terrain of NM and AZ. A stagnant upper trough/ULL centered off the CA coast will meander over the next 24 hrs to the east before finally pushing further inland and opening up into quite a prolific trough providing large scale ascent to much of the Desert Southwest east of the Colorado river basin. Presence of monsoonal moisture will be amplified moving into Wednesday as the amplified flow from the approaching trough and ridge positioning over the Four Corners will create the textbook funneling affect of deeper moisture poleward through West TX to points north and northwest. The highest PWAT anomalies will be centered over Southeast NM, Southern NM, and the Mogollon Rim creating a generally buoyant environment over the aforementioned areas. With MUCAPE between 1000-2500 J/kg and PWAT anomalies ~2 deviations above normal as depicted via the ECENS and NAEFS outputs, expectation is for scattered heavy convective cores capable of hourly rates approaching 1"/hr with generally slow cell motions leading to some training concerns across the terrain. 12z HREF 24hr ARI exceedance probabilities are between 40-70% for exceeding 10yr intervals and 10-30% for even some 100yr ARI threats, a testament to the expected magnitude of precip falling during the period. Locally 1-2" of rainfall within the area is plenty to cause significant flash flood issues in any one area across the Sacramento's through the terrain west and northwest. There is enough evidence given the expected environment and widespread convective regime for a broad SLGT risk positioned across El Paso, Southern NM, Southeast AZ, and the Mogollon Rim across Central AZ. ...Western Florida Coast... 20Z Update: The combination of a slow-moving frontal progression and potential for weak surface reflection over the Eastern Gulf will create a period of unsettled weather in-of the Western FL Peninsula. The prospects for heavy rainfall capable of widespread flash flood concerns is still on the lower end with the best threat relegated to the urban zones along the coast with the best threat likely over western Pasco and Hillsborough counties, along with Pinellas county where the Tampa metro is the center of where the threat lies. When assessing the hi-res guidance today, you would think there's a chance of 10+ inches of rainfall along the coast, but a lot of that precip stems from the CAMs struggling with the surface reflection and likely enhancing the baroclinicity along the front, an issue that has cropped up in the past. Other deterministic members within the global suite are closer to 4-7" for maxima with ensemble depiction closer to the lower end of the range. This is subjective to a multitude of factors ranging from frontal positioning, surface convergence, location of the low proxy, and other finer mesoscale details. At the current look, the threat is still within the threshold of higher risk, but low to medium confidence considering some of the finer details. At this juncture, with the PWATs and focal point necessary for locally enhanced rainfall potential with rates pushing 3-5"/hr in stronger cells in any location, and the urbanization concerns where the heaviest rain will fall, a SLGT risk was added to the three counties inferred above with the Tampa/Clearwater/St. Petersburg metro the area of greatest concern. Will be a period to monitor for shifts in the risk level, whether downgrade or upgrade. Kleebauer Day 3 Valid 12Z Thu Jul 03 2025 - 12Z Fri Jul 04 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN PORTIONS OF THE FLORIDA PENINSULA... ...Florida and Georgia... 20Z Update: Little changes was necessary for the SLGT risk across the western FL coast as the previous forecast remains on track. This period has the best consistency in the positioning and magnitude of the heavy precip threat among the deterministic. As of now, the risk is lower in terms of magnitude compared to what could transpire in the D2, so the threat could be downgraded if the previous periods doesn't materialize. However, overlap if the threat D2 transpires would ultimately create a greater threat, so some of the threat could be contingent on the evolution. ML is consistent in its interpretation of the heavier rain positioned between Clearwater down to Ft. Myers, so it's worth noting we have a good signal for the location. It will be worth monitoring in the coming days with plenty of time for any adjustments. Kleebauer ..Previous Discussion.. Subtle changes were made to the Slight and Marginal Risk areas inherited from yesterday's Day 4 ERO. Southern periphery of the longwave upper trough crosses the area Thu-Thu night, with the guidance showing embedded shortwaves (possibly convectively- enhanced) reaching South FL toward the end of the period (12Z Fri). Ahead of the nearly stationary surface front, onshore west to southwest low-level inflow from the eastern Gulf will likely lead to a more focused area of low-level moisture transport/flux convergence over much of the west coast of FL, especially north of Ft. Myers to include the Tampa-St. Pete area, where 0-6km bulk shear values do approach 25 kts (allowing for more organized/widespread convective clusters). The RRFS is most particularly robust with the QPF within the Slight Risk area (areas of 3-6+ inches), which considering the thermodynamic environment/deep subtropical moisture (TPW values 2.25 to 2.50"), is certainly plausible. Especially considering the onshore low- level inflow will likely exceed (perhaps double) the mean 850-300 mb wind), enhancing the potential for cell training. Even with a more limited (tall/skinny) CAPE profile, sub-hourly rainfall rates of 2.5-3.0+ inches within this environment will be possible, especially within the Slight Risk area. Hurley ...Southern Plains to Southwest... Continued deep moist advective pattern will lead to scattered or even widespread thunderstorm activity over much of West TX up through the Central Rockies as the upstream synoptic evolution of the ejecting trough will create a pretty robust large scale ascent signature across much of the CONUS west of the 100W marker. Still some discrepancy on the eastern expansion of the heavier convective threat with some guidance inferring the Concho Valley, others the Permian Basin and Trans Pecos, and others as far west as Southwest TX. Too much spread in the deterministic with the ensemble means relatively modest in magnitude. As we move into CAMs range, expect the signal to ramp up in the magnitude with a more defined axis of heavy precip likely to allow for a targeted SLGT risk. Areas within the Central Rockies will be evaluated in the coming days as well with the core of the shortwave energy ejecting out of the Southwest likely to motion overhead. This could be a target for heavy rain prospects along the Southern Laramie Range down through the Foothills of CO Rockies with some guidance depicting 2-3" of rainfall in the period, something that could also spur an upgrade in the risk with the environment in place. For now, a broad MRGL risk encompasses much of the Southwest, Southern Plains, and Central Rockies. Kleebauer Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt