301 FOUS30 KWBC 312013 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 413 PM EDT Fri Jul 31 2026 Day 1 Valid 16Z Fri Jul 31 2026 - 12Z Sat Aug 01 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF MID TO UPPER MISSISSIPPI VALLEY, AND THE UPPER PENINSULA OF MICHIGAN... ...Central US system... A potent shortwave diving across the Northern Plains this morning will deepen as it ejects southeast into the Upper Midwest by Saturday morning. This deepening will create an extremely anomalous mid-level low for late July, reflected by NAEFS height anomalies falling to below the minimum climatological values at 700mb, and to below the 10th percentile at 500mb. An impressively deep system overlapping late July thermodynamics is a clear indicator of excessive rainfall potential, and this event is no different. As the mid-level low dives southeast, it will drive increasing downstream ascent through divergence and height falls, with the subsequent surface low occluding across Iowa. Within this occlusion (and farther downstream warm sector) PWs will climb to 1.75 to 2.00 inches, above the 90th percentile for the date, and overlap with MUCAPE around 1000 J/kg. The accompanying 850mb inflow will be locally accelerated to 30-40 kts, drawing these pronounced thermodynamics northward to support heavy rain production within thunderstorms. At the same time, the associated theta-e ridge is progged to lift cyclonically, creating an impressive (especially for the end of July) TROWAL which will pivot atop the Upper Midwest. This will not only result in enhanced elevated instability, but also support additional moisture to fuel heavy rainfall. Both the HREF and REFS neighborhood probabilities indicate a 40-70% chance for at least hourly rainfall of 1", and although there continues to be some latitudinal uncertainty to the placement, the consensus of the available high-res CAMs is for locally heavy rain rates within a progressive band this morning, becoming more aligned for training later today. This is most likely beneath the TROWAL where Corfidi vectors and mean 0-6km winds become anti-parallel leading to backbuilding/repeating heavy rain rates. The greatest risk for 3"/24hrs from the high-res ensembles is from near St. Louis, MO northward through southern WI, which is also where there are notable probabilities for 5"/24 hrs (30-60%), especially near the Quad Cities of IA. This is also where the CSU First-Guess ERO field is most aggressive, so despite some dryness in the antecedent soils, an elevated SLGT risk is warranted for this region. Otherwise, cosmetic adjustments were made to both the SLGT and MRGL risks across the region. ...Upper Peninsula of Michigan... The impressive system moving through the Upper Midwest will result in increased deformation between 700-500mb pivoting into the Upper Peninsula this aftn/eve. This will encourage enhanced ascent across the region, despite a slow wane in MUCAPE noted via the various models. The accompanying ascent within this persistent deformation axis will support widespread showers and thunderstorms today, which despite the waning instability will be fueled by PWs as high as 1.5 inches, or above the 90th climatological percentile. This will support rainfall rates that are progged by both HREF and REFS neighborhood probabilities to have a 30-60% chance of exceeding 1"/hr, which will occur within aligned Corfidi vectors/mean 0-6km winds to support training. 3-hr FFG across the area is generally 1.5 to 2.5 inches which has 20-40% chance of exceedance. This suggests at least scattered instances of flash flooding are possible, but will be most likely where any more prolonged training can result in 3 inches (50-60% chance) to as much as 5 inches (10-20% chance) of rain. After coordination with WFO MQT, a SLGT risk was added for the increased excessive rainfall potential today and tonight. ...Northern Florida through the Central Gulf Coast... Robust late-July thermodynamics characterized by PWs of 2-2.25 inches and MUCAPE above 2000 J/kg will spread across the area today and tonight ahead of a quasi-stationary front. This will likely result in two periods of convection capable of producing heavy rainfall. The first will be during peak heating when airmass thunderstorms will develop, aided by a modest vorticity impulse digging into MS/AL around the large mid-level ridge to the west. Weak shear (less than 20 kts) during this time suggests storms that develop will be generally of the pulse variety with limited organization and lifespans, but storm mergers, boundary collisions, and any locally enhanced ascent in the vicinity of this shortwave could increase the overage and intensity of storms during the aftn/eve. These storms should wane with convective overturning during the evening, but a secondary signal has shown up in the guidance for late tonight into early Saturday, especially across the Florida Panhandle and into the Big Bend area. Here, the aforementioned shortwave will slow within an area of thickness diffluence, leading to a longer period of enhanced synoptic lift aided by modest jet- level diffluence. This ascent acting upon any residual boundaries and the land breeze could reignite thunderstorms as the LLJ attempts to back subtly more to the WSW from W as the front approaches, drawing even more impressive PWs along the coast. During this time, Corfidi vectors are progged to collapse to 5 kts or less and become increasingly anti-parallel to the mean wind suggesting some greater backbuilding/training potential with rain rates potentially reaching 3"/hr (10-20% chance). Both the HREF and REFS indicate a 20-40% chance for 5" of rainfall from this nocturnal event, but the deterministic models are quite different in the coverage and placement. At this time, after coordination with WFO TAE, the MRGL risk was left unchanged for this area, but an upgrade to a targeted SLGT risk may be needed with later updates, with the SLGT potentially extending (or being more needed) through D2. ...Four Corners States into the Southern-Central High Plains... The monsoon ridge will get suppressed to the south and west in response to the potent system moving through the Plains/Midwest, with a secondary piece of vorticity energy dropping across the southern High Plains into the Texas Panhandle. This will help push a cold front through the Southern Plains and bank against the terrain of New Mexico later this evening. The overlapping ascent from the cold front and shortwave will act upon favorable thermodynamics as a ribbon of PWs above 1.5 inches and pooled MUCAPE of 1000-1500 J/kg get drawn westward ahead of the front. Coverage of monsoonal thunderstorms may be somewhat less than previous days today due to the re-centereing of the ridge. But at least scattered diurnal thunderstorms are expected from eastern AZ, through NM, and into eastern CO with hourly rainfall up to 1 inch at times. The focus for heaviest rain is likely where the shortwave/front move into NM/TX Panhandle where some organized clusters and better training potential exists. This is reflected by both HREF and REFS exceedance probabilities reaching 15-25% (FFG) and 30-50% (3"/24hrs). This still supports the inherited MRGL risk, and only cosmetic adjustments were made based on the new guidance. Weiss/Miller Day 2 Valid 12Z Sat Aug 01 2026 - 12Z Sun Aug 02 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE THE UPPER MIDWEST TO THE GULF COAST AND THE SOUTHERN HIGH PLAINS... ...Upper Midwest... A potent and unseasonably deep low pressure system (ensemble mean forecast MSLP values below the minimum CFSR climatological) will continue to pivot across the Upper Midwest as its parent mid/upper low digs and deepens over the region. Ahead of the system, strong low-level south and southwesterly flow will advect deep Gulf moisture (PWs 2-2.25 inches/150-175% of normal) northward. Combined with impressive dynamics, large scale ascent, and sufficient instability, the threat of convectively driven heavy rain is expected to continue into Day 2/Saturday, especially within the pivoting comma head due north of the low track across parts of Illinois and Indiana. There, the 12Z HREF/RRFS guidance is highlighting the potential for significant QPF, with notable probabilities of exceeding 3"/24 hrs (60-80%) and 5"/24 hrs (25-50%). As a result, the existing SLGT risk can be considered an enhanced SLGT from east-central Illinois to northwest Indiana. Elsewhere across the Ohio and Tennessee Valleys, only cosmetic adjustments were made to the SLGT and MRGL risks. ...Parts of the Southeast to the Gulf Coast... A mid/upper impulse embedded within northwesterly flow on the southern periphery of the deepening low over the Upper Midwest will dive into the Southeast before slowing down near the Florida Panhandle during the Day on Saturday. Anomalously high PWs of 2.25-2.75 inches (125-150% of normal) along with 1000-2000+ J/kg of MUCAPE will support numerous clusters of slow-moving showers and thunderstorms containing intense rainfall rates. The 12Z HREF/RRFS show fairly widespread probabilities of 40-90% for QPF greater than 3"/24 hours and 20-60% for greater than 5"/24 hours across parts of the Southeast, especially for portions of Georgia and the Florida Panhandle. Given this increased signal for potentially significant rainfall, the SLGT risk was expanded southward to include southwest Alabama, southern Georgia, and most of the Florida Panhandle. ...Southern Rockies/High Plains to the Texas Hill Country... Monsoonal moisture and instability interacting with upslope flow and a southward progressing cold front will support scattered showers and thunderstorms from the southern Rockies and High Plains to the Texas Hill Country on Day 2/Saturday. This activity will have the potential to produce heavy rainfall rates in excess of 1" per hour, leading to isolated and scattered instances of flash flooding. 12Z HREF/RRFS probabilities for QPF greater than 3"/24 hours are 20-50% and mostly concentrated across the southern High Plains of New Mexico. The existing SLGT risk covering that area looked on track so minimal changes were made. However, the HREF/RRFS is also beginning to highlight the Texas Hill Country with a 10-40% chance for QPF greater than 3"/24 hours. Also notable are the very low but non-zero probabilities for greater than 5"/24 hrs (5-10%). As a result, the MRGL risk was expanded eastward from far western Texas with this update, and a future upgrade to a SLGT risk can't be ruled out. Miller Day 3 Valid 12Z Sun Aug 02 2026 - 12Z Mon Aug 03 2026 ..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA BIG BEND REGION, AND OVER PORTIONS OF THE NORTHEAST... ...Gulf Coast into the Southeast... Long duration onshore flow event from the Gulf continues into D3 bringing heavy rain to the Big Bend area of Florida and portions of the Southeast. A potent closed mid-level low centered over Indiana Sunday morning will rotate E/SE through D3 bringing height falls to the Gulf Coast, and keeping pronounced S/SW flow downstream. As this closed low elongated to become at least subtly more N-S oriented, onshore flow from the Gulf will locally back and intensify, drawing robust thermodynamics northward into Florida/Georgia. An impressive plume of PWs above 2.25" overlapped with MUCAPE of around 2000 J/kg will be pooled ahead of the approaching surface cold front, and it is this impressive environment that will shift northeast through D3. Within this setup, widespread thunderstorms are likely, and with mean 0-6km winds aligned parallel to the front onshore, and anti- parallel to the Corfidi vectors, the setup appears to suggest a high threat for backbuilding and training convection with heavy rainfall rates of 2"/hr or more. This will result in locally more than 3" of rainfall (SREF/GEFS/ECENS probabilities for 3"/24 hrs as high as 10%) falling atop saturated soils from anticipated heavy rain on D2. For this reason a SLGT was added near the Florida Big Bend region, with the MRGL expanded northeast from inherited. ...Upper Midwest to Northeast and Mid-Atlantic region... The anomalous mid-level low will continue to track slowly eastward from the Midwest into the Ohio Valley on Sunday and Sunday night. Beneath this upper low, an occluded surface cyclone will track eastward in tandem, with the accompanying fronts producing locally enhanced ascent within their vicinity due to overrunning and/or convergence. As the wave pushes east, impressive thermodynamic advection within the warm sector will surge northward as 30-40 kts of wind at 850mb transport PWs of 1.75 to 2.0 inches all the way to the Canadian Border overlapping 500-1000 J/kg of MUCAPE. This will support widespread thunderstorms with rainfall rates of 1-2"/hr, with organization into clusters fostered via 30-35 kts of bulk shear. Within this warm sector, propagation vectors and mean 0-6km winds will become increasingly parallel and aligned to the approaching front, which suggests an increasing training threat from the Mid- Atlantic states northward into Upstate NY. The guidance has trended upward in QPF for this area, and an upgrade to a SLGT risk in parts of this area may be needed with later issuances. However, the current SLGT risk is focused from eastern lower Michigan northeast towards the Adirondacks where an impressive deformation axis will develop and lay beneath a rare August-TROWAL to enhance both ascent and instability. Here, mean winds become anti-parallel to the propagation vectors, and it is likely that some slow moving/backbuilding cells will bring heavy rainfall to areas including Detroit, Cleveland, and Buffalo on D3. This is where the greatest excessive rainfall risk exists, and the inherited SLGT risk was modified to account for recent guidance and highest (albeit still modest) probabilities for rainfall exceeding 3"/24hrs. ...Southwest... The mid-level ridge responsible for the monsoon will remain somewhat flattened Sunday into Monday /D3/ but begin to expand eastward once again as the downstream trough advects east into the Mid-Atlantic states. This will keep much of the favorable instability and moisture suppressed to the southern edge of the typical monsoon region, with both anomalous PWs and SBCAPE above 1000 J/kg confined to generally the Mogollon Rim and points south. Convection is still likely to blossom across AZ/NM, and storms that develop may organize slightly within 25 kts of bulk shear to move SW off the terrain at 10-15 kts. However, the coverage and speed of convection should limit excessive rainfall potential to be isolated, so the MRGL risk was maintained with only subtle cosmetic adjustments. Weiss Day 4 and Day 5 Valid 12Z Mon Aug 03 2026 - 12Z Wed Aug 05 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN MID ATLANTIC INTO SOUTHERN NEW YORK STATE AND SOUTHERN NEW ENGLAND... ...Portions of the East/Great Lakes/OH Valley... The well-defined upper level trough moving through the Ohio Valley will begin to fracture on Thursday. There is agreement that an axis of anomalous PW values, 2+ standard deviations above the mean, 2 to 2.25" PW values, will stretch from North Florida, northeastward across the coastal Southeast, Mid- Atlantic and from eastern NY State into New England. Generally favorable right entrance region jet dynamics will accentuate lift in this anomalous PW axis, supporting potential for locally heavy rainfall totals. A slight risk remains over portions of the northern Mid-Atlantic (including portions of NY) into southwest New England where recent heavy rains have lowered FFG values/saturated soils. The closed low over the Upper OH Valley will become nearly stationary on Friday. An area of anomalous PW values will remain to the east of this closed low, across the Upper OH Valley into the Mid- Atlantic, Southern New England and south into the coastal southern Mid-Atlantic. A broad marginal risk area was depicted in this anomalous PW axis for locally heavy rains and isolated runoff issues. The surface front moving through New England Thursday may become stationary and west to east oriented across southern New England into the northern Mid-Atlantic Friday. A few models are showing more defined heavy rains in the vicinity of this front where there is potential for persistent south southwesterly inflow. Still a lot of spread with qpf details, warranting only a marginal risk at this time, with changes possible with future updates. ...Southwest/Southern High Plains... For Thursday and Friday, a marginal risk was depicted for monsoonal convection across southern Arizona into New Mexico. Not a lot of confidence with qpf details here, but locally heavy rains and isolated runoff issues possible in the above average PW values expected across this area. ...Portions of the Central/Northern Plains & Midwest... A surface front expected to push southeastward from the Upper MS Valley into the Upper Lakes and south through the Central Plains. On Thursday, there is a decent model signal for 1-2" of rain which could fall in a short period of time, so added a Marginal Risk area for portions of the Dakotas and northern MN -- it would not be a surprise if the guidance trended upward on amounts. For Friday, a model consensus exists for an axis of potentially heavy rains from Nebraska, eastward into Iowa and southern MN where the front may become more west to east oriented. Moist southerly low level inflow into the front at this time may support organized convection, heavy rains and isolated runoff issues. Roth/Oravec 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 $$