FOUS30 KWBC 010045 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 845 PM EDT Fri Jul 31 2026 Day 1 Valid 01Z Sat Aug 01 2026 - 12Z Sat Aug 01 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MIDWEST & UPPER PENINSULA OF MICHIGAN... ...Central US system... An extremely anomalous mid- level low exists for late July across IA. An impressively deep system overlapping late July thermodynamics is a clear indicator of excessive rainfall potential. Near the occluded cyclone in IA (and farther downstream warm sector) PWs range from 1.75 to 2.00 inches, with ML CAPE of 500-3000 J/kg at the writing of this discussion. Effective bulk shear of 25-35 kts should continue convective organization. This environment supports hourly rain amounts to 2.5", with the 18z HREF/12z REFS supporting additional local totals to 5" this evening/tonight. The three hourly flash flood guidance values have lowered due to earlier rainfall. Overall, the risk levels from continuity appear reasonable but areas were reshaped based on recent convective evolution and the 18z HREF/12z REFS guidance. ...Upper Peninsula of Michigan... Increased deformation between 700-500mb pivoting into the Upper Peninsula this aftn/eve along with lake breeze circulations have led to convection across eastern portion of the UP of MI. PWs are as high as 1.8 inches. Along with ML CAPE of 500+ J/kg, hourly rain amounts up to 2.5" remain possible in the short term. This would exceed the 3-hr FFG, suggesting at least scattered instances of flash flooding are possible. The Slight Risk remains intact to deal with convective development here over the next several hours. ...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. Afternoon and evening thunderstorms are presently on the wane, but a secondary signal exists early Saturday morning, especially across the Florida Panhandle and into the Big Bend area. A slow moving shortwave moving within an area of thickness diffluence leads to a longer period of enhanced synoptic lift aided by modest jet- level diffluence. Low-level inflow backs subtly more to the WSW from W as the front approaches, drawing even more impressive PWs along the coast and instability from the Gulf. 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 if everything aligns perfectly prior to 12z. The 18z HREF/12z REFS indicate the potential for local 2-4" by 12z, with the HREF less bullish. Left the Marginal Risk intact but Slight Risk impacts can't be ruled out. ...Southern-Central High Plains... The monsoon ridge gets 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. Radar reflectivity trends show some clustering of thunderstorms in eastern NM which could merge into preceding activity across northwest TX in the short term. Activity should be on the wane midnight or so. Left the Marginal Risk level but resculpted the area to reflect recent radar reflectivity and 18z HREF/12z REFS guidance. Roth 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 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 $$