FOUS30 KWBC 141955 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 355 PM EDT Fri Aug 14 2026 Day 1 Valid 16Z Fri Aug 14 2026 - 12Z Sat Aug 15 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE MIDWEST... ...Iowa to the Appalachians and Southeast states... 16Z Update: After coordination with the local field offices, the existing Moderate Risk area was expanded a couple rows of counties to the east to the Indiana state line to account for highly impactful rainfall overnight and early this morning, and the expectation for additional heavy rainfall later today. In addition, the Slight Risk area was expanded about a row of counties to the south of the existing area to include more of southern Illinois and southwestern Indiana where deeper instability feeding into the MCS could allow for heavier storms to build farther south that what the CAM guidance currently suggests. There was also an extension of the Marginal Risk area southward to include most of Georgia and into the northern half of interior Florida given recent heavy rainfall yesterday and the potential for scattered but potentially very high QPF maxima with slow moving storms that develop later this afternoon, with rainfall rates up to three inches per hour in isolated instances. The latest 12Z HREF exceedance probabilities are now up to 25% across portions of northern Florida into southern Georgia. The previous forecast discussion for this region is included below. -------------- A flash flood threat will continue today into tonight on the periphery of the strong upper ridge to the south, and near and north of a surface front. Convection will be ongoing at 12z this morning from NE to IN and spreading into WV. While the activity over IL/IN should generally weaken as it tracks southeast, a continuous localized flash flood risk should persist along this instability/moisture axis. The primary, higher end event is expected to materialize this afternoon into the overnight hours. A strong shortwave/MCV advancing out of the Plains is forecast to enter IA by 00z, accompanied by a sharp increase in 850mb moisture transport and convergence. This uptick in forcing will interact with a very moist airmass characterized by PWs approaching 2.4". While convection may eventually consolidate into a forward propagating MCS, backbuilding and cell training are still likely, especially along the south-southwestern flank. HREF FFG exceedance probabilities exceed 50%, with the HREF PMM QPF exceeding 200% of FFG and depicting an FFG exceedance spatial coverage over 25%. These high signal metrics support an organized flash flood event this afternoon into tonight, with scattered to numerous instances of flash flooding, some of which could be locally significant. Some latitudinal uncertainty regarding the primary heavy rainfall axis remains among the model suite. In fact there is a split in recent guidance, with some trending north and others south. Based on current observational trends and the overall model consensus, think an axis across central/southern IA and into west central IL is most likely, possibly extending into far northern MO. The inherited Moderate risk area was in decent shape, but we did expand it a bit southeast. This generally aligns with the 00z/06z HRRR/RRFS and 00z ARW/ARW consensus, which closely matches the typically reliable AIFS and AIGFS track (leaving a few northern models as outliers). Additionally, the Slight risk was expanded southward into the southern Appalachians to account for an uptick in HREF FFG exceedance probabilities and coverage. ...High Plains... A Slight risk is maintained from northeast CO into southwest NE. Convective initiation this afternoon should focus along the periphery of the upper level ridge centered to the southeast. In a setup similar to yesterday, thunderstorms should initiate over the higher terrain before tracking eastward into the instability pool and low level inflow. While cell motions should be largely progressive, some cell mergers are again expected to produce isolated to scattered instances of flash flooding. HREF and REFS FFG exceedance probabilities remain comparable to yesterday. The updated ERO features a reduction of the Marginal Risk area over north-central Nebraska in the wake of the departing MCV, and rainfall rates over the sandhills region will likely remain under flash flood guidance. ...Southwest... A Slight risk remains across portions of northwest AZ, southeast NV and southwest UT. While PWs are slightly lower than over the past few days, a robust pool of 1000-2000 J/kg of CAPE should compensate for this. Furthermore, large scale forcing will increase ahead of an eastward moving mid level trough. Slow moving storms and cell mergers will drive a scattered flash flood threat, supported by HREF/REFS FFG exceedance probabilities that are forecast similar to or slightly higher than yesterday across this corridor. For the midday update, the existing Marginal Risk area was reduced in areal coverage, with generally lower probabilities of heavy rainfall from central Wyoming southward to extreme northwestern New Mexico. Intense convection is already developing across northwestern Arizona this morning, and this merits keeping the Slight Risk area there intact. Chenard/Hamrick Day 2 Valid 12Z Sat Aug 15 2026 - 12Z Sun Aug 16 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL OHIO AND INTO EASTERN INDIANA... ...Midwest and Ohio Valley... A Moderate Risk has been introduced in the update Day 2 outlook across portions of east-central Indiana into central Ohio, between Fort Wayne and Zanesville. The latest 12Z CAM guidance suite has impressive QPF totals on the order of 2 to 4+ inches, with the RRFS, ARW, and ARW2 more widespread with these higher totals, and the HRRR generally has a narrower axis. In addition, the HREF 3 hour flash flood guidance exceedance probabilities are impressive at nearly 60% for this region during the 00Z-09Z time period Sunday, and low end probs for 100-year ARI. There is still some latitudinal differences in the main QPF axis, but given the severely saturated ground conditions across this region from antecedent rainfall over the past few days, there is now enough confidence for the Moderate Risk area. A Slight risk extends from northern Illinois eastward into West Virginia. A favorable environment for convective training will persist along the northern periphery of the broad upper ridge and near a lingering surface frontal zone. At 12z Sat, an MCS will likely be ongoing, with additional afternoon and overnight redevelopment expected along this corridor. PW values around 2.2" and CAPE exceeding 2000 J/kg will readily support intense rainfall rates. This axis may overlap areas heavily impacted by flash flooding on prior days, where saturated soil conditions will heighten hydrologic sensitivity. ...Central Plains to the Northern Rockies... A Slight risk is maintained from eastern CO into western KS and southwest NE. The overall synoptic setup will resemble previous days, with shortwave forcing riding the periphery of the ridge and interacting with a moist, unstable airmass. While model spread remains regarding the exact location of the heaviest QPF footprint, good spatial overlap exists among the 00z RRFS, Gem Reg and AIGFS. The Slight risk was shifted a bit south to reflect this consensus. For the 20Z Update, the Slight Risk was extended a little eastward across northern Kansas given 12Z CAM guidance trends. The Marginal Risk was also extended back across northern Wyoming into northeast Idaho and western Montana where some isolated but potentially heavy showers and storms could develop during the afternoon and evening hours. Chenard/Hamrick Day 3 Valid 12Z Sun Aug 16 2026 - 12Z Mon Aug 17 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID-ATLANTIC AND NORTHEAST NEW MEXICO INTO SOUTHEAST COLORADO... ...Mid-Atlantic... A Slight risk is delineated from WV eastward into PA, MD, NJ, DE and into southeast NY. A mid level shortwave/MCV will track into the region alongside a synoptic cold front. Strong moisture advection will increase PWs towards 2.3", which combined with strong low level moisture transport will create an environment primed for heavy rainfall rates. Stronger synoptic scale forcing will broaden the overall convective coverage, though it may also increase the forward speed of convection. Should convection move through rapidly, the flash flood threat could remain somewhat limited. However, given the very high PW values and robust moisture transport, any mesoscale training or backbuilding will quickly result in some flash flooding, particularly over sensitive urban corridors. Additionally, strong westerly low level moisture transport impinging on the central Appalachians could promote terrain enhanced training and localized flash flooding. For the 20Z update, the Slight risk was expanded a little to the north to include the southern tier of counties in Upstate New York, and the southern portion of the DelMarVa trimmed back some given the latest 12Z guidance trends. ...Southwest and High Plains... The Slight risk over this region has been shifted southward relative to previous forecasts, now covering northeast NM into southeast CO. A southward advancing cold front will provide focus, enhancing low level convergence and easterly upslope flow. The 00z AIGFS and RRFS focus organized convection within this corridor. While PW values are not anomalously extreme, they remain above average...which when combined with strong CAPE values, slow storm motions and cell mergers will support an isolated to scattered flash flood threat. No changes were needed for this Slight Risk area with the 20Z update, although the Marginal Risk area was connected into a continuous corridor across Kansas. Chenard/Hamrick Day 4 and Day 5 Valid 12Z Mon Aug 17 2026 - 12Z Wed Aug 19 2026 ...THERE IS A SLIGHT RISKS OF EXCESSIVE RAINFALL ON TUESDAY FOR AREAS OF THE UPPER MIDWEST... 2030Z Update... Maintained the Slight Risk of excessive rainfall on Tuesday across parts of the Upper Midwest with only some minor change. The Marginal risk areas on each Day were expanded to cover a growing signal...albeit not a resounding signal...for convection to develop in a moisture-laden atmosphere over parts of the middle third of the county. Also expanded the Marginal risk area surrounding the Slight risk given the uncertainty about where an upper low north of the border is located and any associated mid-level height falls brushing the northern states. Bann ...Day 4/Monday... Overall synoptic scale pattern across the CONUS will be in a relatively unchanged state when it comes to the primary upper features over North America by Monday. Some shifting in the general ridge across the Southern U.S. will lead to some deviations in the typical shortwave propagation as we've seen for several days prior. That said, the main theme of the setup for the beginning of next week will continue to be prevailing westerly flow aloft leading to instances of convection initiating and impacting areas om the northern periphery of the ridge leading to isolated/scattered bouts of flash flooding in their wake. The most notable areas of interest will reside over the North-Central U.S. as a shortwave out of the Prairies of Canada is forecast to migrate southeastward into the Northern Plains Plains and Upper Mississippi Valley leading to some convective initiation on the diffluent side side of the disturbance. This feature will be moving fairly quickly offering more of a threat for heavy rainfall Monday evening into early Tuesday before the chances dwindle. PQPF for >1" remains fairly low across the region, but environmental conditions do favor at least some isolated instances of heavy rainfall and perhaps some flash flooding in those hardest hit zones. Elsewhere over the CONUS, the Southwest will continue to lie within the western fringes of the upper ridge centering over the Lower Mississippi Valley, extending through the Southern and Central Plains as we move into the beginning of next week. Prevailing southerly flow and sufficient heating will maintain a suitable environment for at least scattered thunderstorms across eastern AZ into NM, extending north into the CO Front Range. Another case of heavy rain prospects over the terrain and any burn scars in the above areas will lend to at least a MRGL risk for excessive rainfall, maintaining continuity from the previous forecast. Last area(s) of interest reside over the east as a linger front along the Tidewater/Eastern NC, and shortwave propagation into the Central Appalachians will offer more chances for flash flooding given the expected pattern evolution. As of now, the signal is less prevalent for flash flood concerns compared to previous periods, however, it stands to reason that the areas in question will be monitored closely due to the local sensitivity factors that typically crop up with each individual setup, especially WV given the saturated ground conditions. ...Day 5/Tuesday... Main threat for the CONUS on Tuesday will reside across the Upper Midwest/Mississippi Valley thanks to a strong mid-level trough sliding out of western Canada providing a significant increase in large scale forcing across the North-Central U.S. with a target on MN/WI as of the latest ensemble trends. Environmental conditioning will occur prior to the trough's appearance as amplified flow ahead of the mean trough will allow for a steady poleward advection of rich warm, moist air up from the Mid and Lower Mississippi Valley. Surface low will propagate southeast out of Canada with an expectation for the low to deepen as it moves east-southeast over the Upper Midwest providing sufficient low to mid-level ascent with its presence. A trailing cold front will extend over the Dakotas up into the northern Great Lakes by the end of the period. Along and ahead of the front, widespread convective initiation is forecast leading to a swath of heavy rain prospects, including the opportunity for >3" of rain in areas hardest hit. PQPF 90th percentile is already between 2.5-3" across southern MN where the consensus is strongest for where the heaviest precip potential may occur. ML guidance is also in agreement on the heavy precip axis located between eastern SD across southern MN into southwest WI with the max located south of I-94. A SLGT risk was added for the new D5 across the above areas. This setup will be monitored closely as any further south push in the QPF core would put it closer to areas that will still be recovering from previous bouts of flash flooding over the last week. 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 $$