FOUS30 KWBC 170051 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 851 PM EDT Thu Jul 16 2026 Day 1 Valid 01Z Fri Jul 17 2026 - 12Z Fri Jul 17 2026 ...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH-CENTRAL TEXAS... 01Z Update... Previous update captured the evolution of convection well so only some minor nudging of the risk area boundaries were needed. Texas remained the prime candidate for catastrophic and life-threatening flash flooding in the overnight hours given additional rainfall on top of what has already overwhelmed some places. The channel of moisture/instability fueling convection from Arizona/southwestern New Mexico northward into parts of Wyoming and Montanan pretty well established...changes were pretty small and largely made to fit the latest radar trends. Bann 16Z Update... ...Texas... Catastrophic and life-threatening flash flooding continues in the Texas Hill Country as the pain-stakingly slow MCV responsible for the copious amounts of rainfall in recent days continues to cause widespread excessive rainfall rates. Through the early afternoon, the low-level jet will continue to supply low-level moisture and shear into the Hill Country, helping to sustain the current thunderstorm activity and their prolific rainfall rates between 2-4"/hr in many cases. Meanwhile, 700mb flow is convergent west of the Rio Grande and is aiding in providing some mid-level ascent on the southern and eastern flanks of the MCV. WPC's Metwatch issued an MPD (#740) that goes into more detail on the evolving setup through early afternoon. CAMs generally show the same pattern as recent days with thunderstorms decreasing in areal coverage later this afternoon, only to re- develop overnight as the low-level jet strengthens and diffluent 500-700mb flow supports upscale ascent. PWs tonight will continue to be highly anomalous (>2.0") over the Hill Country on north and west through north-central TX and the Edwards Plateau. The ongoing stream of Gulf moisture will also accompany additional instability as well, priming the atmosphere for another round of widespread storms in areas hit this morning and even a little farther north and west that include areas north and east of Del Rio towards the Concho Valley. CAMs continue to disagree on exact placement, but recent days of thunderstorm activity would suggest the more southern and eastern envelope of solutions should be favored. New 12Z HREF and REFS shows moderate-to-high chances (50-70%) for >5" of rainfall north and east of Del Rio, TX with a highly concerning 30-50% area for >8" through 12Z Friday when utilizing both ensemble suites. The High Risk was expanded a little farther N&W into areas north and east of Del Rio where the remnant MCV will be tracking across tonight, and the Moderate Risk encompasses more of the Concho Valley. The region is facing tremendous ongoing impacts from urban, stream, and river flooding and any additional rainfall is going to exacerbate this ongoing catastrophic event. TX Hill Country residents should continue to follow guidance from local officials and maintain multiple ways to receive weather alerts during this ongoing flood disaster. ...Elsewhere... The Slight Risk in Arizona and southern Utah remains in good shape, although there are locally some moderate chance probabilities (40-60%) between the 12Z HREF and REFS for >3" of rainfall along the southern periphery of the Mogollon Rim. The setup has more of a look of a high-end Slight here, as areal extent of flash flooding may not be high enough to warrant a Moderate Risk, but locally significant flash flooding cannot be ruled out given the sensitivities of the region and the potential 2"/hr rainfall rates. The Marginal Risk was maintained from the Middle MS Valley on east to the TN Valley. Signals in probabilistic guidance are not in great agreement on exactly where to favor a Slight Risk at the moment. That said, the Lower OH Valley and TN Valleys have 1-hr FFGs that are <2" today and could be more favored for areas of localized flash flooding this afternoon. Mullinax ---Previous Discussion--- ...Southwest into the Great Basin... No significant changes were made to the risk areas out West for this update. A prime monsoonal setup remains in place for southern Arizona, where a Moderate Risk remains in place. PWs are expected to climb above 2 inches, or exceeding 2 std dev normal, across portions of southern Arizona. This moisture along with sufficient instability and upper level support, will likely support terrain- initiated thunderstorms. Subsequent rain-cooled outflows will drive additional intense cells into the evening hours, pushing rainfall rates up 2 inches/hr in some locations. A broader Slight Risk encompasses much of Arizona, extending north into the slot canyons of southern Utah and eastward into far western New Mexico. ...Mid Mississippi Valley into the Lower Ohio/Tennessee Valleys and Southern Appalachians... The Marginal Risk has been adjusted and expanded father east, stretching from the Mid Mississippi Valley into portions of the lower Ohio and Tennessee valleys, as well as the southern Appalachians. A remnant mid-level shortwave moving into the region will provide weak ascent. Southwesterly inflow into a downstream boundary will support deepening moisture (PWs increasing to 1.75-2 inches). Both the HREF and REFS guidance are showing notable probabilities for localized rainfall totals exceeding 2 inches. Hourly rainfall rates along the boundary may support isolated flash flood occurrences, particularly in complex terrain and urban areas. Pereira Day 2 Valid 12Z Fri Jul 17 2026 - 12Z Sat Jul 18 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF WEST TEXAS, SOUTHERN NEW MEXICO, ARIZONA, AND THE SOUTHERN GREAT BASIN... 20Z Update... ...Texas... The MCV responsible for the catastrophic flooding in the Hill Country will finally begin to make its way N&W on Friday. There remains concern that the eastern and southern flanks will be close enough to affected areas of central TX to further exacerbate flash flooding, as well as along streams, creeks, and rivers. Moisture content will remain quite anomalous for the time of year (1.8-2.0", above the 90th climatological percentile) for much of central TX. A revitalized low-level jet will also play a prominent role in supplying both low-level moisture/theta-e advection, additional MUCAPE, and an increase in low-level shear, giving storms additional longevity into the late morning hours. CAMs show less areal coverage compared to recent days, but given the strength of the low-level jet (surpassing 30 kts) it will provide sufficient inflow and some upslope enhancement into western portions of the Hill Country and the Edwards Plateau through midday. The gradual westward shift will mean more scattered to widespread showers and storms throughout West Texas, and hourly rainfall rates around 2"/hr are possible even towards the Davis Mountains. Most probabilistic guidance is at least in better agreement on an axis of thunderstorms from the Rio Grande on north through the Edwards Plateau and the Conch Valley Friday morning. Rainfall rates between 2-3"/hr with peak maximum approaching 4"/hr remain possible. In total, another 2-6" of rainfall is possible late tonight and through Friday morning within that band of thunderstorm activity, with locally higher amounts possible within the Slight Risk from Del Rio on north to the Concho Valley. Additional flash flooding is expected with significant flooding possible. Should any storms ensue over areas hit in recent days over the Hill Country, it could rejuvenate areas with lingering flood waters and may result in renewed areas of dangerous flooding. ...Western Florida... A cut-off 500mb low just west of Tampa Bay will reside within an area where PWs between 2.0-2.2", which is hovering around the 90th climatological percentile. MLCAPE over 1,000 J/kg and warm cloud layers approaching 14,000' deep will provide developing thunderstorms with a favorable environment to generate highly efficient rainfall rates that could surpass 3"/hr in the most intense cells. Given the greater Tampa/St. Petersburg area may also have slightly more sensitive soils following today's storms, it is possible localized flash flooding occurs within the more urbanized areas of west-central FL. For these reasons, a Marginal Risk was introduced this forecast update. ...Northern Arizona... Newest 12Z HREF/12Z REFS guidance has shown an increased signal for >3" and locally >5" rainfall totals in portions of the Mogollon Rim for Friday. On the heels of an active Thursday, it is possible the atmosphere is more over-worked and struggle to produce the too excessive of rates. On the flip side, soils will be more sensitive to additional thunderstorms. The setup supports a more "high-end" Slight in the Mogollon Rim, suggesting more scattered instances of flash flooding with the potential for localized significant flash flooding, particularly near burn scars and dry washes. Mullinax ---Previous Discussion--- ...Southern New Mexico... In southern New Mexico, storms are expected to develop along and near the Sacramento Mountains by the afternoon and continue into the evening before diminishing with the loss of diurnal heating. Active wildfire burn scars in this region make it particularly susceptible to rapid runoffs, supporting the continuation of the Slight Risk. ...Western U.S./Great Basin... Overall, only minor changes were made to the risk areas in the West, as a persistent monsoonal pattern remains locked in place. A robust moisture profile will sustain widespread convective coverage from southern Arizona north-northeastward into the Great Basin. Moisture anomalies will remain high, with standardized anomalies of 2-3 extending all the way from the Southwest to the northern Rockies. This moisture, along with with sufficient instability will support highly efficient rainfall rates. A broad Slight Risk was maintained from southern Arizona to southern Utah, with complex terrain, urbanized areas, and other vulnerable areas likely to a be a focus for the greater runoff concerns across the region. ...Ohio/Tennessee Valleys into the Central and Southern Appalachians.... A Marginal Risk covering much of the Ohio and Tennessee Valleys into the central and southern Appalachians was maintained. Storms developing across this region will be fueled by the same high-PW airmass noted in the Day 1 period as it spread farther north and east. These diurnally-driven storms are once again expected to raise isolated runoff concerns. ...Northern Great Lakes... A progressive upper trough digging southeast across central Canada, will shift a notable jet max south into northern Minnesota. Strong low level convergence along with favorable upper jet forcing will support nocturnal storms from the Minnesota Arrowhead eastward into Upper Michigan. Although fast storm motions will the heavy accumulation and flash flooding threat, anomalous moisture supporting heavy rates, along with some potential for brief training, may raise isolated concerns. Pereira Day 3 Valid 12Z Sat Jul 18 2026 - 12Z Sun Jul 19 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM WEST TEXAS AND SOUTHERN NEW MEXICO TO SOUTHERN UTAH, AND OVER PORTIONS OF THE NORTHERN MID-ATLANTIC... 20Z Update... ...Northern Mid-Atlantic... A deepening area of low pressure in southern Ontario will work in tandem with high pressure south of Bermuda to cause an acceleration in southerly low-level winds over the Northern Mid-Atlantic Saturday morning and into the afternoon hours. PWs will jump to above 2.0" Saturday morning for areas such as northern MD, southeast PA, all of NJ, and northward through NYC/Long Island and along the southern New England coast. In the northern DelMarVa and Delaware Valley, some guidance shows >2.2" PWs which tops the 97.5 climatological percentile. Strong low-level flow and rising dew points will support pre-frontal thunderstorm activity Saturday afternoon; some cases firing off the higher terrain to the west, and in other cases through strong daytime heating and mid-70s dew points simply breaking the capping inversion. Sufficient wind shear will also be present to support potential mesocyclones, which would further enhance excessive rainfall rates. Surface winds out of the south to start the day would help direct high theta-e air over the Chesapeake into these areas initially and provide a more buoyant air-mass to support hourly rainfall rates approaching 3"/hr. Additionally, various model guidance shows a corridor of >2,000 J/kg MLCAPE moving from northeast MD into the Delaware Valley Saturday afternoon. Given the region in the Slight also sports a larger urbanized population, rainfall rates to this caliber would be a recipe for flash flooding with such a high concentration of hydrophobic surfaces. Parts of the Lehigh and Susquehanna Valleys may be a little more resilient initially, but additional thunderstorms look to come through Saturday evening as the cold front approaches. In collaboration with PHI/CTP/LWX, a Slight Risk was issued for portions of northeast MD, northern DE, eastern PA, and much of NJ, while also including the greater Philadelphia metro area. Should more guidance come into better consensus on the positioning of heaviest rainfall over the I-95 corridor, the Slight Risk could see additional expansion in future forecast cycles. Mullinax ---Previous Discussion--- ...Western U.S.... An expansive monsoonal convective pattern will continue, prompting the inclusion of a Slight Risk stretching from West Texas and southern New Mexico northwestward across Arizona and into southern Utah. Overnight guidance indicated a notable uptick in low level moisture transport into these region on Saturday. This surge will act to revitalize the potential for additional rounds of high rainfall rate convective cores capable of producing flash flooding. Once again, the combination of anomalous moisture and instability will support highly efficient rainfall rates within the stronger storms. The threat of rapid runoff and flash flooding will be elevated across the complex terrain, normally dry washes, and slot canyons, as well as over highly sensitive soils and wildfire burn scars. ...Ohio Valley/Central and Southern Appalachians to the Mid Atlantic and Northeast... The core of the high-PW airmass will continue to shift east, with moisture pooling ahead of a strong cold front dropping south across the Northeast. Strong synoptic forcing, driven by an amplifying trough over the Northeast and favorable upper jet dynamics, will support an axis of organized storms from the upper Ohio Valley into the Northeast. Given the high PWs and strong forcing, heavy rainfall rates producing at least localized runoff concerns are expected. Given the uncertainty regarding where the axis of heaviest rains will occur, maintained a Marginal Risk for now. However, a targeted Slight Risk may be introduced in future updates if confidence increases. Pereira Day 4 and Day 5 Valid 12Z Sun Jul 19 2026 - 12Z Tue Jul 21 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE WEST ON DAYS 4 AND 5, THE VIRGINIA TIDEWATER ON DAY 4, AND PORTIONS OF FLORIDA ON DAYS 4 AND 5... 2030Z Update... Models still depict an active pattern between a risk of excessive rainfall to portions of the western United States and parts of the eastern/southeastern part of the country. Little run to run change in the synoptic pattern meant little change in the QPF associated with the monsoon in the western United States, Placement and timing of QPF and any associated risk of excessive flooding in Florida/adjacent part of the southeastern US states needed little adjustment based on latest guidance. Bann Previous Discussion... ...Western U.S... A traditional Monsoonal pattern will continue across the Western CONUS with scattered to widespread bouts of heavy rainfall across much of the Desert Southwest up through the Great Basin with an northern inflection into portions of the Rockies. Ridging will prevail across the west as we move through the weekend into early next week with a solidified Monsoonal trough positioned over AZ down through Mexico. Even at leads, there's a well- defined axis of elevated instability coupling with PWAT anomalies between +2 and +3 standard deviations positioned from the Great Basin to points south with the strongest anomalies situated over NV and UT was assessing both the ECENS and NAEFS anomaly forecast. QPF maxima are currently situated within the Mogollon Rim and portions of southern UT, both of which are the more susceptible areas given the persistence of heavy rainfall leading in, plus the complex topography and slot canyon allotment. This is really a seasonal setup which could likely spur short term upgrades in spots as we move closer to both the D4 and D5 time frame. Broad MRGL risks exist for both days in similar locations outlining much of the aforementioned area(s) above. ...Florida... Models continue to depict heavy rainfall across the western coast of FL on D4 (Sunday), spreading further east towards the northern half of the state on D5 (Monday) thanks to developing mid-level disturbance over the eastern Gulf. General model consensus is for a development of heavier rains across the western FL coast with a northern inflection into the Florida Big Bend thanks to increasing low-level convergence on the eastern flank of a weak low center progged off the coast. Ensemble QPF for both periods indicate multiple inches of rain possible which could enhance further if there is a greater likelihood of tropical cyclogenesis as noted via the latest National Hurricane Center T.W.O for a disturbance of interest (Disturbance 2) at 20% chance for development the next 7-days. This is a period to monitor for the prospects of this being something more organized which models might not have a great grasp of yet considering the lead time, and the slow maturation of any organized low the next 5-7 days. For now, MRGL risks exist on both D4 and D5 for the threat of heavy rainfall. ...Virginia Tidewater into Northeast North Carolina... Slow-moving front will make headway through southeastern VA and northeastern NC by Sunday with a deep moisture pooling anticipated along and ahead of the front which will likely lead to areas of heavy thunderstorms prior to fropa. Ensemble consensus lends credence to a localized QPF maxima positioned somewhere around the VA Tidewater through the northeastern corner of NC, coincident with the progged frontal positioning around the time of Sunday afternoon. PQPF for >1" is between 20-40% across the region which at D4 is formidable enough to monitor closely. Considering some of the more appreciable outputs via the global deterministic and bias corrected ensemble, and in coordination with the local Wakefield, VA WFO, opted to add a D4 MRGL risk for the threat, highlighting that Tidewater area down into northeastern NC. 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 $$