FOUS30 KWBC 171950 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 350 PM EDT Fri Jul 17 2026 Day 1 Valid 16Z 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... 1600Z Update: There were 2 notable adjustments made to the Day 1 ERO, both within Slight Risk areas. The Slight Risk in western AZ and far southeast NV was expanded westward a bit to include the Las Vegas metro region, while the Slight across parts of Central TX was expanded northward to include Abilene and areas east of Midland. Both of these adjustments were based on current observational trends (especially with the meso-enhanced vort lobe in TX), along with the 12Z HREF and REFS QPF exceedance probabilities. Hurley Previous discussion... ...Western U.S.... A persistent monsoonal pattern will remain in place across the West, supporting widespread convective coverage. Standardized moisture anomalies of 2-3+ std dev extend from Arizona and southern California to the northern Rockies, sustaining a broadly unstable environment conducive to highly efficient rainfall. A "high-end" Slight Risk remains centered along northern Arizona's Mogollon Rim. The HREF and REFS guidance have remained consistent in signaling the potential for localized amounts of 3+ inches in this area, raising the potential for scattered to localized significant flash flooding, especially given the already moist soil conditions. Additionally, the Slight has been expanded eastward to encompass portions of northeastern Arizona and northwestern New Mexico, where HREF and REFS are also indicating the threat for localized heavy amounts (2-3 inches). Farther south and east, storms are expected to develop along the Sacramento Mountains of southern New Mexico, threatening active wildfire burn scars susceptible to rapid runoff. ...Texas... Lingering mid-level energy over south-central Texas will slowly track north and west on Friday. The overnight hi-res models continued to suggest significantly less coverage of heavy amounts than in previous days. However, remaining deep moisture, along with a revitalized 30+ kt low level jet, will maintain at least a localized threat for additional heavy rains and therefore a Slight Risk covering much of Southwest to South-Central Texas was maintained. Fortunately, the general consensus of the HREF and REFS indicates the greater threat for heavy amounts will center west of the areas most severely impacted earlier this week and closer to the Davis Mountains today. Farther north, moisture and energy lifting out will carry some potential for localized heavy rain and perhaps isolated flash flooding into parts of Northwest Texas, where a broad Marginal Risk was maintained. ...Western Florida... A cut-off 500mb low lingering over the eastern Gulf will reside in a favorable environment for highly-efficient rainfall (PWs at or above 2 inches, MLCAPE over 1,000 J/kg, and deep warm-cloud depths). This will easily support rainfall rates exceeding 3 in/hr. Therefore, a Marginal Risk was maintained along portions of Florida's West Coast, highlighting the potential for isolated runoff concerns, especially in urbanized areas. ...Ohio/Tennessee Valley to the Central/Southern Appalachians... A Marginal Risk was maintained as a broad, high-PW airmass continues to spread north and east, with the expectation that diurnally-driven storms may produce isolated, short-duration runoff concerns this afternoon and evening. ...Northern Great Lakes... A progressive upper trough and associated jet max diving into northern Minnesota will initiate nocturnal convection from northern Minnesota into Upper Michigan. While rapid storm motions should limit widespread heavy accumulations, anomalous moisture and localized training profiles may produce isolated runoff concerns within the area highlighted by the Marginal Risk. Pereira Day 2 Valid 12Z Sat Jul 18 2026 - 12Z Sun Jul 19 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE FOUR CORNERS AND SOUTHWEST, AND ACROSS PARTS OF THE UPPER MID ATLANTIC INTO SOUTHERN NEW YORK AND NEW ENGLAND... 2000 UTC Update: The most notable change to the Day 2 ERO was the eastward and northward expansion of the Slight Risk area across northeast AZ, southeast UT, central NM, and into southwest CO. The expansion incorporates the Slot Canyons across southern UT, and was supported by the high HREF and REFS probabilities (>50%) of hourly rainfall rates of at least .50". Maximum FFG probabilities (40km neighborhood probs) of the 1/3/6 hr FFG peak above 25% in these areas per the 12Z HREF, while climb above 40% (over 70% in northern AZ) per the 12Z REFS. Based on the 00Z guidance, and particularly over UT, the ECMWF EFI does indicate spotty values over 0.7, with shift- of- tails values < 1.0. In addition, also based on the latest guidance/trends (particularly the CAMs), have expanded the Slight Risk over the Northeast to include more of CT, southern NY, eastern PA, much of NJ, and far northern DE. Quite a few CAMs show spotty 3-5" totals ahead of the mid/upper shortwave and associated surface cold front, with the 12Z REFS showing 30-40% probabilities of >5.00" across CT-RI and southern MA. Hurley Previous discussion.. ...Western U.S..... An expansive monsoonal convective pattern remains locked in place across the Western CONUS, supporting the continuation of a broad Slight Risk extending from West Texas and southern New Mexico northwestward across central and northern Arizona into southern Utah. An increase in low level moisture transport into the region, coupled with the moisture already in place will support PW anomalies 1.5-3 std dev above normal across much of this region. This moisture will likely once again support widespread convective development across the area. With ample daytime heating and sufficient instability, these storms will be capable of producing efficient rainfall rates. Given the history of recent precipitation, soils have become increasingly sensitive across portions of the region, elevating the potential for rapid runoff and flash flooding concerns. ...Ohio Valley/Appalachians to the Mid Atlantic and Northeast... A progressive cold front dropping southeastward will interact with an anomalously moist airmass pooling ahead of it. Atmospheric profiles will be highly favorable for efficient warm-rain processes, featuring PWs over 2 inches and deep warm-cloud layers. Where daytime heating and mid-70s dewpoints break capping inversions, prefrontal convection will tap into greater instability and raise rainfall rates. This environment along with the concentration of urbanized areas susceptible to fast runoff provided enough confidence to extend the Slight Risk farther east from parts of eastern Pennsylvania and northern New Jersey across southern New York and New England. Limiting factors to highlighting a more widespread flash flooding threat include fast storm moisture and lingering model discrepancy regarding the exact placement of the heaviest precipitation axes. Farther west through the central Appalachians into the Ohio Valley, a broader Marginal Risk remains in place to cover what is anticipated to be more isolated concerns. ...Florida Gulf Coast into Southeast Alabama and Southwest Georgia... Deep tropical moisture and a slow-moving mid-to-upper level low over the eastern Gulf will maintain a heavy rainfall threat, which translates into the Day 3 ERO. Model QPFs have come up in this area, now within the CAM windows, with high (>60%) probabilities of 24hr QPF exceeding 3" per both the 12Z HREF and REFS. Both are also fairly bullish with the >5" probabilities west of the FL Big Bend (30-40% per the HREF, 40-50% per the REFS). Hurley/Pereira Day 3 Valid 12Z Sun Jul 19 2026 - 12Z Mon Jul 20 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE WESTERN U.S., SOUTHEAST, AND LOWER MID ATLANTIC... 2000 UTC Update: Minor changes were made to the Day 3 ERO, based on the latest (12Z) guidance suite. Per collaboration with WFO RAH, felt that an expansion of the Marginal Risk area into central NC and northeast SC was warranted. Have also expanded the Marginal along the eastern Gulf Coast, while again nudging the western periphery of the Marginal Risk to include more of southern NV (including Las Vegas) and portions of southeast CA. Not much change in the overall monsoonal pattern, though most of the global guidance is a bit more diffuse with the heavier QPF totals. Still think a Slight Risk will be likely somewhere, probably very similar to the Slight Risk area on the current Day 2 ERO, but for now given the variance in the model QPFs, will keep the Marginal Risk going and reassess with the next 1-2 forecast cycles. Hurley Previous discussion... ...Western U.S.... The monsoon pattern will persist across the Western CONUS, maintaining at least scattered convection from the West Texas, New Mexico and Arizona into the Great Basin and Rockies. PW anomalies of 2-3+ standard deviations will continue to center over portions of the Great Basin. The higher areal average precipitation amounts are expected to once again align along the Mogollon Rim into southern Utah. Given the prior rainfall and moist soil conditions, these areas will remain vulnerable to rapid runoff, with the area's complex terrain and slot canyons raising localized concerns. A broad Marginal Risk was maintained to highlight the daily convective potential and runoff concerns. ...Florida Gulf Coast... Deep tropical moisture and a slow-moving mid-to-upper level low over the eastern Gulf will maintain a heavy rainfall threat. Favorable low-level convergence along the eastern flank of the system may produce heavy rainfall along Florida's West Coast. Some models show the system lifting out to the north this period, bringing the threat for heavy rain into the Big Bend region. A Marginal Risk was maintained from the Tampa Bay area to the Big Bend to highlight the potential for heavy rain along this area. ...Virginia Tidewater and Eastern North Carolina.... A cold front dropping out of the north is expected to slow across this region, maintaining a deep moisture pool in advance. Pre- frontal convergence and diurnal heating will likely produce pockets of heavy, slow-moving thunderstorms prior to its passage. With some differences in the details, model consensus continues to indicate that 1-2 inch, with locally heavier amounts, are likely within the Marginal Risk area, producing at least isolated concerns. A targeted upgrade to a Slight may be required, especially if the model consensus for heavy amounts begins to center across the more vulnerable Tidewater region. Pereira Day 4 and Day 5 Valid 12Z Mon Jul 20 2026 - 12Z Wed Jul 22 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST/MID ATLANTIC REGION AS WELL AS THE WESTERN US... 2030Z Discussion Introduced a Marginal Risk area on Day 4 from the Great Lakes to the Mid Atlantic region on Day 4 given a strengthening signal in both the operational models and ensemble QPF guidance and the magnitude of the moisture in place. Also made some minor adjustments on Day 5 in the Northeast US and Mid-Atlantic region. Maintained continuity in Florida and coastal Southeast US as an area of low pressure tracks across the Florida peninsula. No change needed in the West where weak and difficult-to-time shortwave energy and anomalous moisture lingers on the western periphery of an upper high in region of broad ridging. Bann Previous Discussion... ...Western U.S... A continuation of a traditional monsoonal pattern will continue across the Western CONUS with scattered to widespread bouts of locally heavy to excessive rainfall each day across much of the Desert Southwest up through the Great Basin and into portions of the Rockies. Deep moisture will be drawn northward around the periphery of a building upper high extending from the Great Basin to the Southern Plains. This sets up a well-defined axis of elevated instability coupling with precipitable water anomalies between +2 and +3 standard deviations above climatology for July...with the strongest anomalies situated over Nevada and Utah. QPF maxima are currently situated within the Mogollon Rim and portions of southern Utah...both of which are the more susceptible areas given the complex topography and slot canyons. Broad MRGL risks exist for both days in similar locations outlining much of the aforementioned area(s) above although short term upgrades in spots are not our of the question. ...Florida... Models continue to depict heavy rainfall across portions of the northern Florida peninsula on Monday (Day 4) which spreads farther northward in association with an area of low pressure. Ensemble QPF for both periods indicate multiple inches of rain. This continues to be a period to monitor for the prospects of this being something becoming more organized than what the latest model guidance indicates. For now, MRGL risks exist on both D4 and D5 for the threat of heavy rainfall. Northeast US... The deepening of a mid- and upper level trough by a digging upper level jet will push a surface cold front into the Northeast US. Deep moisture gets drawn northeastward ahead of the digging system and should be in place as convection develops in vicinity of the front. With such a moist environment and favorable low level instability along with the upper support afforded by the jet...downpours that lead to heavy or excessive rainfall amount are possible. Bann 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 $$