Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
673 FOUS30 KWBC 162005 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 405 PM EDT Tue Jul 16 2024 Day 1 Valid 16Z Tue Jul 16 2024 - 12Z Wed Jul 17 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PARTS OF THE CENTRAL HIGH PLAINS TO THE OHIO VALLEY... ...16Z Update... Adjustments this forecast cycle were to expand the Slight Risk area over the Central Plains farther south to include more of the northern TX Panhandle, northern OK, and northern AR. Latest guidance has shown the nearby stationary front inching a little more south compared to overnight guidance, which would allow for segments of storms tonight being farther south than initially progged over northern OK and even as far west as the TX Panhandle. Closer to northern AR, strong surface based heating that further destabilizes the atmosphere ahead of the front may lead to strong storms by itself given the 89F convective temp via the 12Z LZK sounding. Then there is the concern for outflows from thunderstorm activity over northern OK that may approach and act as another trigger tonight over the Ozarks. In the Northeast, the soils are more primed in parts of NY`s North Country and around the Finger Lakes following yesterday`s stormy afternoon. Another MCV approaching from the west may lead to a near carbon-copy setup for today, but storm motions should remain progressive enough to limit the areal extent of flash flooding to be more localized. One wildcard to factor in would be areas where more extensive tree damage occurred that could be more prone to flash flooding. The 12Z HREF also showed moderate-to-high probabilities (50-70%) for 3-hr QPF surpassing 3-hr FFGs just east of Lake Ontario and along the Tug Hill. Still, the progressive nature of the storms kept any Slight Risk from being issued for the time being. One adjustment was to expand the Marginal Risk across most of northern New England as the soils (particularly in northern ME) are a little more saturated (NASA SPoRT-LIS sows >80% soil moisture percentiles). Given their added sensitivities and PWATs that are topping 1.5" (>90th climatological percentile according ot ECMWF SATs), the Marginal Risk extension was decided upon this forecast cycle. Mullinax ---Previous Discussion--- ...Mid-Mississippi and Ohio Valleys... Strengthening southwesterly flow ahead a shortwave moving across Kansas will support deepening moisture ahead of a cold front sliding southeast into the mid Mississippi Valley this morning and the lower Ohio Valley later today. Persistent inflow into this slow-moving boundary along with favorable forcing aloft is expected to support periods of training storms, with areas of heavy rainfall likely, especially from central and southern Missouri eastward into the lower Ohio Valley. Excessive rainfall is especially a concern from central and southern Missouri through southern Illinois to the western Indiana and Kentucky border, where the 00Z HREF is showing high neighborhood probabilities for accumulations of 3 inches or more through the period. ...Central Plains... Moist upslope flow behind a cold front settling south through the central Plains will support storms developing over the high terrain before these storms spread east into the Plains during the evening. Merging storms along with increasing organization ahead of a shortwave digging southeast through the Plains is expected to support locally heavy amounts from southeastern Colorado through southwestern Kansas and northwestern Oklahoma, where the HREF is also showing some notable probabilities for 3 inches or more. ...Upper Ohio Valley to the Northeast... Ample moisture ahead of an amplifying upper trough over the Great Lakes and its associated cold front will fuel additional storms later today. Overall, storms that develop are expected to be progressive in nature. However, intense rainfall rates may produce isolated runoff concerns. ...Southwest... An upper high sitting over the Four Corners will allow moisture to funnel across the region, with an expansion of convective activity expected today, bringing the risk for isolated heavy amounts and flash flooding to a greater portion of Arizona and New Mexico. Pereira Day 2 Valid 12Z Wed Jul 17 2024 - 12Z Thu Jul 18 2024 ...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR PORTIONS COLORADO AND NEW MEXICO, FROM THE ARKANSAS AND RED RIVER BASINS TO MID-SOUTH, AND FOR THE NORTHERN MID-ATLANTIC I-95 CORRIDOR... ...2030Z Update... ...Northern Mid-Atlantic I-95 Corridor... As daytime heating unfolds, the atmosphere will rapidly destabilize as high temperatures rise into the mid 90s and dew points average around 70F. Latest CAMs guidance shows thunderstorms firing initially along a pre-frontal trough Wednesday afternoon with potential redevelopment Wednesday evening as the cold front traverses the region. PWs are expected to range between 2.0-2.2", which is between the 90-97.5th climatological percentile for the time of year. Soundings in the region also show no shortage of MUCAPE (at least 2,000 J/kg) and hodographs that are not only supportive of organized clusters of storms, but potentially capable of containing organized mesocyclones (which are more efficient rainfall producers). The storms will have a rather progressive motion and soils can most definitely use the rain. However, the potential for >2"/hr rainfall rates along a highly urbanized corridor that contains no shortage of hydrophobic surfaces is a recipe for potential flash flooding. The potential for additional storms in the evening in wake of the initial pre-frontal storms may also make some soils more sensitive for the final round of storms along the approaching cold front. Given these reasons, and in collaboration with LWX and PHI, a Slight Risk was introduced for Wednesday. Otherwise, did adjust the Slight Risk in the Lower Mississippi Valley and ArkLaTex a little farther south given the slightly farther south progression with the cold front. The rationale behind the threat area remains unchanged. Made just minor adjustments to the Marginal and Slight in the Southwest to account for recent QPF changes and 12Z HREF guidance. Mullinax ---Previous Discussion--- ....Southwest to the Central to southern Rockies and High Plains... As the previously noted front continues to slide to the south through the Plains, increasing moisture afforded by low- level easterly flow will support an increasing threat for locally heavy rainfall and flash flooding concerns. Ample moisture along with increasing lift will support storms capable of producing heavy rainfall rates, that will develop and drop south across the region. The greater threat continues to center from the Colorado Sangre de Cristos into the northern and central New Mexico ranges, where models show some of the better low level inflow and greater PW anomalies. Elsewhere, a more typical monsoon pattern will continue, with diurnal convection generating isolated heavy rainfall and flash flooding concerns across much of the Southwest. ...Southern Plains to the Northeast... An upper trough will continue to amplify over the Great Lakes, pushing a cold front that will extend from the Northeast to the southern Plains this period further south and east. While locally heavy rainfall and an isolated threat for heavy rainfall cannot be ruled out for any area along the front, deeper moisture and stronger forcing are expected to elevate the threat for some areas. This includes portions of the Red River and Arkansas basins into the Mid-South. Deepening moisture and increasing ascent ahead of a shortwave approaching from the northeast is expected to support organized heavy rainfall across the region. With plenty of typical difference in the details, several of the overnight deterministic models indicate locally heavy amounts of 2-3 inches within the Slight Risk area. Pereira Day 3 Valid 12Z Thu Jul 18 2024 - 12Z Fri Jul 19 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS SOUTHEASTERN VIRGINIA AND EASTERN NORTH CAROLINA AND THE SOUTHERN ROCKIES... ...2030Z Update... Little in the way of adjustments were made given guidance has generally remained steadfast in support of the ongoing risk areas. Only made some subtle adjustments based on the latest Day 3 QPF. While QPF is not as high in parts of the Southern Rockies as on Day 2 at the moment, soils will likely be more sensitive following yet another day of heavy showers and storms throughout the region on Wednesday. For that reason, I kept the Slight Risk that was inherited from the previous forecast. Otherwise, no additions or subtractions of threat areas for this forecast cycle. Mullinax ---Previous Discussion--- ...Southern Mid-Atlantic and the Southeast to the lower Mississippi Valley... The previously noted cold front will continue to settle further south and east, bringing heavy rain and the threat for flash flooding into portions of the southern Mid Atlantic, the Southeast, and the lower Mississippi Valley. A Slight Risk was maintained across portions of southeastern Virginia and eastern North Carolina, where PWs are forecast to increase to ~2.25 inches as the front settles and begins to stall across the region. This moisture along with some mid-to-upper level support is expected to fuel heavy amounts across the region. Elsewhere, models suggest less organized storms with more isolated threats for flash flooding further west along the front into the lower Mississippi Valley. ...Southwest to the central and southern Rockies... With no significant change to overall pattern expected and plenty of moisture remaining in place, maintained much of the same outlook areas from Day 2 into Day 3, including a Slight Risk centered over north-central New Mexico extending into far south-central Colorado. Pereira 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