Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
445 FOUS30 KWBC 171913 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 313 PM EDT Sun Aug 17 2025 Day 1 Valid 16Z Sun Aug 17 2025 - 12Z Mon Aug 18 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF THE UPPER MIDWEST... ...Northern Plains, Upper Midwest, Ohio Valley, Northern Mid- Atlantic and southeast New England... Showers and thunderstorms linger across portions of eastern SD and southwest MN near a front and associated outflow boundaries. Other dying activity is moving into the Northern Mid-Atlantic States and towards the Lower Ohio Valley. Across the Upper Midwest, there should be some boundary return before evening/overnight convective development occurs near southwest MN due to strong southwest flow importing decent instability into the region. The thunderstorms then move into portions of northern IA and southwest WI. With the signal waning in the mesoscale guidance towards the International Border with Canada, trimmed the northern portion of the Slight Risk area. Due to heavy rains overnight and early this morning, shifted the southern extent more southward to account for at least partially saturated/compromised soils near the IA/MN border and in case the mesoscale guidance is still too poleward with its heavy rain footprint. Farther east, renewed scattered thunderstorm activity is expected across the Northeast ahead of a dying precipitation area across PA, which appears to have an MCV in tow. The Appalachians and possible lee trough/sea breeze front closer to the New England coast should also act as foci near and ahead of the incoming front. Stronger NWly flow around the central CONUS upper ridge should keep activity fairly progressive, so the risk level was left as Marginal. Remnant moisture over Montana and near the Black Hills from the atmospheric river that pushed into the Northwest a couple days ago could cause repeating convection to cause heavy rain to be excessive, so reworked the Marginal Risk there. ...New Mexico and Western Texas... Continued east shift in the monsoonal moisture plume places an isolated flash flood risk over eastern NM and far western TX into the TX Panhandle today where the PW anomaly remains 1.5 sigma above normal. Few changes were made to continuity in this region. ...Florida... Persistent boundary over the northern FL Peninsula maintains high moisture with 2.25" PW (2 sigma above normal). Mainly diurnally- driven convective activity may produce locally excessive rainfall even with the high FFG (around 4"/3hr). Roth/Jackson Day 2 Valid 12Z Mon Aug 18 2025 - 12Z Tue Aug 19 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN WISCONSIN INTO NORTHERN ILLINOIS... ...Upper Midwest/Great Lakes... Ongoing Monday morning convection is progged to be moving into portions of WI and northern IL before diminishing by midday. The remnant boundary then allows further activity to fire over similar areas later that afternoon. Moisture is quite elevated with PW peaking at or just over 2" in the afternoon. Hourly rain amounts to 3" with local totals to 5" are possible. The overlap of these repeating rounds of heavy storms over already saturated ground and urban areas warranted a Slight Risk which was expanded to include Chicagoland on this afternoon update. Given the mesoscale processes over the persistent frontal pattern generous coverage of the Marginal Risk is used to cover much of the Midwest. ...CO/KS/NE... A convective complex is expected to form in the Front Range and propagate eastward, which the guidance weakens as it crosses the 100th meridian. As the guidance can sometimes undersell Front Range convection, added a Marginal Risk to account for the heavy rainfall it could produce. Hourly amounts up to 2" are possible where cells merge or manage to train. ...Southwest... The upper ridge axis shifts west to NM on Monday suppressing the monsoonal flow and warranting a Marginal Risk over southern NM and far western Texas under its base where moisture is more than sufficient for isolated flash flood issues. Hourly amounts to 2.5" are possible where cells are stationary, backbuild, merge, or train. ...Central Gulf Coast... An easterly wave is expected to traverse areas of southernmost MS and southern LA, leading to heavy rainfall. Precipitable water values are forecast to rise to 2"+, and ML CAPE up to 3000 J/kg is expected. Daytime heating should play a role in the heavy rain production. Hourly amounts to 3" with local amounts to 5" are possible where cells merge or manage to train. Effective bulk shear is forecast by the GFS to be capped around 20 kts, so pulse convection is expected. ...Southeast... A Marginal Risk remains over the southern Appalachians/Piedmont and northern FL Peninsula for pooled moisture anomalies and perhaps some remnant frontal boundary in FL. These areas would see mainly diurnally driven convection. Roth/Jackson Day 3 Valid 12Z Tue Aug 19 2025 - 12Z Wed Aug 20 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE SOUTH CENTRAL GREAT PLAINS THROUGH EASTERN MIDWEST AND IN THE SOUTHWEST... ...Central Plains to the Midwest... Westward motion to the upper ridge axis allows the frontal wave pattern over the Upper Midwest to finally eject southeast Monday night. Positive moisture anomaly with PW 1.5 to 2 sigma above normal extend from MI through MO by Tuesday afternoon, with the wave itself spending time across southeast MO. Frontal forcing should allow for progressive motion. Effective bulk shear appears low enough for an expectation for pulse convection, but hourly amounts to 3" on a local basis is sufficient for an isolated to widely scattered flash flood/Marginal Risk. The main change was to split the risk area in two, one covering the Midwest/Plains and the other focused in the Southern Appalachians. ...Southern Appalachians... A wave of moisture/spoke of energy moves by the region as an anticyclonic wave breaking event occurs, with an upper level packet of energy moving dropping in from the north. Effective bulk shear is scarce, so pulse convection is expected in this region. Hourly amounts to 3" are possible locally which could lead to flash flooding on an isolated basis. ...Southwest... Remnant moisture with PW anomalies around 1 sigma above normal are over eastern AZ/much of NM on Tuesday. Given the precipitable water values available, hourly amounts to 2" are possible where cells stall, backbuild, merge, or manage to train. An isolated terrain driven flash flood risk is possible in the diurnal convection, so the Marginal Risk is maintained. Roth/Jackson 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