Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
318 FOUS30 KWBC 022025 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 425 PM EDT Tue Sep 2 2025 Day 1 Valid 16Z Tue Sep 02 2025 - 12Z Wed Sep 03 2025 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN CALIFORNIA AND SOUTHERN ARIZONA... 16Z Excessive Rainfall Discussion Update... Removed the Marginal Risk area from the Upper Midwest but the remainder of the Excessive Rainfall Outlook remained fundamentally the same as the initial issuance. The environment sampled by the MPX sounding was characterized by precipitable water values around 1.25 inches and sufficiently strong flow to support cells being progressive. Both considerations should limit the risk of excessive rainfall even if there is a period of brief heavy rainfall rates. The Mid-South/Tennessee Valley and Southwest U.S. portion of the outlook appears to be on-track with the earlier outlook and forecast reasoning. Bann ...Previous Excessive Rainfall Discussion... ...Southwest... There will be a nearly continuous anomalous surge in monsoonal moisture into the Sierra Nevada due to the position of the upper ridge axis to the east and a weak upper low along the central California coast to the west. PW anomalies of 2 to 3 sigma are forecast from the lower Colorado River up trough the Sierra Nevada and even into southern Oregon by 00Z Wed. Impressive CAPE will also be present across southern Arizona and southern California, showing support for heavy rainfall especially over flashy prone areas. This environment has the potential for more than just isolated areas of flash flooding, therefore a Slight Risks were raised for southern Arizona and southern California. ...Mid-South through Tennessee Valley... Remnant boundaries from ongoing convection today combined with additional lift from a digging trough from the central U.S. should allow convective activity to be in similar areas (and west) from yesterday`s coverage. However, moisture is limited to around 1.5". This uptick will allow for some greater rates and motion should remain slow overall, but overall the rainfall magnitude continues a decreasing trend. A Marginal Risk remains in effect from central Mississippi to Kentucky. ...Upper Midwest... During this period a cold front is expected to traverse across the Dakotas and encounter pooled moisture with a PW of 1.25", which is 1 sigma above normal. Diurnally enhanced convection is expected fire up along and ahead of the frontal boundary and will have the potential to produce heavy rainfall for Minnesota, northern Iowa, Wisconsin and the U.P. of Michigan. A Marginal Risk was kept for this area. Campbell/Jackson Day 2 Valid 12Z Wed Sep 03 2025 - 12Z Thu Sep 04 2025 ...THERE IS A SLIGHT RISK FOR PORTIONS OF SOUTHERN CALIFORNIA AND SOUTHER ARIZONA... 2030Z Excessive Rainfall Discussion Update... Main change was to remove the Marginal Risk area over the Great Lakes region. Model and deterministic QPF had come down to values under half an inch...and in many cases the areal average amounts were closer to one-quarter inch. Model-derived instability does maximize above 500 J per kg during the afternoon...enough instability to support locally heavy rainfall. However...the cells should be progressive enough to limit the risk of excessive rainfall to less than a 5 percent probability. Farther south, the concern about excessive rainfall due to the threat of repeating convection remains and the Marginal Risk area remained in place. Concern for excessive rainfall across the Southwest US remains as described below. Previous Excessive Rainfall Discussion... ...Southwest... Anomalous monsoonal moisture will continue to affect northward from the lower Colorado Valley through the Sierra Nevada and much of Nevada. Diurnally- driven activity can be expected again over the Sierra Nevada which may be locally excessive, as well as much of Nevada through western Arizona and southwest Utah. A broad Marginal Risk cover much of Arizona,southeast Utah, southern Nevada, and eastern/southern California. The presence of strong CAPE embedded with the deep column of moisture, especially across southern Arizona and across the Transverse and Peninsular Ranges of southern California will be conducive for heavy rainfall and scattered areas of flash flooding. These locals will be vulnerable to the high rainfall rates, especially in the flashy prone locations. A Slight Risk was raised in coordination with the local forecast offices. ...Central U.S... Elevated moisture ahead of the strong cold front sweeping down the Plains will trigger heavy rainfall again. Enough focus is present to warrant maintenance of the Marginal Risk around the central Great Lakes though timing is in question. While much of the activity should be progressive, there is a repeating threat on the southern end of activity along the southern Kansas/Missouri border- a Marginal Risk was carried on for this period. ...Florida... Enhanced rainfall expected to develop within the very moist airmass along the stalled frontal boundary. Individuals cells will focus heavy rainfall over the southern peninsula and the Keys thus keeping an elevated threat for flash flooding. Campbell Day 3 Valid 12Z Thu Sep 04 2025 - 12Z Fri Sep 05 2025 ...THERE IS A MARGINAL RISK AREA FOR PORTIONS OF FLORIDA, SOUTHWEST/GREAT BASIN, AND THE NORTHEAST... 2030Z Excessive Rainfall Discussion Update... Shrunk the Marginal risk area in the eastern US...keeping portions of New York and Pennsylvania in the Marginal area where there is some overlap between instability and moisture. The shear profile has become less favorable for cell training compared with 24 hour ago...which should work against the risk of excessive rainfall. Only a few changes needed elsewhere. Bann Previous Excessive Rainfall Discussion... ...Florida... The environment will remain nearly the same as the Day 2 period, thus convection will persist. Heavy rain will be possible therefore the Marginal Risk was maintained southern Florida and expanded southward to cover the Keys. ...Northeast... The cold front passing through the Lower Great Lakes and into the Northeast will be fairly progressive, however there are signals for higher QPF to focus across central and northern portions of New York. Parts of the region have been drier with some areas with notable drought conditions, which will limit the potential for impacts from heavy rainfall. The highest amounts are expected for the more elevated locations which will increase the threat for flooding concerns. A Marginal Risk area was maintained from the previous Day 4 but with portions of western and eastern new York trimmed out given the D0/D1 drought conditions. ...Southwest, California and southern Great Basin... The monsoonal moisture will continue to advect into the southwestern U.S. underneath the mean upper ridge, promoting scattered showers and thunderstorms. Moisture anomalies are expected to be the greatest for portions of California and Nevada. A broad Marginal Risk encompasses eastern California, most of Nevada, southeast Utah, Arizona and west/central New Mexico. Campbell 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