Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
727 FOUS30 KWBC 031957 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 257 PM EST Wed Dec 3 2025 Day 1 Valid 16Z Wed Dec 03 2025 - 12Z Thu Dec 04 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA... ...16Z update... A notable mid-level dry layer observed on this morning`s OSPO ALPW imagery will moisten up over the next 24 hours as winds in the lower/middle levels back in advance of an approaching mid-level trough currently over the Southwest. Since the surface front is forecast to barely edge inland along the middle/upper Texas coast, most parcels within the outlook area will be elevated. Recent RAP guidance supports a plume of 500-1500 J/kg MUCAPE moving northward across the middle Texas coast into eastern Texas, western and central Louisiana. WSW steering flow is expected to allow training of showers/thunderstorms along elevated axes of convergence aligned with the mean flow supporting training and repeating of heavy rain. The 12Z HREF and 06Z REFS support 12 hour maxima of 3-5 inches (ending 12Z Thursday) from the upper Texas coast into southwestern Louisiana with probabilities for 3 inches from the HREF at 50-60 percent and 70-80+ percent from the REFS. Peak hourly rainfall of 2 to 3 inches appears likely, although 3+ inch hourly totals cannot be completely ruled out near the coast. Minor edits were made to the existing Marginal Risk area for this update. Otto ...previous discussion follows... CIRA LPW shows the slug of enhanced moisture along the central Mexican Gulf coast starting to lift northward through the western Gulf jet under response from the digging mid-level shortwave across the Four Corners of the Southwest U.S. Twenty to 30kts of southerly low level flow will advect the moisture north, bring the surface front toward the central Texas coast through late afternoon into the evening; CAPE values will rise into the 2000-3000 J/kg range. As night-falls, stronger isentropic ascent will increase through depth as the upper-level southwesterly jet stream flow expands and strengthens providing the solid ascent plane for sufficient moisture convergence with total PWats over 2" for expanding region of elevated thunderstorm activity across the central and upper Texas Coast. Northward expansion remains the greatest uncertainty but overall 00z CAMs continue denoting solid rainfall rate potential mainly along and south of the I-10 corridor with cell motions being slow but also slightly veering to more easterly with solid back-building potential to allow for some repeating training. HREF probability driven by the 00z CAMs, still suggest best signals will remain off-shore but there was also a slight northeastward trend in some of the convective elements into southwest to south-central LA with streaks of 2-3" totals. This will retain the solid Marginal Risk (5-15% coverage) of FFG exceedance with isolated rapid inundation flooding possible. Gallina Day 2 Valid 12Z Thu Dec 04 2025 - 12Z Fri Dec 05 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL GULF COAST... 20Z Update... Made some small adjustments based on the 12Z HREF/RRFS probabilities, the 12Z RRFS Mean, and recent deterministic RRFS runs. With the HREF/RRFS guidance showing the heaviest amounts remaining more confined to the coast, pulled the Marginal Risk a little bit further south and west with this update. While the footprint for heavy amounts may not be as broad, the previously noted HREF and RRFS guidance continue to indicate heavy amounts (3+ inches) are likely within the highlighted area, with the greatest threat centered along the southwest Louisiana coast. Pereira Previous Discussion... Upglide/warm-advective elevated convective activity should be ongoing start of the forecast period (04.12z) across the central Gulf coast. Steering flow will continue to flatten within fairly unidirectional west-southwesterly deep layer flow. Right entrance ascent to 150-170kt jet centered over the Ohio Valley will keep isentropic moisture flux across the surface front that will oriented along and south of the coast. A weak mid-level shortwave will slide from west to east along the southern periphery of the jet streak maintaining 20-25kt of west-southwesterly 850mb flow which given 1.75-2" total PWats and modestly unstable ribbon (up to 1000 J/kg) and should maintain the elevated convective development. Internal training of back-building convective elements should be the greatest potential for higher rainfall totals across the Bayous of south-central LA. A slow eastward propagation of the SSW- NNE oriented line will occur with the translation of the flat shortwave energy and potentially expand into coastal MS/AL and perhaps as far as western FL Panhandle by the end of the forecast period. There remains some north/south spread in placement of heaviest rainfall cores/training corridor. The GFS continues a traditional northward bias along with the NAM relative to the ECMWF and other global guidance; with some suggestion of overall totals in excess of 5" in spots. Hi-Res CAMs generally trend toward the southern solutions with heaviest rainfall along and south of I-10, which appears more plausible given the overall flow orientation (unstable air upstream over the waters). Still, there is some solid suggestion of rainfall rates/totals and environmental conditions that may warrant an upgrade to a Slight Risk, however, the split in placement and wider overall total rainfall total spread continues to be too great to delineate one at this time, but will continue to evaluate with future updates. As such, the broad Marginal from Galveston Bay to the Pensacola area of FL remains, though have broadened it slightly northward to account for the latitudinal variance. Gallina Day 3 Valid 12Z Fri Dec 05 2025 - 12Z Sat Dec 06 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL GULF COAST THROUGH CENTRAL GEORGIA... 20Z Update... Made only minor adjustments based on the 12Z guidance. Pereira Previous discussion... The deep layer unidirectional west-southwesterly flow regime will remain in place for the day 3 period as well. The subtle, flat mid- level shortwave feature will be translating quickly across the South, through the Carolinas and offshore. The connection to the western Gulf moisture pool/theta-E source will continue to further narrow and stretch through an elongated isentropic ascent plane in the wake of the wave draped across SC, central GA toward the central Gulf coast. By this time period, the ascent across the front will be fairly oblique and lapse rates will have moderated toward limited elevated MUCAPE below 500 J/kg...becoming more of an Atmospheric River with prolonged moderate rates with 24hr totals of 1-2" across the length of the stream with scattered localized maxima of 2-3". To be expected, much like the day 2 period, there remains a latitudinal spread to the placement of the AR stream and the width of the inherited Marginal Risk reflects this. However, at this point, FFG exceedance will be more likely in the longer duration of 6, 12 and 24hr exceedance, with any flash flooding potential most likely upstream across LA/S AL, where multiple days of rainfall should saturate the upper soil profiles and FFG values may be much lower than currently analyzed. Gallina 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