Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 412 PM EDT Sat Jul 5 2025 Day 1 Valid 16Z Sat Jul 05 2025 - 12Z Sun Jul 06 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF CENTRAL TEXAS AS WELL AS THE COASTAL CAROLINAS... ...16Z Update... ...Central Texas... A higher end Slight is in effect for a portion of central Texas from San Antonio north. An ongoing MCS that has been responsible for the catastrophic flooding further west will remain active through the day today, as excessive amounts of Gulf moisture continue to stream northward into the thunderstorms. There remain a few cells producing multiple inch per hour rainfall rates, especially just east of San Antonio with this update. Over the next few hours with daytime heating, the storms are likely to reintensify, and track westward with time. There remains some potential that strong storms with very heavy rainfall may move over areas already hard hit with heavy rains, though that's not explicitly forecast in the guidance, likely because those areas have been worked over. Nonetheless it goes without saying that should heavy rain move over hard-hit areas, then additional flooding impacts are very likely. There also remains some potential for refiring of storms in the predawn hours of Sunday in some of the areas of the Slight, based on some of the guidance, so despite likely waning of thunderstorm activity after sunset, new storms could pose a threat. Should strong thunderstorms reform over hard hit areas, a Special update with an upgrade to a Moderate Risk may be needed. ...Carolinas/T.S. Chantal... Much of the high resolution guidance on Chantal have shifted the focus for the heaviest rain through 7am Sunday a bit to the south into coastal South Carolina. Given the very slow movement of the storm, a higher end Slight is in effect from southwest of Myrtle Beach through Wilmington. Much of the rainfall that may result in flash flooding in those coastal communities will fall after sunset tonight through the overnight. In the meantime, expect the outer bands of Chantal to impact the coast with briefly heavy rain and gusty winds. ...Midwest... Trimmed the western end of the inherited Marginal behind where the rain has already fallen, but otherwise very few changes expected as all looks on track in this area. Wegman ...Previous Discussion... ...Central Texas... Concerns remain for additional heavy rain and flooding across portions of South-Central Texas and the Hill Country. Overnight guidance shows another surge of deeper moisture pushing north across central Texas, with PWs at or above 2 inches bisecting the state today. Many of the hi-res members show scattered storms developing along this axis this afternoon. Fortunately, most depict these storms initiating outside of those areas hardest hit by yesterday's rains. However, there is some indication that storms may drift west back into those areas and there is some overlap between those inundated areas and where the new HREF is showing high neighborhood probabilities for additional accumulations exceeding 3 inches. ...Southeast... Tropical Depression Three is expected to intensify some as it moves northwest and is expected to make landfall along the central South Carolina coast near the end of the period. The potential for efficient, heavy rainfall producing bands will increase as onshore flow ahead of system pushes PWs above 2.25 inches along portions of the South and North Carolina coasts. This moisture along with deep, warm cloud layers will support periods of heavy rain, with locally heavy amounts. The forecast track and general consensus of the guidance shows the greatest threat for heavy amounts centering from the Grand Strand toward Cape Fear. HREF neighborhood probabilities for amounts over 3 inches are highest in this region. A small targeted Slight Risk was placed over this area, with the greatest threat for flash flooding expected to focus over urbanized and poor drainage areas. Further to the south, a trailing boundary and axis of deep moisture will support showers and storms with locally heavy amounts across central Florida. ...Northern High Plains... A well-defined shortwave trough will move from the Northwest into the northern High Plains. The associated large-scale forcing, along with increasing moisture, supported by low level southeasterly flow, will encourage shower and thunderstorm development. PWs are expected to increase to ~1 to 1.25 inches (1 to 1.5 std dev above normal), with the deeper moisture and greater anomalies centering from southeastern Montana into the Black Hills region. While a widespread heavy rainfall event is not expected, heavy rainfall rates and some potential for redeveloping storms may produce locally heavy amounts (greater than an inch) and isolated runoff concerns. ...Upper Midwest to the lower Missouri Valley... A shortwave trough will continue to advance east out of the northern Plains and across the Upper Midwest/Great Lakes. This will push the associated cold front further south and east, with low level southeasterly flow supporting a deep moisture pool (PWs ~2 inches). This will support widespread shower and thunderstorm development across the region. While some southwest to northeast training may elevate the potential for heavy amounts and flooding concerns, storms are expected to be generally progressive. One area where a potential upgrade may be necessary is across portions of central and eastern Iowa, where some of the hi-res guidance shows an initial round of storms developing along a prefrontal trough, followed by a second round along the front. HREF neighborhood probabilities indicate that totals in excess of 2 inches are likely, with some potential amounts over 3 inches across this area. Pereira Day 2 Valid 12Z Sun Jul 06 2025 - 12Z Mon Jul 07 2025 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL TEXAS AS WELL AS FOR PORTIONS OF THE CAROLINAS... ...2030Z Update... ...Central Texas... In coordination with SJT/San Angelo, TX and FWD/Fort Worth, TX forecast offices, a Slight Risk upgrade was introduced with this update for portions of central Texas. While moisture amounts and advection will both be waning by Sunday, especially as compared with previous days, there will certainly still be enough moisture and forcing to allow for a renewed round of slow-moving showers and thunderstorms to affect this area. The biggest contributing factor to the upgrade is the ongoing flooding and its associated impacts. Thus, even lesser amounts of rain, as forecast on Sunday, will have outsized impacts given the vulnerabilities in that area. The storms should taper off by sunset across central Texas, ushering in a prolonged period of much drier weather. ...Carolinas/TS Chantal... With the guidance better handling TS Chantal and its track through the Carolinas, and a bit stronger storm forecast to make landfall in South Carolina tonight, by Sunday the storm will be rapidly weakening. However, its associated rainfall and abundant moisture will persist well inland from the landfall point. Most of the guidance is in very good agreement on where the swath of heaviest rainfall will occur on Sunday, namely from north-central South Carolina through central North Carolina. For now...the consensus keeps the rainfall shield just east of Charlotte, but may impact Greensboro, and perhaps Raleigh and Winston-Salem. Forecast rainfall has increased markedly, with the swath of rainfall now featuring amounts exceeding 3 inches in 24 hours (of course local rainfall amounts will be higher). Despite antecedent dry soil conditions, the potential for very heavy rainfall with Chantal's remnants are very likely overcome the initially dry soils in that area, resulting in flash flooding. However, the dry antecedent conditions should at least delay any flooding, and of course take a little off the top of any flooding's severity. Thus, have introduced a Slight Risk for north-central South Carolina and portions of central North Carolina, with an area from Greensboro south into northern South Carolina in a higher-end Slight Risk. Any slowing of the storm or a better signal for heavy rainfall over a bigger urban center would require a targeted Moderate Risk upgrade with future updates. ...Central Gulf Coast... Widely scattered showers and thunderstorms across southern Louisiana will have ample Gulf moisture to feed upon Sunday afternoon. With the potential for any of those storms moving over a sensitive urban area such as New Orleans or Baton Rouge, a Marginal Risk was introduced with this update. Wegman Day 3 Valid 12Z Mon Jul 07 2025 - 12Z Tue Jul 08 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE UPPER MIDWEST TO THE SOUTHWEST, THE NORTHEAST TO THE OZARK REGION, PORTIONS OF CENTRAL TEXAS, AND EASTERN NORTH CAROLINA TO THE DELMARVA... ...2030Z Update... ...Eastern North Carolina and Southeastern Virginia... The threat for heavy rainfall will continue to decrease, however some additional heavy amounts are possible as Tropical Storm Chantal moves over eastern North Carolina and southeast Virginia. The inherited Marginal Risk was expanded north across much of the Delmarva and the DC and Baltimore metros with this update for the potential for widely scattered storms capable of very heavy rain. While the heavy rain threat will be greater towards the Delmarva, given the sensitivity of the DC and Baltimore metros to heavy rain, opted to include them for that limited heavy rain potential. ...Northeast to the Ozark Region... The previously noted cold front will push across the Northeast while lingering back across the Ohio into the mid Mississippi Valley. Overnight models indicate a greater threat for heavy amounts will focus along with some right-entrance region upper jet forcing and greater moisture anomalies across northern New England. However, sufficient moisture is expected to remain in place ahead of the boundary to support at least localized heavy amounts and an isolated flooding threat further southeast along and ahead of the boundary. ...Northern Plains and Upper Midwest... Models show a well-defined shortwave moving across the region this period. With plenty of differences in the details, models indicate some potential for organized heavy rains developing ahead of this wave as it interacts with an influx of deeper moisture. ...Central Plains to the Southern High Plains/Rockies... Similar to the previous day, the models are presenting a notable signal for showers and storms, supported by moist low level inflow, to develop over High Plains, with some potential for locally heavy amounts to occur as they move east. Besides minor model differences, the only big changes was to carve out the Nebraska Sand Hills from the Marginal Risk with this update. Meanwhile, the coverage of storms and potential flooding concerns is expected to expand across New Mexico as the monsoon pattern builds, with moisture increasing across the region. Pereira/Wegman Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt