


Hydrometeorological Discussion
Issued by NWS Tuscaloosa, AL
Issued by NWS Tuscaloosa, AL
262 AGUS74 KWCO 151458 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT TUE JUL 15 2025 .Synopsis... Isolated flooding potential continues across Central Texas and the Mid-Atlantic and the Central/Southern Appalachians... Increasing potential for flooding impacts across the Central Gulf Coast and Florida... Isolated flooding possible across the Northern Plains in the Midwest, Southwest, and the Ohio and Tennessee Valleys... .Central Texas... Isolated flash, urban, and renewed river rises will remain possible through this evening as locally heavy rainfall continues over already wet basins. While the system is expected to gradually weaken throughout the day, the hydrologic environment remains highly sensitive soils are nearly or fully saturated, and in-channel storage is limited due to lingering high flows. Given these conditions, flash and river flooding could develop rapidly with localized heavy rainfall, and even modest additional rainfall amounts may trigger renewed flood responses. This is supported by the National Water Model (NWM) Short-Range Forecast (SRF), which continues to highlight rapid-onset flooding across portions of the Hill Country, with the strongest signals occurring between Ozona and Brownwood, some of which is likely ongoing per the Rapid-Onset Flood Arrival Time Forecast, and some that are expected to begin later this evening. In addition, higher magnitude (between 10 - 2%, annual exceedance probability) streamflows can be seen throughout this area, supporting the potential for isolated, yet new out-of-bank rises. .Mid-Atlantic and the Central/Southern Appalachians... Isolated flash and urban flooding, some locally significant, remains possible across portions of the region through this evening as additional periods of locally heavy rainfall develop over already hydrologically sensitive areas. Of particular concern is eastern VA, where 7-day rainfall totals of 5 - 10"+ (RFC QPE) have left soils saturated and streamflows elevated, with little to no recovery time. The NWM SRF is highlighting the potential for rapid-onset flooding across eastern VA into the NC Piedmont, however, overall streamflow responses remain modest, likely due to the convective nature of the rainfall. Nonetheless, flooding impacts will be possible anywhere training rainfall or intense rainfall rates develop, especially in urban areas and areas of complex terrain. .Central Gulf Coast and Florida... In the short term, flash and urban flooding is likely across portions of central FL as a low pressure system continues to move onshore, bringing locally intense rainfall rates of up to 4"/hr and the potential for localized totals between 4 - 7". Regardless of antecedent conditions, the expected intensity of rainfall will likely exceed infiltration and drainage capacities, and flash and urban flooding is expected should these higher rates materialize. This is supported by the NWM SRF, which is beginning to highlight the potential for rapid-onset flooding across portions of the region, with the greatest consistency from Orlando eastward along the coast from Palm Coast to Palm Bay. Looking ahead, the potential for flooding impacts continues to increase across the region as multiple rounds of moderate to heavy rainfall are expected through the forecast period. Rainfall is expected to range from 2 - 5" (7-day totals), with higher totals of 5 - 7" (locally higher possible) along the Central Gulf Coast as tropical moisture surges into the region, bringing a prolonged period of heavy rain, especially across southeastern LA. Antecedent conditions across this area are more dry, and flooding may initially be limited by sandy, well-drained soils and generally near-normal streamflows. However, repeated rounds of rainfall, with efficient warm cloud processes capable of producing very high rainfall rates, could eventually overwhelm local infiltration capacity and lead to flooding impacts. Across the FL Peninsula, antecedent conditions are wetter following several days of rainfall, and streamflows are locally elevated, with isolated minor flooding forecast later this week. While sandy soils and karst topography will still help absorb initial rounds of rainfall, capacity may be exceeded more quickly given the existing wet conditions. Urban corridors along I-10 in the Central Gulf Coast and I-95 in FL remain particularly vulnerable to flash flooding due to impervious surfaces and poor drainage in some areas. .Northern Plains into the Upper Midwest... Isolated flash and urban flooding is possible across portions of central MN and northern WI today and in the Quad Cities region through day 2 (Wed). Antecedent soil conditions have recovered since the previous rainfall event (50 - 65% RSM, 0 - 10 cm, NASA SPoRT) however, streams and rivers are still running higher than normal for this time of the year, suggesting the hydrologic environment remains somewhat vulnerable, particularly in areas with flashy responses or limited channel capacity. While widespread flooding is not expected, isolated flooding impacts cant be entirely ruled out, especially if higher rainfall rates materialize in urban areas. After a brief reprieve in rainfall on day 3 (Thu), additional rainfall returns to the region on days 4 - 7 (Fri - Mon), although each round appears modest (less than 1.5"), and the placement of the highest QPF each day does not overlap. However, given the current convective pattern and differences in model guidance, the exact location and magnitude of any potential hydrologic responses remain uncertain. .Southwest... Isolated flash flooding is possible this week across portions of AZ and NM as monsoonal moisture increases. Given ongoing drought conditions, rainfall will be mostly beneficial in this region, but heavy downpours may lead to flooding over sensitive basins, urban areas, complex terrain, and burn scars. The greatest potential will be in southeast AZ today and NM on day 3 (Thu). A drying trend is expected to gradually reduce flood potential by the weekend. .Ohio and Tennessee Valleys... A wet weather pattern bringing daily rounds of rainfall through the forecast period will increase the potential for isolated flooding impacts. Antecedent soil conditions are generally near normal to slightly wet and streamflows are near to below normal for this time of the year. Combined with the expected progressive nature of the convection, this should initially allow for adequate infiltration. However, each subsequent round may further increase hydrologic vulnerability, particularly in areas that experience repeated rainfall. The greatest potential for flooding impacts will be in areas where high rainfall rates or training storms develop, which could quickly overwhelm current ground conditions and lead to enhanced runoff and rising streamflows. For now, confidence in the exact placement or magnitude of any hydrologic responses remains low given the extended timeframe. //Freeman $$