####018006296#### AGUS74 KWCO 021508 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT THU MAY 2 2024 .Synopsis... Considerable flooding impacts possible today for Texas and the Lower Mississippi Valley... Isolated flooding impacts remain possible across portions of the Central and Southern Plains into the Midwest... Potential for isolated flash and urban flooding impacts continues for Puerto Rico and the USVI... Snowmelt runoff and ice jams are causing isolated river and small stream impacts in Alaska... Localized flooding impacts possible and river rises expected in Northern California and the Pacific Northwest... Ongoing small stream and river flooding across the Great Basin and Intermountain West... .Discussion... .Texas and the Lower Mississippi Valley... Considerable flooding impacts, including new and renewed moderate to isolated major river flooding and significant small stream, flash and urban flooding, are possible in portions of eastern TX today as widespread 2 - 5" (locally up to 9") of rainfall has already fallen and up to 5" will be possible locally today. NASA SPoRT data indicate that soils top and mid-layer soils remain near saturated from recent rainfall and streamflows remain much above normal (USGS) in the region. As a result, rainfall is expected to quickly become runoff, and intense rainfall rates will only reduce time to runoff if they occur. Portions of the Trinity and Neches rivers remain in flood stage this morning, and renewed rises on these rivers and new rises on other rivers in the region are expected. Considering the antecedent soil conditions and rainfall forecasts, significant flash, urban, and small stream flooding is also possible in these areas. The HRRR-forced NWM Short-Range Forecast (SRF) continues to indicate the potential for rapid rises on small streams with Rapid-onset Flooding probabilities generally greater than 50% and locally exceeding 75%. Additionally, widespread SRF AEPs between 2 - 4% exist between Waco, Austin, and Houston, TX helping to increase confidence in significant small stream rises. The focus shifts toward the ArkLaTex and along the TX/LA border and into the Lower MS Valley this afternoon though tonight, where 1 - 2" of rainfall is expected. Top and mid-layer soils are also wet to near saturated in these areas, but streamflows are a mix of above to much above normal. Isolated flash, urban, and small stream flooding impacts and minor river flooding are possible. Moderate to heavy rainfall will be possible days 3 into 4 (Sat into Sun) over portions of west Texas, bringing the potential of flash and urban flooding to the region. .Central Plains into the Midwest... Minor to isolated major river flooding is ongoing or forecast over southeastern KS, through MO, and into western IL. Many locations have crested or are cresting over the next couple of days with only a few locations experiencing broader crests from routed flows into this weekend. Steady rainfall totalling 1 - 2", with locally higher amounts possible, will continue to threaten the region through 2 (Fri) with additional flooding impacts. Soils remain wet (0 - 100 cm, NASA SPoRT) and streamflows are generally above normal (USGS), creating favorable conditions for rapid runoff into elevated streams. Additionally, isolated flash and urban flooding impacts can not be ruled out across the entire region, particularly where training occurs. Isolated minor river flooding continues in portions of IA and MN from previous rainfall. Moderate rainfall totals of 1 - 2" are forecast through portions of the Midwest with the bulk of the forecast rainfall occurring through day 2 (Fri). This may result in isolated new and renewed rises on smaller streams. Drier conditions settle across the area for a few days before another wet pattern is forecast to return by day 5 (Mon), but the confidence in exact placement and magnitude of forecast rainfall is low due to the extended timeframe. The NWM MRF continues to signal AEPs are around 50% with some isolated smaller order streams signaling AEPs as low as 20% lending confidence that most small stream rises will not be significant. .Puerto Rico and the USVI... Persistent rainfall over the next several days will continue to provide a threat of flooding impacts, including mudslides, across PR and the USVI. Soils remain saturated across PR and streamflows remain elevated, especially across the eastern half of the island. The heaviest rainfall is expected on days 2 and 3 (Fri and Sat). Considering the antecedent conditions, any additional heavy rainfall will likely lead to rises on rivers and isolated flooding impacts. .Alaska... Flooding impacts from spring breakup and snowmelt runoff will continue for the next several days and beyond. Out-of-bank flows on Moose Creek and Trooper Creek near Glennallen could impact Glenn Highway and the surrounding floodplain. An ice jam on the Nushagak River between Dillingham and Portage Creek has caused localized flooding across the floodplain. An ice jam is in place on the Tanana River downstream of Manley, and has caused some minor flooding within the town. Finally, ice jams have been reported on the Yukon and Forty Mile rivers in Canada with the breakup front reaching Eagle yesterday, flooding will be possible in the area if any jams form near the town. .Northern California and the Pacific Northwest... Moderate to heavy rainfall over northern CA, OR, and western WA will bring a threat for localized flooding impacts to those areas. Rises on rivers are also expected, but river flooding is not anticipated at this time. .Great Basin and Intermountain West... Isolated minor to moderate river flooding and elevated flows will continue along area rivers, creeks, and streams across portions of southern ID and northern NV in response to runoff from snowmelt and recent rainfall. //Watson/GKendrick $$