####018006528#### AGUS74 KWCO 061523 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT MON MAY 6 2024 .Synopsis... Considerable flooding impacts continue in portions of East Texas... Isolated flooding impacts through Tuesday morning portions of the Southern and Central Plains ... Isolated flooding impacts possible through Wednesday in Central and Eastern Montanna... Isolated flooding impacts possible across the Middle Mississippi, Lower Ohio, and Tennessee Valleys, Puerto Rico and the USVI, and Alaska through mid week... Isolated snowmelt induced flooding continues in portions of the Great Basin and Intermountain West... .Discussion... .East Texas... Considerable river impacts are ongoing and will continue through much of this week across portions of southeast Texas. Major river flooding will continue this week along the Neches, West Fork San Jacinto, and Trinity rivers, with scattered moderate river flooding impacts throughout much of east Texas. Rivers should be able to recede unimpeded as QPF on any given day is expected to be less than 1" and the heaviest 7 day total is expected to be over the ARKLATEX (1 - 2", WPC). .Southern and Central Plains... Thunderstorms this evening into tonight will bring the potential for localized flooding impacts to portions of eastern Oklahoma into the Ozarks and northward into Iowa. Soils within this region are near-saturation with soil moisture exceeding 70% (0 - 10 cm RSM, NASA SPoRT) in eastern Oklahoma, and Kansas into the Ozarks. Though this suggests there is some available infiltration capacity, the combination of heavy rainfall and complex terrain will result in rain quickly converting into overland flow and running off into already elevated streams (USGS). Additionally, this will enhance the flash flood potential across the region. With the convective nature of thunderstorms this afternoon, the HRRR is most likely doing a poor job at depicting where storms will be in Oklahoma therefore, the probabilistic services of the National Water Model (NWM) Short Range forecast (SRF) are most likely underrepresenting the flooding potential. The deterministic NWM SRF does indicate some potential for small stream rises with isolated High Flow Magnitude Forecast (HFMF) AEPs as low as 10% in eastern OK. Both flash and small stream flooding impacts in Oklahoma are going to depend on a slow moving or training thunderstorm moving over a vulnerable location. For eastern Kansas into Iowa, storms should be less isolated. Though it is a little early for NWM SRF probabilities, the GFS-forced Medium Range Forecast (MRF) is indicating low-end probabilities for rapid-onset flooding. The most recent run of the SRF has also started to indicate the potential for rapid-onset flooding for portions of eastern Kansas. SRF AEPs within this region are generally between 20 - 50% with isolated values near 4% indicating the potential for isolated significant flows on small streams. Soils in northeast Kansas, northern Missouri, and Iowa are a little drier with soil moisture near 50% within those regions. This will allow for increased infiltration capacity however, with the less isolated and potentially training nature of these storms, these soils will most likely become overwhelmed as well but it will take additional time. .Central and Eastern Montana... Periods of rain through day 3 (Wed) are expected across the region, will likely produce small stream rises and potentially isolated minor to moderate river flooding on the Milk River. Isolated flash flooding cannot be ruled out either. The NWM SRF does indicate a localized potential for rapid-onset flooding with a small area of probabilities greater than 50% south east of Billings. Though this is most likely over done, it does hint at the potential for rapid rises on streams within the region. Additionally, HFMF AEPs are generally near the highwater threshold, with isolated values near 4%. This suggests that though some small streams may see some significant flows, most streams should remain within banks. .Middle Mississippi, Lower Ohio, and Tennessee Valleys... Rainfall shifts east across the Middle Mississippi, Lower Ohio River, and TN Valleys through day 3 (Wed) where isolated small stream and flash flooding will be possible. There is ample soil infiltration capacity and rivers are generally flowing at near normal levels (USGS) with exception to portions of the lower Ohio Valley, so most basins across the region should be able to handle the large majority of the expected rainfall (1 - 3"), and flooding impacts should be isolated there. Rainfall this morning over portions of TN/KY and northern MS has increased soil moisture, some with isolated values greater than 65% (0 - 10 cm, NASA SPoRT), potentially increasing the flooding potential on day 3 (Wed) across these regions. Even with the increased soil moisture, training or stationary thunderstorms will most likely be required to result in impactful flooding outside of urban areas. .Puerto Rico and the USVI... Persistent rainfall through mid week will continue to provide a threat of flooding impacts, including mudslides and flash flooding, across PR and the USVI. Soils remain saturated across PR and streamflows remain elevated. Considering the antecedent conditions, any additional heavy rainfall will likely lead to rises on rivers and flooding impacts. .Alaska... Significant rises on Moose creek near Glennallen due to snowmelt runoff are expected and minor flooding is already occurring. The ice breakup front has already passed Eagle and is 50 miles upstream from Circle as of Saturday afternoon. There is potential for minor to moderate flooding in Circle as a heavy run of ice moves through. An ice jam that caused flooding in Kalskag has released and water levels are subsiding, however, there is potential for a rejam to impact Kwethluk. .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. //GKendrick $$