AGUS74 KWCO 281517 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT MON APR 28 2025 .Synopsis... Considerable flash and urban flooding possible across the Southern Plains into the Middle Mississippi Valley...Isolated flooding across the Northern Plains and Upper Midwest...Considerable flooding possible in Puerto Rico and the USVI...Rain and snowmelt induced flooding in Montana...Significant flooding continues along the Lower Mississippi River... .Discussion... .Southern Plains into the Middle Mississippi Valley... Considerable flash and urban flooding will be possible again on day 2 - 3 (Tue - Wed), with isolated river flooding also possible. Past rainfall over the last 48 hours (1 - 4" locally higher, MRMS) has resulted in increased soil moisture and stream flows over the region, with the Deep Red Creek near Randlett, OK and East Cache Creek near Walters, OK reaching moderate to major stages, respectively. These are not expected to fall out of flood stage until mid-week. This wet pattern that has taken shape over the region over the past several days has contributed to wetter soils (60 - 75%, 0 - 10 cm RSM, NASA SPoRT) and elevated streamflows to much above normal historical flows, indicating diminished infiltration capacity and vulnerability to hydrologic responses. Any additional rainfall may quickly overwhelm current capacity, leading to rapid runoff into nearby urban drainages and small streams. Overflowing of ditches/culverts/storm drains and areas of standing water in typical flood prone areas are possible. Significant stream rises and flooding may occur in areas where storms reoccur and where more robust rainfall rates materialize, especially in portions of southern OK/northeast TX . The National Water Model (NWM) Medium Range Forecast (MRF) is signaling low annual exceedance probabilities in portions of OK and northeast TX. While the GFS model runs show an extensive, aggressive pattern, the NBM displays probabilities more so near 50% with isolated probabilities as low as 2% suggesting locally considerable small stream responses are also possible. .Northern Plains and Upper Midwest... Multiple rounds of showers and thunderstorms through today will bring the potential for isolated flash and small stream flooding to portions of the Dakotas through WI. Antecedent soil conditions are generally mixed across this region however, areas with wetter soils occur in portions of south-central SD and much of IA (50 - 75% RSM, 0 - 10 cm NASA SPoRT). Regardless of the soil conditions, isolated enhanced rainfall rates may locally overwhelm infiltration capacity and lead to flooding of ditches, culverts, and low water crossings, as well as standing water in fields, on roadways, and in typical flood prone areas across the region. .Puerto Rico and the USVI... Repeated rounds of heavy rainfall will likely generate urban and small stream flooding across the region through much of the week, with considerable impacts possible. Mudslides, rapid river rises, and flash flooding will become increasingly likely as soils become more saturated, especially in areas of steep/hilly terrain. .Montana... A combination of rainfall (1 - 2") and snowmelt may produce areal and small stream flooding impacts across portions of south-central MT through today. The most vulnerable areas are the Beartooth, Abasroka, Crazy mountains and associated foothills. Any heavy rainfall over areas of frozen ground could generate immediate runoff into nearby small streams and rivers, leading to rapid rises, flooding of low-lying and poorly drained areas as well as minor flooding. A drier pattern for the remainder of the week should largely mitigate more widespread and significant small stream responses. .Lower Mississippi River... Significant river flooding along the mainstem of the Lower Mississippi River (AR/MS/LA) will continue for the foreseeable future as the flood wave continues downstream. Significant rises are still expected from just downstream of Vicksburg to New Orleans this week into early next week. Showers and storms are expected across the region over the next several days, which may briefly delay ongoing recessions and crests however, renewed rises are not expected. //TMK $$