Hydrometeorological Discussion
Issued by NWS
Issued by NWS
432 AGUS74 KWCO 191442 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 0942 AM CDT SAT OCT 19 2024 .Synopsis... Isolated flooding potential in the Southern Rockies into Southern Plains... Ongoing river flooding in Florida... Prolonged period of rainfall and flooding potential for Puerto Rico and the USVI... Weekend rainfall for Western Washington... .Discussion... .Southern Rockies into Southern Plains... Rounds of heavy rainfall will impact eastern New Mexico through tomorrow morning, bringing potential for localized flooding impacts, some of which may be significant in eastern New Mexico. Over the past 24 hours rainfall totals of .5 - 3" (MRMS) have begun to wet soils, though the heaviest rainfall is forecast tonight, with additional rainfall totals of 2 - 4"+ possible. Antecedent conditions remain climatologically dry, mitigating any widespread hydrologic response, though potential for localized cell training may result in excessive runoff and flooding of rivers, creeks, streams, and other low lying and flood prone areas. Terrain enhancement and orographic lift will add to the flooding threat, particularly in vulnerable recently burned areas. The National Water Model (NWM) Medium-Range Forecast (MRF) is signaling peak flow arrival times in the 30 - 40 hour range on the majority of smaller streams in the middle-to-upper Canadian and Upper Beaver Basins. Though peak flows on the main stem rivers are forecast in 3 - 5 days. Agreement between NBM and GFS NWM MRF annual exceedance probabilities (20 - 4%) increases confidence in small stream responses if rainfall totals materialize, though due to the number of ephemeral streams in the region and its impact on the NWM`s statistics, signals may be overdone. The NWM Short-Range Forecast 12-hour rapid onset flooding probabilities are increasing, with probabilities generally within 25 - 50% in many small basins between Santa Fe and the NM/TX border. Additionally, the 18-hour deterministic rapid onset flooding forecast is signaling over 70% waterway length flooding in the same region, supporting the likelihood of rapid onset flooding. Overall model agreement adds to confidence that small stream responses are likely, and recently burned areas remain especially vulnerable. .Florida... Major flooding will continue along the St. Johns and Withlacoochee rivers into next week. Little to no precipitation over the next week should allow for unimpeded recessions of elevated rivers across the central FL. .Puerto Rico and the USVI... A continued wet weather pattern into next week will extend the potential for flooding of urban areas, roads, small streams, and washes, as well as isolated flash floods. Successive days of rainfall moistening soils and elevating streamflows into mid next week will increase the risk of flooding, mudslides, and rapid river rises. .Western Washington... An atmospheric river will bring rainfall to the region through day 2 (Sun). Flooding impacts are not expected due to the dry antecedent conditions and much below normal streamflows (USGS) in place ahead of this rainfall. Nonetheless, there will be non-impactful within-bank river rises across basins draining the Olympics and western slopes of the Cascades. Nuisance urban flooding including water ponding over roadways and flooding associated with low lying poor drainage areas is possible. //Ayala $$