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

$$