945
AGUS74 KWCO 291517
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1017 AM CDT SAT JUN 29 2024

.Synopsis...
Renewed flooding possible next week for the Upper and Middle Mississippi
Valley.... Isolated flooding potential across portions of the Northeast
today... Daily convection across the Four Corners Region... Heavy rainfall
potential early-to-mid next week across Puerto Rico/USVI as TS Beryl tracks
south of the region... Increased snowmelt and glacier runoff in Alaska...

.Discussion...

.Upper and Middle Mississippi Valley...
Widespread moderate to major river flooding is ongoing across far southeast
SD, southern MN, and northern IA and is forecast through next week along
the Missouri (moderate) and Mississippi (moderate to major) River
mainstems. Rain returns to the region beginning day 3 (Mon) and lingers
through day 5 (Wed). Ample deep layer soil moisture remains in place (60 -
80% relative soil moisture (RSM) 0 - 100 cm NASA SPoRT), suggesting that
the already elevated/flooded rivers across the region will likely respond
fairly efficiently to the expected rainfall/runoff. Generally 1 - 2" inches
of rain is expected for the entire event, which is likely not enough to
cause widespread new and renewed river flooding, however some basins could
see some new and renewed river rises/flooding (National Water Model (NWM)
Medium Range forecast (MRF) High Water Probability) if heavier totals (2 -
3"+) materialize with any convection. At the very minimum, delayed
recessions of ongoing flooding and isolated flash flooding can be expected.

New river flooding impacts will be possible, with some new and renewed
rises into minor and moderate flood being possible (HEFS, CR Ensemble QPF
hydrographs) if the heavier aforementioned rainfall totals come to
fruition. The NWM MRF (NBM and GFS forced) continue to indicate potential
for widespread new and renewed river rises early next week in response to
this rainfall with peak flows mostly on days 4 - 7 (Tue - Fri) across
southern MN, western WI, and IA. The magnitude of response is still
uncertain, but the NWM MRF is indicating potential for 4 - 20% AEP flows on
many smaller tributary rivers across the aforementioned region, so trends
will need to be closely monitored heading into next week.

.Northeast...
Moderate to heavy rainfall today (Sat) will bring the potential for
isolated flash and urban flooding to portions of eastern OH,
western/northern PA, and western NY. Soils are generally moist, with room
for infiltration (50 - 65% RSM, 0 - 10 cm NASA SPoRT). Though there is
available infiltration capacity, prolonged periods of moderate-to-heavy
rain could overwhelm soils, increasing the chance of rapid runoff and
flooding impacts, especially in any areas of complex terrain. The
HRRR-forced NWM Short Range Forecast (SRF) has consistently been signaling
potential for small stream flooding across northeast OH, through northwest
PA, and into western NY. This is where rapid onset flooding (ROF)
probabilities are highest (25%), albeit still relatively low. This is the
area that received 1 - 3" of rain over the past 2 days as well, and will
see some additional priming rainfall today ahead of the more intense
rainfall later this afternoon/evening, so isolated flooding impacts can be
expected.

.Four Corners Region...
Daily scattered thunderstorms will bring the potential of isolated flash
and urban flooding to the Four Corners region through next week. Locations
that have received multiple rounds of rainfall over the past week are most
susceptible to flooding impacts as soil moisture increases. The highest
flood threat is in areas with recent burn scars, slot canyons, dry washes,
and regions where training and more persistent storms occur.

.Puerto Rico/USVI...
Moderate to heavy rainfall early-to-mid next week will bring the potential
for isolated flooding impacts across the islands. Streamflows across the
region are generally normal to above normal in comparison to both the daily
and annual climatological normals, suggesting soil capacity is nearing
saturation in response to recent rainfall. This increases the potential for
rapid runoff and flooding concerns, and trends in forecast rainfall amounts
will need to closely be monitored heading through the weekend as Tropical
Storm Beryl progresses west.

.Alaska...
Recently warm temperatures continue to lead to increased snowmelt and
glacier runoff, leading to rivers running high in areas across southern AK.
Minor flooding on the Chilkat River near Klukwan continues through at least
the weekend. Also, elevated flows and localized flooding is possible along
the Skwentna, Yentna, and Nuyakuk Rivers.

//JEC

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