####018003248#### AGUS74 KWCO 211512 HMDNWC National Hydrologic Discussion - EXPERIMENTAL NWS National Water Center - Tuscaloosa AL 1015 AM CDT THU MAR 21 2024 .Synopsis... Isolated flooding impacts possible in Southern Plains into the Lower Mississippi Valley...Potential urban flooding in South Florida...Flash, urban, and small stream flooding impacts this weekend for Coastal Mid-Atlantic and Northeast...Ongoing river flooding with potential renewed rises late this week into the weekend in the Southeast... .Discussion... .Southern Plains into the Lower Mississippi Valley... Isolated flooding impacts, along with minor riverine flooding, will be possible in response to locally heavy rainfall through day 1 (Thu) along portions of the eastern Southern Plains and western Lower Mississippi Valley. Soils (NASA SPoRT) and streamflows (USGS) are generally around normal, suggesting widespread flooding impacts should be mitigated and only isolated hydrologic responses can be expected. Additionally, the primary riverine concern may be limited to a few isolated new rises or slowed recessions. .South Florida... Isolated urban flooding is possible day 2 (Fri) and day 3 (Sat) due to locally heavy rainfall of 2 - 5" (WPC QPF) particularly over the southern FL I-75 and I-95 corridors. Dry soil conditions (NASA SPoRT) and ample storage in area streams and rivers (USGS) will help to mitigate a majority of potential flooding impacts, which will serve to contain the flood threat primarily to low-lying and poorly drained urban areas. .Coastal Mid-Atlantic and Northeast... Isolated flash, urban, and small stream flooding impacts will be possible beginning day 2 (Fri) through day 3 (Sat) for portions of the coastal Mid-Atlantic region into the Northeast. A frontal boundary positioned across the Eastern Seaboard may produce training convection with moderate to locally heavy rainfall producing totals of up to 4" (WPC QPF), particularly over portions of DE and NJ. The National Water Model (NWM) Medium-Range Forecast (MRF) is signaling scattered rapid-onset flooding probabilities and isolated AEPs near 10% in the lower order stream reaches. Riverine responses are also expected with ensemble guidance (MMEFS) indicating minor to isolated river flooding will be possible in northern NJ and RI. .Southeast... Minor river flooding will continue to recede unimpeded through day 1 (Thu) as dry conditions continue to prevail across the region. A couple rounds of rainfall beginning on day 2 (Fri) may bring renewed rises or delayed recessions across the region. Ensemble guidance (MMEFS) indicates minor to isolated moderate riverine flooding is possible across the region in response to the forecast rounds of rainfall. Urban and small stream flooding impacts will also be possible as moderate to locally heavy rainfall associated with disturbances that are forecast to sweep across the region. The NWM MRF indicates scattered low-end rapid-onset flooding across the region, suggesting widespread flooding impacts should not be expected. //Capp/Whisnant $$ ####018004003#### AGUS76 KRSA 211514 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 830 AM PDT Thu Mar 21 2024 ...A LOW PRESSURE SYSTEM WILL BRING PRECIP TO THE REGION FRIDAY INTO THE WEEKEND... ...ANOTHER SYSTEM WILL BRING ADDITIONAL PRECIP CHANCES TO THE NORTH EARLY NEXT WEEK... .METEOROLOGICAL CONDITIONS (SHORT TERM: THU AM - SUN AM)... A low pressure system around 45N and 140W with high pressure over the region this morning bringing generally dry conditions during the day today. The low pressure system strengthens a little as it approaches the west coast tonight with the cold front reaching the Nrn CA coast Friday morning and moving through the region into Saturday. The low is off the Pac NW coast Saturday with trough moving into the region. Moisture plume about an inch along the CA coast ahead of this system. Light precip along the NW CA coast early Friday morning then increasing and spreading south and east across the region as the front moves through. Precip spreads to around the I-80 corridor Friday afternoon and into Central CA and Srn Sierra and Nrn Nv Friday night and into Srn CA and Ern NV on Saturday as weakening front moves through the region. Precipitation amounts through Saturday night are expected to generally be around 1.5-3.5 inches with local amounts to around 4 inches along the NW CA coast and 1-3 inches for the Shasta Basin and Nrn and Central Sierra and 1- 2 inches for the Srn Sierra and 0.5-1.5 with local amounts up to 2 inches for the Central Coast and 0.25-0.75 for Sac Valley and 0.1- 0.75 for SJ Valley and generally half an inch or less for Srn CA. Freezing levels around 6500 ft over NW CA coast and around 7000-8000 ft for the Nrn Sierra and 8000ft and higher elsewhere Friday morning and dropping to around 3500-5000 ft behind the cold front over Nrn and Central CA Friday night and around 5000-8000 ft over Srn CA and NV Saturday dropping to around 3500-5500 ft over most of the region Saturday night. .METEOROLOGICAL CONDITIONS (LONG TERM: SUN AM - WED AM)... The axis of the broad upper level trof is forecast to begin shifting inland by Sunday morning, with s/wv activity on the upstream portion of the trof providing support for additional shower activity across the forecast region. Best chances for precipitation on Sunday are for coastal southern California (up to 0.5 inches) with lighter amounts (0.20 inches and lower) over central California from the Coast to the Sierra (lower in the San Joaquin Valley and northern Sierra) and a few tenths over the North Coast. Precipitation will diminish across the south on Monday as the upper level trof begins to shift further inland. Additional and weaker s/wv activity is forecast to produce light precipitation across the northern portions of the forecast region with up to 0.25 inches over the Smith basin and lighter amounts over the northern Sierra and northern Nevada. Chances for heavier precipitation ramp back up on Tuesday as a digging trof and surface low push enhanced moisture transport into northern California. Current guidance differs on timing and exact magnitude of this system, but forecasts currently suggest over an inch of precipitation in the Smith Basin, half an inch over the Shasta Basin, and a ~0.25 inches over the northern Sierra and North Bay. Only a few hundredths of an inch are currently forecast for the Sacramento Valley. Forecasts will continue to update as guidance begins to converge on a solution. Freezing levels are forecast to start the forecast window around 4,000 feet in the North and 5,000 feet in the south, rising slightly on Monday before lowering across the north again on Tuesday to below 4,000 feet. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php Osborne/CH $$