Quantitative Precipitation Forecast
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309 FOUS30 KWBC 131422 AAB QPFERD Excessive Rainfall Discussion...UPDATED NWS Weather Prediction Center College Park MD 1022 AM EDT Thu Jun 13 2024 Day 1 Valid 1422Z Thu Jun 13 2024 - 12Z Fri Jun 14 2024 ...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN FLORIDA... ...1420Z Update... After collaboration with the local Miami WFO, have opted to upgrade a portion of the southern FL Peninsula to a High Risk to account for significant impacts expected with the next round of heavy rainfall over extremely sensitive areas that include the urban corridor in Southeast FL through the I-75 corridor over Alligator Alley. Additional totals of 2-5" are likely with locally as high as 10+" in isolated locations along the southwest coastal areas extending through the interior of the Peninsula. Considering the ongoing flooding with many reports of standing high water and the historically low FFG indices for all 1/3/6/12 hour intervals, the prospects for significant impacts will continue through the afternoon and evening. Thus, the High Risk was issued to account for the general expectation. Kleebauer ...Previous Discussion... ...Florida... Several inches of rain focused over South Florida yesterday which has left soils water logged and have lowered the 1/3/6 hr FFG to as low as 0.25 inch. The latest hi-res guidance show another very heavy band developing potentially over the same areas by late morning and into the afternoon hours. It will take very little additional rain to aggravate ongoing flooding in rural and urban locations. A Moderate was raised for a majority of the southern counties which includes the Miami metro where areal averages with be around 3 inches with isolated maximums up to 8 inches possible per hi-res guidance. Totals in the periods prior will be running between 3-12" for an areal average across the above corridor with some maxes approaching 15" in the areas that have been hit the hardest over successive days. Considering the repeated nature of the heavy precip, expectation is for more flash flooding to arise late Thursday morning through the afternoon as diurnal destabilization within the convergent axis provides another round of significant rainfall for those that have seen a prolific amount already. ...Midwest... Shortwave over the Northern Plains will pivot around the northern periphery of the mid-level ridge located across the Southwest U.S with sights on the central Midwest by Thursday afternoon. At the surface, a cold front will be pressing south-southeast over portions of the Central Plains through the Mid-Mississippi Valley. The coupling of the two distinct features in the midst of a prolific thermodynamic regime located over the above area (MLCAPE exceeding 4000 J/kg) will help initiate a robust line of convection with cores capable of locally enhanced rainfall as they move southeast with the forecast steering flow. The Marginal Risk was maintained to allow for more consensus with guidance as they get inside 24 hrs of the event. While there continues to be some variance in where the convection will be, consensus favors a line from the borders of Iowa/Missouri/Illinois to east/northeast of Chicago where areal averages of 1 to 3 inches are forecast. The environment may be conducive for locally significant rainfall in the strongest convective cores, particularly if backbuilding cells become anchored to the front. Campbell/Kleebauer Day 2 Valid 12Z Fri Jun 14 2024 - 12Z Sat Jun 15 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHERN FLORIDA... ...South Florida... The frontal boundary will begin to sink south as a cold front through central Florida during this period and heavy rain will continue across South Florida. Although the PW values across the state will be reducing there will still be adequate moisture to help produce and additional 1 to 2+ inches over the over-saturated region. A Slight Risk remains in effect for South Florida and a Marginal Risk for central Florida. ...Rockies and Plains... A strong upper level disturbance exits northeast out of the Four Corners with a strengthening low in the lee of the Rockies. Scattered heavy rain signatures with some isolated totals exceeding 2" are forecast. Local enhancement of QPF is expected within the higher elevations of northeast New Mexico otherwise the bulk of the high QPF is expected across the Central Plains, roughly from Boulder to Sioux Falls and could easily pick up 1 to 3+ inches of rainfall. A vast majority of this region has 3-hr FFG near 1.5/2 inches however there are very isolated locations as low as 0.25 inch. A Marginal Risk is in effect from northeast New Mexico to Iowa/Minnesota/South Dakota. There may be a need for a small Slight Risk area with future updates if QPF trends continue to increase. ...New England... A cold front will advance through Ontario/Quebec and reach the Northeastern U.S during peak diurnal destabilization. Convection is expected to develop along and ahead of the front and will be capable of isolated heavy rain instances from Pennsylvania to New England and into the Canadian maritimes. The highest QPF is focusing across southeast New England where guidance suggests areal average of 1 to 2 inches. The progressive nature of the convection will limit the threat to marginal territories, although the urbanization factors in-of the Lower Hudson up through southern New England could produce some locally enhanced risks if a storm overperforms. Campbell/Kleebauer Day 3 Valid 12Z Sat Jun 15 2024 - 12Z Sun Jun 16 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF IOWA, MINNESOTA AND WISCONSIN... ...Upper Mississippi Valley to Southern Plains... During this period a cold front will be pushing through the Northern Plains while a warm front lifts from the Central Plains into the Upper Mississippi Valley. PW values of 1 to 1.5 inches will be drawn into this system, reaching a peak of +2 standard deviations above average over Iowa and Minnesota. There will be strong mid-level ascent embedded with this pooled moisture which will help enhance rainfall amounts and coverage from the Plains to the Upper Mississippi Valley. Guidance is showing 1 to 3 inches will be common although local maximums may reach 5 inches. A Slight Risk is in effect from northwest Iowa to west-central Wisconsin. A Marginal Risk area spans from North Dakota eastward to Lake Michigan and southwest to Oklahoma. ...South Florida... Convection is expected to linger nearing the decaying front boundary and may produce an additional 1 inch or so. The soils will be over-saturated and sensitive to any additional rainfall. A Marginal Risk is in effect given the ongoing flooding concerns. Campbell Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt