Quantitative Precipitation Forecast
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741 FOUS30 KWBC 131558 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Thu Jun 13 2024 Day 1 Valid 16Z Thu Jun 13 2024 - 12Z Fri Jun 14 2024 ...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHERN FLORIDA... ...16Z Update... A SLGT risk was issued across portions of the central Midwest through the Mid-Mississippi Valley for later this evening. Advancing cold front will move south-southeast out of the northern Midwest later this afternoon with an increasing convergence pattern along and ahead of the front. Ahead of the boundary, some significant increase in areal theta-E`s will prompt an improving environment for convection and heavy rain potential. Soundings out of KILX this morning were approaching the 90th percentile for PWATs with a value of 1.37", and only expected to increase prior to the incoming convective event. Latest 12z HREF neighborhood probabilities have increased from prior runs for the upper thresholds of >3" and >5" with the former running between 25-40% in a broad area from the IA/MO border across into northern IN. 5" probabilities are running between 10-15% across central IL which is the consensus for best area to see the max potential rainfall. Totals of 2-3" with upwards of 6" are going to be littered across the outlined area within the SLGT as discrete supercell development ahead of the front potentially garnering some scattered heavy rain chances even prior to the upscale growth pattern along the boundary as it slowly moves southward. In coordination with the central Midwest WFO`s involved, the SLGT risk was agreed upon given the favorable environment and forecasted probabilities. The High Risk across FL was maintained from the previous special update as the area from Fort Meyers/Naples over to the other coast near Miami/Fort Lauderdale will see another round of significant rainfall to exacerbate the remnant flooding in place from the past few days. The highest threat aligns with the I-75 corridor across into the urban areas extending from just north of FLL down into Miami proper. Latest 12z HREF probabilities correlate well with the expectation for at least 2-3" as the fields are both respectively above 90% for the neighborhood probability, coast-to-coast along the southern peninsula. Even more impressive is a swath of 20-35% EAS probabilities for at least 3" running along the aforementioned area which given the conservative nature of the EAS field is statistically significant. The High Risk aligns very well with the EAS field in question adding confidence to the issuance of the risk. The rest of central and southern FL will see scattered instances of significant rainfall with totals between 2-4" with locally as high as 8" within the SLGT/MDT risks surrounding the High risk area in place. Heaviest rainfall will occur this afternoon through the evening before some marginal clearing of precip overnight. ...1425Z 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