Quantitative Precipitation Forecast
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568 FOUS30 KWBC 072228 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 628 PM EDT Fri Jun 7 2024 Day 1 Valid 2212Z Sat Jun 08 2024 - 12Z Sat Jun 08 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL PLAINS... ...22Z Update... Expanded the Marginal Risk area some towards the south-southwest and (moreso) to the west, based on the current observational and mesoanalysis trends, especially across central and south-central NE. Starting to get hint of some upscale growth potential late this afternoon per the mosaic radar and longwave IR satellite imagery. Given the highly favorable thermodynamic environment in the warm sector (ML CAPEs 2000-3000+ J/Kg and PWs of 1.5-1.75"), the strongest supercells will be capable of 2-2.5+ inch/hr rainfall rates within the forward flank downdraft. As a result, isolated/localized flash flooding will be a concern anywhere within the Marginal Risk area, with the potential for more scattered instances of flash flooding within the Slight Risk area. Hurley ...16Z Update... General continuity from the previous forecast with some minor adjustments of the SLGT risk to account for the latest forecast QPF accompanying the expected MCS. HREF and associated CAMs are in good agreement on the axis of heaviest precip expected from this evenings MCS across the central plains into the Mid-Mississippi Valley. HREF blended mean QPF is a solid stripe of 2-4" within the zone of the MCS influence with some deterministic output entering the 4-5" range despite the progressive nature of the complex. The the reasoning is due to increasingly favorable low to mid-level moisture advection occurring this evening from a developing nocturnal LLJ that will move rich Gulf air poleward into portions of the central plains and adjacent Mississippi Valley. Probability fields are fairly robust for both total precip and potential rates with the >3" neighborhood probability settling between 20-40% over a large area encompassing southeast NE through northeast KS and northwest MO. This was slightly better than even the overnight HREF iteration, likely in part to the better agreement among the CAMs members integrated into the ensemble. The prospects for rates exceeding 2"/hr also improved with an area of 30-45% located within the same zones above, and >3"/hr within low probabilistic means (10-15%), so certainly not zero and statistically significant considering the environment. As a result, the previous SLGT inheritance was generally maintained with a focus over southeast NE through the adjacent plains states, including KS/MO. A quick note on the setup across ME....increasing ascent within the confines of an approaching shortwave rounding the upper level circulation over Ontario will induce a period of convection across northern New England with a focus on northern NH into western ME. After some collaboration with the local WFO`s within the impacted area, a MRGL risk was entertained, but deemed unnecessary for the non-zero threat of flash flooding. Area soil moisture is running tremendously below average with much of western ME experiencing a class 2 (Severe) drought according to the National Drought Monitor. Outside pockets of heavier thunderstorms anchoring to the terrain in the White Mountains and northern Appalachian front in ME that could generate isolated flooding, much of the rainfall will be beneficial in the areas encompassing. Thus, refrained from any issuance, but will be an area to monitor pending the convective evolution. Kleebauer ...Previous Discussion... The setup continues to look favorable for a heavy rainfall event across portions of the Central Plains later today through tonight. Early morning analysis showed a strong ridge of high pressure anchored over the Four Corners into Texas while over the Central Plains, northwest flow is present. Across the Northern Rockies, shortwave trough energy is noted and it`s this feature that will dive southeast into the Plains later today to help ignite a few rounds of deep convection. In the lower levels, southerly flow in response will bring northward anomalous moisture with the PWs forecast to quickly rise above 1.5" through KS into southern NE. The favorable forcing aloft with the higher moisture and expected instability will ignite the storms and then the expectation is for the storms to grow upscale into a MCS as it moves into portions of Missouri and clip southwest Iowa. The 00Z guidance has come into better agreement on the details and expected locations of the heavy rainfall, with the 00Z HREF neighborhood probabilities for at least 3 inches jumping to above 50 percent now for far eastern NE, northeast KS, southwest IA, and northwest MO with a slight (10-15 percent) chance of 5" totals. Hourly rain totals may exceed 2 inches in localized spots. The Slight Risk was adjusted minimally to the north, to adjust toward the latest guidance and probabilities where the setup for training/repeating rounds is greatest. Taylor Day 2 Valid 12Z Sat Jun 08 2024 - 12Z Sun Jun 09 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF KANSAS, MISSOURI, AND THE EASTERN COLORADO FRONT RANGE... Previous SLGT risk area was maintained with a large expansion to the west to include all of southern KS, curving northwest into the eastern Colorado Front Range along with the inherited risk over eastern KS through the southern half of MO. The combination of a southward moving cold front in tandem with a strong mid-level shortwave ejecting out of the central Rockies will create a primed dynamical environment for widespread thunderstorm coverage and associated heavy rainfall. Return flow pattern ahead of the cold front will lead to ample low to mid-level moisture advection as noted by a regional PWAT anomaly between 2-3 deviations above normal as depicted by the latest NAEFS and GEFS/ECENS guidance. Deterministic output from various models, whether CAM or global based are all fairly bullish on the prospects of a QPF footprint of at least 2-3" of precip over a large area correlating with the trajectory of the shortwave with the proposed frontal positioning across the high plains into the Mid Mississippi Valley. Individual outputs also denote areas of 4+" in pockets across KS and MO, mainly within areas of potentially repeating convection. HREF probabilities are also aggressive for totals exceeding 3" with a broad neighborhood probability of 20-40% spanning from the eastern Front Range through southern MO. Scattered pockets of higher probabilities upwards of 50-60% are also co-located within the spatial coverage of the 3" markers. Even some low-end probabilities of 10-20% for >5" are showing up within the HREF fields, a sign of a higher potential and greater agreement for heavy rain prospects. Rates of 2-3"/hr are increasingly likely within the heaviest cores given both the probabilities (20-40% for >2"/hr), and the forecasted environment signaling high MUCAPE (2500+ J/kg) within the stout moisture advection regime. Strong convergence pattern with flow running parallel to the cold front is a textbook way to achieve a larger areal extent of flash flooding concerns when coupled with the above environmental characteristics. This has lead to the aforementioned expansion with note that some areas will see the higher end of the SLGT risk threshold, likely over a portion of KS or MO given the latest probabilities. Kleebauer Day 3 Valid 12Z Sun Jun 09 2024 - 12Z Mon Jun 10 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHEAST COLORADO, NORTHEAST NEW MEXICO, AND THE TEXAS PANHANDLE... A cold front will slowly press southward through the southern plains with the western extent becoming elongated to the north- south against the lee of the Rockies. Elevated moisture will pool along the front and expand westward with PWAT indices generally between 1.25 in the Southern Rockies and upwards of 1.75-2" across the high plains in the Panhandle. This is a solid 2-3 deviations above normal climatologically, a significant aspect to promote heavy rain chances. Thermodynamically, the setup is favorable to the south of the sagging boundary with ample diurnal heating expected on Sunday to warrant suitable low-level lapse rates and surface based instability. The most favorable part of the setup, however is the dynamical nature of the expected convection as a well organized shortwave perturbation will pivot northeast out Mexico creating a focused large scale ascent pattern in-of the high plains in NM and TX. Much of the deterministic output signaled a cluster of heavy convection forming over the northern Caprock with a general expansion to the north and east due to the progression of the mid-level shortwave. Totals exceeding 1-2" are now cropping up on the latest global consensus with some totals over 3" being shown in a few ensemble members and the latest GFS. Ensemble QPF footprint is fairly impressive at these leads considering the forecast evolution, so the confidence for flash flooding has grown over subsequent forecasts. There was enough of a signal to warrant an upgrade to a SLGT risk across the Panhandle and adjacent high plains of NM and southeast CO with MRGL risks spanning eastward over the southern plains the Mid Mississippi Valley due to more thunderstorms forming along just behind the cold front. Kleebauer 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