Quantitative Precipitation Forecast
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Issued by NWS
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830 FOUS30 KWBC 250056 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 856 PM EDT Fri May 24 2024 Day 1 Valid 01Z Sat May 25 2024 - 12Z Sat May 25 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID MISSISSIPPI VALLEY AND FROM THE EASTERN RED RIVER VALLEY TO PARTS OF THE MID SOUTH... ...0100Z Update... Hoisted a short-term Slight Risk area over parts of the Mid Mississippi Valley, from east-central MO into southern IL, to account for the clusters of pre-frontal convection that has exhibited more upscale growth this evening in an increasingly difluent upper level pattern with ample deep-layer instability (MUCAPEs 1000-2000 J/Kg) and moisture flux (PWs 1.51.75"). The orientation of these multicellular segments and kinematic/shear profile will support cell training through late this evening/towards midnight. For further details, please refer to Mesoscale Precipitation Discussion or MPD #319 at www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd.php. Hurley ...1930Z Update... Expanded the Slight Risk a little farther west to include more of northeast TX, including the eastern portions of the DFW Metro. This is based largely on the latest FFG and 0-10cm RSM trends from the recent heavy rainfall, while also supported by some of the more recent CAMs (including the HREF exceedance probabilities) with the next bout of convection late this afternoon/into the evening hours. Have also expanded the Marginal Risk areas across parts of the Midwest-western OH Valley, along with the Southeast to Mid Atlantic. This too is supported by the observational trends (radar, satellite, mesoanalysis) while also encompassing SPC`s updated outlook areas. Isolated pockets of 2+ inch/hr rates are anticipated with the strongest cells across all Marginal Risk areas outside of the northern portions (i.e. Upper Midwest, where the flash flood risk is predicated on overall lower FFG, thus runoff response would be more likely with less-intense rain rates). Hurley Day 2 Valid 12Z Sat May 25 2024 - 12Z Sun May 26 2024 ...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS IN AND NEAR THE KANSAS/MISSOURI BORDER... ...2030Z Update... The biggest change was to expand the Marginal/Slight Risk area south and west across portions of the Southern Plain given the convection expected to develop late in the day on Saturday and Saturday night. Expectation is that atmosphere between the passage of a warm front earlier in the day and prior to the passage of a dry line will be unstable enough to support heavy rainfall from any cells that form...with convective coverage growing by Saturday evening. A midlevel shortwave trough looks to support convcetion through favorable shear profiles and cooling mid-level temperatures. Precipitable water values in excess of 1.75 inches get advected over eastern Kansas by a 35 to 50 kt low level just by 26/06Z as shown by the NCEP guidance. Given the probabilistic nature of the Excessive Rainfall outlook...allowed some coverage of the Marginal risk to extend into QPF-sparse regions given the difficulties of the models in handling dry-line convection early on and to account for uncertainty in exactly where convection develops. Models are more unified in developing QPF farther north and the potential for excessive rainfall was already well-covered by the prevously-issued Slight Risk area...only minor changes needed there. Bann ...Previous Excessive Rainfall Discussion... The Marginal Risk remains similar to continuity, with some changes made to the Slight Risk area. A cyclone emerging into the central Plains will bring precipitable water values of 1.5"+ across the region on the heels of sufficiently strong low level inflow/effective bulk shear. The region lies within a general instability gradient, with CAPE expected to rise to 4000+ J/kg within an increasingly capped atmosphere across the southern Plains. Pockets of moderate to heavy rainfall are forecast within this region. There is increasing overlap in the QPF pattern near the KS/MO border within the 00z guidance where three hourly flash flood guidance is modest, so went ahead with an upgrade to a Slight Risk for this update. However, given the ingredients, hourly rain totals to 2.5" with local amounts to 5" are possible where mesocyclones form and/or cells manage to train. ...Portions of the East... Near western PA and WV, showers and thunderstorms along a progressive front could drop locally heavy rainfall within an area of modest flash flood guidance. Hourly rain totals to 1.5" with local amounts to 3" are possible where short bouts of cell training or cell mergers manage to occur. Since the flash flood threat appears to be isolated, added a Marginal Risk. Down south in the Carolinas, higher moisture pools near the coast as a front slowly moves through. With MU CAPE as high as 3000 J/kg and effective bulk shear expected to be sufficient to organize convection to some degree, added a Marginal Risk within a regime that can lead to isolated flash flooding during the warm season. Roth Day 3 Valid 12Z Sun May 26 2024 - 12Z Mon May 27 2024 ...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF THE MIDWEST AND THE MISSISSIPPI & OHIO VALLEYS... ...2030Z Update... Few changes were made. The models continue to show a cyclone making its way east across the Upper Midwest and the Great Lakes with time. There were some run to run differences in QPF but the previous outlook still seemed to cover any resulting shifts in excessive rainfall potential. Bann ...Previous Excessive Rainfall Discussion... A cyclone moving across the Midwest and Great Lakes is expected to draw ample moisture (precipitable water values of 1.50-1.75") into the region. The area that is expected to see the greatest residency time with higher moisture and instability is across portions of TN and KY. However, warm temperatures at 700 hPa appear to be a limiting factor the farther down its front you go. The best warm air advection ahead of the low is slated to occur from portions of IL across OH, where the guidance is more robust in its QPF signal, with local amounts in the 3-5" range. Considering the progression of the warm air advection pattern and best moisture across the region, that degree of heavy rainfall would need to fall quickly; hourly rainfall potential to 2.5" is possible within the organized thunderstorms, with embedded mesocyclones, could get them there given the low- level inflow and effective bulk shear expected. Went ahead and added a Slight Risk across the region, where flash flood guidance values are modest. Roth 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