Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
303 FOUS30 KWBC 081552 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1052 AM EST Fri Nov 8 2024 Day 1 Valid 16Z Fri Nov 08 2024 - 12Z Sat Nov 09 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS... ...16z Update... Little change needed for the 16z update, as the inherited Slight Risk was maintained and adjusted a bit based on observational and CAM trends. Much of the Slight Risk area (particularly the western half) is on the lower-end of the probability spectrum, owning to longer duration rainfall resulting in isolated to widely scattered flash flooding. A good portion of the TX Hill Country has received impressive 4-10" totals over the past 24 hours, resulting in highly depressed FFGs with little additional rainfall needed to cause problems. Even so, localized short-term totals going forward should be capped around 1.5", greatly limiting the extent of any additional flash flooding. Farther east into the Heart of TX (mainly southeast of the Dallas-Fort Worth metro area), the Slight Risk is considered to be on the higher-end of the probability spectrum (25%+), as this region has the best chance of realizing the highest rainfall rates (1-2"/hr) and resultant short-term totals (20-30% odds of 5" exceedance, per 40-km neighborhood HREF probabilities through 12z). Drier antecedent conditions in this region should limit the extent and intensity of flash flooding (with FFGs generally ranging from 3-4", coverage should remain scattered and below significant flash flood thresholds). Churchill ...Previous Discussion... The upper level low over the Southwest and its attendant surface low will continue moving northeast across the Plains on Friday. With a continued influx of Gulf moisture with precipitable water values of 1.5-2.25" expected near the cyclone`s cold front, the typical comma shaped precipitation footprint will develop farther up the warm conveyor belt from Texas to Oklahoma which should occur with precipitable water values at or above an inch. Out west in Colorado and New Mexico the precipitation will be mostly in the form of snow. Where it remains all rain, the heaviest rain will be from north Texas across Oklahoma and into south-central Kansas. Instability should be sufficient for heavy rain-related issues. While somewhat lesser amounts of rain are expected overall for southern Oklahoma and Texas...greater instability there as high as 1500 J/kg of MU CAPE will favor at least some storms capable of heavy rainfall in that area, with hourly rain totals to 2.5" and local amounts as high as 6" where cells train. Meanwhile, north of Oklahoma City, expect a much longer duration rainfall as the surface low takes its time getting its act together. So while hourly rain totals will likely be lower than further south, perhaps 1" where slantwise convection/frontogenesis aloft forces greater precipitation efficiency, it will be made up for by the longer duration of the rain. Roth/Wegman Day 2 Valid 12Z Sat Nov 09 2024 - 12Z Sun Nov 10 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE LOWER MISSISSIPPI VALLEY... An upper level low will move faster towards the northeast. As Rafael moves west over the central Gulf, a plume of moisture with precipitable water values of 1.5-2" gets drawn north ahead of the surface low`s strong cold front. The front will likely be the dominant forcing for storms in this region. As on Friday, the southern areas of Louisiana and Mississippi will have the greater moisture. MU CAPE rises towards 1000 J/kg across parts of LA/MS/TN. Areas further north have soils which are more saturated/flash flood guidance is lower. The front should progress slow enough that training storms tracking north along the front could still cause flooding problems, especially over portions of LA, MS, and TN. Hourly rain totals to 2.5" and local amounts of around 6" appear likely. Lingering disagreement on exactly where the maxima are expected kept the risk level from being raised to Moderate, though an upgrade remains possible in future updates should this placement issue resolve itself and model QPF magnitudes don`t back off. Roth Day 3 Valid 12Z Sun Nov 10 2024 - 12Z Mon Nov 11 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE PACIFIC NORTHWEST, LOWER MISSISSIPPI VALLEY...TENNESSEE VALLEY... AND UPPER OHIO VALLEY... Central Gulf Coast northeast towards southwest Pennsylvania... Moisture and instability from the Gulf gets advected from the vicinity of Raphael northeast across portions of the Central Gulf Coast through the Tennessee and Upper Ohio Valleys. The forward progress of the front across much of the East should keep any excessive rainfall concerns minimal -- some of the risk area from eastern AR to the east-northeast just south of the OH river accounts for recent rains/some soil saturation. The latest NCEP and CMC guidance suggests that Raphael gets much closer to the Gulf Coast than the NHC forecast, which led to avoiding use of the GFS, NAM, and Canadian guidance explicitly. Since the distance of the storm from the region at this time frame is unclear, it`s also unclear how high precipitable water values get, though they should rise above 1.5", particularly in the southern portion of the area near the coast, which should be enough for heavy rain concerns. It appears that enough instability could be available along the immediate Gulf Coast for convection with heavy rainfall. Hourly rain totals to 2" with local totals to 5" appear achievable along or near the immediate Gulf coast. Whenever better agreement amongst the guidance on the future of Rafael as well as the placement any rainfall maximum near the coast occurs, a Slight Risk could prove useful at that later time. To the north, hourly totals up to ~1" with local totals to 2" appear to be the maximum potential. Pacific Northwest... Precipitable water values rise to 0.75-1" with a front moving into the area. Inflow from the Pacific rises to 50-60 kts from the south-southwest near the front. In the wake of the front, instability moves in due to colder air aloft. Hourly rain totals exceeding 0.5" appear likely here, which would be most problematic in burn scars. Left the Marginal Risk area intact though simplified the area`s appearance. 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