Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
489 FOUS30 KWBC 090748 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 248 AM EST Sat Nov 9 2024 Day 1 Valid 12Z Sat Nov 09 2024 - 12Z Sun Nov 10 2024 ...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL IN AND NEAR IMPERIAL CALCASIEU IN LOUISIANA... 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 it stalls, which have already begun to evolve in recent radar imagery. The southern areas of Louisiana and Mississippi will have the greater moisture. MU CAPE rises to 1000 J/kg or so 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 8" due to cell training appear likely based on the 00z HREF probabilities of 8" totals. There is much better agreement on the placement when compared to this time yesterday. Portions of Central LA have received 300%+ of their average seven day rainfall, so soils should have some sensitivity. Coordination with the LCH/Lake Charles LA forecast office led to the increase to a High Risk. Roth Day 2 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 guidance remains unclear as to whether heavy rainfall gets ashore or not. Precipitable water values 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 3 Valid 12Z Mon Nov 11 2024 - 12Z Tue Nov 12 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE PACIFIC NORTHWEST & CENTRAL GULF COAST... Central Gulf Coast... Precipitable water values north of Rafael are expected to remain in the 1.5-2" range in the vicinity of a slowly progressive front near the Central Gulf Coast. While much of the guidance keeps rainfall amounts minimal, the 00z NAM showed local amounts of 3"+, though it gets there by allowing Rafael to get much closer to the Gulf Coast than other model guidance. Considering that heavy rainfall is possible over the previous couple of days, figured a new Marginal Risk was a sensible precaution in case the NAM is close to correct and/or soils are saturated by that time. Pacific Northwest... Precipitable water values of 0.5-0.75" and MU CAPE of a few hundred J/kg are expected in a post-frontal environment. Inflow off the Pacific is expected to remain around 40 kts. Hourly rain totals exceeding 0.5" remain possible, which would be most problematic in burn scars. Left the inherited 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