Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
048 FOUS30 KWBC 030900 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 500 AM EDT Fri May 3 2024 Day 1 Valid 12Z Fri May 03 2024 - 12Z Sat May 04 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE GULF COAST AND SOUTHERN PLAINS... ...West Texas to Gulf Coast into Tennessee Valley... Main concern for excessive rainfall today will be along the Gulf coast due to one or more rounds of thunderstorms over region that has become water- logged recently. Of most immediate concern is how much convection that developed overnight in eastern Texas will persist into the Day 1 period at 12Z and how much of an overlap will there be with parts of the state that received 2 to 5 inches of rain in the previous 24 hours and 5 to 10 inches of rain since early this week. With cloud tops still cooling as of 08Z...the expectation is that some areas of higher intensity rainfall will still be occurring at 12Z with the concern for the rainfall to exacerbate on-going flooding and for the additional rain to push some areas into flood. However...weaker instability immediately downstream and the progressive nature of the convection should lead to weakening rainfall rates during the morning. The 03/00Z suite of guidance has continued the idea from earlier runs that focus any convection that forms later today or this evening will be shifting either east with a mid-level trough or shifting out west near the dryline. As a result...opted to propagate the Slight Risk area from the Day 2 period into todays Day 1 outlook period rather than issue a focused, short term extension of the Moderate risk after collaboration with HGX/SHV. Maintained a Marginal Risk area farther eastward from the Gulf coast towards the Tennessee Valley as the mid-level trough propagates into better instability and out in West Texas near the dryline. ...Western High Plains... A fairly robust mid-level perturbation will eject east-southeast out of WY/CO with convection initiating over the Front Range, potentially developing into a MCS as it migrates eastward through southern NE into KS. Models are in agreement of at least some modest QPF with 1-2" scattered across the aforementioned areas. Present indications are that the convection looks to be progressive enough over areas with sufficiently high flash flood guidance that a Marginal Risk area still adequately covers the risk. ...West Aspect of the Appalachians... Showers capable of producing locally intense downpours will be moving towards parts of the Appalachians/far eastern Ohio Valley later today. Given 3-hour Flash Flood Guidance around 1.5 inches per hour...and some ensemble guidance suggesting an inch of rain in the outlook area was possible...maintained the previously issued Marginal Risk area although spaghetti plots of QPF showed more enthusiasm for 2 inch amounts from the ARW core. Bann Day 2 Valid 12Z Sat May 04 2024 - 12Z Sun May 05 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE WESTERN AND SOUTHERN HIGH PLAINS... Height falls aloft ejecting eastward from the Southern Rockies and the presence of a dryline over West Texas will foster an environment for thunderstorms capable of producing heavy rainfall by later in the day on Saturday that persists into Saturday night/early Sunday morning. Precipitable water values will have increased to nearly 1,5 inches...some 2 to 2.5 standardized anomalies greater than climatology...over portions of central and west central Texas by 00Z Sunday in response to a period of southeasterly flow off of the Gulf of Mexico. Consensus of model guidance QPF in the range of 1 to 3 inches seems reasonable...although the UKMET was a notable outlier. ...Northern Sierra Nevada Foothills... A fairly robust IVT pulse will slide down the west coast with southwesterly flow aimed orthogonally to the northern and central Sierra`s by Saturday. Higher elevations will be greeted with more snow, but the adjacent foothills will remain warm enough to benefit from all rainfall. Rates will be borderline overall, but the prospects for over 1" of precip has grown in the past succession of runs with the ensemble bias corrected guidance now upwards of 2" now forecast within the elevations below 8000` MSL, falling mainly in a span of 8-12 hours. The threat is on the lower end of MRGL. Maintained continuity from previous forecast and will assess whether it needs adjusting, or removal pending future trends in guidance. Bann Day 3 Valid 12Z Sun May 05 2024 - 12Z Mon May 06 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE SOUTHERN PLAINS... The potential for excessive rainfall makes its way eastward on Sunday in association with a closed low aloft and a cold front at the surface. Model QPF was not as heavy as forecast on Day 2 as shifting low level flow results in weaker low level moisture flux convergence along the front. Despite model QPF generally being 2 inches or less...opted for a Slight Risk given the wet antecedent conditions over portions of eastern Texas and eastern Oklahoma. Bann 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