Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
999 FOUS30 KWBC 232240 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 640 PM EDT Thu May 23 2024 Day 1 Valid 2230Z Fri May 24 2024 - 12Z Fri May 24 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE ARKLATEX TO ARKLAMISS AS WELL AS FOR PORTIONS OF THE TENNESSEE VALLEY AND SOUTHERN APPALACHIANS... ...22Z Update... Updated the Slight and Moderate Risk areas across the Southern Plains-ArkLaTex areas to Lower MS Valley and TN-Lower Ohio Valleys, as well as with the Marginal Risk over the Lower MO Valley, based on the latest observational and mesoanalysis trends along with the latest HRRR and HREF guidance. There are active Mesoscale Precipitation Discussions or MPDs in these outlook areas; for further information, please go to www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd.php. ...16Z Update... The inherited Slight risk area was divided into 2 separate smaller ones with this update based on the latest guidance. The theme from the ensemble CAMs was to highlight the area around southern Arkansas with a separate area on the west side of the southern Appalachians into Kentucky, eastern Tennessee and extreme southwestern Virginia. Areas east of the mountains have somewhat higher FFGs and more tolerance for the possibility of localized training convection, so the Slight was cut off at the Great Smokies, which fits well with where current convection is adding moisture to the environment across southeast Kentucky and northeast Tennessee. Additional convection expected this afternoon with daytime heating and a period of a few hours of clearing between current areas of convection should allow for this afternoon`s storms to have the potential to produce locally heavy rainfall and resultant flash flooding. The squall line crossing southeast Arkansas and into northwest Mississippi is also adding moisture to the environment and locally lowering FFGs as it crosses the area. The line alone is unlikely to produce flash flooding given its fast movement perpendicular to the axis of the line...however it will set the stage for additional convection likely to develop this afternoon, which in areas with training could cause widely scattered instances of flash flooding. Elsewhere only minor changes to the Marginals, including a small southwestward expansion in central TX for the currently-weakening convection, trimming out the Sand Hills and dry slot of the northern Plains low, and including the northernmost counties in Georgia into the Marginal for possible southward development of this afternoon`s convection. Wegman ...Previous Discussion... ...ArkLaTex into the Mid-South... A stationary front is expected to stretched from northeast Texas/ southeast Oklahoma into Arkansas, while slowly weakening. Precipitable water values expected to remain 1.5 to 2 standard deviations above the mean along the boundary. Additional shortwave energy moving in from the west across the Southern Plains will support additional convection in this high moisture axis and there is potential for additional heavy rains from northeast Texas/southeast Oklahoma, east across the Lower Arkansas Valley into the Lower Mississippi Valley. The stationary front weakens and southerly low level flow pushes the high PW values farther to the north. Hourly rain totals to 2.5" and local amounts to 5" are possible. While some model spread continues, convergence seen in the 00z Canadian Regional, 00z UKMET, and 00z ECMWF in the Slight Risk area led to some increased confidence, despite the weaker look in the 00z HREF probabilities and more bifurcated 00z GFS solution in this region. The Slight Risk remains and has shown some expansion equally due to the heavy rainfall which occurred Wednesday and because of future heavy rainfall concerns Thursday and Thursday night. ...Northern Plains/Upper Midwest... The marginal risk area across eastern portions of the Northern to Central Plains into the Upper Mississippi Valley remains. Additional convection is likely ahead of the next strong area of height falls/cooling aloft rotating from the Northern Rockies into the region. This area has seen heavy rainfall amounts as of late, keeping stream flows high. The strong upper trof, and associated strengthening low level southerly flow and increasing PW values, there will be potential for localized heavy rainfall amounts that may fall across areas that received heavy totals over the past 24 hours. Roth Day 2 Valid 12Z Fri May 24 2024 - 12Z Sat May 25 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM CENTRAL TEXAS TO THE MID-ATLANTIC AS WELL AS PORTIONS OF THE UPPER MIDWEST... ...2030Z Update... No significant changes were made to the Marginal risk areas across portions of the south and the upper Midwest. From Texas to Virginia, storms are once again expected to develop along the stalled out front. However, with lesser upper level support and moisture flow parallel to the front out of the southwest rather than perpendicular, supporting flow into the storms will be reduced Friday as compared with today. Thus, the threat level remains Marginal across this area. It`s possible that portions of the front may need a local Slight by Friday, with the most likely area in the same portions of the current Slight in and around southern Arkansas. However, for now the signal for heavy rain in the guidance is diffuse enough that confidence is not there for a Slight. This could change if afternoon convective development across southern Arkansas overperforms tonight. The Marginal in the Upper Midwest remains largely unchanged with the cold frontal rainfall expected across Wisconsin and Illinois. Wisconsin up to Minnesota has been very wet in recent days, while urbanization in and around Chicago, the Quad Cities, and points in between locally lower FFGs in this area. Some training storms may pose an isolated flash flooding threat into Friday evening. Wegman ...Previous Discussion... ...Upper Mississippi Valley into the Upper Great Lakes... The next strong area of height falls moving into the northern High Plains will continue to push eastward through the Northern Plains and into the Upper Mississippi Valley. The overall favorable large scale conditions ahead of these height falls from Thursday will continue into Friday along the associated front where strong frontal convergence in an axis of PW values 1 to 1.5 standard deviations above the mean will support potential for moderate to locally heavy rainfall totals. This front does look progressive, which may limit very heavy amounts. The marginal risk was drawn to where there may be overlap of locally heavy rains Friday through Friday night with heavy rains that have fallen as of late. Hourly rain totals to 2" and local amounts to 4" are expected where cells merge or manage to train. ...ArkLaTex, Tennessee Valley, & southern Appalachians... A broad marginal risk area continues and was expanded in areal coverage from continuity based on the most recent QPF guidance and to some degree heavy rainfall that occurred near the ArkLaTex on Wednesday. Precipitable water values across these regions will remain above average, with additional shortwaves in from the west supporting scattered convection and locally heavy rainfall amounts. Spread remains within the guidance, which keeps the threat level Marginal. The ingredients in place support hourly rain totals to 2.5" with local amounts to 5". Should the guidance show more convergence in future runs, a Slight Risk could be prudent as portions of the area saw heavy rainfall Wednesday and should see heavy rains again on Thursday. Roth Day 3 Valid 12Z Sat May 25 2024 - 12Z Sun May 26 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS... ...2030Z Update... Few overall changes were needed as the area covering much of eastern Kansas and Missouri remains the area of focus for convection on Saturday. However, as convection in this region will be largely dependent on the behavior of convection from previous days, guidance agreement is poor. Since there is a large amount of spread in this area, and with recent heavy rainfall, the Slight was expanded to cover more of the potential scenarios for flash flooding in this area. Most of the guidance took the unusual step of trending north, which is the direction much of the expansion of the Slight went, but since convective behavior tends to trend south, very little change was made to the southern end of the Slight. It`s likely that with better agreement closer to the event that the Slight will be able to be shrunk to follow those trends. Wegman ...Previous Discussion... The Marginal Risk in the area continues and was expanded in areal coverage to account for the most recent QPF guidance, with the Slight Risk a new addition. 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. 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