Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
160 FOUS30 KWBC 230050 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 850 PM EDT Wed May 22 2024 Day 1 Valid 01Z Thu May 23 2024 - 12Z Thu May 23 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR NORTHEAST TEXAS AND EXTREME SOUTHEAST OKLAHOMA INTO SOUTHERN ARKANSAS AND NORTHERN LOUISIANA... ...22Z Update... Have made minor changes to both the Marginal and Slight Risk areas, mainly to expand the Marginal Risk area into portions of West TX, based on the latest observational and CAM guidance trends (especially HRRR and HREF). There are a couple active Mesoscale Precipitation Discussions or MPDs within the outlook areas; for more information, please visit www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd.php. Hurley ...Previous Discussion... The southern portion of the frontal boundary emanating from the low moving from the Upper Mississippi Valley into southern Ontario this morning will slow significantly from the Southern Plains into the Lower Arkansas and Mid Mississippi Valley during the upcoming day 1 period, becoming aligned more parallel to the southwest flow aloft. Additional convection likely to form in the axis of PW values 2+ standard deviations above the mean as shortwave energy moves east northeastward across the Southern Plains and along this slowing frontal zone. There has been a significant southward shift in nearly all of the models with the forecast axis of heaviest precip along this front. The individual hi res runs and the HREF mean are the farthest south now, with global models to the north of the HREF mean, closer to the 18Z axis of the RRFS and 06Z May 21 axis of the RRFSMEAN. The 00Z EC is the farthest south global model, closer to the hi res and HREF mean axis. WPC has followed the southward trend in our latest qpf and we will also trend farther to the south with the Excessive Rainfall probabilities. Training of cells parallel to the boundary is a concern for heavy to locally excessive rainfall totals day 1, although confidence is not great with placement given the spread and significant changes run to run. With respect to the previous outlook for this period, there has been approximately a 60-80 mile southward adjustment to the marginal and slight risk areas, extending them farther south into northeast Texas and northern Louisiana and reducing the risk from the OH/MS river confluence into northern Arkansas. Oravec Day 2 Valid 12Z Thu May 23 2024 - 12Z Fri May 24 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM FAR NORTHEAST TEXAS/ FAR SOUTHEAST OKLAHOMA, ACROSS SOUTHERN ARKANSAS INTO NORTHERN MISSISSIPPI... ...2030Z Update... ...Mid-South... No significant changes were made to the Slight risk area a from northeast Texas to northern Mississippi this afternoon. The second day in a row of strong and moisture-laden showers and thunderstorms expected to develop across the Slight Risk area will be capable of producing widely-scattered flash flooding. Expect the FFGs in this area to be lower by Thursday after today and tonight`s rain. ...Mid-Atlantic... The surrounding Marginal Risk area was expanded several states east to include much of the Mid-Atlantic. In addition to localized decreases in FFG expected as a result of today`s storms, another several lines of storms may track along the front from the Southern Appalachians to the Mid-Atlantic. While each line will be rather fast-moving, if 2 or 3 separate lines move across the region, then isolated flash flooding is possible, especially in urban and flood-prone areas. ...Northern Plains... The Marginal in the upper Midwest was expanded west to include much of North Dakota and southeastern Montana with this update. A developing storm system will tap Gulf moisture in place to become a typical comma-shaped storm as it moves into the Dakotas. The northern and western side of the storm, while on the "cold" side, will cause steady rain over a long period of time over a typically dry area. Thus, isolated flash flooding is possible, particularly where convection can develop on the interface with the dry slot, where higher rainfall rates will be possible. Wegman ...Previous Discussion... Similar to the day 1 time period, a stationary frontal boundary expected to remain stretched in a west southwest to east northeasterly direction across northeast Texas/southeast Oklahoma into Arkansas, although this front will be weakening with time. PW values expected to remain 1.5 to 2 standard deviations above the mean along this weakening front during day 2. Additional shortwave energy moving west to east across the Southern Plains will support additional convection in this high PW axis and potential for additional heavy rains from northeast Texas/southeast Oklahoma, east across the Lower Arkansas Valley into the Lower Mississippi Valley. Given the low confidence with how convection will develop day 1 and whether there will be an outflow boundary still in tact for the day 2 convection, confidence does remain low on qpf placement. Models do seem to support a farther northward axis day 2 compared to day 1 as the stationary front weakens and southerly low level flow pushes the high PW values farther to the north. There still is potential for overlap of day 1 heavy rains with day 2, but with low confidence in the day 1 axis, confidence is low as to where this overlap will be. The new day 2 Excessive Rainfall Outlook did trend southward from the previous issuance for this period by approximately 50 miles to better match the latest WPC and model qpf consensus. ...Eastern portions of the Northern to Central Plains into the Upper Mississippi Valley... No significant changes made to the marginal risk area across eastern portions of the Northern to Central Plains into the Upper Mississippi Valley. Additional convection likely ahead of the next strong area of height falls rotating from the Northern Rockies into the Northern and Central Plains day 2. This region has seen heavy rainfall amounts over the past 24 hours, keeping stream flows high prior to the potential day 2 mounts. There is a lot of spread with qpf details, leading to low confidence in any one solution. However, with 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. Oravec Day 3 Valid 12Z Fri May 24 2024 - 12Z Sat May 25 2024 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY INTO THE UPPER GREAT LAKES AND FROM THE LOWER ARKANSAS/LOWER MISSISSIPPI VALLEYS INTO THE TENNESSEE VALLEY AND SOUTHERN TO CENTRAL APPALACHIANS... ...2030Z Update... No major changes to the southern Marginal across many of the same areas as Day 2/Thursday...from northeast Texas to the southern Appalachians. While this may be the 3rd straight day of storms for some, convective coverage is expected to be lesser on Friday as compared with previous days...such that despite the lower FFGs likely to be in place, lesser coverage of storms should keep any new flash flooding isolated. The northern Marginal across much of the upper Midwest and Great Lakes was expanded south to include Milwaukee and Chicago over to the Quad Cities. The same low spreading rain further west Thursday will move into this region on Friday. Much of Minnesota and Wisconsin were hard hit yesterday with heavy rain, so some of these areas may still be sensitive to heavy rain and resultant flash flooding again on Friday, particularly if Thursday`s rain in Day 2 overperforms. For both Marginal Risk areas, confidence is not there for any upgrades at this time. Wegman ...Previous Discussion... ...Upper Mississippi Valley into the Upper Great Lakes... The next strong area of height falls moving into the Northern High Plains at the end of day 2 will continue to push eastward through the Northern Plains and into the Upper Mississippi Valley during day 3. The overall favorable large scale conditions ahead of these height falls day 2 will continue into day 3 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 very progressive day 3, which may limit very heavy amounts. The marginal risk was drawn to where there may be overlap of locally heavy rains day 3 with heavy rains that have fallen over the past 24 hours. ...Lower Arkansas/Lower Mississippi Valley, Tennessee Valley into the Southern to Central Appalachians... A broad marginal risk area was maintained from the Lower Arkansas/Lower Mississippi Valley region, east northeast across the Tennessee Valley and into the Southern to Central Appalachians. PW values across these regions will remain above average for the day 3 period, with additional shortwave energy moving west to east supporting scattered convection and locally heavy rainfall amounts. Not a lot of confidence in where the scattered convection will become more organized, with a fairly large spread in model qpf details. Oravec 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