Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
773 FOUS30 KWBC 210809 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 409 AM EDT Tue May 21 2024 Day 1 Valid 12Z Tue May 21 2024 - 12Z Wed May 22 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY... Models remain fairly consistent with the overall evolution of the large scale flow across the mid section of the nation. A strong vort ejecting northeastward on the eastern side of the amplifying Rockies trof forecast to becomes increasingly negatively tilted, pushing northeast across the Central Plains into the Upper Mississippi Valley. This will help deepen surface low pressure across the eastern portions of the Central Plains early day 1, moving northeast into the Upper Mississippi Valley/Upper Lakes region later day 1. While there has been some run to run changes with qpf details, there continues to be pretty good consensus for a widespread axis of heavy precip across large portions of the Upper Mississippi Valley. Hi res models continue to show two well defined areas of precip pushing northeastward across the Upper Mississippi Valley into the Upper Lakes, comprised of a comma head/deformation precip area on the northwest side and a more progressive convective precip area on the southeast side. Heaviest day 1 totals expected to be in the comma head/deformation precip area, where precip will be somewhat slower moving and may pivot for a time, compared to the expected more progressive convection on the southeast side of the system. The latest HREF neighborhood probabilities show the two precip mode areas well and was used to model the new day 1 Excessive Rainfall Outlook. With respect to changes, there were no significant changes from the previous issuance. The risk gradient was tightened up on the western end and minor changes made elsewhere based on the HREF neighborhood probabilities. Oravec Day 2 Valid 12Z Wed May 22 2024 - 12Z Thu May 23 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM FAR NORTHEAST TEXAS/SOUTHEAST OKLAHOMA, ACROSS THE LOWER ARKANSAS VALLEY INTO THE MID MISSISSIPPI VALLEY... The trailing frontal boundary from the low moving northeastward from the Upper MS Valley into the Upper Lakes region day 1, will slow significantly on the southern end from the Southern Plains into the Lower Arkansas and Mid Mississippi Valley during day 2 as it becomes aligned more parallel to the southwest flow aloft. PW values expected to rise to 2+ standard deviations above the mean along this slowing frontal zone, supporting potential for heavy rainfall total from far northeast Texas, southeast Oklahoma, east northeastward across much of Arkansas and toward the Mid Mississippi and Lower Ohio Valley regions. Shortwave energy embedded in the southwest flow aloft will enhance uvvs in this anomalous PW axis Wednesday afternoon continuing into the early hours of Thursday. Training of cells parallel to the boundary is a concern for heavy to locally excessive rainfall totals day 2. There is some spread with respect to the latitude of this potential training/heavy rains axis. The NAM is a northern outlier across from northeast OK, northern Arkansas, far southern MO, far western KY and far southern IL. The EC and GFS are considerably farther to the south, while the FV3LAM and multi model ensemble qpf mean are in between. We have drawn the slight risk area to better fit our preferred more southern qpf solution. This is about 60-80 miles farther to the south with the marginal and slight risk areas from the previous issuance along the northern portion of the risk areas across southern MO into northern AR. With respect to stream flows, there is overlap between heavy qpf of 1.5 to 2.5" and high stream flows, as per the National Water Model, for areas of far northeast Texas into Southeast Oklahoma, with this area possibly having a greater risk of runoff issues compared to other areas in the slight risk area. Oravec Day 3 Valid 12Z Thu May 23 2024 - 12Z Fri May 24 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM FAR NORTHEAST TEXAS/SOUTHEAST OKLAHOMA, ACROSS THE LOWER ARKANSAS VALLEY... Similar to the day 2 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 day 3. 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 Arkansas and into the Lower Mississippi Valley. Still some latitude differences with the model qpf axes. Similar to the day 2 period, WPC is favoring the more southern qpf axis of the GFS, EC, UKMET and multi model ensemble qpf mean. There is potential for overlap of day 2 heavy rains with day 3. This may lead to a higher threat level in later updates, especially given the high stream flows across northeast Texas/southeast Oklahoma as per the National Water Model. ...Eastern portions of the Northern to Central Plains into the Upper Mississippi Valley... Introduced a marginal risk area to eastern portions of the Northern to Central Plains into the Upper Mississippi Valley for convective potential ahead of the next strong area of height falls rotating from the Northern Rockies into the Northern and Central Plains day 3. This region likely will see heavy rainfall amounts during the upcoming day 1 period, keeping stream flows high prior to the potential day 3 amounts. 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 receive heavy totals day 1. 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