Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
125 FOUS30 KWBC 220053 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 853 PM EDT Tue May 21 2024 Day 1 Valid 01Z Wed May 22 2024 - 12Z Wed May 22 2024 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY... ...01Z Update... For the 01Z Update, removed the western extent of the Marginal and Slight Risk areas over the upper Mississippi Valley where favorable forcing aloft will support additional periods of rain through the evening hours, but a lack of instability will likely keep rainfall rates in check and limit the threat for flash flooding. Also, removed areas further to the south that are now or will soon be behind the advancing cold front. A small Slight Risk area was maintained over Wisconsin. Ample moisture (PWs ~1.5 inches) and instability supported by strong low level inflow is expected to continue to support rainfall rates of 1-2 in/hr as the ongoing convective complex moves across this area over the next few hours. The threat for flash flooding will likely be confined to the evening hours as the system moves progressively through the region. Further to the south, broadened the Marginal Risk area across Arkansas. Training storms are expected to continue to develop this evening ahead of the advancing cold front, with rainfall rates of 1-2 in/hr expected. The hi-res guidance, including the most recent HRRR, show notable differences on the scope and placement of heavy amounts, but most show a good signal for heavy amounts on the order of 2-4 inches developing somewhere within this area during the evening into the overnight hours. Pereira 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... 20Z Update... Previous outlook still looks to be on-track based on the 12Z suite of guidance. The focus for heavy rainfall will be a slow moving frontal zone that cuts into a moist and unstable atmosphere with divergent flow aloft. See below for details. Bann Previous Excessive Rainfall Discussion... 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... 20Z Excessive Rainfall Discussion... Few changes needed based on 12Z global/coarser scale models. Bann Previous Excessive Rainfall Outlook... 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