Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Tue Sep 23 2025 08:43:57 FOUS30 KWBC 230825 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 425 AM EDT Tue Sep 23 2025 Day 1 Valid 12Z Tue Sep 23 2025 - 12Z Wed Sep 24 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHERN MISSOURI, FAR SOUTHEAST KANSAS, EASTERN OKLAHOMA, FAR NORTHEAST TEXAS, ARKANSAS, WESTERN TENNESSEE, WESTERN KENTUCKY, AND SOUTHERN ILLINOIS AND SOUTHERN INDIANA... ....Lower Arkansas Valley, Lower Mississippi Valley into the Lower Ohio Valley... The strengthening low level southerly flow/anomalous 850-700 mb moisture flux that have supported organized convection over the Central to Southern Plains early Tuesday will continue to support the downstream push of this organized convection post 1200 UTC, with these anomalous 850-700 mb moisture flux values of 2-3+ standard deviations above the mean moving from the eastern sections of the Southern Plains into the Lower AR Valley, Lower MS, TN and OH Valleys. There continues to be some north south spread in the models with respect to the position of the max precip axis. Generally, the non-CAMs are farther north and the CAMs farther south. WPC continues to support the farther south qpf solutions, with our day 1 risk areas drawn toward them. Overall, not a lot of changes to the previous slight risk areas. We did extend the slight risk farther east into the Lower OH Valley where there is expected to be overlap of day 1 heavy precip with observed precip over the past 24 hours. We also extended the slight risk area farther south into northeast TX where several of the new 0000 UTC hi-res runs and subsequently the new HREF mean show heavy precip. Otherwise, the slight and 25% areas fit well with where the HREF and RRFS neighborhood probabilities are high day 1 for 2" and 3+ amounts. ....Coastal Central California... There continues to be good model agreement with the nearly stationary closed low off the Southern CA coast beginning to slowly move back to the north on day 1 toward the Central CA coast. This slow north movement will also allow for a northward expansion of the anomalous PW values over Southern CA into coastal Central CA, with values as high as 3-4 standard deviations above the mean. With good model agreement on the closed low track day 1, there is also good agreement on potential for areal average moderate precip totals, with potential for locally heavier amount along the Central CA coast. Isolated runoff issues are possible, especially over any burn scars. Oravec Day 2 Valid 12Z Wed Sep 24 2025 - 12Z Thu Sep 25 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE TENNESSEE AND OHIO VALLEY REGIONS... Anomalous PW and 850-700 moisture flux values will stretch across a large area from the Lower MS Valley, and into the TN & OH Valleys, Central Appalachians and the Mid-Atlantic, ahead of the amplifying longwave trof stretching from the Great Lakes, southward into the Lower MS Valley. There still is a fair amount of qpf spread with the max axis day 2. WPC is leaning more toward the multi model ensemble qpf mean/NBM to drive our qpf and excessive rainfall axes. This will support a widespread axis of moderate to heavy precip amounts from eastern TX into the Lower MS Valley, TN and OH Valleys. While a large portion of the day 2 QPF and ERO axes are currently in moderate to severe drought, there may be overlap in qpf areas from day 2 and what has fallen over the past 24 hours from eastern TN into central to eastern KY, and the Upper OH Valley region. The previous slight risk was narrowed to better fit this potential overlap areas. The marginal risk was also trimmed significantly from southern L.P. of MI, IL, southeast MO and AR to better fit the latest qpf update. ....Central California... The slow moving closed low approaching the central CA coast late day 1 will continue to push slowly eastward day 2 and push inland by early Thursday morning. Similar to the day 1 period, an axis of anomalous PW values, 2 to 3 standard deviations above the mean, will persist to the east northeast of the closed low across Central CA. Scattered convection in this anomalous PW axis will support locally heavy rains across Central CA and isolated runoff issues, especially across burn scar regions. ....Far southeast Arizona into New Mexico... No changes made to the previous marginal risk area across this region. Scattered convection possible, with localized heavy rain and isolated runoff issues, especially in burn scar regions. Oravec Day 3 Valid 12Z Thu Sep 25 2025 - 12Z Fri Sep 26 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST ARIZONA AND FAR SOUTHWEST NEW MEXICO... The slow moving closed low moving inland into Central CA day 2 will drop back to the south southeast toward Southern CA day 3. This system will continue to have an area of anomalous PW values in the vicinity of the upper center across Central CA into the Great Basin. This closed low will also begin to tap anomalous PW values over northwestern Mexico, transporting them into southeast Arizona day 3. Model consensus is for a max precip area over Southeast Arizona and far southwest New Mexico. The previous slight risk across this area was only modified slightly, expanding it slightly to the north and east to cover the model max qpf spread. Only some minor changes to the marginal risk to the northwest of this across northern AZ, southern NV, far southwest UT and into the central Sierra. Locally heavy rains and isolated runoff issues possible across these areas, especially over burn scars. ....Southern to Central Appalachians... There will continue to be a broad axis of above average PW values pushing eastward day 3 ahead of the elongated upper trof stretching from the Great Lakes into the OH and TN Valleys. There is a lot of qpf differences in this high PW axis, leading to low confidence in where to put risk areas. Much of the eastern U.S. is in drought conditions with low relative soil moisture levels. One exception is over portions of the Southern to Central Appalachians from eastern TN/far western NC/far southwest VA and eastern WV. Kept the day 3 marginal confined to these areas and removed the broader marginal from the previous issuance that extended north and east into the Mid-Atlantic and southwestward to the Gulf Coast. Oravec $$ --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1) .