505 FOUS30 KWBC 090749 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 349 AM EDT Wed Sep 9 2026 Day 1 Valid 12Z Wed Sep 09 2026 - 12Z Thu Sep 10 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHEAST KANSAS INTO SOUTH CENTRAL MISSOURI, OVER SOUTHEAST COLORADO, SOUTHEAST ARIZONA AND FAR SOUTHWEST NEW MEXICO... An axis of above average PW values, 2+ standard deviations above the mean, expected along the surface cold front pressing generally southeastward day 1 through the Great Lakes into the Northeast and southward through the Mid Mississippi Valley and into the Central Plains. The northeastern portion of the front moving across the Great Lakes into the Upper Ohio Valley and Northeast will be very progressive, limiting any widespread runoff issues. Widespread moderate to locally heavy rains possible along and ahead of this potion of the front, with the risk level kept at marginal given the expected progression. ..Central Plains into the Lower Missouri Valley... Slower movement of the frontal boundary expected from the Central Plains into the Lower Missouri Valley/Mid Mississippi Valley where it will become more aligned to the westerly mid to upper level flow. Simulated radars from the CAMS show general agreement with the potential for training of cells in a west to east direction in the 0000- 1200 UTC Thursday time period. HREF and RRFS neighborhood probabilities for 1, 2 and 3"+ totals remain high in the slight risk area from southeast Kansas into south-central Missouri. A small slight risk area was introduced over southeast Colorado where there is consensus for potentially heavy rains where low level easterly to southeasterly flow is expected to strengthen in the early hours of Thursday. HREF and RRFS probabilities of 3 hourly precip exceeding FFG values are in a similar area over southeast Colorado early Thursday, with probabilities as high as 30 to 40%+ in the 0600-1200 UTC Thursday period. ...Southwest... No changes made to the coordinated slight risk area across southeast Arizona into far southwest New Mexico. Additional scattered convection likely in the above average PW axis. The slight risk area continues to coincide well with where the RRFS and HREF show max probabilities of 3 hourly precip exceeding FFG values. The RRFS is more emphatic than the HREF with these probabilities, with values as high as 45-60%, compared to the HREF range of 15-30%. No changes made to remainder of the broad marginal risk from the Sierra, southward into Southeast CA and eastward across portions of AZ and NM. ...Southwest Florida... A weak mid level wave pushing west across South Florida will help enhance uvvs in the tropical airmass, PW values 2.00-2.25"+. A marginal risk area was added for Southwest Florida where HREF and RRFS neighborhood probabilities are high for 1, 2 and 3"+ amounts. The HREF is more emphatic about heavy rains, showing probabilities of 3 hour precip exceeding FFG values as high as 40-60% late Wednesday afternoon. This heavy rain potential may lead to localized runoff issues, especially in more urbanized areas. Oravec Day 2 Valid 12Z Thu Sep 10 2026 - 12Z Fri Sep 11 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE UPPER OHIO VALLEY INTO THE CENTRAL APPALACHIANS... ...Upper Ohio Valley into the Central Appalachians.. PW values 2+ standard deviations above the mean are forecast along the west-east oriented frontal boundary sinking south through the Ohio Valley, Central Appalachians and Mid-Atlantic region day 2. The previous slight risk area was adjusted southward by approximately 80-100 miles to fit the latest model qpf consensus for potentially heavy rains. H85 flow parallel to this front will support training potential and also enhance uvvs in the upslope regions of the Central Appalachians. Marginal Risk areas. ...Southwest... A marginal risk area was continued over portions of the Southwest for potential for local heavy rains and isolated runoff issues in the continued axis of above average PW values forecast across this area. A marginal risk was also added for the Transverse Range of Southern California where the RRFS was showing neighborhood probabilities as high as 45%+ for 1"+ totals. ...Lower OH Valley, Mid to Lower MS Valley into the Southern Plains... A broad marginal risk area was maintained to the southwest of the Upper OH Valley/Central Appalachians slight risk area, extending into the Lower OH Valley, Mid to Lower MS Valley and westward into the Southern Plains of OK and northwest TX. Scattered convection likely along the surface frontal boundary where PW values will remain high, 1.75-2.00"+, but with FFG values high and confidence low with where convection may maximize, the threat level was kept at marginal. Oravec Day 3 Valid 12Z Fri Sep 11 2026 - 12Z Sat Sep 12 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY AND SOUTHERN APPALACHIANS, OVER THE UPPER MISSISSIPPI VALLEY INTO THE CENTRAL PLAINS AND OVER PORTIONS OF THE SOUTHWEST AND SOUTHERN GREAT BASIN... ...Lower MS Valley, TN Valley into the Southern Appalachians... Above average PW expected across much of the southeast quarter of the nation from the Lower MS Valley, eastward across the TN Valley and into the Southern Appalachians during day 3. Models are showing some trof amplification across this area, with broad upper difluence in this above average PW axis supporting widespread scattered convection. With low confidence in qpf details and high FFG values across these areas, the threat level is kept at marginal. ...Upper MS Valley into portions of the Central Plains... A surface front expected to push east southeastward across the Northern-Central Plains into the Upper MS Valley day 3. Model consensus is for potential of locally heavy rains along and ahead of this front. The previous broad marginal risk was narrowed to fit the latest qpf axis consensus. ...Southwest into the southern Great Basin... Increasing westerly mid level flow on the south side of the amplifying closed low over the Pac NW day 3 will help push the primary anomalous PW axis over the Southwest eastward from the day 2 position, becoming oriented from Southeast CA, into Arizona and northward into the Great Basin. While there are the typical amount of model qpf spread in this type of flow regime at day 3, there is general consensus for scattered convection in this anomalous PW axis, 1 to 2+ standard deviations above the mean. Locally heavy rains and isolated runoff issues possible, with low confidence in any qpf details. Oravec Day 4 and Day 5 Valid 12Z Sat Sep 12 2026 - 12Z Mon Sep 14 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL PLAINS AND MISSOURI VALLEY ON SATURDAY... ...Central Plains and Missouri Valley... Multiple rounds of storms are possible across the Central Plains and Missouri Valley on Saturday. A well-established low-level jet will be in place across the area as a progressive cold front sweeps across the upper Great Lakes Friday night. The front will stall out over this region due in part to the countering southerly flow of the LLJ. Meanwhile, in the upper levels, disturbances will move northeast with the flow, in part spurred on by those thunderstorms. At the surface, a leeside low over the TX/OK Panhandles into Kansas will keep the southerly LLJ going right into the stalling front. The result will be likely training storms over some part of the area, with the guidance showing their usual spread as to exactly where that happens. For the second consecutive day, the guidance has been largely targeting eastern Kansas as the centroid of the action. Given the relative consistency from 24 hours ago, increased forecasted rainfall, and a favorable pattern for slow-moving and training storms, confidence increased to issue a Slight Risk for the area on Saturday. All of this not to mention that there will likely be storms into eastern Kansas on Friday night that will likely prime the soils in advance of the storms Saturday and Saturday night. Elsewhere, large Marginals remain in place from tech central Gulf Coast into the Mid-Atlantic. The I-95 corridor from DC to NYC was added to the Marginal with this update. Plentiful tropical moisture will surge northward in the wake of a warm front that made for a nice Labor Day Weekend in the Mid-Atlantic when as a back-door cold front the moisture was shoved out of the Mid-Atlantic and into the Southeast. Late in the day Saturday, a strong cold front moving through will allow that moisture to fuel numerous thunderstorms. Those storms will have the potential for training ahead of the front in the unidirectional southwesterly flow. Given the urban sensitivities, that allowed the Marginal to be expanded. On Sunday, a developing Plains leeside low, fueled by a strong upper level bowling ball low, will track northeastward across the northern Plains. The aforementioned LLJ over KS/MO on Saturday will continue northward into the upper Midwest due to that low driving it and all its associated moisture northward with it. Since the low itself will be tracking roughly parallel to the flow with the upper level low also moving northeast, a prolonged period of unidirectional southwesterly flow will allow for training and backbuilding storms, that while moving, will impact many of the same areas repeatedly Sunday into Sunday night. The area of greatest concern is from far northeastern Nebraska northeast across much of Iowa, southern Minnesota, and into western Wisconsin. PWATs of 2-2.25 inches will allow the storms to be very capable of heavy rainfall. Both surface and upper level lows will be on the stronger side compared to climatology, so forcing will also not be a problem. Additional upgrades are likely in the coming days should this pattern persist in the guidance. For now it remains a Marginal until consistency on where the strongest storms will occur is better ironed out. Wegman 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 $$