FOUS30 KWBC 101558 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Tue Mar 10 2026 Day 1 Valid 16Z Tue Mar 10 2026 - 12Z Wed Mar 11 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN PLAINS AND THE SOUTHERN GREAT LAKES... 16Z Update... Changes to continuity include some expansion of the Marginal Risk across the OH Valley and locally across the central and southern Plains given what should be a relatively complex evolution of multiple convective clusters/MCSs going through tonight. The upper OH Valley in particular remains rather sensitive fairly low FFGs and at least scattered areas of convection capable of producing 1 to 1.5 inch/hour rainfall rates may be possible over some of these areas. For areas of the central and southern Plains, the Marginal Risk generally follows the overall convective footprint in the warm sector ahead of the approaching upstream height falls/frontal system. More specifically, the latest guidance continues to support multiple areas of well-organized convection extending from the TX Hill Country northeastward to near the Red River. Multiple linear bands of convection with high rainfall rates locally exceeding 2 inches/hour are expected as ejecting shortwave energy interacts with an increasingly moist and unstable boundary layer. MLCAPE values exceeding 2000 J/kg along with PWs of 1.5 to 1.75 inches and a strongly sheared kinematic profile will support organized convective segments including supercells. Some localized mesoscale boundary interactions will support areas of convection becoming locally focused with at least some cell-training concerns possible. As such, the Slight Risk over the southern Plains has been adjusted a bit south and east to accommodate the 12Z HREF/06Z REFS, 06Z EC- AIFS and recent HRRR/RRFS solutions. This includes some trimming of it the northern portion of it closer to the Red River. The end- result is expected to be a concern for locally several inches of rain and scattered areas of flash flooding including an urban flooding threat. For areas of northern IL, northern IN, southern Lower MI and northwest OH, the Slight Risk here has been only modestly tweaked as the setup here favors a well-organized convective impact with thunderstorms this evening and into a part of the overnight period capable of producing 1 to 2+ inch/hour rainfall rates. An ejecting wave of low pressure along a strong front coupled with a moist, unstable warm-sector airmass should yield strong MCS activity with a concern for areas of cell-training. The low-level jet this evening is forecasting to increase to locally 50+ kts, and this will being aimed into a strong front oriented west to east downwind from the approaching low center. Locally several inches of rain will be possible and this will drive concerns for flash flooding. Orrison Previous discussion... The signal for potentially two heavy precip axes persists in the guidance..in the very favorable coupled jet entrance/exit regions expected between the southern stream closed low moving into the Southern Plains and the northern stream jet across Mid Mississippi Valley and the Midwest region. Gulf moisture gets drawn northward over parts of the central U.S. from Texas into the central portion of the Mid-Mississippi Valley during the day. There has been a trend in the model guidance over the past 24 hours for the core of the higher precipitable water values to get shunted more eastward than northeastward...resulting in lower model QPF despite the upper support and mid-level mesoscale forcing remaining favorable. Consequently...trimmed the Slight Risk area to cover only portions of Illinois and Indiana where QPF exceeded an inch and which overlapped areas that experienced moderate to heavy rainfall a few days ago and have suppressed flash flood guidance. The better instability...and associated higher rainfall rates...still look to be over portions of Texas into southeast of Oklahoma as flow aloft becomes increasingly diffluent in response to an approaching upper low. .Mixed layer CAPE values of 1500 to around 2500 J per kg develop ahead of the low where precipitable water values will have risen into the 1.25 to 1.5 inch range resulting in the potential for 1+ inch per hour rates. The axis of model QPF and WPC deterministic QPF align well with modestly- lowered flash flood guidance from rainfall several days ago. Bann Day 2 Valid 12Z Wed Mar 11 2026 - 12Z Thu Mar 12 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE SOUTHERN US... The upper low over the southern states will continue to translate eastward on Wednesday. The upper support will be weakening as the system weakens/fills with time. Model run to run consistency has been poor and another round of changes were made this cycle. The changes included introduction of a Slight Risk over parts of eastern Texas and western Louisiana where model QPF exceeded two inches. In addition...there was some overlap between locally heavy rainfall a couple of days ago and the QPF. ...Pacific Northwest... Persistent on-shore flow of deep moisture into parts of coastal Washington and northern Oregon should result in occasional moderate rainfall...mainly in the west face of the coastal ranges. Amounts on the order of 2.5 inches to 3.5 inches in 24 hours is forecast which could result in isolated flooding ot run off problems in areas of poor drainage. Bann Day 3 Valid 12Z Thu Mar 12 2026 - 12Z Fri Mar 13 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHWEST UNITED STATES... ...Pacific Northwest... On-shore flow of deep moisture into parts of coastal Washington and northern Oregon persists into the Day 3 period that results in occasional moderate to locally heavy rainfall continuing along the coastal ranges. An additional 1 to 3 inches in 24 hours are possible...which could result in isolated flooding ot run off problems in areas of poor drainage. Bann 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