189 FOUS30 KWBC 120055 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 855 PM EDT Wed Mar 11 2026 Day 1 Valid 01Z Thu Mar 12 2026 - 12Z Thu Mar 12 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE SOUTHEAST AND THE LOWER MS VALLEY... 01Z Update... A Slight Risk was maintained over portions of the lower Mississippi Valley and the Southeast, but modified based on recent radar trends and hi-res guidance (HREF/RRFS). A moist and unstable airmass persists with PWs climbing toward 2 inches. Strong ascent from coupled upper jet forcing and an approaching southern stream shortwave will sustain heavy rainfall through the overnight hours. Convection is expected to become more organized into a QLCS advancing from the lower Mississippi Valley into the Southeast overnight. Rainfall rates of 1-2"/hr are possible, with the HREF/RRFS showing high probabilities for accumulations over 2" within the Slight Risk area overnight. Heavier totals are more likely where cell-training occurs, raising the threat for localized flooding concerns. The Slight Risk was removed from the upper Ohio Valley, but a Marginal Risk that extends into the the Northeast was maintained. While localized heavy rainfall remains possible, guidance suggests storms will be progressive. Widespread flash flooding is not expected; however, isolated flash flooding remains a concern, especially in areas made more sensitive by melting snowpack in the Northeast. In the Pacific Northwest, the Marginal Risk remains unchanged as the ongoing atmospheric river continues to impact the region. IVTs peaking near 750 kg/m/s will drive enhanced moisture into the terrain, fueling an additional 3"+ overnight along portions of the coastal ranges of southwestern Washington and northwestern Oregon, as well as the windward slopes of the Cascades. Localized totals exceeding 5" remain possible along the favored terrain. Pereira Day 2 Valid 12Z Thu Mar 12 2026 - 12Z Fri Mar 13 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE PACIFIC NORTHWEST... 19z Update: No major changes to the inherited Marginal risk area. Chenard ...Previous Discussion... Only change was to nudge the Marginal risk back to the west just a bit given the placement of heavier snowfall in the Cascades. Despite that change...much of the shift made by the previous shift was retained in this outlook. On-shore flow of deep moisture into parts of coastal Washington and northern Oregon persists into the Day 2 period...with occasional moderate to locally heavy rainfall continuing along the coastal ranges. An additional 1 to 3 inches of rainfall in 24 hours is possible...which could result in isolated flooding ot run off problems in areas of poor drainage. Bann Day 3 Valid 12Z Fri Mar 13 2026 - 12Z Sat Mar 14 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE PACIFIC NORTHWEST... 19z update: An additional 1-4" of rain is expected across northwest OR into southwest WA. This will bring 72hr rainfall into the 3-10" range, likely resulting in at least some minor runoff concerns even if a lack of instability keeps rainfall rates low. Chenard ...Previous Discussion... The on-shore flow which has been anchored along coastal portions of Washington and northern Oregon will finally start to shift its focus southward a bit from Friday into early Saturday morning. The axis of a precipitable water plume with values of 0.75 to 1.00 inches will gradually be shifting southward into Oregon which allows precipitation rates to weaken farther north. With the rain moving into an area with drier antecedent condition...maintained a Marginal Risk area. 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