114 FOUS30 KWBC 160730 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 330 AM EDT Mon Mar 16 2026 Day 1 Valid 12Z Mon Mar 16 2026 - 12Z Tue Mar 17 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-ATLANTIC AND NORTHEASTERN U.S... Broad axis of diffluence positioned over the Ohio Valley into the Northeast will lead to multiple rounds of convection once east of the Appalachian front. Warm moist air will continue to funnel poleward ahead of a very amplified trough axis centered over the Midwest to Mid-Mississippi Valley. PWATs across the Mid Atlantic have already surged beyond 1", a solid 3 standard deviations above normal compared to climatology putting into the 97-99th percentile for mid-March. Expectation is for this surge to continue pushing further north within the amplified flow east of the Mississippi leading to a large swath of the east coast to exhibit an environment favorable for at least the threat of heavy rainfall. A multi-round scenario of convective impacts are anticipated as weak mid-level perturbations usher north-northeast ahead of the mean trough and cold front migrating through the Ohio Valley. Prior to the cold front arrival and associated precip field along and ahead of the front, moderate to locally heavy rains from convective clusters could help prime local soils before the main time frame of impact after 18z occurs. One of the trends within guidance was a relatively skinny convective segment that will be the main player in the higher rates exhibited in this setup. The linear segment will be relatively progressive, but rates between 0.75-1.5"/hr at peak intensity are plausible as it moves through the Mid Atlantic and Northeast leading to a threat for flash flooding as it migrates into the Piedmont and urban zones characterized within the Northeastern Megalopolis. Areal average of 0.75-1.5" is forecast for much of the area from northern VA up into NY state and Northeast New England. The maxima of over 2" is still showing up within deterministic output via both global and CAMs physics. The area of interest continues to point to CT/RI/Southern MA as the primary spot for more appreciable totals >2". This is supported via the neighborhood prob fields of 50-80% for at least 2" by the latest 00 HREF output. Other notable areas include high probs >70% for at least 1" aligned along the Blue Ridge to the I-95 corridor for VA/MD/PA extending into the Lower Hudson and Catskills area of NY state. Another axis of higher probs exists across eastern ME and parts of Northern New England which coupled with high SWE presence should allow for rapid snow melt and potential for local hydrologic issues stemming from both the precip and snow/ice melt. This signal was sufficient for maintenance of the previous MRGL risk with only some minor adjustments on the southern edge of the risk area to account for the latest model trends. The progressive nature of the precip should curb some of the flash flood concerns making this a solid MRGL risk with perhaps a bump in the risk magnitude if guidances trends more aggressive in QPF output. For now, this is a classic setup for early spring convection and modest flash flood prospects. Kleebauer Day 2 Valid 12Z Tue Mar 17 2026 - 12Z Wed Mar 18 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WASHINGTON STATE... Active pattern across the Gulf of Alaska will lead to another AR contribution into portions of the Pacific Northwest as the main IVT surge will adjust south into WA state after impacting neighboring British Columbia the day prior. Looking at IVT values between 500-700 kg/ms across northwest WA state with the surge propagating far enough inland to impact the Northern Cascades. Rainfall amounts between 2-3" will be common in the hardest hit areas, mainly into the Olympic Peninsula, Chehalis River valley, as well as the Cascades to the east of Seattle. Rates will lack vigor to the point for a more substantial impact, so the threat is mainly due to prolonged moderate to locally heavy rain prospects falling over relatively moist soil layer present after being impacted for weeks leading in. The previous MRGL risk was generally unchanged with the threat leaning towards the lower-end of the risk threshold. Areal hydrologic concerns are still viable with river and small stream flooding the most notable potential impacts. Kleebauer Day 3 Valid 12Z Wed Mar 18 2026 - 12Z Thu Mar 19 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WASHINGTON STATE... Occluded low over the Gulf of Alaska a strong mid-level ridge positioned across the Southwest U.S. will lead to a continued transport of modest IVT into WA state for the D3 period. AR dominated pattern will enhance rainfall prospects for the northern half of WA leading to cumulative rainfall totals breaching 4" in spots within the Northern Cascades, Olympics, and adjacent coastal areas of northwest WA. Real concern is the growing hydrologic factors with river flooding coupled with moderate rainfall posing a problem for areas around the main rivers and tributaries for the aforementioned areas. Flash flood threat remains low due to the rates anticipated with the rainfall as hourly rainfall will remain <0.5"/hr for a majority of Wednesday. However, the coupling of the previous days rain and the already saturated soils will likely lead to some hydro concerns mid-week, so maintained the previous MRGL risk inherited with only some minor tweaks at the southwest edge of the risk. Kleebauer 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