251 FXUS02 KWBC 271955 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 355 PM EDT Mon Apr 27 2026 Valid 12Z Thu Apr 30 2026 - 12Z Mon May 04 2026 ...Heavy rain and flooding threat increasing across the south- central U.S. late this week... ...Overview... An amplified upper level pattern will persist through the period, with mean ridging over the eastern Pacific and mean troughing over the eastern United States. This pattern will result in active weather for the south-central U.S. and East Coast, with increasing potential for heavy rain and flooding late this week over the southern Plains and lower Mississippi Valley. A coastal low may also bring locally heavy rainfall and isolated flooding concerns to the Northeast on Thursday. ...Guidance/Predictability Assessment... Model guidance remains in good agreement on the pattern through the period as an increasingly amplified and blocky pattern develops across the nation. An upper level low will move into the Southwest late this week and trigger heavy rainfall across the south-central United States. Most of the deterministic, ensemble, and AI guidance has come to a consensus on the timing of this feature, but the ECMWF seems to be much slower than all other guidance. The spread in guidance has resulted in a broad precipitation field in the National Blend that accounts for the slower and faster possibilities. Another upper low is expected to move south just offshore of the West Coast early next week, and there is quite a bit of uncertainty with the position of this feature. The ECMWF and CMC are on the western side of the spread while the GFS and UKMET are on the eastern side. AI guidance seems to fall in between, which is the most reasonable solution at this point. The eventual position of this feature may impact winds and precipitation chances along the West Coast Sunday into Monday The WPC forecast was composed of a near even blend of the available deterministic guidance as a starting point, which produced a reasonable middle of the road solution through the end of the week. Ensemble means were added to the blend in increasing amounts for the weekend into early next week to help smooth out model differences. This maintained continuity with the National Blend and previous forecast. ...Weather/Hazards Highlights... A frontal system associated with a deepening trough over the Northeast will begin to spread much needed rainfall into the region on Thursday. The primary low pressure system will weaken as it tracks into southeastern Canada, but secondary coastal development off the Mid-Atlantic will take control soon after as it approaches southern New England later Thursday into Friday. The newly formed low will then begin to draw a long fetch of anomalous Gulf/Atlantic moisture northward, supporting an axis of heavy rainfall totaling 1-3" across northern New England and especially from eastern New Hampshire into the southern half of Maine. While the signal for heavy rain is noteworthy and could lead to runoff and/or localized flooding, the majority of the rainfall should be beneficial given moderate to severe drought conditions. As a result, no Day 4/Thursday ERO was highlighted for the time being. The coastal low should stall over the Canadian Maritimes Friday into the weekend, allowing intensity to wane but keeping conditions cool, windy, and wet/unsettled through early next week. A little snow wrapping in on the back/colder side of the storm can't be ruled out either across the higher elevations of northern New England or the Interior Northeast. Meanwhile, a southern stream Pacific low will slowly track into the Southwest on Thursday and interact with a frontal boundary over the southern Plains. Anomalous Pacific and Gulf moisture overrunning this frontal boundary combined with impressive dynamics and forcing from a strong upper jet will lead to the increasing potential for significant rainfall across the southern Plains and locally heavy snow in the southern Rockies. For the Day 4/Thursday ERO, the existing Marginal Risk was expanded northwestward to account for increasing QPF amidst decent instability. Friday into the weekend, waves along the frontal zone will expand the rainfall footprint eastward into the Lower Mississippi Valley and Southeast, with additional risks of heavy rain and potential flooding. The Day 5/Friday ERO features a Marginal Risk area from Texas to the Lower Mississippi Valley that was expanded eastward to account for a slightly faster progression of the frontal system. This risk area may be expanded further east and could potentially be upgraded with future updates. Elsewhere, another Pacific closed low may approach northern California and the Great Basin later this weekend into early next week, bringing cooler and unsettled weather featuring low elevation rain and high elevation mountain snow. Dolan/Miller Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw $$