Extended Forecast Discussion NWS Weather Prediction Center College Park MD 302 PM EDT Sun Apr 24 2022 Valid 12Z Wed Apr 27 2022 - 12Z Sun May 01 2022 ...Overview... Modest cyclogenesis near/east of New England midweek is forecast to bring lingering mixed precipitation and gusty winds late this week into next weekend for parts of the Northeast. Meanwhile, multiple shortwaves moving onshore into the Pacific Northwest will likely push a broad trough through much of the western U.S. late this week, reaching into the northern/central Plains by the weekend where a low pressure system is forecast to form. A broad shield of precipitation ahead of this system is forecast to expand across the midsection of the country into the Ohio and Tennessee Valleys and then toward Appalachians by next weekend, although details remain uncertain at this point. ...Model Guidance Evaluation... Model guidance remains quite agreeable in keeping a slow-moving low pressure system over the Canadian Maritimes through much of the medium-range period after modest cyclogenesis is forecast to occur near/east of New England on Wednesday. There is also good agreement on the broad ridge over the central U.S., though with uncertain details on embedded shortwaves. In contrast, models continue to indicate much uncertainty with multiple shortwaves forecast to move onshore across the Pacific Northwest, leading to diverging model solutions by next weekend as the system reaches into the midsection of the country. While there has been a wide variety of possible outcomes as shown by recent deterministic model solutions, ensemble means have generally agreed to develop and consolidate a broad low pressure system to be centered over the central Plains on Saturday, and heading generally toward the east or east-northeast, with a broad swath of precipitation ahead of the entire system. This multi-model/ensemble approach yielded a solution that is quite compatible with the previous WPC medium-range forecast package. Toward the end of the forecast period, the GFS and GEFS have generally slowed down the eastward progression of the central U.S. system in better agreement with the ECMWF and CMC means. Therefore, a slower solution is preferred. The WPC medium-range morning package begins with a blend of 40% from the 00Z ECMWF/00Z EC mean, 40% from the 06Z GFS/GEFS, and 20% from the 00Z CMC/CMC mean, transitioning to a blend of 45% from the 00Z EC/EC mean, 30% from the 06Z GEFS and 25% from the CMC mean by Day 7. ...Sensible Weather/Threats... The northeastern U.S. could receive multiple rounds of precipitation through much of the week as the upper level and surface lows pivot and linger over the area. Periods of precipitation should generally be light to moderate; amounts will add up over time but still are not expected to be too hazardous. Higher elevations of New England may see snow during the night but mixing with rain during the day. Some rain may begin in the central U.S. as early as Wednesday near a warm front and surface low, but rain is likely to increase in coverage and amounts as the week progresses as the main upper trough exits the Rockies and consolidates a low pressure a low pressure system in the central U.S. The entire system is forecast to push eastward toward the eastern U.S. later next weekend. Unsettled weather should also occur in the western to north-central U.S., with amounts increasing from Thursday into Friday and begins to lessen by next weekend. Conditions will likely be cold enough for snow in the northern Rockies on the backside of the surface low, and there is once again some threat of wintry precipitation spreading into the northern High Plains as well. But the full details of these threats may not realized for a few more days given the current model uncertainty. Cooler than average temperatures are in store for the eastern third of the U.S. Wednesday into Thursday, with the core of the cold air moving through the Great Lakes/central Appalachians, where temperatures 10-20F below normal will make for the possibility of a few daily record lows on Wednesday. On the other hand warmer than normal temperatures should spread from the Southwest/Four Corners states into southern and central parts of the Plains underneath upper ridging. By Friday into the weekend, the pattern should generally shift to cooler than average temperatures in the North and warmer than average in the South. The northern Plains to Midwest are forecast to see highs nearing 20F below average, but lows may be closer to normal. Meanwhile, the southern tier should be around 10F above average. Kong/Tate 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, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices 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