Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Wed Apr 27 2022 Valid 12Z Sat Apr 30 2022 - 12Z Wed May 04 2022 ...Overview... The medium range period begins Saturday with a closed upper low over the central/northern Plains along with a modestly deep surface low, and these features will slowly lift northeast into early next week. This will spread rain across much of the central U.S. with some chance of wintry weather spreading into the northern High Plains on the backside of the low. Much of the central and eastern U.S. can expect periodic showers and thunderstorms through the first half of next week as fronts linger. Additionally, periodic unsettled weather is forecast in the Northwest as a series of upper troughs and frontal systems move through. ...Model Guidance Evaluation... Recent model guidance is reasonably agreeable as the medium range forecast begins in terms of the central U.S. upper-level and surface lows though with some slight spread in exact placement, as well as an upper low slowly pulling away from the Canadian Maritimes. There is good consensus for these features to track east-northeastward with a general weakening trend for the central U.S. lows through Sunday-Monday. There is somewhat more variability with upstream energy coming into the Pacific Northwest Saturday and its evolution going forward. GFS runs have been a bit weaker with the shortwave initially but hold onto it perhaps longer before getting absorbed in the east-central U.S. around Monday-Tuesday. The early part of the WPC forecast featured a blend of the deterministic guidance before gradually phasing out some UKMET and CMC influence in favor of the ECMWF ensemble mean. Another round of upper energy should spill into the West for the early part of the workweek, likely closing off another upper low as it tracks through the western and central CONUS. The 12Z GFS was the fastest/farthest east with this feature, with the 18Z and newer 00Z GFS and the rest of the deterministic guidance slower. However, CMC runs have perhaps been too slow with the upper low's movement, with even its 12Z ensemble mean faster. The ECMWF and EC ensemble mean seemed like a good middle ground between these slower and faster ends of the spectrum, so favored those for the WPC forecast blend by the latter part of the period, with some inclusion of the 18Z GFS and GEFS mean. ...Sensible Weather/Threats... The first surface low pressure system affecting the lower 48 over the weekend will spread precipitation across much of the central and eastern U.S., with some wintry weather possible in the Dakotas, with the best chances in the higher elevations of the Black Hills. In portions of the Dakotas, precipitation may begin as rain and transition to mixed precipitation or snow, though details of these threats remain somewhat uncertain. Additionally, rain could become heavy to locally excessive from parts of the Plains into the Mississippi/Ohio Valleys on Saturday. Then as the low pressure system shifts eastward early next week, precipitation chances are expected to spread eastward, but linger in the central U.S. as well as the front there may stall. Current forecasts show potential for heavy rainfall on Sunday across the southern Plains, though the axis of heaviest rainfall may shift in future forecasts. Scattered showers and thunderstorms will likely persist from the Plains eastward through the first half of next week. Furthermore, rounds of light to moderate precipitation (snow in the higher elevations and rain in the lower elevations) are forecast across the Northwest as a series of fronts cross the region along with upper-level energy. One such front and low pressure system could eject into the central U.S. around midweek. Temperature-wise, the general trend over the lower 48 will be for cooler than average weather in the northern tier and cooler than average in the southern tier. The core of the coldest air should be across the northern High Plains to Midwest, where highs will be around 15-25F underneath periodic upper troughing. Meanwhile, slightly above normal temperatures should stretch across much of the southern tier, and into the Ohio/Tennessee Valleys as well, particularly in terms of warmer than normal lows. 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