Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Wed Mar 31 2021 Valid 12Z Sat Apr 3 2021 - 12Z Wed Apr 7 2021 ...Weather Pattern Overview... A deep upper trough departing the East Coast this weekend will allow the cold airmass to modify some across the northeastern quadrant of the nation. An upper level ridge building across the Plains will bring unseasonable warmth to the central and northern Plains. The next trough and potential closed upper low builds across the West Coast region by early next week, bringing a greater chance of precipitation across this region. ...Model Preferences and Predictability Assessment... The models and ensembles are in good overall agreement synoptically across the continental U.S. to begin this forecast period, with model differences in the 00z suite first becoming evident across the eastern Pacific. Through Sunday, a blend of the UKMET/CMC/ECMWF sufficed as a starting point, with less weighting to the GFS given a slightly more suppressed ridge axis across the Plains. By early next week, the most challenging aspect of the forecast is the level of northern and southern stream flow separation across the western U.S. as a trough sinks southward from the Gulf of Alaska and an upper low slowly approaching the California coast. Over the past 36 hours, the GFS has trended closer to the idea of a cut-off low near northern California by Tuesday, which the ECMWF has been indicating over the past two days. For the second half of the forecast period, additional weighting was applied to the ensemble means and also included some previous WPC continuity. ...Sensible Weather and Potential Hazards... Most of the continental U.S. should be relatively quiet in terms of precipitation through the upcoming weekend, with no episodes of heavy rain expected since a large surface high will be governing the overall weather pattern across the central and eastern states. Precipitation coverage should begin to pick up in coverage and intensity across portions of California, Washington, and Oregon as the next storm system slowly approaches that region by Monday and into Tuesday, and potentially bringing some heavy snow to the Sierra Nevada and perhaps reaching the northern Rockies by the middle of next week. Temperatures will still be chilly for much of the eastern half of the nation this weekend, although modifying some compared to Friday. Widespread subfreezing low temperatures are likely Saturday morning from the greater Atlanta metro area to eastern North Carolina, and points northward. This will include areas that are already well beyond their normal last freeze date. Very warm weather will be making headlines for much of the central U.S. in time for the weekend, as an upper level ridge builds in along with southerly flow ahead of the next frontal boundary, and results in readings of 15 to 25+ degrees above normal. Highs could reach the low to mid 80s across portions of Nebraska and South Dakota, and well into the 90s for the lower elevations of the Desert Southwest with perhaps some daily record highs being established. Some 100 degree readings here are within the realm of possibility. A slow cooling trend is expected for the West Coast and especially the Pacific Northwest where the next upper trough/low is forecast to approach. Hamrick 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, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml