Extended Forecast Discussion NWS Weather Prediction Center College Park MD 358 PM EDT Mon Mar 29 2021 Valid 12Z Thu Apr 01 2021 - 12Z Mon Apr 05 2021 ...Overall Weather Pattern... A deep upper trough and a cold surface high pressure system will settle across the eastern U.S. late week into weekend behind a deepening cyclone exiting New England. On the other hand, an upper ridge edging into the Plains will bring persistent warmth into the northern Plains. Meanwhile, models continue to show uncertainty across the Pacific Northwest where the next upper trough/low should bring an increasing chance of light to possibly moderate precipitation across the Northwest and the northern half of California by next Sunday into Monday. ...Model Guidance and Predictability... The model guidance suite this morning continues to show excellent agreement on predicting the amplitude and timing of the deep upper trough settling across the eastern U.S. late this week into the weekend. The excellent model agreement also extends westward through much of the Plains and into the southern Rockies as the cold high in the East gradually modifies and persistent southerly flow expands the warm air mass across the northern Plains. The greatest uncertainty is across the Pacific Northwest where models continue to show some difficulties in handling an upper trough digging down from the Gulf of Alaska and its interaction with a southern stream wave lifting across the eastern Pacific. The ECMWF has continued to be the slowest guidance with a closed off upper low off the West Coast early next week. The GFS is not as slow. The ECMWF and GEFS means agree quite well however. The CMC offers the fastest solution regarding this system. The WPC guidance was based on a general compromise of the 00Z ECMWF/00Z EC mean and the 06Z GFS/06Z GEFS together with some contributions from the 00Z CMC and CMC mean. This yielded a solution quite similar to the previous WPC forecast package. ...Sensible Weather and Potential Hazards... A cold air mass will be ushered into the eastern U.S. in the wake of an intensifying low pressure system exiting New England on Thursday. Rain initially over Maine should change over to a period of snow before ending as light snow tapers off across northern New England Thursday night. Windy conditions are likely for the East Coast on Thursday with a strong pressure gradient in place. Temperatures will then dip well below freezing by Friday morning over much of the interior eastern U.S., with many daily record low temperatures forecast for Friday morning. Warmer air will gradually filter in from the west as the cold high pressure system modifies and settles into the Southeast into the weekend. Meanwhile, an extended period of very warm and dry weather is forecast to settle across the northern Plains under a slow-moving upper ridge and persistent southerly surface flow. This could enhance the fire danger across the region by this weekend and early next week. 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 by the weekend. This will likely be accompanied with an increasing chance of light to possibly moderate precipitation moving inland across the Northwest and the northern half of California by Sunday into Monday depending on the speed of progression of the system. Kong 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 Hazards: - Heavy snow across portions of the Northeast, Thu, Apr 1. - Flooding possible across portions of the Southeast, the Mid-Atlantic, the Southern Appalachians, and the Tennessee Valley. - Flooding occurring or imminent across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, the Ohio Valley, and the Tennessee Valley. 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