Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 AM EDT Thu Apr 1 2021 Valid 12Z Sun Apr 4 2021 - 12Z Thu Apr 8 2021 ...Weather Pattern Overview... A broad upper level ridge will be governing the overall weather pattern across much of the nation to begin the forecast period on Sunday. An upper level low will be slow moving east of New England while another trough amplifies along the West Coast and moves slowly inland. This pattern will lead to warm and dry conditions for much of the central and southern U.S., and some precipitation for the West and the northern tier states. ...Guidance 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 by Sunday night. The past few runs of the GFS have been much faster and stronger than the ECMWF/CMC and the ensemble means with the trough/closed low crossing the Rockies and then the Plains. In fact, the GFS is about 1000 miles ahead of the ECMWF by Day 7 (Thursday morning), and therefore received much less weighting in the forecast blend for fronts and pressures for the second half of the forecast period. Through Monday, a blend of the UKMET/GFS/ECMWF sufficed as a starting point. By the Tuesday to Thursday time period, the past two runs of the CMC have been severely out of phase with the other guidance across the northeast Pacific and western Canada, with much less signature of a second trough emerging from the Gulf of Alaska compared to the ensemble spaghetti plots. With the differences in the guidance noted above, forecast confidence for the middle to end of next week is below average, with significant revisions possible in future forecasts. For the second half of the forecast period, additional weighting was applied to the ensemble means and also included some of the 12Z ECMWF along with previous WPC continuity. ...Sensible Weather and Potential Hazards... Most of the continental U.S. should be relatively uneventful 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 Pacific storm system slowly approaches that region by Monday and into Tuesday, although the timing of this remains in question. This could potentially bring some heavy snow to the Sierra Nevada early in the week and perhaps reach the northern Rockies by the middle of next week. Rainfall should be generally light for most of the valley locations. Across the Eastern U.S., a weak system may bring some light rain to the Great Lakes next week while the Atlantic system stays just offshore near the Canadian maritimes, along with most of its precipitation. Very warm temperatures are forecast for much of the central U.S. in time for the weekend, making it feel more like late May or even early June. This will be the result of an upper level ridge building in along with southerly flow ahead of the next frontal boundary. Afternoon high temperatures will likely be on the order of 15 to 30 degrees above normal. Highs could reach near 70 degrees along the Canadian border, 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. Some 100 degree readings are becoming more likely for the hotter desert locations. A slow cooling trend is expected for the West Coast as the upper trough/low moves through and cloud cover increases. 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