Extended Forecast Discussion NWS Weather Prediction Center College Park MD 109 AM EDT Wed Jun 24 2020 Valid 12Z Sat Jun 27 2020 - 12Z Wed Jul 01 2020 ...Guidance/Predictability Assessment... The medium range period begins Saturday with a shortwave moving from the Upper Great Lakes into the Northeast by Sunday. By early next week, the guidance indicates the pattern should transition to more of a high amplitude/blocked regime with amplified troughing along both coasts and a building ridge in between. The guidance shows better agreement with the initial shortwave into the Northeast this weekend compared to recent days. After this, timing and intensity differences begin to arise in the deterministic models regarding possible closed low lingering over the Northeast, though there is enough run to run variability to stick close to the ensemble means at this time frame. Out west, amplified troughing dives into the Northwest by Saturday, with closed low development over the Northwest/Great Basin likely by Monday. After this the details get murky on how this evolves. The GFS is quick to lift the low into the Northern Rockies/west-central Canada, while the ECMWF holds a fairly strong system over the Western U.S. for a few days. While the GFS does have support from the latest run of the deterministic CMC, a look at the spaghetti charts show the vast majority of ensemble solutions holding the system back as either a closed low or amplified troughing, very similar to that of the ECMWF. Given this, WPC preferred a blend of the ensemble means with the deterministic ECMWF for days 5-7. ...Overview and Weather/Hazard Highlights... A cold front moving from the Great Lakes into the Northeast should focus showers and potentially strong storms from the Northeast to the Ohio Valley/mid-Mississippi Valley this weekend, with models continuing to show a signal for at least locally heavy rainfall. Showers and storms will continue to linger into next week across much of the Southern/Southeast states as the western portion of the boundary becomes stationary and troughing builds in aloft. Temperatures across the Eastern states should stay near normal underneath the trough, but a defined warming trend should happen across the Central U.S. with the best chance for above to much above normal temperatures from the Northern Plains into the Great Lakes. The next cold front dives into the Northwest by Saturday morning with showers and storms likely developing along and ahead of it as it shifts and becomes stationary into the Rockies/Northern Plains early next week. Potential upper low development over the West brings a threat for heavy precipitation with models indicating the best chance for this across western Montana Sunday and Monday. Significant height falls and cooling temperatures should allow precipitation to fall as snow across the higher elevations of the northern Rockies. Temperatures across the West will trend cooler with a period of temperature anomalies 10 to 15 degrees below normal possible across portions of the Great Basin early next week. Santorelli Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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