Extended Forecast Discussion NWS Weather Prediction Center College Park MD 117 AM EDT Thu Jun 25 2020 Valid 12Z Sun Jun 28 2020 - 12Z Thu Jul 02 2020 ...Guidance/Predictability Assessment... The beginning of the medium range period (Sunday) should transition into a much more amplified/blocky pattern which persists into the middle of next week. A closed low should settle into the Northeast, while deep troughing builds across the Western U.S. and a ridge builds in between from the Southern Plains to the Upper Mississippi Valley. In the Northeast, there is good agreement on the presence of at least deep troughing (with several models consistently showing a closed low) lingering through Tuesday before slowly beginning to lift northward. The first half of the period shows good agreement on this set up, though typical timing/intensity and run to run inconsistencies begin to develop by the end of the period. Out West, models have come into better agreement with amplified troughing diving into the Southwest this weekend and a closed low developing over the northern/central Great Basin by Monday. The GFS continues to be quicker than the rest of the guidance on kicking this low north/eastward by early to mid next week, while the better cluster of ensemble guidance along with the deterministic ECMWF/CMC would suggest it lingering a day or so longer. With the above assessment, WPC favored a majority of mostly deterministic guidance (ECMWF/CMC) the first half of the period, with increasing weighting of the ensemble means thereafter to account for increased uncertainty and model inconsistencies. This approach fits well with previous WPC continuity as well. ...Overview and Weather/Hazard Highlights... Most impactful sensible weather of the extended range should be across the Western U.S. as amplified troughing and a lingering closed low leads to multiple weather hazards. Showers and storms are likely to develop along the leading cold front as it moves slowly through the Rockies and into the High Plains. Models continue to indicate the best potential for heavy rainfall will be across portions of western Montana Sunday and Monday as upper dynamics combine with orographic effects. Significant height falls and cooling temperatures should allow precipitation to fall as snow across the highest elevations of the Northern Rockies. To the south, strong low to mid level winds combined with dry conditions may also lead to an increased fire weather threat across portions of the southern Great Basin/Four corners region early next week. Expect temperatures across the West to be well below normal for late June/early July standards, with some places averaging 10 to 20 degrees below average daytime highs. A cold front pushing off the Northeast coast on Sunday will continue some showers and storms across the region and back into the Ohio Valley. Showers and storms will continue to linger into next week down across much of the South/Southeast states along the slow moving trailing front and upper trough amplification. The upper trough should keep temperatures near normal for the South/East, but a building ridge will result in above to much above normal temperatures stretching from the Northern Plains into the Upper Midwest/Great Lakes. 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