Extended Forecast Discussion NWS Weather Prediction Center College Park MD 456 PM EDT Thu Jun 25 2020 Valid 12Z Sun Jun 28 2020 - 12Z Thu Jul 02 2020 ...Excessive Rainfall/Runoff Threat for the Northern Rockies Sunday/Monday... ...Guidance/Predictability Assessment... Guidance heralds a transition into a much more amplified/blocky pattern for next week in a pattern with active weather. An amplified upper trough will settle down from the Northeast, while more deep troughing builds across the Western U.S. as a hot ridge builds in between from the Southern Plains to the Upper Mississippi Valley. The blocky nature of the upcoming flow seems to favor holding onto a closed low for the Northeast through the forecast period, probably most in line with the ECMWF. Out West, guidance has come into somewhat better agreement with amplified troughing diving into the West/Southwest this weekend and a closed low developing over the northern/central Great Basin into early next week. However, recent GFS runs continue to be quicker than the rest of the guidance on kicking this low northeastward, but are lately trending a bit slower. A more pronounced cluster of ensemble guidance along with the deterministic ECMWF/CMC would suggest it lingering a day or so longer. With the above assessment, WPC primarily favored the ECMWF along with weighting of the ensemble means days 3-7 to address increased uncertainty and model inconsistencies. This approach fits well with previous WPC continuity as well in a pattern with average to better forecast predictability. ...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 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. The slow translation of energies downstream into the nrn Plains early-mid next week should also set up a heavy convective rainfall pattern there as moisture/instability pool into a slow moving frontal zone. 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. Schichtel/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 Hazards: - Heavy rain across portions of the Northern Plains and the Northern Rockies, Sun-Mon, Jun 28-Jun 29. - Heavy rain across portions of the Upper Mississippi Valley and the Northern Plains, Tue, Jun 30. - Flooding possible across portions of the Upper/Middle Mississippi Valley, and the Great Lakes. - Flooding occurring or imminent across portions of the Upper/Middle Mississippi Valley, the Mid-Atlantic, and the Northern Plains. - Flooding likely across portions of the Upper/Middle Mississippi Valley. - High winds across portions of the Central Rockies, the Central Great Basin, California, the Northern Great Basin, and the Southwest, Sun, Jun 28. - Much above normal temperatures across portions of the Northern/Central Plains, and the Upper Mississippi Valley, Sun-Mon, Jun 28-Jun 29. - Much above normal temperatures across portions of the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Tue-Thu, Jun 30-Jul 2. - Enhanced wildfire risk across portions of the Central Great Basin and the Southwest, Sun, Jun 28. - Enhanced wildfire risk across portions of the Southern Rockies, the Central Rockies, the Central Great Basin, and the Southwest, Mon, Jun 29. 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