Extended Forecast Discussion NWS Weather Prediction Center College Park MD 424 PM EDT Mon Jun 22 2020 Valid 12Z Thu Jun 25 2020 - 12Z Mon Jun 29 2020 ...Guidance/Predictability Assessment... The overall theme for the medium range will be a transient wave traverse the northern tier of states from west to east days 3-6, moving off the New England coast Day 7. The pattern transitions to more of a high amplitude, blocked pattern early next week. The models indicate a closed low sfc-aloft develop over the northern Rockies and then Northern Plains. Downstream from this a high amplitude ridge develops in the central to eastern US early next week. Models and ensembles continue to have timing differences regarding the upper trough exiting the Northwest on Thursday/Day 3, and continuing as it crosses the northern plains to upper MS Valley Day 4, Great Lakes Day 5, and northeast Day 6 (Sun 26 Jun). The deterministic ECMWF continues to be faster with this trough and associated sfc low and front. The ensemble means generally follow suit with their deterministic counterparts. Given the lack of run to run continuity and agreement a blend of the 00z ECMWF/ECMWF Ensemble Mean, 06z GFS and 06z GEFS Mean was used, with less weighting on the 00z UKMET. By day 7, this system should move off the northeast coast. The 00z Canadian/ECMWF/06z GFS indicate renewed amplified troughing across the West Coast on day 6, with a closed low developing on the northern Rockies/northern high Plains Day 7. Typical intensity differences exist, with modest timing offsets, so a blend of the 00z ECMWF/06z GFS/00z ECMWF Ensemble Mean, and 06z GEFS Mean was used for the height/adjusted sea level pressure forecasts. ...Overview and Weather/Hazard Highlights... Height falls across the Northeast will drive a cold front off the East Coast on Thursday with showers and thunderstorms likely across south Texas across the southeast. Locally heavy rain is possible Thu into Fri in southern Texas. A ridge of high pressure surface/aloft builds across the south over the weekend into early next week, resulting in a warming trend. Temperatures may approach records warm minimums across the southeast to mid Atlantic Sunday into Monday. The trough aloft/surface cold front should focus showers and potentially strong thunderstorms from the Northern Plains, into the Upper Midwest, and lower Great Lakes late week into the weekend, and then the northeast this weekend. Models show the possibility for moderate to locally heavy precipitation, though timing remains in question given model uncertainties. As the upper low forms in the northern Rockies early next week, the 00z ECMWF and 06z GFS indicates potential for locally heavy precipitation to develop over northern Wyoming and Montana. A cold pool develops over the Pacific northwest Sunday and moves into the northern Rockies Monday. This may allow precipitation in the northern Rockies to fall as snow at higher elevations. Also, the cold pool surges south across most of California, with temperatures on Monday becoming below normal. Downstream from the high amplitude western trough, building heights in the central Plains to upper Mississippi Valley and upper Great Lakes leads to a warming trend Sunday into Monday 29 June. Petersen 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 Southern Plains, Thu, Jun 25. - Heavy rain across portions of the Upper Mississippi Valley, the Northern Plains, and the Northern Rockies, Mon, Jun 29. - Heavy rain across portions of the Great Lakes, and the Upper/Middle Mississippi Valley, Fri, Jun 26. - Heavy rain across portions of the Great Lakes, the Northeast, the Central Appalachians, and the Ohio Valley, Sat, Jun 27. - Flooding occurring or imminent across portions of the Mid-Atlantic, the Southern Plains, the Upper Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Mid-Atlantic. - Much above normal temperatures across portions of California, the Central Great Basin, the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Fri, Jun 26. 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