Extended Forecast Discussion NWS Weather Prediction Center College Park MD 229 AM EDT Tue Jun 23 2020 Valid 12Z Fri Jun 26 2020 - 12Z Tue Jun 30 2020 ...Guidance/Predictability Assessment... The medium range begins Friday with a transient shortwave traversing the northern tier of the country from the Northern High Plains into the Midwest/Northeast this weekend. Early next week, the guidance indicates the pattern may transition to more of a high amplitude/blocked regime with a possible closed low developing over the Northwest states and ridging building downstream across the Central and Eastern U.S.. Deterministic model solutions continue to struggle with timing of the upper shortwave exiting the Northern High Plains on day 3/Friday and continuing into the Upper Midwest this weekend and the Northeast early next week. The ECMWF continues to be the fastest solution both with the upper shortwave and the associated surface low and front, followed by the GFS and the UKMET/CMC. Generally, the ensemble means follow suit with their deterministic counterparts, but are still close enough to be blendable. WPC preferred a blend of the GFS/UKMET with ensemble means for this system, which fits closer to continuity as well. Troughing over the Northwest U.S. amplifies by Sunday, potentially closing off an upper low over the Northern Rockies by Day 6/Monday. Models generally agree on the overall existence of this amplified trough, but struggle with intensity and timing. With run to run variability still high at this time range, prefer a blend of mostly ensemble mean guidance with this system. ...Overview and Weather/Hazard Highlights... Cold front should focus rain and potentially strong storms across the Upper Midwest/Upper Mississippi Valley on Friday, moving eastward into the Great Lakes and New England on Saturday. Model uncertainty on timing is considerable still, but there remains a signal for at least a locally heavy rainfall threat with this system. Showers and storms should linger through the weekend across the Southern states as well along a weakening frontal boundary and within a region of favorable dynamics aloft. Upper ridging builds in behind this system across the Central and Eastern states bringing a warming trend to the region this weekend into Monday especially across the Northern Plains and Great Lakes. The next cold front dives into the Northwest by Saturday morning with showers and storms likely developing along and ahead of it this weekend as it shifts into the Rockies. Potential upper low over the northern Rockies early next week brings a threat for locally moderate to heavy precipitation with models indicating the best chance for this across Montana into northern Wyoming. Significant height falls and cooling temperatures could allow precipitation to fall as snow across the higher elevations of the northern Rockies. Temperatures across the West trend from above normal on Friday, to below or well below normal in spots by 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