Extended Forecast Discussion NWS Weather Prediction Center College Park MD 413 PM EDT Tue May 26 2020 Valid 12Z Fri May 29 2020 - 12Z Tue Jun 02 2020 ...Much above normal temperatures to progress from the West into the northern/central Plains... ...Overview and Guidance/Predictability Assessment... The strong upper ridge positioned over the southwest U.S. at the start of the period will continue to bring much above normal temperatures to much of the western U.S. Friday and Saturday. The ridge is then expected to work slowly eastward late in the weekend and early next week. A pair of upper level lows off the west coast will absorb into a longwave trough that settles over the immediate west coast, bringing periods of rainfall that could be locally heavy at times. For the eastern U.S., troughing will primarily be the theme, especially for the Northeast and New England. A sharp cold front drops through the Great Lakes and eastern U.S. this weekend and early next week, bringing seasonably cool temperatures and lower humidity to much of the region. That front is forecast to reach the southeast U.S. before washing out in the weak upper level flow. The latest model guidance shows average to above average agreement and consistency from previous cycles on day 3 and for the most part, a near equal weighted blend of the 00Z ECMWF, 06Z GFS, 00Z UKMET, and 00Z CMC was incorporated. On day 4 and especially day 5, the GFS (both 00Z and 06Z cycles) was considerably too fast with shortwave energy ejecting out of the northern/northeast Pacific that translated toward the Pac NW well ahead of the other deterministic guidance as well as the ensemble means. This speed bias translated to faster progression over the northern tier late in the period. So overall the GFS was incorporated less on day 5 and almost none at all for late in the period with heavy components of the ECMWF and its ensemble mean. ...Weather/Hazard Highlights... Within the large area of much above normal temperatures progressing from the West into the Plains, the forecast has been consistent so far in highlighting plus 20-25F anomalies for highs from the far northeast corner of California across parts of Oregon/Nevada/Idaho during Fri-Sat. Greatest anomalies may be closer to plus 15-20F or so over the northern-central High Plains by Sun-Tue. The West Coast states will see highs settle to near or slightly below normal. Meanwhile cool high pressure behind the cold front dropping through the East will bring an area of temperatures up to 5-12F below normal from the Upper Midwest eastward/southeastward. Ahead of this front the Northeast should see temperatures of 10-20F above normal on Fri. Morning lows over a larger area in the East could be close to record warm values but rainfall later in the day could result in lower mins for the calendar day. The evolution/progression of the large scale pattern will favor decreasing precipitation coverage over the lower 48 with time. Over the East the majority of rain/thunderstorm activity will be during Fri-Sat ahead of the cold front pushing into the region and the upper shortwave crossing the South. Some activity could be locally moderate/heavy. Parts of Florida and southern Texas will remain south of the front through the period and may see some rainfall linger into next week. Potential remains for areas of moderate to heavy rainfall over some locations of extreme northern California and the Pacific Northwest for part of the weekend due to the upper low tracking northward across the region. Later in the period this feature will likely support Canadian low pressure that brings a frontal system across the Northern Plains, with some rainfall possible ahead of it late in the period over the Upper Midwest and/or Great Lakes. The trailing upper trough reaching the West Coast should support mostly light precipitation early next week, mainly over parts of the West Coast states. Expect scattered diurnally favored rainfall over the central-southern Rockies. Rausch/Taylor 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 California, the Pacific Northwest, and the Northern Great Basin, Sat, May 30. - Heavy rain across portions of the Southeast and the Mid-Atlantic, Fri, May 29. - Flooding possible across portions of the Lower Mississippi Valley, the Southern Plains, the Northern Rockies, the Middle Mississippi Valley, the Southeast, and the Great Lakes. - Flooding occurring or imminent across portions of the Northern Plains, the Southern Plains, the Northern Rockies, the Middle Mississippi Valley, the Mid-Atlantic, the Southeast, and the Great Lakes. - Flooding likely across portions of the Central Plains, the Southeast, the Middle Mississippi Valley, and the Southern Plains. - Much above normal temperatures across portions of the Central Great Basin, the Northern Rockies, California, the Northern Great Basin, the Pacific Northwest, and the Southwest, Fri-Sat, May 29-May 30. - Much above normal temperatures across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, the Northern Great Basin, and the Southwest, Fri-Tue, May 29-Jun 2. - Much above normal temperatures across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains, Sun-Tue, May 31-Jun 2. - Much above normal temperatures across portions of mainland Alaska, Fri-Tue, May 29-Jun 2. 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