Extended Forecast Discussion NWS Weather Prediction Center College Park MD 248 AM EDT Wed May 26 2021 Valid 12Z Sat May 29 2021 - 12Z Wed Jun 02 2021 ...Record highs possible in the Pacific Northwest next week... ...Heavy rain potential over portions of the Plains... ...Overview... Upper ridging will likely build into the Pacific Northwest early next week while a trough takes shape over the Great Basin/Southwest. Farther east, Upper Midwest shortwave energy will push along eastern U.S. low pressure Friday into Saturday with the trailing front sinking well southward over the eastern half of the country into the northern Gulf of Mexico. The western end of the front should linger over the Plains while another front moves in from the west/northwest, helping to promote episodes of showers and storms which may contain locally heavy rainfall. After a recent spell of warm weather in the East and cool temperatures in the West/Northwest, the opposite will manifest itself through the weekend into next week. ...Guidance Evaluation and Preferences... Through the 12Z/18Z cycle, deterministic models offered reasonable clustering for the first two days of the period this weekend as a wave of low pressure exits the southern Mid-Atlantic but lingers along a frontal boundary just off the East Coast. For the Mon-Wed period, models diverge in the East and West with the handling of both troughs/upper lows, so a trend toward the ensemble means was prudent. In the East, 18Z GFS was on the slower/southwest side with its low pressure near the New York Bight Sunday evening while the ongoing preference/consensus has been near or just outside the 40/70 benchmark. In the West, 12Z ECMWF became quicker with the trough (like the 12Z GFS) as it released the northern part of the trough but allowed the southern part to close off over the Baja. For now, preferred a simplified progression of the upper trough via the pace of the ensemble means (18Z GEFS and 12Z ECMWF ensemble mean) which was near the 18Z GFS. Upstream ridging into the Pac NW (at least +2 sigma) may be squeezed by next Wednesday as a Pacific front edges into Washington. ...Weather Highlights/Hazards... The main focus for rainfall during the period will be over the central/southern Plains along the west end of the wavy frontal boundary and ahead of a weaker northern stream cold front. High pressure that builds in behind the latter front could lead to some areas of low level upslope flow that would help to enhance convective development over the High Plains. It will take additional time to monitor potential overlap of heavy rainfall potential with areas that have seen above normal rainfall over the past week or so. The West Coast will see little to no precipitation but areas near and east of the Great Basin to the Divide may see at least scattered showers as the upper trough moves in. Along the East Coast, offshore frontal boundary and low pressure may only bring light showers to coastal areas but this will depend on how the system evolves and how close it may be to the coast. Again kept the heaviest rain offshore for now. Temperatures will be cool in the Great Lakes/Northeast/Mid-Atlantic Saturday with northeast winds over most areas. Expect readings to be 10-15F below normal in general (many areas only in the 60s). Though the cold front may dip into the Gulf of Mexico by Sunday, this may only cool temperatures in the Southeast to a few degrees below normal (low 80s but dew points in the 50s to low 60s). The Pacific Northwest will see a warming trend with temperatures 10-25F above normal by Memorial Day into next Tue-Wed. This could approach or exceed record levels for parts of WA/OR/ID and northern CA. On the other hand the cloudy/stormy pattern setting up over the central/southern Plains and eastern slopes of the Rockies will bring highs down to 10-15F below normal by next Mon-Wed. Fracasso Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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