Extended Forecast Discussion NWS Weather Prediction Center College Park MD 245 AM EDT Tue May 25 2021 Valid 12Z Fri May 28 2021 - 12Z Tue Jun 01 2021 ...Record highs possible in the Pacific Northwest next week... ...Overview... Upper ridging is forecast to build into the Pacific Northwest early next week as a front in the East sinks southward. The western end of the front will linger over the Plains, helping to promote a few chances of showers and storms which may contain some 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, the deterministic models showed reasonable clustering for the Fri-Sun period as low pressure in the Ohio Valley moves off the Carolina/southern Mid-Atlantic coast. Trend in the guidance has been for a stronger wave aloft and a farther push southward of the surface cold front (into the northern Gulf of Mexico) late Sat/early Sun. With increased sharpness overall, offshore frontal boundary has the potential to form one or more surface waves as the boundary slowly lifts northeastward. How close this may be to the coast will influence the amount of clouds/rain. Over the West, ensembles show good agreement on building upper ridging (to at least +2 sigma) into the Pacific Northwest, downstream of equally-as-deep troughing south of Alaska. Blend of the 18Z GFS and 12Z ECMWF/Canadian/UKMET served well for Fri-Sat, before the UKMET appeared too weak in the East and was discounted. Thereafter, dropped the Canadian from the preference as it was much more progressive off New England with low pressure, but much slower over California with a potential upper low next week. The 18Z GFS/12Z ECMWF were then used in conjunction with their ensemble means for the Mon-Tue period as either was plausible in light of the ensemble spread. ...Weather Highlights/Hazards... Highest chances of rainfall during the period will be near the exiting low pressure in the East Friday, then back over the central/southern Plains to the Corn Belt along the west end of the wavy frontal boundary and ahead of a weaker northern stream cold front. 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 and a weak cold front sinks through. Temperatures will be cool (about 10 to 15 degrees below normal) in the Upper Midwest/Great Lakes/Northeast Friday/Saturday, expanding south down the Mid-Atlantic Saturday with a cold air damming setup. Warm temperatures in the Southeast will cool as the cold front works down to the Gulf. The Pacific Northwest will see a warming trend with temperatures 10 to 25 degrees above normal by Memorial Day into next Tuesday. This could approach/exceed record levels for parts of Oregon/northern California and could continue into the week beyond this period. See the latest CPC day 6-10 forecast and 8-14 day U.S. Hazards Outlook for more information. 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