Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 PM EDT Wed Jul 14 2021 Valid 12Z Sat Jul 17 2021 - 12Z Wed Jul 21 2021 ...Western Heatwave with some records from the Great Basin to the northern Rockies/Plains... ...Weather Highlights/Hazards... Out West, potent upper ridge building from the Great Basin to the northern Rockies/Plains this period will lead to a heatwave across these regions. Temperatures are forecast to be the 90s and lower 100s at lower elevations this weekend into next week, which may reach 10-20 degrees above normal. Expect some record values will be observed. Temperatures in the Southwest will be slightly below normal due to increased cloud cover and higher rainfall chances. Showers and storms will be scattered across AZ/NM/southern CO during the afternoon and early evening. Downstream under the influence of rejuvenating upper troughing, a wavy and slow moving front will work across the Plains, MS Valley, OH Valley, Appalachians, Mid-Atlantic, and settle over the South/Southeast this period and spread less certain local foci for convective rainfall. Showers and storms will be scattered to numerous, with locally heavier amounts where thunderstorms locally train. High temperatures are forecast to fall below normal into early next week due the clouds and showers in the vicinity of the modestly cooling front. ...Guidance/Predictability Evaluation... The bulk of guidance seems in good agreement through medium range time scales in a pattern with overall above normal predictability. The WPC medium range product suite was primarily derived from the best clustered 06 UTC GFS/GEFS, 00 UTC ECMWF/Canadian and ECMWF ensembles along with the 13 UTC National Blend of Models. The 00 UTC UKMET was not included in this blend as it seemed a bit overdone with weekend closed low development over the Great Lakes given lead-in flow. The favored WPC composite blend generally maintains good continuity. Latest 12 UTC guidance now also seems in line with this solution. This includes the 12 UTC UKMET that has trended toward other guidance. Schichtel 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