Extended Forecast Discussion NWS Weather Prediction Center College Park MD 116 AM EDT Tue Jul 13 2021 Valid 12Z Fri Jul 16 2021 - 12Z Tue Jul 20 2021 ...Remaining hot in the northern Great Basin to the High Plains... ...Overview... Upper pattern will remain slowly evolving during the period with troughing just west of British Columbia and over the Great Lakes and Ohio Valley with building upper ridging into the Four Corners Region across the central Rockies and northern Plains. This will promote above normal temperatures for much of the interior West, especially into Montana and the High Plains. A frontal boundary will slowly push south across the MS, OH and TN Valleys, the Northeast and Mid-Atlantic with showers and storms along and ahead of the boundary. Some rainfall may be locally heavy. Over the Southwest, the Monsoon will help touch off some showers and storms around the upper high across portions of AZ/NM/CO. ...Guidance/Predictability Evaluation... Models and ensembles showed better than average predictability in the longwave pattern evolution/orientation out west due to the large sprawling, and slowly moving anticyclone and eastern pacific trough. There remains differences in the timing/amplitude of the downstream developing eastern US trough. The 18z GFS was an outlier with the deepest closed low developing over the northeast US within the upper trough axis. Manual progs blended the 12Z ECMWF/12z ECMWF Ensemble Mean/18z GEFS Mean, with continued good agreement on the trough axis among the means. The GFS and Canadian were slower to move the upper trough eastward than the ECMWF, with the ensemble consensus a little on the slower side. ...Weather Highlights/Hazards... In the West, rising heights will maintain dry and warming conditions for the northern Great Basin through Montana where temperatures will climb from the 90s to low 100s in eastern lower elevation areas by next Sun/Mon (as well as in favored/warmer valley locations in ID and UT). Anomalies next Sun 18 Jul-Tue 20 Jul climb to near 15 degrees above normal in eastern MT and portions of northern ND and northern MN. 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/CO during the afternoon and early evening. Below normal temperatures may also develop in the southern high Plains as northerly flow advects cooler air aloft across the area. As the cold front moves out of the Midwest to the East, showers and storms will be scattered to numerous, with locally heavier amounts where thunderstorms locally train. Temperatures will be near to above normal ahead of the front by a few degrees, with only a few to several degree drop in its wake. Areas of highest rainfall chances will slowly shift southward across the MS Valley, TN Valley, Appalachians, and mid Atlantic to the southeast. Petersen/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