Extended Forecast Discussion NWS Weather Prediction Center College Park MD 207 AM EDT Wed Jul 07 2021 Valid 12Z Sat Jul 10 2021 - 12Z Wed Jul 14 2021 ...Overview... An amplified western ridge/eastern trough pattern will be in place by Saturday morning as an upper trough digs down the northern Plains closed off into a low near the MO/IA border Saturday night. This low then persists/drifts northeast to the Great Lakes through Monday as shortwaves spread across the Northwest. The western ridge/high center continues to drift west to central CA through Saturday night before drifting southeast to the lower CO River Basin into the middle of next week. The slow motion of the pattern favors repeating rain ahead of the Midwest low this weekend while the heat wave in the west persists under high pressure. ...Guidance/Predictability Evaluation... There is good agreement among global deterministic guidance on the over all ridge/trough pattern across the CONUS this weekend into next week, but there are differences in the details of the Midwest low strength and motion. The 18Z and now 00Z is weaker with the trough crossing the northern Plains on Saturday and therefore keeps an open trough and a more eastward motion than the deeper, more closed and therefore slower 12Z ECMWF and 12Z and now 00Z UKMET. The 12Z CMC was unavailable again for analysis/use in our blend. Therefore, more weight was given to the 12Z ECMWF/UKMET in the blend through Day 5. Given that low confidence shortwave activity in the Northwest/southwest Canada dominates the pattern early next week, a heavier than recent usage of the ECENS/GEFS ensemble means was used for Days 6/7. ...Weather Highlights/Hazards... The trough digging down the northern Plains Saturday will have access to Gulf-sourced moisture and should result in significant rainfall for the northern Plains through the Corn Belt to the western Great Lakes as the system becomes blocked/stalls. The axis of heaviest rain on Saturday looks to be over a similar area to the rain on Friday night over IA/northern MO and across central IL/IN. This potential for a quick repeat over areas that both had rain the night before and had a rather wet second half of June sets up a flooding threat. The ongoing heat wave continues for the Great Basin to the Coastal Ranges and lower CO River Basin this weekend and into next week with temperatures 10-15F above normal each day with locally higher readings possible. Several daily high temperature records are under threat each day primarily over the western Great Basin through interior California to Arizona. Relief from the heat would come from a low shifting south from the Gulf of Alaska Monday which should start causing height falls over the Pacific Northwest by midweek. Highs 5-10F below average will spread down the northern to central Plains over the weekend with clouds/rain and Texas will remain below average for highs under continued cloudy/rainy conditions. Jackson 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