Extended Forecast Discussion NWS Weather Prediction Center College Park MD 208 AM EDT Tue Jul 06 2021 Valid 12Z Fri Jul 09 2021 - 12Z Tue Jul 13 2021 ...There is a heavy rain threat this weekend over the Midwest which had a recent period of heavy rain... ...Overview... The western CONUS ridge/eastern mean trough pattern will amplify this weekend as a shortwave trough from the Pacific rounds the ridge before stalling over the Upper Mississippi Valley Saturday potentially through Monday. The upper ridge over the Great Basin/Desert Southwest will strengthen in the wake of the ridge-riding trough and intensify the ongoing heat wave across The West. The initial shortwave trough over the interior Northeast, which will direct Elsa remnants off the Northeastern Seaboard on Friday, will push a weak cold front through the Northeast with the tailing front over the Midwest lifting back as a warm front ahead of the ridge-riding shortwave trough over the weekend. An upper level trough lingers over northern Mexico, but most of the associated rain should be contained south of the Rio Grande. ...Guidance/Predictability Evaluation... There is good agreement in the most recent guidance with the ridge-riding shortwave trough that stalls over the Upper Midwest this weekend, with the departure of Elsa off the Northeastern Seaboard Friday, and with the upper trough/low lingering just southwest of Texas this weekend into next week. The main difference in guidance now is a second ridge riding shortwave trough pushing east into southern BC around a Gulf of Alaska low Saturday night or Sunday. The 18Z GFS is the slowest solution with this feature Saturday evening, though the 00Z GFS has sped up again and is now similar to the 12Z UKMET for timing which is a little ways behind the 12Z CMC/ECMWF which are to the BC/Alberta border by 12Z Sunday. The heavy rain threat associated with an upper low/trough southwest of Texas looks to mainly end by Friday with the threat pushing south of the Rio Grande. The 12Z CMC is a bit farther north with the feature and is now an outlier solution with a heavy rain threat continuing through the weekend for far southern Texas. Therefore, a general deterministic model blend was used through Day 5 (with less CMC by Day 4) with increasing use of the GEFS/ECENS means for Days 6/7. ...Weather Highlights/Hazards... The cold front moving through the Northeast Friday should bring an area of modest to perhaps heavier rain to upstate New York and the Adirondacks/North Country before pushing off the coast (with effects from Elsa remnants remaining off the Northeastern Seaboard). The ridge-riding trough forecast to reach the Upper Midwest by 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 may set up near northern Missouri/north-central Illinois into northern Indiana which had a rather wet second half of June and is still experienced main-stem river flooding. The heat wave over a significant portion of The West will shift slightly west this weekend in the wake of the ridge-riding trough. The Coast Ranges, Central Valley of California, Great Basin, and northern Rockies/Columbian Basin should all see highs 10-15F above normal each day with locally higher readings possible. Meanwhile the strengthening and westward expansion of the upper ridge will promote a hotter trend over interior locations of California where temperatures will climb into the 100s and 110s. Several daily high temperature records are under threat each day primarily over the western Great Basin through interior California. The southern High Plains/Texas will likely see highs 5-12F below average for most of the week due to cloudiness and light to moderate rain. The Midwest and Great Lakes will see below normal highs over the weekend due to rainfall. 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