Extended Forecast Discussion NWS Weather Prediction Center College Park MD 151 PM EDT Tue Sep 07 2021 Valid 12Z Fri Sep 10 2021 - 12Z Tue Sep 14 2021 ...Overview... The CONUS weather pattern by this weekend and into next week will feature quasi-zonal flow as the upper high over the Great Basin is suppressed southeast to the southern Rockies where it weakens and eastern troughing will be more focused over eastern Canada than over the Great Lakes as current. The pattern is rather dry on the whole, with a notable exception of the western Gulf Coast next week, with generally normal temperatures for the central and southern parts of the CONUS. ...Guidance Evaluation and Preferences... Models and ensembles showed decent longwave agreement with continued spread in the shorter wavelength features. The ECMWF remains more consistent than the GFS or Canadian/UKMET, but even it has wavered in the strength and timing of the main trough that crosses the Northwest early next week. Thus, continued to favor a blended solution of the recent deterministic guidance to start, with increasing weight to the ensemble means (06Z GEFS and 00Z ECENS) staring this weekend as uncertainty grows. The trend with the trough in the Northwest/northern Rockies early next week is back to less amplified, but the east-west (fast-slow) spread continues, with the GFS quickest and Canadian slowest. This left the ECMWF closes to the ensemble means. A tropical system is still likely to form in the East Pacific over the next day or so but is forecast to track offshore/west of Baja California. In the Gulf of Mexico, tropical development remains uncertain but while part of the energy could track into the Atlantic, a trough looks to develop and linger over the western Gulf of Mexico. The GFS remains the strongest with this trough and the 12Z run even develops a surface low near the lower Rio Grande Valley by Monday. Please see the NHC outlooks for the latest information. ...Weather/Hazard Highlights... Lingering rainfall will remain focused along and ahead of a cold front over north Florida Friday night into Saturday. Daily showers/storms are likely for much of the FL peninsula to the south of the boundary as it washes out into early next week. Moisture will lift northward on the backside of the western upper high and converge on a frontal boundary over the northern Rockies Friday night and Saturday with steady and perhaps locally heavy rain. Precip weakens with this frontal system across the northern Plains Sunday, but the additional of Gulf-sourced moisture bring moderate rain chances to the Great Lakes Monday night/Tuesday. Tropical moisture looks to spread some organized and lingering locally heavy rain toward western parts of the Gulf Coast with the GFS continuing to be the heaviest solution, particularly over south Texas/the lower Rio Grande Valley. Temperatures will be above normal under the ridge that is suppressed south over the Rockies this weekend and ahead of the following cold front that tracks across the northern tier. Friday high temperatures along the central High Plains to the Front Range will be 15 to 20 degrees above normal where several high temperature records will be challenged. This area of warmth weakens as it moves into the southern/central Plains over the weekend and toward the Middle Mississippi and Ohio Valleys next week, with few if any high temperature records challenged. Temperatures in the northern Plains quickly shift below normal from Friday to Saturday which shifts east over the Great Lakes/Northeast behind the aforementioned cold front. 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