Extended Forecast Discussion NWS Weather Prediction Center College Park MD 236 AM EDT Mon Sep 06 2021 Valid 12Z Thu Sep 09 2021 - 12Z Mon Sep 13 2021 ...Overview... An upper high initially over the Four Corners region will weaken and slip eastward across the southern Plains. This will allow quasi-zonal flow to take hold across much of the CONUS, suggesting lower confidence in system timing/details. The patter remains rather dry with generally near to above normal temperatures. ...Guidance Evaluation and Preferences... The guidance continues to struggle with the flow out of the Pacific, with no clear consensus among the deterministic models and poor run-to-run consistency. Questions remain as to how strong northern troughing through southern Canada may be, which may influence the shape/departure of the Northeast troughing Thu-Fri. Ensemble means generally followed their deterministic parent models but were a bit closer to each other (GEFS and ECMWF EPS) so that a trend toward that blend was preferred by the end of the period. To start, a deterministic blend sufficed for the first two days of the period before incorporating a majority ensemble weighting. Confidence was lower than normal over the northern tier due to the inconsistent model signal (yet fairly consistent broader ensemble agreement). Possible tropical development in the East Pacific has trended offshore and was reflected in the NHC-WPC coordination yesterday. In the Gulf, tropical development remains uncertain but moisture transport northward/northeastward continues to look likely into the northern/northeastern Gulf. Maintained a modest QPF signal into the FL Panhandle and southeastern GA but ultimately need to wait and see if any organization will occur. Please see the NHC outlooks for more information. ...Weather/Hazard Highlights... Rainfall will focus along and ahead of a cold front along I-95 Thursday morning, with its tail-end lingering over the Southeast for a few days before dissipating. Amounts will generally be light except over the northeastern Gulf where tropical moisture may support modest to perhaps locally heavier amounts. Daily showers/storms are likely for much of the FL peninsula to the south of the boundary. Some moisture will work back through the Southwest around the upper high as it drifts southeastward, focused over inland CA (Sierra) into the Great Basin and parts of the Desert Southwest. This may lift northward into the northern Rockies by later in the week into the weekend, ahead of another Pacific front. Amounts have trended less which was reflected in the updated QPF. Temperatures will be near to above normal over most areas, especially over the Rockies ahead of the incoming Pacific front/trough Thu-Fri. Temperatures 5-15 degrees above normal are possible as the area of warmth moves into the southern/central Plains later in the week into the weekend and toward the Midwest next week. Temperatures in the Great Lakes/Northeast will be near to a bit below normal via northwest flow behind the cold front later this week, moderating a bit over the weekend as the surface high settles over the region. 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