Extended Forecast Discussion NWS Weather Prediction Center College Park MD 226 AM EDT Wed Sep 08 2021 Valid 12Z Sat Sep 11 2021 - 12Z Wed Sep 15 2021 ...Overview... Quasi-zonal flow over the CONUS next week amid a mostly dry pattern should spell a relatively quiet period, but with uncertainty in system details. The western Gulf/south Texas has the best chance for appreciable rainfall depending on how much moisture a possible tropical wave brings to the area. Temperatures will be near to below normal along the U.S./Canadian border and near the Gulf, but warmer than normal in between. ...Guidance Evaluation and Preferences... Models and ensembles showed decent longwave agreement with continued spread in the shorter wavelength features. Continued to favor a blended solution of the recent deterministic guidance to start, minus the UKMET which was quite slow into the Northwest this weekend, with increasing weight to the ensemble means (18Z GEFS and 12Z ECENS) Mon-Wed as uncertainty grows. Unclear/inconsistent trends or shifts in the guidance (not unusual in lower amplitude flow) have made it difficult to favor one solution over another. In the Gulf of Mexico, the GFS remained the strongest with any tropical entity (though likely just a weak surface reflection) and thus rainfall. Favored a more modest depiction and subsequent QPF. ...Weather/Hazard Highlights... Daily showers/storms are likely for much of the FL peninsula to the south of the boundary as it washes out early next week. Frontal boundary over the northern tier will likely only support light rainfall for the High Plains before a modest injection of moisture from the south may promote more scattered showers across the Great Lakes Monday night/Tuesday. This should slide into the Northeast next Tuesday into Wednesday per current timing. Will continue to adjust rainfall forecasts for the western Gulf, particularly over south Texas/the lower Rio Grande Valley pending any organization of favorable ingredients. Temperatures will be above normal under the ridge and south of the surface boundary this weekend from the southern Plains eastward. High temperatures may be 5 to 15 degrees above normal where several high temperature records will be challenged. This area of warmth will temper a bit as it moves toward the Middle Mississippi and Ohio Valleys next week and then to the Mid-Atlantic. Temperatures along the Canadian border will linger near to below normal through the period. Areas around the Gulf will see typical mid-September temperatures in the upper 80s to around 90F. 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