Extended Forecast Discussion NWS Weather Prediction Center College Park MD 251 AM EDT Sun Aug 28 2022 Valid 12Z Wed Aug 31 2022 - 12Z Sun Sep 04 2022 ...Overview... An amplified flow pattern is expected to start the forecast period featuring strong ridging through the interior West with deeper troughing across the eastern Pacific as well as the Great Lakes into the Northeast U.S., the latter of which helps drive a cold front across much of the central to eastern U.S. mid to late week. Drier and early fall-like temperatures can be expected in its wake from the Upper Midwest to the East Coast while the West is likely to see much above normal temperatures. The cold front is forecast to settle along the southern tier of the U.S. from the Texas Gulf Coast eastward to Florida late in the week into next weekend, and this will be focus for scattered to numerous showers and thunderstorms each day, some of which could produce locally heavy rainfall. ...Guidance Evaluation/Predictability Assessment... Through day 5, the latest model guidance shows strong agreement and run to run consistency with the upper level pattern and weather features across the CONUS. The amplified ridge is expected to persist or even build some over the Four Corners region northward through the interior West while eastern Pacific troughing digs and the Great Lakes trough begins to flatten out somewhat. At the start of the period, a cold front will be sweeping across much of the central to eastern U.S. and the latest runs of the GFS, ECMWF, CMC, and UKMET show fairly high consistency and agreement. That front is expected to settle along the Gulf Coast and back across Texas, where aloft there continue to be hints of a weakness in the ridge that may help support unsettled weather across Texas, the GFS being the more aggressive model showing this scenario. Otherwise, another area of model differences is day 5 onward over the Northwest. While the ensemble means show the eastern Pacific shortwave energy lifting more into British Columbia, the recent deterministic runs, particularly the GFS and CMC, show a more compact shortwave troughing advancing faster and further south, tracking across the Pacific Northwest late in the week into early next weekend. Given the typical fast bias there and the uncertainty for a day 6/7 forecast, the WPC blend leaned on the ensemble means for about 50 percent of the blend and the latest ECMWF/GFS for the other half, which trended well with the latest trends and maintained WPC continuity. ...Weather/Hazards Highlights... A cold front sweeping across the central to eastern U.S. mid to late week will be the main sensible weather feature of note across the CONUS. Ahead of it, enough warm and moist air will lift northward to support scattered to numerous showers and thunderstorms, some of which could be locally heavy across portions of New England Wednesday into Thursday where the system will have better dynamics/lift to support more organized convection. Further south along the southward moving boundary, better instability and moisture across the Southern Plains and potentially along the Florida Gulf Coast could support intense rain rates and localized heavy rainfall. The front then is expected to settle across the southern tier of the U.S. and will be the focus for daily showers and thunderstorms, some of which could be locally heavy next weekend across Texas eastward along the Gulf Coast. Elsewhere, the rest of the country looks to be mainly dry aside from light precipitation chances across the Colorado Rockies and a frontal passage possibly clipping the Pacific Northwest bringing generally light precipitation. The greatest temperature anomalies through the period will be found across the western U.S. mid to late week, particularly across the Northwest into Northern Rockies where highs could reach 10-20F above normal and some daily high temperature records could be challenged. As the calendar turns to Meteorological Fall, much of the Upper Midwest, Great Lakes, and Northeast should see at or slightly below normal highs, with cool lows in the 40s to 50s in portions of those areas. As the upper flow pattern becomes more zonal next weekend, the above normal temperatures look to spread across much of the northern tier of the U.S. with highs next weekend possibly 5-10F above normal. Conversely, the southern U.S. is likely to see near or slightly below normal temperatures through the period, particularly the Southern Plains and Gulf Coast where widespread clouds and precipitation look to keep temperatures in check. Taylor/Tate 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml