Extended Forecast Discussion NWS Weather Prediction Center College Park MD 302 PM EDT Fri Aug 26 2022 Valid 12Z Mon Aug 29 2022 - 12Z Fri Sep 02 2022 ...Overview... The upper-level pattern over the CONUS is forecast to amplify next week, after fairly flat/zonal flow with embedded shortwaves dominate the short range period. Troughing will dig over the eastern Pacific, potentially reaching the Northwest by late next week, while ridging amplifies over the interior West and the central U.S. as another potent trough pushes from the north-central to northeastern U.S. during the period. A reasonably strong and progressive cold front ahead of the latter trough will provide a focus for rain and thunderstorms for the eastern half of the U.S. as it tracks southeastward, with cooling temperatures behind it as a surface high settles in. The West is likely to remain relatively dry next week, with warm to hot temperatures underneath the upper ridge. ...Guidance Evaluation/Predictability Assessment... Fortunately model guidance has settled on better agreement for the track of the initial shortwave in the Northern Plains Monday and as it progresses eastward and combines with additional energy to produce a trough axis shifting through the Great Lakes region with time, compared to a day or two ago. The updated WPC forecast for the early part of next week ended up with a slightly faster track of the trough and thus the cold front position over the lower 48 compared to the previous forecast, which also lowered QPF totals in the central U.S. slightly. Utilized a blend of the deterministic 00Z ECMWF/CMC/UKMET and 06Z GFS in the forecast given the reasonably good model agreement. By Wednesday-Friday, a handful of model runs over the last couple of days have been showing the possibility of energy to split off into a separate upper low and drift somewhere over the south-central or southeastern CONUS, including the 00Z CMC. This still seems like a lower probability solution, so reduced/eliminated the CMC from the WPC forecast with time, in favor of the EC and GEFS ensemble means. The proportion of the means vs. deterministic models (06Z GFS and 00Z EC) was right at half by day 7. Preferred the 06Z GFS over the 00Z given the 00Z was faster than consensus with the eastern trough lifting away from the northeastern CONUS. This blend also worked well for the agreeable ridge to the west and the trough in the eastern Pacific edging toward the Pacific Northwest, though it is likely that the details of the timing of the eastern edge of the trough and associated cold fronts may vary with time. The newer 12Z guidance appears generally in line with the previous cycle, with no deterministic guidance showing the rogue southern tier upper low as aggressively. ...Weather/Hazards Highlights... A cold front ahead of the central-eastern U.S. trough will be a primary feature to watch through next week weather-wise. Moisture pooling along and ahead of the front may lead to pockets of moderate to locally heavy rainfall at times next week as it advances southeastward from the central U.S. into the Eastern Seaboard and Gulf Coast. South-central parts of the Plains and Mississippi Valley may be one area of focus for higher rainfall potential as interaction with Gulf moisture may boost rainfall intensity and amounts, while the Northeast has seen forecast rain totals increase around Wednesday-Thursday. The West should generally stay dry until some showers may increase for the Southern/Central Rockies and High Plains, and eventually in the Pacific Northwest depending on cold frontal and upper trough positions. Ahead of the front, temperatures are likely to be 5-15F above normal for highs in the northeastern quadrant of the U.S., but temperatures should switch to below normal behind the front for the Upper Midwest into the Great Lakes and Ohio Valley as a cool surface high settles in. The Southern Plains may also see temperatures a few degrees below average with the rain and cloudiness potential. Meanwhile, ridging in the West and a gradual shift eastward with time will lead to warmer than average temperatures for much of the West, with the highest anomalies of 10-20F above normal occurring in the Northwest and northern High Plains, before a cooling trend for the Pacific Northwest late next week with the approaching trough. Daily high temperature records for highs and warm lows could be challenged. 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