Extended Forecast Discussion NWS Weather Prediction Center College Park MD 226 AM EDT Wed Oct 5 2022 Valid 12Z Sat Oct 8 2022 - 12Z Wed Oct 12 2022 ...Synoptic Overview... A rather amplified upper level flow pattern is expected to be in place for the upcoming weekend and extending into the early to middle portion of next week. For the eastern U.S., a strong cold front will be exiting the coast and heralding the arrival of a truly autumnal airmass with a big Canadian surface high settling in from the Plains to the East Coast, and this high will gradually move offshore early next week ahead of the next cold front across the Plains and Great Lakes by that time. For the western U.S., a persistent weak upper low/trough axis will maintain additional showers and storms from Arizona and especially New Mexico. By Tuesday, a more impressive upper trough begins building across the north-central U.S. which will likely bring much cooler conditions for much of the western U.S. by the middle of next week. ...Guidance Evaluation/Predictability Assessment... Overall, the 00Z deterministic guidance is in good overall agreement on most features for Saturday, with the main difference at this time being a more progressive solution with the GFS across the Mid-Atlantic with the trough exiting the coast. The models also agree well on the upper low that evolves into a trough near the Desert Southwest through the weekend. Looking ahead, spread and run-to-run variability have improved with the 00Z model cycle for the deep trough amplifying into Canada and the northwestern U.S. early next week. Recent ECMWF runs have been more consistent in indicating more troughing over the Northwest and northern Rockies, and this also holds true for the past two runs of the CMC. The GFS has varied considerably over the evolution of this trough, however the most recent 00Z run falls more in line with the model consensus and the ensemble means. A multi-deterministic model blend suffices early in the period, followed by increasing the weighting of the ensemble means for early next week and removing the 18Z GFS from the fronts/pressures forecast by Wednesday. For the QPF, the NBM combined with some of the operational GFS/ECMWF was used as a baseline through about Monday, and then mainly went with NBM for Tuesday/Tuesday night. ...Weather/Hazards Highlights... The combination of persistent monsoonal moisture and an upper low over northwest Mexico will continue to fuel diurnal showers and thunderstorms over parts of the Desert Southwest/southern Rockies through the weekend, with the greatest rainfall totals expected for central and southern New Mexico based on latest model guidance. The upper low should evolve into an open trough by Monday, but may be replaced by additional weak energy building in from the northwest. This evolution may help to spread some of the moisture eastward into the Plains where it could interact with a front. An amplifying upper trough and a strong cold front reaching the Northwest/northern Rockies by next Tuesday will likely produce showers and perhaps even high elevation snow for portions of the northern Rockies for the Tuesday and Wednesday time period. Elsewhere, light to locally moderate rainfall will likely spread northward over the Florida Peninsula as easterly low level flow strengthens behind a front. Much of the West should have above normal temperatures at least through Monday, with highs 10-15F or so above normal most likely over the Northwest, with a noticeable cooling trend commencing by Tuesday as the cold front drops southeastward, and then temperatures more typical of mid-late November are expected across the Rockies and northern Plains by next Wednesday with highs up to 20 degrees below average. Farther east, an area of well below normal temperatures is forecast from the Midwest to the East Coast this weekend, and some areas may have highs 15-20F below normal on Saturday. Morning lows will also be rather chilly with readings into the 30s for many locations from the northern half of the Plains into the central Appalachians, with the potential for the first frost/freeze of the season for many areas. Hamrick 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