Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 PM EDT Wed Oct 05 2022 Valid 12Z Sat Oct 08 2022 - 12Z Wed Oct 12 2022 ...Overview... Rather amplified upper level flow is expected to be in place this weekend, with a general pattern of troughing across the East and West Coast ridging (though with a weak upper low/trough across the Southwest into northern Mexico maintaining additional showers and storms there). At the surface, a strong cold front will be exiting the Atlantic coast, heralding the arrival of a truly autumnal airmass with a big Canadian surface high settling in from the Plains to the East Coast, before the next cold front comes into the Plains and Great Lakes early next week. As next week progresses, a pattern flip is becoming increasingly likely as potent energy digs a trough and possibly an upper low into the West Tuesday-Wednesday, bringing much cooler temperatures and the possibility for precipitation including higher elevation snow there. Meanwhile, ridging could form downstream into the east-central CONUS. ...Guidance Evaluation/Predictability Assessment... For the early part of the medium range period this weekend, model guidance is in reasonably good agreement with a broad mid-upper trough in the central/eastern U.S. and even with an initial shortwave near the Lower Great Lakes Saturday morning. Models also show good consensus for an upper high centered over the eastern Pacific with its ridging influence into the West Coast, while a weak upper low over northwestern Mexico extending into southern Arizona opens into a trough. Thus the WPC fronts/pressures model blend began with a deterministic multi-model combination. More differences start to arise with shortwaves in the north-central U.S. during the Sunday-Monday timeframe, and these model differences led to the inclusion of the GEFS and EC ensemble means into the blend to temper them. By Monday, energy is likely to dive across western Canada and deepen troughing over the West into Tuesday-Wednesday. This pattern has been persistently shown by multiple runs of the ECMWF and the past couple of the CMC runs, while GFS runs have waffled. But the 00Z/06Z GFS showed a similar pattern of troughing, and most 00Z/06Z guidance also indicated not only a trough but a closed low forming in the West. The 00Z CMC was an exception but the 12Z CMC does form a closed low, along with other 12Z model runs. The WPC forecast used a model/mean blend for the latter part of the medium range period, which led to a trend toward this upper low feature in the WPC 500mb charts and also with higher QPF and some extension of QPF westward in the West compared to continuity, as confidence grows somewhat in this type of pattern. QPF from the 13Z NBM was generally followed, though with an expansion of the lighter amounts, as a known bias of the NBM is to have not enough light precipitation. ...Weather/Hazards Highlights... The combination of persistent monsoonal moisture and an upper low evolving into a trough 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. Moisture may stream farther east into the southern half of the Plains and interact with a front, leading to rain chances in that area as well. Then the amplifying upper trough and a strong cold front reaching the Northwest/northern Rockies by next Tuesday-Wednesday will likely produce precipitation across those areas, with snow becoming more likely for higher elevations of the northern Rockies for the Tuesday and Wednesday time period. Moisture streaming in ahead of the trough and a frontal system could help produce rain showers across much of the central U.S. by that time as well. Elsewhere, light to locally moderate rainfall is forecast to 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. Then a cooling trend will commence by Tuesday as the cold front drops southeastward, producing high temperatures more typical of mid-late November across the Rockies and northern Plains by next Wednesday as highs could be up to 20 degrees below average. Farther east, an area of well below normal temperatures by around 10-15F is forecast from the Midwest to the East Coast this weekend, with highs perhaps closer to 20 degrees below normal in the central Appalachians. 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 and interior Northeast, with the potential for the first frost/freeze of the season for many areas. Tate/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