Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Fri Nov 03 2023 Valid 12Z Mon Nov 06 2023 - 12Z Fri Nov 10 2023 ...Overview... Quasi-zonal upper flow is forecast across the contiguous U.S. into much of next week, before perhaps amplifying somewhat by late next week. But a few shortwaves embedded within the flow will be impactful in spinning up low pressure/frontal systems, including one moving from the Great Lakes into southern Canada Monday-Tuesday and another tracking from the north-central to northeastern U.S. Wednesday-Thursday, with some associated precipitation. The West Coast should see precipitation continue into Monday-Tuesday, with a relative break around midweek, but rain/snow chances could return late next week. Meanwhile, much of the U.S. can expect warmer than average temperatures next week, but a cold front will gradually suppress the area of above normal temperatures farther southeast through the week. ...Guidance Evaluation/Predictability Assessment... In this quasi-zonal and progressive pattern for the early medium range period, there are some minor differences in the timing and depth of shortwaves that lead to surface low/frontal and sensible weather differences. The first one of note is the shortwave crossing the Great Lakes around Tuesday. 12/18Z GFS runs are a bit flatter than consensus with the shortwave and thus show less QPF farther south compared to the non-NCEP guidance. The 12Z CMC meanwhile seemed to be too far west with the shortwave and the surface low. Overall continued to prefer the ECMWF solution with this feature. Fortunately the newer 00Z model suite seems to be coming into better agreement with the details. Another shortwave moving from the northwestern to north-central U.S. Monday-Wednesday shows some model variations, and differences with Canadian energy coming in to reinforce the feature by the latter half of the week in the Midwest/Great Lakes lead to some differences, including how far east the troughing will extend--models are out of phase with each other into the Mid-Atlantic, for example. Most solutions look reasonable at this point so some sort of blend/middle ground seems best. Meanwhile farther west, models generally agree on a bout of ridging tracking across the West while eastern Pacific energy gets going. Models do vary in the eastern Pacific from a deep closed upper low (12Z GFS farthest west) to energy within a phased trough. But at least the general idea for somewhat more amplified flow is there by the late period. The WPC forecast was based on a deterministic model blend early in the forecast, favoring the 12Z ECMWF with lesser amounts of the 12/18Z GFS, 12Z UKMET, and 12Z CMC. Introduced and increased the proportion of the GEFS and EC ensemble means with time to around half by late period. ...Weather/Hazards Highlights... The western U.S. will see active weather into Monday with the possibility of a weak atmospheric river. Onshore flow will continue into the coastal ranges and into the Cascades in the Pacific Northwest, with shortwave energy providing upper-level dynamical support and some instability for slightly enhanced rainfall rates. Locally heavier rainfall on the west facing slopes may be enough to cause some minor flooding concerns, particularly for urban areas and burn scars, and especially as rainfall from the prior days brings wetter antecedent conditions. Thus a Marginal Risk is planned in the Excessive Rainfall Outlook for Monday. Precipitation should reduce in magnitude by Tuesday, allowing for no heavy rainfall or flash flooding risk areas. But some areas of heavier snow are possible for higher elevations of the Cascades and into the northern Rockies for Monday-Tuesday. Expect precipitation from the Pacific Northwest into the Rockies to generally trend lighter by the middle of next week as upper-level ridging briefly builds back in, before precipitation chances increase again late week. Farther east, the Midwest/Great Lakes region to Northeast should see rounds of precipitation next week in conjunction with low pressure and frontal systems tracking across. Amounts and north-south extent of the precipitation remains uncertain though. Locations near the Canadian border and the higher elevations of northern New England may see some snow or mixed precipitation during the period. Rain should be the prevailing precipitation type elsewhere through midweek, though snow levels may lower by Thursday for some snow chances in the Interior Northeast, but confidence is low at this point. Temperatures will be generally above average across the country as the period begins Monday, with the central U.S. seeing the largest anomalies at 10-20F above normal. On Tuesday and Wednesday the south-central U.S. can expect highs around 15-20F above normal, potentially setting some record highs as temperatures could rise into the mid-80s. Cold fronts tracking south and east should gradually limit the area of above normal temperatures across the CONUS, cooling temperatures across the northern tier, then the central U.S. to Ohio Valley, and finally across the Southeast by around Friday. Areas behind the front should see near to below normal temperatures, spreading across the West and into the south-central U.S. late week. 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw