Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Thu Nov 2 2023 Valid 12Z Sun Nov 5 2023 - 12Z Thu Nov 9 2023 ...Synoptic Overview... A general quasi-zonal flow across the continental U.S. is expected going into the weekend, with broad cyclonic flow aloft over southern Canada and a shortwave trough quickly traversing the northeastern U.S. on Sunday. The trough that develops across the Plains by Monday will spur surface cyclogenesis across the Upper Midwest and Great Lakes region, and then the low reaches New England on Tuesday. Unsettled conditions are expected to continue across the Pacific Northwest with multiple troughs passing overhead along with additional rounds of rainfall and mountain snow for the Northern Rockies. A Canadian surface high will continue to govern the overall weather pattern across the Northern Plains with cold weather continuing. ...Guidance Evaluation/Predictability Assessment... The models continue to struggle with timing of shortwave features tracking east in the progressive flow pattern, even as early as Sunday with the ECMWF/ECENS faster with the lead trough across the Ohio Valley and the GFS/GEFS/CMC slower. For the second and more impactful shortwave trough/surface low, there is actually better timing agreement among the GFS/ECMWF and their ensemble means, but the CMC begins to diverge significantly from this group of guidance and the low is considerably slower and maintains the high over New England longer. These differences with recent runs of the CMC only grow further going into the middle of the week, and given the differences between it and the ensemble means, it was not part of the preferred blend for this forecast cycle. By the end of the forecast period next Thursday, the 18Z GFS is quicker to bring in the next storm system for the Pacific Northwest compared to the ECMWF (00Z GFS more in line), which maintains the ridge axis near the West Coast longer. Ensemble means accounted for 50-70% of the forecast blend by the Wednesday-Thursday time period. ...Weather/Hazards Highlights... Most of the continental U.S. should not see any significant rainfall hazards through this coming weekend. Similar to the past few days, the only region where there will be a risk of excessive rainfall leading to potential flooding concerns will be in the coastal ranges of the Pacific Northwest with the enhanced onshore flow that will continue into the weekend. A Marginal Risk of Excessive Rainfall has been maintained on Day 4 (Sunday) from northwestern California to the Oregon Cascades and coastal ranges. Locally heavier rainfall on the west facing slopes may just be enough to cause some minor flooding concerns, especially in urban and burn scar areas. Looking ahead to Day 5 (Monday) an abatement of the onshore flow and associated rainfall is expected, and therefore no risk areas are planned. Heavy snow is likely for the highest elevations of the Northern Rockies. 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. Across the eastern half of the country, a leading weak wave brushing the Great Lakes and associated front may produce some light precipitation over the northern tier, Great Lakes, and northern New England during the weekend. A better defined system may bring a broader area of precipitation from the Great Lakes to the Northeast states. Confidence is still limited for the regarding the areal coverage and timing of this precipitation due to significant guidance differences of the potential primary surface system, as well as possible secondary wave development along the trailing front. There has been a northward trend in the guidance compared to yesterday for this event overall. Locations near the Canadian border may see some snow or mixed precipitation during the period while rain will be the prevailing precipitation type elsewhere. Temperatures are expected to be pleasantly mild for this time of year across much of the Central U.S. on Sunday with highs generally running 5 to 15 degrees above early November averages. This will likely remain the case going into early next week as well, mainly from the Southern Plains to the Southeast states. Most of the nation will likely have a cooling trend going into the middle to end of next week, with highs running up to 10 degrees below average from the Intermountain West to the Great Lakes and Northeast states. 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 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