Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Wed Oct 25 2023 Valid 12Z Sat Oct 28 2023 - 12Z Wed Nov 01 2023 ...Heavy Snow threat for the Central Rockies/adjacent Plains this weekend... ...Arctic Surge through the Central U.S into next week.... ...Overview... It remains the case that renewed troughing will envelope the West through the weekend before shifting into Plains and eventually the East next week. Initial strong ridging over the Southeast this weekend will create a pronounced contrast between unseasonably warm weather over the East and an expansive area of much below normal cold over the West and the Plains. This pattern brings a threat for heavy snow to the north-central Rockies and possible parts of the High Plains with a multi-day period of enhanced rainfall over parts of the south-central Plains to Midwest Saturday and Sunday along a frontal boundary. Upper ridging should build over the West again by next midweek as the next trough works into the East Pacific/West Coast. ...Guidance Evaluation/Predictability Assessment... 06 UTC GFS/GEFS and 00 UTC UKMET/ECMWF/ECMWF ensemble mean solutions seem best clustered and reasonably through the upcoming weekend, even with lingering timing issues that become more prominent into next week. A composite blend along with input from the 13 UTC National Blend of Models (NBM) seems to provide a solid forecast basis for the weekend. Given growing forecast spread into next week, opted to switch preference closest to the ensembles and the 00 UTC ECMWF ensemble mean best matches WPC product continuity and messaging. The ECMWF ensemble mean continues to offers a slightly more amplified and less progressive solution overall compared to the GEFS mean. ...Weather/Hazards Highlights... Instability and anomalous moisture along a slow moving front this weekend will provide focus for a multi-day period of heavy rainfall from parts of the south-central Plains into the Midwest/Ohio Valley with potential for repeat/training of storms. Some lingering uncertainty on exactly where the heaviest totals set up, and dry antecedent conditions could limit a widespread flash flood threat, but latest model QPF amounts combined with the potential for additional rains over the next few days leading into the medium range forecast period do seem to still support a slight risk area on both the days 4 and 5 EROs across the Mid-Mississippi Valley, with a marginal risk extending northeast and southwestward along the span of the frontal boundary. Potential exists for some snow in the northern periphery of the precipitation shield, but specifics remain very uncertain and require monitoring. However, there is a growing signal supporting a threat for heavy snow for the north-central Rockies and into the less uncertain adjacent Plains this weekend that remains denoted in the WPC Winter Weather Outlook. There is also some potential for a transition zone of freezing rain/sleet on the leading edge of precipitation down across the south-central Plains and Mid-MS Valley this weekend into Monday with cold air advance. Beyond that next week, much of the country should be mainly dry as high pressure dominates the CONUS. There should be modest lake effect rain/snow showers downwind of the Great Lakes. Of note is also an uncertain lifting of a low up from the Caribbean to the southwestern Atlantic in some guidance in advance of a main cold front that is now being monitored by NHC. Meanwhile, the approach of an amplified eastern Pacific upper trough/height falls and surface system energies does overall favor a moderately wetter pattern in about a week for the Northwest. Much below normal temperatures across the West into the northern/central Plains on Saturday will expand south and eastward bringing the first real cold snap of the season to many across the central U.S., including as far south as the Southern Plains/Texas and coinciding with outdoor Halloween festivities next Tuesday. Daytime highs 20-30 degrees below normal are likely with a few daily records possible within this cold air mass. The Climate Prediction Center (CPC) has shown an extension of the cold air threat into early November over the central states as well. Meanwhile, well above normal temperatures will continue into this weekend/Monday for the Southeast/East underneath a retreating upper ridge. Expect a broad area of highs 10-20 degrees above normal with some morning lows 20-25 degrees above normal. Daily records are possible, with record warm lows likely to be more numerous than record highs. The chilly central U.S. airmass should push eastward with time next week (with some moderation) with much of the country east of the Rockies below normal next Tuesday-Wednesday behind the strong cold front. Santorelli/Schichtel 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