Extended Forecast Discussion NWS Weather Prediction Center College Park MD 210 AM EDT Wed Oct 25 2023 Valid 12Z Sat Oct 28 2023 - 12Z Wed Nov 01 2023 ...North-central Rockies heavy snow threat with winter cold to overspread the Plains... ...Overview... 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 slow moving frontal boundary. Upper ridging should build over the West again by mid next week as the next trough moves through the East Pacific towards the West Coast. ...Guidance Evaluation/Predictability Assessment... Latest guidance, including the new 00z runs, have been trending towards a faster trough progression through the West with less emphasis on southern stream energy or possible closed low hanging back over the Southwest (although the GFS does still show this potential). A general model blend sufficed for the first half of the period, maintaining good continuity with the previous WPC forecast. By early next week, a couple of potent shortwaves may drop into the northern tier/Great Lakes with plenty of lingering timing and strength differences, especially concerning possible amplification of the shortwave/troughing into the East next Wednesday. The GFS is noticeably weaker and much faster with energy swinging through while the ECMWF and CMC suggest more amplification and a slower frontal progression through the East. Opted to lean mostly towards the ensemble means (with minor ECMWF and CMC additions) for the WPC day 6 and 7 progs which provided a nice middle ground between the GFS and ECMWF/CMC camps. Some timing differences too with the next East Pacific trough, but an ensemble mean blend seemed to offer a good starting point for this late period feature. ...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 do 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 in this pattern for the north-central Rockies and into the less uncertain adjacent Plains into Saturday that remains denoted in the WPC Winter Weather Outlook. By next week, much of the country should be dry as high pressure dominates the CONUS with only some lake effect showers downwind of the Great Lakes. 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) shows 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 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