Extended Forecast Discussion NWS Weather Prediction Center College Park MD 249 PM EDT Thu Oct 26 2023 Valid 12Z Sun Oct 29 2023 - 12Z Thu Nov 02 2023 ...Arctic Surge through the Central to Eastern U.S into next week offers some early season Wintry Weather potential including a widespread Frost/Freeze risk... ...Overview... Guidance still indicates that upper troughing looks to be sliding through the West as the period begins on Sunday, with shortwaves working to maintain and renew the troughing as it moves through the Midwest and eventually into the East next week. This allows for a much below normal airmass to spill into the Central U.S., including as far south as Texas and the Gulf Coast, sliding to the East with time. Heavy rain looks to be a threat Sunday along a frontal boundary through the south-central Plains and Midwest, but conditions should overall dry out thereafter as surface high pressure envelopes much of the nation. 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 Canadian/UKMET/ECMWF/ECMWF ensemble mean solutions now overall seem better clustered and generally reasonable for Sunday and Monday, bolstering forecast confidence. A composite blend along with input from the 13 UTC National Blend of Models (NBM) and WPC continuity seems to provide a solid forecast basis. Given growing forecast spread later next week, opted to switch preference closest to the 00 UTC ECMWF ensemble mean that of the ensembles best matches WPC product continuity, latest model trends over much of the nation and adjoining waters including somewhat more amplitude and slower progression along with associated messaging. ...Weather/Hazards Highlights... Instability and anomalous moisture along a slow moving front into Sunday will continue to provide focus for 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 the day 4/Sunday ERO across the Mid-Mississippi Valley, with a marginal risk extending northeast and southwestward along the span of the frontal boundary. Some potential for lingering snow across the central Rockies and adjacent High Plains on Sunday on the north side of the precipitation shield, with transition zone freezing rain/sleet just south of this area. Beyond that into next week, much of the country should be mainly dry as high pressure dominates the CONUS. However, there should be modest lake effect rain/snow showers downwind of the Great Lakes with wavy frontal system passage. Additionally, a growing but still uncertain guidance signal for downstream coastal low development over the western Atlantic seems to offer some opportunity to wrap organized precipitation back into the Northeast by next midweek that with cold air advance could support a window for areas of early season snows, especially for the interior. There is also an uncertain lifting of a low up from the Caribbean to the southwestern Atlantic in some guidance in advance of the main cold front. This is being monitored by NHC. Meanwhile, the approach of an amplified eastern Pacific upper trough/height falls and surface system energies still overall favors a moderately wetter pattern in about a week for the Northwest and vicinity. Much below normal temperatures across the West into the northern/central Plains will continue to expand south and east on Sunday 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. Meanwhile, well above normal temperatures will continue Sunday and 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-Thursday. Significantly, there is a widespread first frost/freeze risk with this post-frontal cold snap next week, broadly from the south-central Plains through the Northeast as depicted on the WPC Hazards Outlook. Schichtel/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