Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Sun Oct 06 2019 Valid 12Z Wed Oct 09 2019 - 12Z Sun Oct 13 2019 ...N-Central Rockies to Northern Plains/Upper Midwest Autumn Snow Threat Wed/Thu... ...Guidance/Uncertainty Assessment... The 06 UTC GFS and 00 UTC ECMWF/UKMET deterministic models offer reasonably similar guidance Wed-Fri and a composite blend was adopted for Day 3-5/Wed-Fri. This solution is strongly supported by ensembles, bolstering forecast confidence. Forecast confidence remains above normal into day 6/7, but gradually increasing model variance and run to run continuity issues suggest more influence into the forecast process may from ensembles may be prudent at these longer time frames. Accordingly, the WPC forecast during this period was mainly derived from a composite blend of the 06 UTC GEFS/00 UTC ECMWF ensemble means that cluster best with the 00 UTC ECMWF. The ECMWF was included for increased local detail consistent with increased forecast confidence. Model trends toward amplification and decreased progression also seem to better favor the ECMWF over the other models. This forecast plan maintains good WPC continuity. ...Weather Highlights/Threats... Strong cold front will push out of the Northern Rockies on Wednesday which will drag down well below average temperatures through the region. Record cold is likely for many areas in its wake for both lows and highs (record cold max temperatures) as readings may be 20-40 deg F below average. Cooler air will spread southward to Texas and eastward to the mid-Mississippi Valley by Friday but with less intensity. Still, a large area of the CONUS will see temperatures below average by about 5-15 deg F. The exception will be east and south of the front, mainly from the Appalachians eastward and into the Southeast/Florida until the front passes. Along with colder temperatures, wrapback moisture and upslope flow supports a heavy snow threat from the Northern and Central Rockies out across the Northern Plains and Upper Midwest with frontal low track/development. Ahead of the cold front, rainfall will expand and offers a risk to become locally heavy from the s-central Plains to the mid-MS Valley/Midwest later in the period with moisture inflow return from the Gulf. Rain threat in general will decrease farther east as the system lifts into Canada. An organized coastal low off the Mid-Atlantic and New England offers a significant maritime threat and a risk of locally heavy rainfall to these coasts next week, but this is dependent on how close the low tracks to the coast. The models are trending a bit closer and deeper. NHC is also monitoring this system for potential tropical or subtropical development. Regardless, stiff easterly onshore flow will be prevalent through southern New England into the coastal Mid-Atlantic around its circulation. Fracasso/Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml