Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1045 AM EDT Fri Oct 12 2018 Valid 12Z Mon Oct 15 2018 - 12Z Fri Oct 19 2018 ...Impressive record cold for the central/southern Plains early next week... ...Pattern Overview... An upper low near Baffin Island/Davis Strait will slowly translate southeastward as upper ridging in the Northeast Pacific breaks down. This will allow troughing initially over the Great Lakes to split between a northern and southern portion with the former exiting much quicker than the latter. Across Florida, subtropical ridging will hold in place, preventing a cold front from slipping southward to Lake Okeechobee. ...Guidance/Predictability Assessment... A multi-model deterministic blend (including the ECMWF/GFS/UKMET) served as a starting point for the forecast during days 3-5 (Mon-Wed). The GFS remains a bit quicker than the ECMWF/UKMET with shortwave energy crossing the Great Lakes on Mon, but has moved closer to the slower solutions relative to yesterday and is now usable. Consensus remains high that energy will separate from the trailing end of the central U.S. trough and cutoff/linger across the Southwest, and the described blend represents this process well. By days 6-7 (Thu-Fri) consensus suggests that the energy previously cutoff over the Southwest will begin to slowly drift eastward toward the central U.S. Spread among the deterministic guidance/ensemble means with respect to this is relatively low, although a number of individual ensemble members (particularly in the GEFS/NAEFS) show slower solutions which are not necessarily out of the question given the broad flow amplification in place. Boosted weighting of ECENS/NAEFS ensemble means in the forecast during days 6-7, with a majority ensemble means by day 7 to account for somewhat increased spread in the Southwest/central U.S. as well as with additional northern stream shortwave energy crossing central Canada. ...Weather Highlights/Threats... Well below average temperatures (likely breaking record low minima and maxima over many stations and states) will sink southward behind a strong cold front late this weekend into next Monday. Highs in the 40s are forecast for most of the central Plains into Texas even to the Big Bend which will be about 25-35 degrees below average. Some locations may break their record low daytime high temperature by 5-10 degrees even where records go back over 100 years. The cold will start to relent after Monday as it settles to the Gulf Coast and Lower Mississippi River Valley. The cold front will have less bite farther east from the Great Lakes to the Northeast/Mid-Atlantic where temperatures will only be a few degrees below average. To the south, Florida will maintain above average temperatures thanks to upper ridging. Precipitation may be heavy from Texas northeastward as the upper low behind future ex-Sergio meanders eastward through the Four Corners region and moisture from the western Gulf flows northward atop the front. The rain axis will extend to the Mid-Atlantic but in lessened amounts. The rest of the lower 48 behind the front will be largely dry with some showers around the Lakes (some snow, some rain). Widespread snow (some lower elevation rain) will exit the Southern Rockies on Monday with some snow accumulation thereafter as the upper low swings through. Ryan/Fracasso WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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