Extended Forecast Discussion NWS Weather Prediction Center College Park MD 215 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... Multi-model/ensemble blend sufficed for a starting point for much of the period over much of the CONUS, except for a couple areas. Firstly, exiting compact upper low through the Great Lakes has been trending slower though the GFS runs remained quicker (parallel FV3-GFS was a little slower than the operational run). Relied on the ECMWF/Canadian/UKMET there. Secondly, the embedded vorticity rounding the base of the trough through the Lakes on Wednesday has mostly trended slower as well and the 18Z GFS regained its clustering with the others except for the UKMET which appeared much too aggressive the break down the upper ridge off the west coast. By the end of next week, blend of the deterministic and ensemble guidance smoothed out some uncertain features in the northern stream around the upper low in northeastern Canada but maintained the upper low in the Southwest that should slowly lift northeastward through the week. ...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 locally heavy across 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. 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