Extended Forecast Discussion NWS Weather Prediction Center College Park MD 152 AM EST Sun Dec 23 2018 Valid 12Z Wed Dec 26 2018 - 12Z Sun Dec 30 2018 ...Significant Plains/Midwest winter storm Wed-Fri... ...Overview... A robust and impactful winter storm will lift through the central Plains to the Midwest Wed-Thu bringing wind-driven snow to parts of Nebraska/South Dakota/Minnesota and locally heavy rain to portions of the Gulf Coast. The system will move into the Great Lakes on Friday and then off the Northeast/Mid-Atlantic coast Saturday as the front settles into the Gulf. Another storm is forecast to move through the West/Southwest just behind the first storm which will spread precipitation through the Great Basin/Four Corners region. ...Guidance Evaluation/Preferences... A majority deterministic model blend was used for the first few days of the forecast as the models remain in good synoptic agreement. This blend included the 12Z ECMWF/GFS/FV3/Canadian/UKMET for Wed-Fri which was a bit slower than the ensemble means given the trend but not as slow as the ECMWF/UKMET given the ensemble spread (only a few members slower than them). By next Sat/Sun, the ensembles diverge in the West (and eastern Pacific) as the pattern becomes much less predictable even at the synoptic scale. Agreement is best over the Bahamas/Cuba where the ensembles show upper ridging building westward from north of Puerto Rico late this week. In the Pacific, question is how much separation in the flow will occur around 150-160W later this week which will determine the shape/strength of ridging just off California. Teleconnections to a deep negative height anomaly around 38N/163E (south of Kamchatka) point to a positively tilted trough from NW Mexico to the Great Lakes with ridging into California, which is more in line with the ECMWF/Canadian ensembles rather than the GEFS. Trended toward a majority ECMWF/ECMWF ensemble mean blend by next Sat/Sun but did not rule out the GEFS solution of a farther west trough axis given the upstream uncertainty. ...Weather Highlights/Hazards... Focus will be on the major system in the central Plains Wednesday as it lifts northeastward through Kansas. Precipitation will expand around and ahead of the deepening low and cold front with the flow out of the Gulf. To the northwest of the surface low, snow will come down heavy at times with increasing wind and possible blizzard conditions (blowing and drifting snow with limited visibility) over parts of Kansas and Nebraska Thursday. This will make travel difficult if not impossible. Several inches of snow are likely over a large area with over a foot quite possible for some areas, especially from NW Kansas/NE Colorado northeastward to Minnesota/Wisconsin as the surface low tracks toward Lake Michigan. Please consult the latest winter weather probabilities for a daily graphical depiction of the best chance of snow. In the warm sector, rainfall could become locally heavy near the Gulf Coast as the system infuses Gulf moisture northward up and over the warm front. Several inches of rain are possible in some areas with a more widespread 1-2" likely between I-10 and I-20. The system will exit through southern Ontario and northern New England where some onset frozen precipitation (perhaps appreciable freezing rain as warm air advances over in situ lower level cold air) is likely. Next system in the West will bring more snow and some lower elevation rain to the Four Corners region but will be dependent on the trough strength. Temperatures will be cooler than average in the West behind the front but will be well above average over the Mississippi Valley eastward (10-30 deg F anomalies especially overnight). With reinforcing troughing into the West later in the week, temperatures will stay below average from the Great Basin/Rockies into the Plains, especially over newly snow-covered areas. Cooler air will filter into the East next weekend as the front sinks into the Gulf and northern Florida. 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