Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1101 AM EST Wed Feb 20 2019 Valid 12Z Sat Feb 23 2019 - 12Z Wed Feb 27 2019 ...Significant winter storm from the south-central Plains to the Upper Midwest/Great Lakes and interior New England this weekend... ...Heavy rainfall/flooding threat in the Southeast Saturday and again next week... ...Pattern Overview... The Pacific Northwest will see additional/reloading troughing out of western Canada downstream of a very strong upper high over Alaska next week. To the east, a potent shortwave will deepen and lift northeastward into the Great Lakes as the upper ridge over the Bahamas remains in place. This will keep the storm track inland well west of the coastal plain to the south of a Hudson Bay upper low. ...Guidance/Predictability Assessment and Preferences... Guidance was reasonably well-clustered at mid-larger scales through the medium range period until about Monday. A composite blend of the latest GFS/ECMWF/UKMET/Canadian offered a reasonable starting point for Sat-Mon as a rapidly deepening system (central pressure fall of about 20mb/24 hrs between Sat and Sun morning) lifts into the Great Lakes and then exits out the St. Lawrence Valley Sunday into Monday. This system has the potential to deepen into the upper 970s mb or at least low 980s mb which may be close to monthly record low pressure values for portions of Lower Michigan Sunday morning. In the West, the models/ensembles diverge on how to handle the upper high over Alaska and downstream flow over southwestern Canada/Pacific Northwest -- ECMWF and many of its ensembles take shortwave vorticity back westward underneath the upper high while the GFS and many of its ensembles (as well as the Canadian/UKMET) took it southward then slowly eastward along the Oregon coast. The parallel 06Z FV3-GFS was less aggressive than the GFS. Pattern would allow a westward/retrograding shortwave so opted to keep some ECMWF influence to the forecast but otherwise trended toward the ensembles which would give way to at least flatter flow by next Wed into OR/NorCal. In the east, some semblance of a system should lift toward the Great Lakes next Tuesday then off the coast next Wednesday but how it evolves is uncertain. ...Weather Highlights/Hazards... Weekend system will bring a threat for significant accumulating snow with some icing possible to the northwest/north/northeast of the surface low with strong/gusty winds and potential blizzard conditions across the Upper Midwest and Great Lakes. Mild air will surge northward east of the front with a brief spike in temperatures into the 60s and 70s across the Mid-Atlantic. Farther south, heavy rain from the end of the short range will be possible into the start of the medium range aided by convection in the warm sector and plenty of Gulf moisture. SPC has denoted a chance of severe weather on Saturday from Arkansas to KY/TN and northern Alabama. Florida may escape most of the rainfall but record warm temperatures will be possible with the mild upper pattern. A long-standing and wintry mean upper trough over the West will again be reinforced Sat-Mon as energy digs to the lee of a blocking Alaska-centered upper high. These systems will be less amplified than prior systems in this recent pattern, but will bring unsettled weather through the Northwest and north-central Intermountain West and Rockies, with the best chance for accumulating snowfall over the Cascades into especially northern California. Focus of the precipitation may remain concentrated over the same area depending on how the pattern evolves offshore into the West Coast, which would result in several days of rain/mountain snow. Fracasso/Schichtel WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation and winter weather outlook probabilities 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