Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1032 AM EST Thu Feb 21 2019 Valid 12Z Sun Feb 24 2019 - 12Z Thu Feb 28 2019 ...Major Upper Midwest/Great Lakes/Interior New England Winter Storm Sunday/Monday... ...Pattern Overview. The Rex block pattern across the central/north Pacific extending from near Hawaii to Alaska will persist or even strengthen during the medium range. The strongest positive height anomaly center will shift northward into the arctic by the early to middle portion of next week. Teleconnections relative to this shift in the anomaly support an eastward shift of the mean trough across the CONUS/Canada, from a position which as been across the western U.S. to a mean position from Hudson Bay to the Upper Midwest by the middle of next week. A shift to a more zonal flow regime across the CONUS southern tier will also be a consequence of this modulation across the Pacific, as shortwave energy take a more northern track and reinforces the mean trough/upper low. ...Guidance/Predictability Assessment and Preferences... Guidance was quite well clustered early in the medium range at the mid and larger scales, and a blend of the latest ECMWF/GFS/UKMET offered a reasonable starting point for the forecast during days 3-4 (Sun-Mon). One issue that emerges by Mon-Tue is exactly what happens as shortwave energy initially across the Pacific Northwest shears apart, with solutions differing on just how much energy moves east across the CONUS and Canada versus westward into the Pacific underneath the ridge. At this time, confidence is low in this aspect of the forecast, and the outcome does have downstream implications such as the amplitude of eastern U.S. troughing by next Tue-Wed. Despite these disagreements, model/ensemble solutions do all show a consistent picture at the larger scales even through day 7 as energy consolidates into an upper near/south of Hudson Bay, with shortwaves traversing the southern periphery through broad cyclonic flow from the Midwest to the Northeast. Given the increased uncertainty at mid/small scales, weighting of ECENS/GEFS ensemble means was gradually increased during days 5-7 (Tue-Thu). ...Weather Highlights/Hazards... A threat for significant snows/some icing exists around a deep surface low. The 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 which may be close to monthly record low pressure values for portions of Lower Michigan Sunday. Expect strong/gusty winds and potential blizzard conditions over the Upper Midwest/Great Lakes and into Canada Sunday-Monday. Mild air will surge northward east of a trailing cold front with a brief spike in temps to the 60/70s as far north as the Mid-Atlantic. Farther south, a prolonged heavy rain pattern will finally end with cold frontal passage, with lead record warm temps possible over Florida. A long-standing and wintry mean upper trough over the West deamplifies next week, but will still be reinforced over the Northwest into Sun-Mon as energy undercuts and digs to the lee of a blocking Alaska-centered closing upper high. This will bring unsettled weather across the Northwest/Northern CA and the north-central Intermountain West/Rockies. The best chance for heavy snow will be from the Cascades to especially northern CA with emergence of uncertain Pacific flow undercutting the northern stream. Flatter flow downstream over central and eastern U.S. next week reduces potential for big storms, but a series of smaller/less predictable systems will progress over the region. This will still favor cold air surges/anomalously cold temps through the n-central U.S. and snow swaths over the northern tier states. Rainfall also redevelops across the Gulf Coast/FL with the fronts, but guidance has backed off with amounts. Ryan/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