Extended Forecast Discussion NWS Weather Prediction Center College Park MD 148 AM EST Mon Feb 11 2019 Valid 12Z Thu Feb 14 2019 - 12Z Mon Feb 18 2019 ...Overview... Models/ensembles show strong consensus that a Rex block pattern across the central/north Pacific, extending from near Hawaii to Alaska, should persist through the next week, leaving the flow regime across the CONUS largely unchanged. Teleconnections relative to the strongest 500 ha height positive anomaly center continue to favor a positively-tilted mean trough near the Pacific Northwest, with weak positive height anomalies from the southern plains to the Southeast, and a broad region of modestly cyclonic upper-level flow across much of the CONUS. Shortwave energy ejecting from the northeastern Pacific every couple days will move into then cross the CONUS, undergoing gradual amplification in the broad cyclonic flow. Additionally, a persistent and relatively strong thermal gradient from the central U.S. to the Ohio Valley/Great Lakes will serve to intensify another low pressure system by later this week. ...Guidance/Predictability Assessment and Preferences... The developing low pressure system across the central U.S. days 3-4 (Thu-Fri) remains one of the more significant concerns this forecast period. Model cycles from during the day yesterday seemed to show some degree of improved consensus toward the idea of less/slower phasing between the vigorous Pacific shortwave and additional northern stream energy, and a surface low track Thu night/Fri from the southern/central plains to the mid-Mississippi Valley and the lower Great Lakes. The 12Z ECMWF/CMC and 18Z GFS were fairly close on this, and ensemble members showed decent clustering around this type of solution. The WPC forecast depicts a solution along these lines as well, which was fairly close to forecast continuity. The arrival of the 00Z GFS and UKMET threw a bit of a fly into the ointment, returning to a much more phased solution that races the surface low northeastward far more quickly than the previously mentioned consensus. The aforementioned outcome also has downstream affects by Fri night Sat as the system reaches the eastern U.S. with the favored consensus solution likely resulting in the development of a low along the Mid-Atlantic coast tracking northward into New England. A more phased system earlier, however, would quickly move the system north into Canada by that time. Needless to say, confidence remains below average with respect to this system Thu-Sat, and the forecast is subject to significant changes. In the wake of the late week low pressure system, models have at least come into better agreement on the nature of the flow across the western/central U.S. by the weekend. The GFS has backed off its previous attempts to build ridging/anticyclonic flow across the Rockies/central U.S. - now showing a stronger upper jet continuing to transport numerous areas of Pacific shortwave energy inland. A more significant trough should push into the western U.S. by Sun-Mon, as shown by the majority of deterministic solutions and ensemble means. Detail differences emerge by by early next week as to just how quickly this amplified trough moves inland, lending toward heavier use of ensemble means (ECENS and GEFS) in the forecast by days 6-7. ...Weather Highlights/Hazards... The persistent upper trough along the West coast will produce multiple rounds of low-elevation rain and mountain snow from California to the Pacific Northwest. Systems will also spread rain/snow east into the interior western U.S., with heavy snow possible at the higher elevations. The low pressure system moving from the central U.S. toward the Great Lakes Thu-Fri will likely produce an area of wintry weather along/north of the surface low track. The extent of winter weather and the degree to which heavy snow may be possible remains somewhat uncertain given the model differences described above. The same holds true for winter weather potential in the Northeast Fri-Sat. While at least some wintry weather is likely in warm advection ahead of the warm front, any potential coastal low development would enhance the potential for heavier precipitation across New England, with the best chances for significant snows across the interior. Farther south, the cold front will likely produce widespread rains from the lower Mississippi Valley to the Eastern Seaboard. Well below average temperatures are expected to persist from the interior Pacific northwest to the northern plains through the forecast period. Max/min temperatures ranging from 10 to 30 deg F below average will be possible through the week and into the weekend across these areas. Temperatures will initially be above average from the southern/central plains to the Eastern Seaboard Thu, but by late in the week colder temperatures should spread farther south/east in the wake of the low pressure system, with temperatures 5 to 15 deg F below average across much of the central/eastern states. The exception will be areas from the southern plains to the Southeast where temperatures will remain near seasonal norms even into the weekend. Ryan 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