Extended Forecast Discussion NWS Weather Prediction Center College Park MD 137 AM EST Sat Feb 09 2019 Valid 12Z Tue Feb 12 2019 - 12Z Sat Feb 16 2019 ...Overview... A persistent upper ridge axis extending from the North Pacific across Alaska will continue to be a dominant influence on the weather pattern across the CONUS. Teleconnections associated with the strongest positive height anomalies in the ridge support a downstream positively-tilted mean trough near/off the Pacific Northwest and above average heights from the southern plains to the Eastern Seaboard on the northenr periphery of a relatively strong subtropical ridge. A strong thermal gradient in between these dominant features, from the central plains to the Great Lakes, will largely denote the prevailing storm track through the forecast period, with Pacific shortwave energy spawning intensifying surface cyclones as they reach the region of increased baroclinicity and broad cyclonic flow across the central U.S. ...Guidance/Predictability Assessment and Preferences... Models continue to vary with respect to the intensity of a shortwave/surface cyclone initially across the Midwest on day 3 (Tue), but model/ensemble solutions are quite well clustered on the track of the system as it moves into the Great Lakes by day 4 (Wed). The same holds true for a triple point coastal low expected to develop along the New England coast Tue night/Wed morning. While deterministic solutions show some relatively small timing differences, solutions are generally well-clustered. Finally, shortwave energy reaching the Northwest Tue-Wed has shown improved consensus among the guidance relative to this time last night. Models have trended toward ejecting this energy inland Wed as opposed to keeping a more consolidated/elongated upper trough just offshore (as a significant quantity of guidance was suggesting this time last night). Overall, the ECMWF (12Z Fri) and GFS/FV3 (18Z Fri) solutions showed the best consensus across the board during days 3-5, and thus this forecast for this time period was based on a multi-model blend of these solutions. By Thu the aformentioned Pacific shortwave should be crossing the Great Basin/Rockies, and models continue to show improved consensus. By the time the energy reaches the central U.S. and begins to intensify along with the surface cyclone, differences emerge among the guidance, especially with respect to the degree of deepening and any potential interactions with northern stream shortwave energy. Ensemble scatterplots show rather poor clustering among solutions by Fri and continuing into Sat as the system reaches the Great Lakes. Farther west, models agree that yet another shortwave should reach the Pacific Northwest late Thu into Fri, with most solutions showing the energy slowly sagging southward along the coast through Sat. Ensemble means have shown a bit more stability from run to run relative to deterministic guidance during days 6-7 (Fri-Sat). Thus, majority weight was shifted toward the ECENS/GEFS ensemble means for the forecast during this time period. ...Weather Highlights/Hazards... The low pressure system crossing the Midwest/Great Lakes Tue-Wed will bring potentially moderate to heavy snowfall to areas north of the low track. A broad area of overrunning moisture north of the warm front may also bring wintry precipitation to portions of the Mid-Atlantic and Northeast, with the potential for heavier snow across portions of New England as the low develops along the coast Tue night/early Wed. The same areas may see winter weather potential again Thu-Fri as the next low pressure system follows a very similar track evolution. Meanwhile, the mean trough axis off the West Coast with frequent incoming shortwaves will keep precipitation rather widespread from California to the Pacific Northwest. Expect continued potential for heavy mountain snow and lower elevation rain. Persistent cold air north of an arctic frontal boundary may also bring snowfall potential to lower elevations in the Pacific Northwest. Temperatures are forecast to be well below average from the Pacific Northwest to the northern High Plains through the forecast period, with temperatures 15 to 30 deg F below average across a broad area. Farther east, many areas will experience above average temperatures. High temperatures could reach 10 to 20 deg F above average across portions of the Ohio Valley and Southeast Tue in the warm sector of the low pressure system. Otherwise, near to slighly above average temperatures are expected to persist from the southern plains to the Southeast/Mid-Atlantic from Wed onward. 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