Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1059 AM EST Fri Feb 08 2019 Valid 12Z Mon Feb 11 2019 - 12Z Fri Feb 15 2019 ...Overview... A strong mean ridge extending from the North Pacific into Alaska will likely be the dominant influence on the pattern from the eastern Pacific across the Lower 48. In association with this mean ridge, for most of this week multi-day means valid at the extended time frame have been advertising a strong positive height anomaly center just south of the Alaska Peninsula. Teleconnections relative to this anomaly center support a deep mean trough aloft near the West Coast and west-southwesterly flow downstream with somewhat above normal heights over the East. Corresponding to this pattern expect a strong temperature gradient between below/much below normal temperatures over the West Coast states/northern Rockies-Plains and above normal temperatures over the South with a prevailing storm track from the central Plains through the Great Lakes. Specifics of the West Coast trough will affect location/intensity of heaviest precipitation over the West while there is better agreement on another relative maximum of precipitation over the east-central U.S. ...Guidance/Predictability Assessment and Preferences... Over recent days the model and ensemble guidance has shown significant differences ultimately stemming from uncertainty over the exact shape of the Pacific ridge and energy flowing around the eastern side of it. In addition there was a meaningful clustering of guidance that was showing a fair degree of westward trough elongation over the eastern Pacific by the Tue-Wed time frame--an evolution not particularly favored by teleconnections that suggested troughing should be at least as far east as the West Coast and not as elongated. 24 hours ago the GEFS mean was actually closest to the teleconnection-favored pattern by Wed-Thu while probably half ECMWF members actually had ridging just inland from the West Coast. Today's 00Z cycle has brought a pronounced adjustment in the 00Z ECMWF/ECMWF mean toward troughing along/inland from the West Coast around midweek and the CMC/CMC mean concur in principle. Now the GFS runs are pulling off energy over the eastern Pacific, leading to lower confidence solutions downstream. The 00Z GEFS mean strayed toward some aspects of earlier ECMWF/ECMWF ensemble runs but the 06Z version is showing some trending toward the new majority cluster. As a result the extended forecast blend is based on the 00Z ECMWF/CMC and 00Z ECMWF mean/06Z GEFS means with a little 00Z UKMET included early in the week. This represents a significant change from continuity, and while confidence is no better than average due to the spread/variability seen in guidance thus far, the fact that this cluster better matches teleconnection-favored flow does provide greater confidence than was previously the case. As for individual systems, clustering has improved with the leading system tracking from the West through the Midwest/Great Lakes and southeastern Canada/New England Mon-Wed. GFS issues begin with the system dropping southeast off the Alaska Panhandle/BC at the short/extended range interface, with the dominant model cluster showing a much stronger system reaching the northern Pacific Northwest by Tue. Then this system ejects inland and produces another central Plains through Great Lakes storm by Thu-Fri. At the same time the next bundle of shortwave energy should bring another system southeastward toward the Pacific Northwest late in the week, with intermediate timing providing the best starting point given decent clustering for a day 7 forecast. ...Weather Highlights/Hazards... The overall mean pattern featuring storm systems dropping southeastward into the western U.S. and then tracking northeast through the central Plains and beyond will produce active weather over portions of the West as well as the northern Plains and many areas from the Mississippi Valley to East Coast. One strong signal for highest 5-day totals of precipitation extends from western Oregon into northern-central California. Day-to-day variations in upper trough specifics could produce significant activity to the north or south of this area as well. Some of this moisture will extend into the Rockies. Especially over the Northwest expect a continued threat for low elevation snow at times given persistence of below normal temperatures. The other highlighted area for highest 5-day precip totals extends across the Ohio/Tennessee Valley region and to some degree across the Mid-Atlantic/southern New England. Heaviest activity will likely accompany two separate storm systems spaced about three days apart. The northern Plains into northern New England should see mostly snow from these systems with rain over the southern latitudes and a variety of precipitation types in-between. Depending on the degree of development, any individual storm may produce strong winds over some areas. Within the area of below normal temperatures over much of the West and into the northern Plains, expect greatest anomalies to be over the northern Plains with readings consistently 15-25F below normal. Pacific Northwest cold anomalies may not be quite as extreme in absolute terms but could have a better chance to approach or exceed daily record values at some locations. Farther eastward, warm surges ahead of each progressive storm system may bring morning lows 20F or greater above normal and afternoon highs generally 10-20F above normal. Rausch 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