Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1235 AM EST Fri Feb 08 2019 Valid 12Z Mon Feb 11 2019 - 12Z Fri Feb 15 2019 ...Overview... The large scale pattern across North America will remain largely unchanged through the medium range. A persistent upper-level ridge from the North Pacific to Alaska will be the most dominant feature, governing what happens downstream across the CONUS. The evolution of shortwave energy traversing this ridge, either by cresting the ridge or by undercutting it and then diving southeastward toward the western U.S. continues to be one of the more uncertain, and most impactful aspects on the medium range forecast. Downstream of the ridge, a positively-tilted mean trough axis appears likely to persist off the U.S. West Coast, keeping a very stormy pattern in place. Farther east, the subtropical ridge will attempt to exert itself across the South Central and Southeast U.S. A relatively intense thermal gradient will continue through the period across the central U.S., between these two large scale features, resulting in the continued potential for an active cyclone track from the central plains to the Midwest and Great Lakes. ...Guidance/Predictability Assessment and Preferences... A significant degree of uncertainty and run-to-run variability continues in the model guidance with respect to the aforementioned shortwave energy originating in the North Pacific and eventually nearing the western U.S. and eventually crossing the Rockies. One such shortwave should move from the Four Corners region into the Plains on day 3 (Mon), with expected development of another potentially significant low pressure system tracking northeast into the Great Lakes/Northeast Tue-Wed (perhaps dependent on interactions with additional northern stream shortwave energy). Model solutions show more variability with the amplitude of this shortwave rather than the timing, making a blend ideal. Meanwhile, another shortwave reaches the Pacific Northwest on Mon while yet another dives southward along the coast Tue-Wed. The first of these shows relatively good consensus among the guidance, while the second begins to show much more spread by Thu. Whether this second shortwave presses inland by Thu or remains offshore reinforcing the mean trough is a significant question. The ECMWF was the most aggressive to move this feature inland, while the CMC keeps all the energy confined offshore. The ECENS seems to support something more along the lines of the CMC, while the GFS/GEFS are in between. There is some broad consensus among the guidance that the arrival of additional shortwave energy by Thu will continue to reinforce the positively-tilted mean trough offshore. To deal with the varying solutions, a multi-model/ensemble blend was used as a basis for the forecast. This included the ECMWF/UKMET/CMC/GFS as well as the ECENS/NAEFS ensemble means. Majority weight was placed on deterministic solutions during days 3-5 with majority weight placed on ensemble means during days 6-7. ...Weather Highlights/Hazards... Another round of potentially heavy precipitation will spread into the lower to mid-Mississippi and Tennessee Valleys early next week as moisture surges northward atop a warm front along the Gulf Coast. As the low pressure system strengthens in the Midwest on Tuesday, precipitation is expected to push through the Ohio Valley and into the Mid-Atlantic/Northeast. Wintry precipitation will be possible on the northwest/north side of the low and well ahead of the warm front. In the West where persistent troughing will remain with frequent shortwaves/frontal systems, moderate precipitation (valley rain and mountain snow) is expected across the Pacific Northwest at days 4-5, shifting southward and becoming heavier on day 6-7 across much of California. Much below average temperatures will persist north of an arctic front from the Pacific Northwest to the northern Rockies and northern High Plains throughout the period. The coldest temperatures will occur Mon-Tue, when temperatures may reach 30-40 deg F across the northern High Plains and 15 to 25 deg below average below average in the Pacific Northwest. Some record cold temperatures are possible for portions of WA/OR Sun/Mon. Slightly below average temperatures will spread into the Upper Midwest and then Great Lakes behind the midweek system. A surge of above average temperatures will precede the cold front Mon-Tue across the lower Mississippi Valley and the Southeast. 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