Extended Forecast Discussion NWS Weather Prediction Center College Park MD 153 AM EST Tue Jan 28 2020 Valid 12Z Fri Jan 31 2020 - 12Z Tue Feb 04 2020 ...Overview and Guidance/Predictability Assessment... An upper-level ridge is forecast to be in the process of building across the western U.S. on Sat (day 3). This will favor broad cyclonic flow downstream, across the central and eastern U.S., with Pacific shortwave energy undergoing amplification as it spills over the north side of the ridge. Also on Sat, a previously cutoff southern stream system is expected to begin some degree of interaction with an amplifying northern stream wave across the central U.S. As is typical of a situation with expected phasing, models continue to show a fairly large degree of spread (sometimes this can linger even into the short range in such situations). The ECMWF continues to show a fairly large degree of run-to-run variability, while the GFS (and UKMET) have been more consistent. The ECMWF has also trended somewhat toward the GFS, now not quite a slow with the southern stream wave, or as suppressed with the eventual Gulf of Mexico/Southeast U.S. low development. Further, the GFS continues to have more support from the ensembles. The 18Z GFS was well-centered among members from all three ensemble systems, and was the preferred track for the low pressure system along the Eastern Seaboard this weekend. The intensity of the system remains another issue, with the GFS having shown a deep bias for intensifying cyclones during the medium range this season. The 00Z GFS shifted the track a bit farther west (closer to the UKMET) - certainly a possibility, but based on ensemble guidance, not ready to go that far west at this point. The ECMWF, meanwhile, was on the eastern fringe of even its own ensemble members with the system. Elsewhere, models continued to show somewhat better consensus with a positively-tilted Pacific trough forecast to reach the on Sun. Differences do emerge as the system moves inland by Mon-Tue, with the ECMWF/GFS showing some difference in amplitude as well as positive/negative tilt by that time. Overall, however, model differences with this system are smaller than average given the time frame under consideration. Both solutions also agree that some component of leftover southern stream energy (separated from the previous system) should lift out across the central U.S. ahead of the trough early next week. Despite agreement on that aspect, such features have fairly low predictability, so would not be surprised to see variability in future model runs. Given the described solutions/differences, opted to lean heavily on the 18Z GFS during days 3-5 (Fri-Sun). By days 6-7 (Mon-Tue), continued to use a smaller component of the GFS, along with increasing ECENS/GEFS ensemble means. The 12Z ECMWF was used only in a limited capacity early in the forecast period, on day 3. ...Weather/Hazard Highlights... Heavy precipitation (rain and mountain snow) will be a possibility across the Pacific Northwest, especially the Olympics and Washington Cascades, Fri-Sat ahead of the incoming Pacific shortwave/frontal system. Precipitation could linger into Sun-Mon across the Northwest as onshore flow persists in the wake of the front, but precip should not be quite as heavy by that time. Snow levels should fall by the weekend into early next week, however, as the trough moves onshore - thus heavier snow amounts may be possible across the Cascades Sat-Sun even as the overall intensity of moisture inflow decreases. As low pressure develops in the Gulf of Mexico Fri into Sat, and then moves across the Southeast, a good overrunning setup should aid in the development of a shield of widespread rain from the Gulf Coast to the Southeast and Mid-Atlantic. Models do not show an abundance of cold air in place at that time to support winter weather, but some possibility of winter weather is indicated by low probabilities on the winter weather outlook Fri/Fri night across portions of the southern Appalachians and southern Mid-Atlantic region. As the low strengthens and moves northeastward, uncertainty in the exact track lends to uncertainty in both precipitation amount and type along the Eastern Seaboard from the Mid-Atlantic to New England. Continued to indicate low to moderate probabilities on the winter weather outlook for Sat/Sat night from the central Appalachians and portions of the Mid-Atlantic region to the Northeast, continuing into Sun across portions of northern New England. Temperatures are forecast to be well above average across the central and eventually the eastern U.S. during the extended forecast period. High temperatures of 15 to 30 deg F above average are possible across the Northern/Central Plains Fri-Sun. These warm temperatures are forecast to spread eastward by Mon-Tue into the Mississippi/Ohio Valleys and eventually the East Coast (although with some degree of moderation). Meanwhile, the trough/cold front expected to reach the western U.S. this weekend will bring initially well above average temperatures (highs 10-20 deg above normal) to near or below normal by Sun-Mon, with colder temperatures also reaching the High Plains by Tue. Ryan Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are 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 https://www.wpc.ncep.noaa.gov/heat_index.shtml