Extended Forecast Discussion NWS Weather Prediction Center College Park MD 239 PM EST Fri Jan 29 2021 Valid 12Z Mon Feb 01 2021 - 12Z Fri Feb 05 2021 ...Winter Storms over the East early next week and from the West to the Midwest/Northeast mid-later next week... ...Weather Pattern Overview and Guidance/Predictability Assessment... An increasing amplified upper level pattern is forecast over the CONUS during the period with a deep longwave trough expected to evolve over the central U.S. by the end of next week. At the start of the period, a pair of systems impacting the east and west coasts has above average forecast agreement, at least for the large scale setup. The east coast winter storm at the start of the period still have good model agreement though with the finer details including rain/snow/mix zones still to be ironed out. This will of course have sensible impacts including snowfall accumulations but as the storm transition into the short range, the details will become clearer. For the west coast, another low and front should push through the region bringing widespread precipitation. Here model guidance is relatively good. The largest model differences creep up by day 5 through day 7 with the developing Plains system. As the energy comes out of the West and Rockies and deepens, low pressure cyclogenesis in the lee of the Rockies is then forecast to lift toward the Upper Midwest in a classic synoptic setup. Strong warm air advection and moisture return on the backside of the departing high will allow for copious amounts of moisture to work with the better dynamics and forcing. The GFS remained a faster outlier, particularly the 00Z run, which was not used. The 06Z run was more usable and closer to the consensus. While the ECMWF was on the slower side, it was still heavily incorporated into the WPC blend. Overall, the WPC blend started with the deterministic ECMWF/GFS/UKMET/CMC blend with increasing use of the ECENS/GEFS means to address some of the uncertainty. But overall, the forecast confidence is average to above average this cycle. ...Weather/Threats Highlights... Moderate to locally heavy precipitation (mountain snow, lower elevation rain) is expected over portions of the Pacific Northwest and central West Coast into early next week. As the system pushes into the Plains/Upper Midwest, meaningful amounts of snow is increasingly likely on the northwest side of the low pressure track. Across the warm sector, pockets of moderate to heavy rainfall may evolve as the system progresses eastward. For the east winter storm late this weekend into early next week, the signal for potentially significant snowfall remains locked on the interior Mid-Atlantic to Northeast to New England areas where the latest Winter Weather Outlook probabilities remain moderate to high. It will take some time into the short range time frame to resolve more precisely the locations of the rain-snow line/transition zone and axis of heaviest snowfall. Some areas along or offshore the coast may see a period of brisk to strong winds. Farther south expect the highest rainfall totals with some moderate to heavy activity over or near the southern Mid-Atlantic early in the forecast period as a warm front moves in from the south and coastal low pressure develops. Taylor Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy precipitation across portions of the Mid-Atlantic and the Northeast, Mon-Tue, Feb 1-Feb 2. - Heavy rain across portions of California and the Pacific Northwest, Mon, Feb 1. - Heavy rain across portions of the Southeast, the Mid-Atlantic, the Southern Appalachians, the Ohio Valley, and the Tennessee Valley, Thu-Fri, Feb 4-Feb 5. - Heavy snow across portions of the Northeast, the Central Appalachians, the Northern Rockies, the Mid-Atlantic, California, the Northern Great Basin, the Central Great Basin, the Pacific Northwest, and the Southwest, Mon-Tue, Feb 1-Feb 2. - Heavy snow across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, the Northern Great Basin, and the Northern Plains, Tue-Wed, Feb 2-Feb 3. - Heavy snow across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Southern Rockies, the Southern Plains, and the Southwest, Wed, Feb 3. - Heavy snow across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Wed-Fri, Feb 3-Feb 5. - Flooding possible across portions of the Middle Mississippi Valley. - High winds across portions of the Central Plains, the Central Rockies, the Northern Plains, the Southern Rockies, the Southern Plains, and the Southwest, Wed-Thu, Feb 3-Feb 4. 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