Extended Forecast Discussion NWS Weather Prediction Center College Park MD 340 PM EST Tue Jan 26 2021 Valid 12Z Fri Jan 29 2021 - 12Z Tue Feb 02 2021 ...Another significant precipitation event likely along the central West Coast from the weekend into early next week... ...Weekend into early next week system to spread a broad area of rain and wintry weather across the eastern half of the lower 48... ...Weather Pattern Overview and Guidance/Predictability Assessment... The latest guidance show reasonable agreement on the general synoptic pattern evolution across mainland U.S. through the medium range period with some typical spread and trends. The ongoing heavy precipitation event over California in the short range should begin to subside by Friday as the system reaches southern California. However, there was noticeable model differences on how fast the system weakens over the Southwest. The ECMWF tends to slow the weakening rate of this system while the GFS has been quicker with lifting the system across the Southwest. The CMC also depicts a slower progression more in line with the ECMWF. The WPC forecast map for Day 3 leans toward the slower guidance envelope regarding this system. Models have become relatively consistent in forecasting the next low pressure system to develop on Saturday over the central Plains with a broad area of precipitation ahead of it. Models have also trended toward a better-defined high pressure system over eastern Canada which would help the low pressure system to become more negatively tilted as it passes south of New England early next week. The typically fast GFS has been the fastest guidance while ECMWF has been the slowest. The CMC was somewhere in between. A blend of these guidance should offer a reasonable starting point for this system. Along the West Coast, models have been relatively consistent with the timing of the next wave of moisture arriving by Friday night or early Saturday. There is good model agreement for this moisture plume to be first directed toward northern California and the Pacific Northwest coast during the weekend, followed by a gradual southeastward shift into central California early next week. The WPC medium-range forecast package was based on the consensus of the 06Z GFS/GEFS, the 00Z ECMWF/EC mean, and the 00Z CMC/CMC mean, but leaning toward the slower solutions from the ECMWF. More of the ensemble means were used on Days 6 and 7 to handle the increasing model uncertainty. ...Weather/Threats Highlights... The ranges over far southwestern California may still see moderate to heavy precipitation late this week while lighter activity lingers over the rest of the state. Expect generally moderate amounts of rain and higher elevation snow to spread across the remainder of the West as the supporting shortwave aloft crosses the region. Then from the weekend into next week upstream energy aloft and a couple frontal systems will bring additional moisture to the West Coast. Much of the Pacific Northwest may see a period of moderate to heavy rain/mountain snow early in the event followed by a more concentrated emphasis of heavy precipitation on southwestern Oregon and northern California. Some of this moisture should extend into the northern Rockies. Specifics of the heaviest precipitation will depend on the exact amplitude and timing of the approaching upper trough but the general signal for southwestern Oregon/northern California has been fairly stable over recent days. The Northeast will see breezy to windy conditions late this week sandwiched in between strong Atlantic low pressure and Great Lakes high pressure. The system forecast to emerge over the Plains to start the weekend should track eastward and ultimately lead to secondary low pressure off the Mid-Atlantic/New England coast by around late Sunday or early Monday. This system will spread a broad area of precipitation across the eastern half of the country with some wintry weather possible from the northern Plains/Midwest through the Great Lakes/Ohio Valley and Mid-Atlantic/Northeast. Snowfall totals within portions of this area may be significant depending on exact system evolution. Check the Winter Weather Outlook forecasts for a probabilistic depiction of locations expected to see the best potential for meaningful snow. Rain will prevail to the south with some locally moderate to heavy activity possible but system progression may be a limiting factor for rainfall totals. Areas near the East Coast will tend to see below normal temperatures in the late week/early weekend time frame. The upper low crossing the Northeast will bring at least one day of highs 10-20F below normal to locations near its path. As the system initially near the West Coast progresses eastward late this week into the weekend, temperatures over the Plains and then east-central U.S. will rise to above or well above normal values--especially for morning lows which will see broad coverage of 10-20F anomalies. Then closer to the East Coast clouds/precipitation will keep lows above normal but highs should be within a few degrees on either side of normal. Meanwhile some areas over the Plains may see readings 10F or more above normal into next week. The southwestern states will be moderately below normal through the period with mostly single-digit negative anomalies and perhaps a few pockets that are slightly cooler. Kong/Rausch 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, Sun-Tue, Jan 31-Feb 2. - Heavy rain across portions of California and the Pacific Northwest, Sun-Tue, Jan 31-Feb 2. - Heavy rain across portions of California and the Pacific Northwest, Sat-Mon, Jan 30-Feb 1. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Southern Plains, the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley, Fri-Sat, Jan 29-Jan 30. - Heavy rain across portions of the Mid-Atlantic, Sun-Mon, Jan 31-Feb 1. - Heavy snow across portions of California, the Pacific Northwest, and the Northern Great Basin, Sat-Mon, Jan 30-Feb 1. - Heavy snow across portions of the Central Great Basin, California, and the Southwest, Sat-Tue, Jan 30-Feb 2. - Heavy snow across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, the Northern Great Basin, and the Southwest, Fri, Jan 29. - Heavy snow across portions of the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Upper Mississippi Valley, Sat-Sun, Jan 30-Jan 31. - Heavy snow across portions of the Northeast, the Central Appalachians, the Mid-Atlantic, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Sun-Tue, Jan 31-Feb 2. - Flooding possible across portions of the Middle Mississippi Valley. - Much below normal temperatures across portions of the Mid-Atlantic, the Northeast, and the Great Lakes, Fri-Sat, Jan 29-Jan 30. 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