Extended Forecast Discussion NWS Weather Prediction Center College Park MD 110 PM EST Sat Jan 14 2023 Valid 12Z Tue Jan 17 2023 - 12Z Sat Jan 21 2023 ...Active pattern continues for the West and other parts of the lower 48 but with central/southern California trending drier mid-late week... ...Overview... The models and ensembles continue to show an initial pattern featuring a sequence of Pacific systems tracking into the West and then northeastward beyond the Rockies followed by a transition toward a building eastern Pacific upper ridge that would lead to mean upper troughing over the interior lower 48, albeit with some uncertainty over the character of the trough. This evolution will likely begin a period of drier weather to central-southern California after Monday and then the rest of the state after another system brings some rain/mountain snow to the Pacific Northwest/northern California around midweek. The Climate Prediction Center's 8-14 day outlook continues to suggest that the drier pattern for California will extend beyond the medium range period. The dominant system of interest next week will cross the West with rain and mountain snow during the first half of next week and should spread a broad area of significant weather across portions of the central-eastern U.S. Wednesday-Friday. ...Guidance/Predictability Assessment... The suite of 00z and 06z guidance appear to capture the overall synoptic pattern over the lower 48 reasonably well during the medium range period. Some finer details still need to be resolved with respect to the evolution of the second upper trough. A general model blend consisting of the 00z EC/CMC/UKMET and 06z GFS were used through day 5. The 00z UK was an outlier in its handling of the first Western trough axis so it carried less weight in the blend through day 5. Ensembles, with weighting toward the 00z ECE, were introduced on day 5 and increased in prominence through day 7. The 06z GFS appears to strengthen, compared to the past several runs, the upper trough emerging from the West on day 4 while the 00z EC appears to weaken it. The 00z GFS was included on day 4 due to its agreement with this trough feature with the rest of the deterministic guidance. There's reasonable model agreement with the trough orientation of next week's day 6 dynamic storm with trends shifting toward a deeper/more potent upper trough solution than what was previously forecast. The 06z GEFS and 00z ECE means were in reasonable agreement regarding this system which is why they carried more weight in our blend. ...Weather/Hazard Highlights... The system moving through the West on Tuesday should bring rain and higher elevation snow across the Four Corners states. Then expect this system to bring a variety of weather to the central and eastern U.S. mid-late week. This includes the potential for heavy rainfall over and near the lower half of the Mississippi Valley, Tennessee Valley, and lower Ohio Valley. The upper dynamics/low level Gulf inflow and guidance signals appear sufficiently favorable to depict a Slight Risk area on the Day 5 experimental Excessive Rainfall Outlook valid 12Z Wednesday-12Z Thursday. Some locally moderate to heavy rainfall may extend farther through the East thereafter but with lower confidence in details. Meaningful wintry weather will be possible in the cold sector, currently most likely along an axis from the central Plains through the Great Lakes and Northeast. Details will depend on the storm's exact track and strength which are yet to be resolved, so some adjustments to the forecast will be possible. With the evolving pattern change later in the period, the next system to reach the West Coast will bring its brief period of locally moderate to heavy rainfall/mountain snow to the Pacific Northwest and northern California around midweek with lighter totals then extending into the Rockies. The South may see a rebound in rainfall by next Saturday as a front lingering over the Gulf lifts back northward ahead of an approaching cold front. The forecast pattern should maintain highs 5-15F below normal over the southern two-thirds or so of the West through the period, with readings close to or slightly above normal over the far north. Very warm temperatures over the eastern half of the country should erode from west to east mid-late week with system/frontal passage. Ahead of this system, expect a broad area of lows 15-25F above normal and highs 10-20F above normal. Most daily records should be for warm lows, while the best chance for record highs still appears to be over southeastern Texas and lower Mississippi Valley on Tuesday. Kebede/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 WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml