Extended Forecast Discussion NWS Weather Prediction Center College Park MD 341 PM EST Thu Dec 29 2022 Valid 12Z Sun Jan 01 2023 - 12Z Thu Jan 05 2023 ...Winter storm threat for the north-central Rockies/Plains and Upper Midwest early next week as a heavy rain/severe weather threat reemerges for the mid-lower Mississippi Valley/Mid-South then Southeast midweek... ...More rounds of moderate to heavy precipitation for the West with focus across California through midweek... ...Overview... A low pressure system forecast to develop early next week over the central U.S. will likely lead to a winter weather event from the north-central Rockies through the northern Plains, while heavy rain and severe weather appear likely across the Deep South to the Southeast Monday-Wednesday ahead of a cold front. Meanwhile the West should see additional rounds of moderate to heavy precipitation next week, with highest amounts mainly across California through midweek. ...Guidance/Predictability Assessment... Model guidance continues to indicate the formation of the low pressure system over the central U.S. early next week. The ECMWF has continued to show a low track that is quite a bit farther to the south toward the Great Lakes than the rest of the guidance. By midweek, the ECMWF has been faster bringing in the next system toward California. In the meantime, the ECMWF likes to favor the development of another low tracking from the Deep South toward the northern Mid-Atlantic than the GFS and CMC. The WPC forecast keeps a middle ground solution by blending 40% of the 06Z GFS/GEFS, 40% of the 00Z ECMWF/EC mean with the rest of the contributions from the 00Z CMC/CMC mean and the 00Z UKMet, transitioning to mostly a blend of the ensemble means by Day 7. ...Weather/Hazard Highlights... The northeastern U.S. could see some mainly rain showers (with perhaps some minor snow accumulations in higher elevations) early Sunday with an exiting low pressure system. Then, as the next upper trough emerges after producing possibly heavy snow across the central Rockies, surface low pressure consolidating across the central High Plains should bring a swath of snow across the northern half of the High Plains into the upper Midwest, along with increasingly windy conditions with an icy transitional zone. Inflow east of the low and lingering cold air may also support some snow/ice downstream from the northern Great Lakes to northern New England. Meanwhile farther south, the frontal system associated with this low and favorable Gulf moisture/instability and right entrance region upper jet lift should provide a focus for another episode of widespread heavy rain, along with a threat of severe weather as per SPC, across parts of the Mississippi Valley into the Tennessee Valley and Southeast by Monday-Wednesday. Thereafter, a low pressure system could develop under the right entrance region upper jet over the Deep South and then track toward the northern Mid-Atlantic Wed-Thu, as is favored by the ECMWF. This could spread a period of moderate to heavy rain up the Mid-Atlantic states but uncertainty with this scenario is on the high side at this time. The West Coast states can expect a brief break from the heavy precipitation on Sunday as the trough axis shifts farther to the east. But additional rounds of precipitation are expected as the week progresses. There is quite a bit of uncertainty with the timing of additional heavy precipitation events at this point, but generally amounts look to trend upward by Tuesday-Thursday across California as a stronger frontal system approaches from the Pacific. Many areas are likely to be sensitive to additional rainfall by that time given the ample recent rainfall and additional rain during the short range period. Milder than average temperatures for winter will be widespread across the eastern half of the country for early next week. Lows of around 15-30F above average and highs around 10-20F above average will be common, even reaching 20-30F anomalies in the Ohio Valley/Great Lakes Tuesday and the Northeast on Wednesday. Daily records for warm lows could be widespread for parts of the central and eastern U.S., while daily record highs are possible as well especially in the Ohio Valley. Meanwhile in the West, the overall wet/snowy pattern will tend to keep daytime temperatures around 5-10F below normal. Lows are forecast to be above average for the entire country Sunday morning. But as the large-scale upper trough moves through the western U.S. into the Plains, near to below average temperatures are expected to work their way from west to east across these areas. Kong/Tate Hazards: - Heavy precipitation across portions of California, Mon-Thu, Jan 2-Jan 5. - Heavy rain across portions of California, Tue-Thu, Jan 3-Jan 5. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Tennessee Valley, the Great Lakes, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Mon-Tue, Jan 2-Jan 3. - Heavy rain across portions of the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley, Wed, Jan 4. - Heavy snow across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, the Northern Great Basin, and the Southwest, Sun, Jan 1. - Heavy snow across portions of the Central Rockies, the Central Plains, and the Northern Plains, Sun-Mon, Jan 1-Jan 2. - Heavy snow across portions of the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Mon-Tue, Jan 2-Jan 3. - Severe weather across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, the Ohio Valley, and the Tennessee Valley, Mon, Jan 2. - High winds across portions of the Southern Plains, Mon, Jan 2. 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