Extended Forecast Discussion NWS Weather Prediction Center College Park MD 317 PM EST Mon Jan 09 2023 Valid 12Z Thu Jan 12 2023 - 12Z Mon Jan 16 2023 ...Unsettled and Active Pattern Continues for Western U.S. with focus on California Atmospheric Rivers... ...Overview and Guidance/Predictability Assessment... The weather pattern over the CONUS later this week through early next week will be increasingly amplified but progressive. At the start of the period (Thursday), a strong ridge of high pressure will continue to build through the Intermountain West while downstream over the Plains, digging shortwave energy helps induce deepening surface low pressure over the Midwest. The eastern U.S. storm system will bring widespread precipitation and some weather hazards including potential for heavy rainfall and severe thunderstorms to parts of the Southeast. Back to the Western U.S., the next atmospheric river event will brush northwest California and focus more on Oregon and Washington. By this weekend into early next week, the ridge of high pressure moves east while another active and potentially strong atmospheric river aims at California, bringing another round of potentially heavy precipitation. Through this weekend, the latest model guidance showed fairly strong and high consistency and agreement with the main synoptic features. The main question marks remain on any offshore low pressure development this weekend off New England. As the main surface low lifts through the Great Lakes and occludes, models suggest potential secondary low development along the cold front across the Mid-Atlantic/Northeast before that low brushes New England. This more phased scenario could spell additional precipitation back across the Northeast and possibly winter precipitation further inland this weekend. Today's 12Z model cycle suggests a trend toward this idea. This scenario bears watching for nay possible winter impacts. Outside of this system and elsewhere across the CONUS, the relatively good agreement led to a general model blend of the latest guidance including the 00Z/06Z ECMWF/GFS/UKMET/CMC as well as inclusion of the 00Z ECENS and 06Z GEFS means especially by day 6 and day 7 given the increasing model spread. This lines up well with continuity and the latest model trends. ...Weather/Hazard Highlights... Unsettled and active weather is expected to continue across portions of the West as a series of atmospheric rivers move onshore. The highly amplified pattern mentioned above will help focus the best moisture transport and rainfall along the immediate northwest California coast Thursday into Friday, and further up the Pacific Northwest coast affecting coastal regions of Oregon and Washington State. However, by this weekend, another strong weather system approaches central California and will bring another round of widespread precipitation. This system will impact a larger area of California with even more heavy rainfall threats. Worsening flooding or delayed improvement of ongoing improvement is possible again across coastal central to southern California while the higher elevations of the Serra see heavy snowfall. As the energy moves inland on Sunday, rain and higher elevation snows are possible in the Southwest, and eventually return flow out of the Gulf of Mexico may increase precipitation chances into the Plains/lower Mississippi Valley as well. Meanwhile, back to the Midwest/East, a developing and deepening area of low pressure will sweep across the region Thursday into Friday, bringing widespread unsettled weather. A warmer air mass in place will keep the threat of heavy snow or ice fairly limited, except for a possible changeover to wintry precipitation on the northwest side of the low track across the Great Lakes region. On the warm side of the system, some locally heavy rainfall will be possible Thursday into Friday across parts of the Southeast including the Tennessee Valley and Southern Appalachians. A severe thunderstorm risk is also possible, as advertised by the Storm Prediction Center's Day 4 Severe Weather Outlook, Thursday into Thursday night across portions of Alabama and Georgia. As the storm system moves to the East Coast, a secondary area of low pressure may develop just offshore New England and bring additional precipitation threats but there's still some uncertainty in storm track and potential development there. With the more amplified and stormy pattern across the CONUS later this week and this weekend, more anomalous temperature fluctuations are expected across the central to eastern CONUS. Generally warmer than normal temperatures are expected east of the Rockies through the period, particularly by later this weekend into early next week where parts of the Plains could see high temperatures 15 to 20 degrees F above normal. Even more impressive will be the very warm nighttime lows, with readings 20 to 25 degrees F above normal from Texas through Minnesota Sunday and Monday. Santorelli/Taylor Hazards: - Heavy precipitation across portions of New England, Thu-Fri, Jan 12-Jan 13. - Heavy rain across portions of California and the Pacific Northwest, Thu-Mon, Jan 12-Jan 16. - Heavy rain across portions of the Pacific Northwest, Thu-Fri, Jan 12-Jan 13. - Heavy rain across portions of California, Sat, Jan 14. - Heavy rain across portions of the Southeast, the Southern Appalachians, the Ohio Valley, and the Tennessee Valley, Thu, Jan 12. - Heavy snow across portions of California, Sat-Mon, Jan 14-Jan 16. - Severe weather across portions of the Southeast, the Southern Appalachians, and the Tennessee Valley, Thu, Jan 12. - Flooding likely across portions of California. - High winds across portions of California and the Pacific Northwest, Thu, Jan 12. - High winds across portions of the Southern Rockies and the Southern Plains, Mon, Jan 16. 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