Extended Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EST Thu Jan 12 2023 Valid 12Z Sun Jan 15 2023 - 12Z Thu Jan 19 2023 ...Unsettled and Active Pattern Continues for Western U.S. with focus on California Atmospheric Rivers... ...Overview and Guidance/Predictability Assessment... A series of shortwaves will split from their parent along the West Coast and swing across the midsection of the CONUS through next week. A general model blend consisting of the 00z EC/CMC/UKMET and 06 GFS captured the early stages of the synoptic pattern reasonably well. Some more notable differences arise by day 5, namely the 06 GFS 500 heights become displaced from the 00z EC/CMC/UK suite by amplifying and slowing over the southern California coast. This leads to timing differences in QPF downstream in the Southwest, Great Plains and Mississippi Valley through the end of the period. Therefore, less GFS was used beyond day 4. We leaned more toward the 00z EC/ECE through day 7. There's uncertainty with respect to the synoptic progression and QPF of a midweek storm over the Great Plains and Mississippi Valley next week, but there's signal for heavy precip to develop somewhere in that region on days 6 and 7. ...Weather/Hazard Highlights... The West will remain active as a series of shortwaves continues to direct unneeded additional heavy rainfall and mountain snows towards particularly California, but also the Pacific Northwest. The first in this series of extended range storms will arrive on Saturday just before the start of this forecast period, and the heaviest of the precipitation should be over by Sunday as the overall upper system moves inland. Still, any lingering rainfall over an already very over-saturated California may continue to worsen flooding or delay improvement of ongoing issues. Rain and higher elevation snows are possible in the Southwest on Sunday, and eventually return flow out of the Gulf of Mexico may increase precipitation chances into the Plains/Midwest as well early next week. The next in the series should arrive early next week again possibly exacerbating problems across California as it delivers more moisture into the region. Heavy rainfall could develop out into the Plains-Mississippi Valley-Midwest again along the attendant cold front next Wednesday, possibly heavy if a stronger storm manifests. There could be a chance for some snow/ice too in the northern periphery of the storm, amounts again highly dependent on storm strength. Above normal temperatures will move east with time from the Central U.S. this weekend into the Midwest and eventually the East early next week. The greatest anomalies should focus across the Deep South into the Midwest with daytime highs 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 generally across the same region from Sunday onward. Daytime highs across the West and Southwest should be near or below normal amidst plenty of clouds and rainy conditions. Kebede/Santorelli 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 rain across portions of the Pacific Northwest, Tue, Jan 17. - Heavy rain across portions of California, Sun-Mon, Jan 15-Jan 16. - Heavy rain across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Ohio Valley, and the Tennessee Valley, Wed, Jan 18. - Heavy snow across portions of California, the Pacific Northwest, and the Northern Great Basin, Tue-Wed, Jan 17-Jan 18. - Heavy snow across portions of the Central/Southern Rockies, the Central Great Basin, the Southwest, and California, Sun-Wed, Jan 15-Jan 18. - Heavy snow across portions of the Northern/Central Rockies, the Great Basin, and the Southwest, Sun-Tue, Jan 15-Jan 17. - Heavy snow across portions of the Northern Intermountain Region, Thu, Jan 19. - High winds across portions of the Southern Rockies, the Southern Plains, and the Southwest, Sun-Mon, Jan 15-Jan 16. 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