Extended Forecast Discussion NWS Weather Prediction Center College Park MD 212 PM EST Fri Jan 13 2023 Valid 12Z Mon Jan 16 2023 - 12Z Fri Jan 20 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 and Guidance/Predictability Assessment... Latest guidance shows a continued progression of Pacific systems that will bring precipitation into the West and then to areas east of the Rockies as low pressure tracks northeastward from the Plains. A notable aspect of next week's evolution should be amplification of an eastern Pacific upper ridge that would focus West Coast precipitation more over the Pacific Northwest while at least central-southern California sees drier conditions. This may be the beginning of a longer term drier period over the southwestern states based on the Climate Predication Center's 8-14 day outlook. A general model blend consisting of the 00z EC/CMC/UKMET and 06z GFS were utilized through day 5. After day 5 the blend was more weighted toward the 00z EC/ECE and less so toward the rest of the deterministic guidance. By day 7 the 00 CMCE is introduced and a heavy ensemble mean blend is used. There were some discrepancies regarding the evolution of the new West Coast system beginning on day 4 with the 06 GFS/GEFS being too progressive with the upper level trough propagating through the Southwest. This GFS/GEFS continue with this faster movement of the upper trough and associated surface wave throughout its evolution over the CONUS. This morning's 13z NBM guidance has generally trended drier in the Mississippi Valley and wetter in the Southwest compared to its overnight iteration. Some of the 00z EC mean was blended with the NBM over the Pacific Northwest to enhance amounts due to the faster arrival of the day 3 Pac NW system noted in the ensemble guidance, also because precip appeared to be underdone in the NBM and deterministic guidance. ...Weather/Hazard Highlights... What should be the last in the series of significant storm systems to affect most of California will likely reach the state on Monday with additional heavy rainfall and mountain snow, with highest totals over the Sierra Nevada and to a lesser degree along favored coastal areas. Rainfall over already very over-saturated ground may continue to worsen flooding or delay improvement of ongoing issues. Expect this moisture to bring rain and higher elevation snow into the Southwest/southern Rockies early in the week as well, with highest totals over favored terrain in Arizona and southwestern Utah. The next system will focus rain and mountain snow more over the Pacific Northwest and northern California around Tuesday-Wednesday, with much lighter amounts reaching inland over the West thereafter. Central-southern California should stay fairly dry. To the east of the Rockies, a system tracking from the western Atlantic northward into the Canadian Maritimes may bring some wintry weather to northern New England early in the week. The first of two Plains-Great Lakes systems should bring moderate amounts of precipitation to the eastern half of the country early in the week, with any snow likely limited to far northern areas. The second system should bring a broader area of heavier precipitation to areas from the Plains eastward mid-late week. With typical sensitivity to exact track, best snow potential currently exists from the central High Plains through the Upper Midwest, parts of the Great Lakes, and New England. Meanwhile Gulf inflow may be sufficient to support some areas of heavy rainfall over and near portions of the Mississippi Valley and Ohio Valley. While system progression will provide some day-to-day variability to temperatures, the overall pattern should support well above normal temperatures over much of the eastern half of the country and below normal temperatures over the southern two-thirds of the West. The warmth east of the Rockies will likely erode somewhat from west to east with the passage of the cold front anchored by the mid-late week storm. Some areas may see one or more days with morning lows 20-30F above normal, and potential for warm low daily records migrating from the eastern Plains/Mississippi Valley into the East. Highs should be a little less extreme with mere pockets of plus 20-25F anomalies, while best potential for any record highs exists over/near southeastern Texas on Tuesday. The southern two-thirds or so of the West will tend to see highs 5-15F below normal. 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