Extended Forecast Discussion NWS Weather Prediction Center College Park MD 111 PM EST Sat Jan 15 2022 Valid 12Z Tue Jan 18 2022 - 12Z Sat Jan 22 2022 ...Pattern Overview... A winter storm will be exiting the Northeast as the period begins while a mean upper ridge works to amplify along/off the West Coast by mid to later next week. This should force an increasingly dominant series of northern stream impulses into the north-central U.S. through the period. The first of which should slide over the Great Lakes into the Northeast Wednesday and Thursday, with the next quickly on its heels digging farther into the mid-South on Friday and off the Mid-Atlantic coast on Saturday. These systems will help carve out and reinforce large mean troughing which should maintain over the Midwest and East late next week and into the weekend. ...Guidance/Predictability Assessment... The latest 00z/06z guidance for today continues to show good agreement on the overall synoptic set-up through much of the extended range. There remains some smaller scale detail uncertainties needing resolving, including timing and amplitude of the couple of shortwaves reinforcing mean troughing centered across the Midwest. The late period shortwave into the mid-South and off the East coast continues to show variability in the models and has potential for a surface low moving through the Southeast and off the East Coast. Most of the guidance right now shows a fairly weak/progressive surface low which should quickly shift well off into the Atlantic. This system is worth monitoring though as we get closer in time because it could have wintry weather impacts for parts of the East Coast, depending on the exact track and overall strength. Out West, models agree that upper ridging should amplify through the period. The GFS has been fairly consistent showing a closed low developing off the southern California coast around Thursday-Friday next week, but it doesn't have much support from other pieces of guidance, most of which are much more progressive with the shortwave into the southern Plains. The ECMWF also shows a compact upper low breaking off troughing across the northeast Pacific which may try to weaken the ridge a bit. Given these small scale details, which don't have a whole lot of run to run continuity, it seems prudent to lean more on the ensemble means later in the period. The WPC forecast for today used a blend of majority deterministic solutions days 3-5. After that, eliminated the GFS due to its outlying southern California low, and replaced it with increasing parts of the ensemble means. This approach afforded a forecast very close to previous WPC continuity as well. ...Weather Highlights/Hazards... A significant winter storm is slated to exit New England into to the Canadian Maritimes by Tuesday, although gusty winds may continue through the day. Another organized low pressure system digs into the north-central U.S. behind this with low development and subsequent track moving eastward along the U.S./Canadian border into Wed/Thu. This should bring some snow to the Upper Midwest, Great Lakes then northern New England, with locally higher totals expected near typical lake enhancement areas as cold high pressure sweeps down across the central and eastern U.S. in the wake of the low. Guidance varies with potential focus, but suspect the wavy trailing cold front on the leading edge of this Arctic blast will gain at least modest moisture from the Gulf of Mexico to fuel an emerging area of precipitation over the Southeast that offers some later next week potential for overrunning snow/ice on the northern periphery of activity. There are some ensemble members which are more robust with frontal/coastal wave amplitude and precipitation extent across the region and over the East Coast at these longer time periods. The main upper trough position is far enough West to not discount this possibility. Meanwhile, The West could see some light precipitation through the period, particularly over the Pacific Northwest and into the Northern Rockies as weakening systems cross the region, with mainly dry conditions elsewhere. A warm day on Tuesday across the central part of the nation will quickly change as a very cold Canadian high pressure digs southward into the region and eventually the East. Much below normal temperatures (-15 to -20F) will slide east from the northern Plains/upper Midwest on Wednesday-Thursday reach the South and East by next Friday. West of the Rockies should generally stay near or slightly above normal throughout the week as upper level ridging becomes anchored over the region. 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 WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml