Extended Forecast Discussion NWS Weather Prediction Center College Park MD 254 PM EST Tue Jan 11 2022 Valid 12Z Fri Jan 14 2022 - 12Z Tue Jan 18 2022 ...Heavy snow likely across parts of the Midwest on Friday, with lingering uncertainties downstream along the East Coast this weekend... ...Overview... Mean ridging is likely over the West during the medium range period, though with the possibility of shortwaves tracking through the mean flow while southern stream troughing lingers near or offshore the California/Baja California coast. Meanwhile, one shortwave will exit the East Coast early Friday as the next one drops through the Midwest, bringing the potential for heavy snowfall to parts of the area. The shortwave should slide through the Southeast and pivot off the East coast to support another East Coast low this weekend into early next week. This could bring potentially impactful wintry weather across parts of the Mid-Atlantic and the Northeast, but confidence in the details remain very low. ...Guidance/Predictability Assessment... The latest model guidance shows fairly good agreement for the large-scale pattern, but with some lingering uncertainties in some potentially impactful details. An initial surface low off the East Coast on Friday looks to remain well offshore to limit any significant impacts to the Northeast, but may affect the Canadian Maritimes this weekend. Farther upstream, the models agree that shortwave energy will be spilling into the Midwest on Friday. Most of the 00z guidance (and incoming 12z guidance) continue to trend southward with the low and associated heavy snow axis across the Midwest on Friday. By this weekend, the shortwave should pivot across the Southeast inducing development of low pressure at the surface which eventually moves up the East Coast early next week. Compared to yesterdays 12z/18z guidance, the 00z/06z (and the new 12z) guidance shows a very notable westward shift, now bringing the low closer to or over the East Coast next Sunday-Tuesday. The 06z GFS was the farthest west with the low, while the 00z ECMWF and CMC kept it well offshore. However, the newest 12z runs have now shifted significantly westward and much closer to the GFS. There also remains considerable spread in individual ensemble members as well, although the means are faster than the deterministic runs (likely due to lower amplitude in the upper pattern). The WPC blend for today was closer to the 00z ECMWF, 00z CMC, and 00z UKMET keeping the low off the East Coast but still closer than the previous WPC forecast. Although, given the newest 12z guidance (which arrived after the forecast was issued), the WPC forecast is now east of the consensus. Needless to say, the details of any potential winter weather impacts to parts of the Mid-Atlantic the Northeast remain highly uncertain at this time as most new model runs continue to change and shift and will likely do so in the coming days. Out West, periodic and weak shortwave intrusions should briefly break up the ridge out West through the period. There's good agreement in the deterministic runs through at least the first half of the period, with less uncertain timing and detail differences arising late. One shortwave should traverse the far northern tier of the U.S., eventually moving across the Great Lakes and amplifying over the East later in the period. There remains plenty of uncertainty around how this energy interacts/combines with the shortwave moving up the East Coast in the days prior, so a trend towards the ensemble means later in the period seemed ideal at this time. ...Weather Highlights... While deepening Atlantic low pressure late this week should stay far enough offshore to keep a majority of precipitation east of New England on Friday, gusty winds may be possible due to the tight gradient between this storm and eastern Canada high pressure. The shortwave and surface low dropping southeastward from the northern tier late this week will likely bring a swath of wintry precipitation across portions of the Midwest, followed by some of this precipitation extending across the eastern U.S. this weekend. Guidance signals are improving for a band of significant snow that may cover parts of Minnesota/Wisconsin/Iowa/Illinois around Friday-Friday night, albeit with some uncertainty remaining for location and magnitude as well as exact timing. Confidence remains low for locations, coverage, and amounts of wintry precipitation farther east. Latest trends continue to suggest a farther west axis over the East which brings the heaviest precipitation along the East Coast, with potential for heavy snow farther inland. Again, this is highly uncertain and subject to change, but the potential is there. The south-central and southeastern U.S. should see mostly light to moderate rain along the southern side of the precipitation shield. An area of light snow may extend across the Upper Midwest into the Great Lakes around Sunday-Monday with the system moving into the region. The most likely forecast scenario has generally light and scattered precipitation over the West during the period. Temperature-wise, the central U.S. will see mild conditions on Friday, with lows 10-20F above average while 10-15F above normal highs are expected for the Southern Plains. Warmer than average temperatures should continue into early next week for portions of the Plains. Meanwhile, colder than average temperatures are likely for the Great Lakes to the Northeast through the weekend, with Saturday the coldest day in the Northeast with temperatures 15-25F below normal. The West should see temperatures within about 5-10 degrees of normal, with a tendency toward slightly warmer than average conditions especially for lows. Santorelli/Tate 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 snow across portions of the Northern/Central Plains, and the Upper/Middle Mississippi Valley, Fri, Jan 14. - Flooding occurring or imminent across portions of the Lower Mississippi Valley and the Pacific Northwest. - Flooding likely across portions of the Pacific Northwest. - High winds across portions of the Great Plains, Fri, Jan 14. - Much below normal temperatures across portions of the Mid-Atlantic, the Northeast, and the Great Lakes, Sat, Jan 15. - Heavy precipitation across portions of the Alaska Panhandle, Fri, Jan 14. - High winds across portions of the Alaska Panhandle, Fri, Jan 14. 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