Extended Forecast Discussion NWS Weather Prediction Center College Park MD 410 PM EST Mon Jan 10 2022 Valid 12Z Thu Jan 13 2022 - 12Z Mon Jan 17 2022 ...Overview... Guidance has similar ideas for the large scale pattern, consisting of general mean ridging over parts of the eastern Pacific/western U.S. and a mean trough over the East. However the models and ensembles have been showing considerable difficulty in resolving details of how Pacific shortwave energy may split as it heads into/around the mean ridge. As a result, over the last several days there has been a lot of spread and variability for details of one or more shortwaves or upper lows that could become embedded within or linger underneath the mean ridge. At the same time these issues have been affecting specifics of shortwaves dropping into the mean trough over the East. The combined uncertainties keep confidence low for how potential surface low pressure development may affect the East by the weekend, though there is a decent signal for an axis of meaningful snow over parts of the Midwest on Friday before solutions diverge. ...Guidance/Predictability Assessment... Review of the 00Z/06Z models and ensembles led to favoring a blend of the 00Z-06Z GFS/00Z ECMWF and small input of the 06Z GEFS/00Z ECMWF means early, transitioning toward a more even weight of models and means late with some 00Z CMC mean included as well. This provided the most coherent overall evolution with the understanding that significant further changes may occur. The most notable adjustments from continuity include reflecting improved consensus for an axis of focused snowfall over the Midwest as a wave drops southeast from the northern tier and a farther south trend for low pressure evolving over the eastern U.S. and western Atlantic. Latest GFS/ECMWF runs and their means (plus the CMC mean) have actually come into better agreement than they have shown in many days, as the GFS in particular gravitated to the ensemble means that have been depicting the energy reaching the West Coast by early day 3 Thursday as an open wave. Multiple days of GFS runs had been closing off a low over the eastern Pacific. Confidence is still not great in spite of this better agreement as even in the new 12Z cycle the UKMET/CMC continue to show different ideas for this shortwave energy. The details of the initial West Coast energy affect low pressure that should track southeastward from the northern tier into the eastern U.S. and then continue over the western Atlantic. Latest CMC runs have been most different from consensus with both aspects of the forecast. General trends over the past 12-24 hours have been for the eastern U.S. surface pattern to become more suppressed in response to more amplified digging of shortwave energy as it reaches the axis of the mean trough. The 06Z GFS/GEFS were on the weak side with Atlantic development by Sunday, favoring some 00Z GFS and 00Z CMCens input. Ahead of this evolution, guidance is steadily consolidating for deep western Atlantic development expected to reach near the Canadian Maritimes by Saturday. Over the past day GFS runs have trended east with their heaviest precipitation while guidance agrees on the potential for windy conditions between this storm and strong eastern Canada high pressure. By Sunday-Monday there is decent clustering in the guidance for a southern Canada/Great Lakes system with associated fronts, as another shortwave originating from the Pacific drops into the east-central U.S. This shortwave should remain more consolidated as it rounds the Pacific ridge, which hopefully will provide better predictability (at least for the front if not low pressure) than has been the case for the initial shortwave near the West Coast. ...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, strong winds will 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 fairly low for coverage and amounts of any wintry precipitation farther east. Latest trends suggest a farther south axis over the East with lower probabilities over the Northeast. 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. There is a lower probability of more organized activity over a larger area if upper flow details end up gravitating to the less likely side of the guidance spread. Temperature-wise, the central U.S. will see very mild conditions on Thursday and into Friday, with widespread plus 10-25F anomalies for highs. Lows will be 15-25F above normal in the Northern Plains. Temperatures should moderate somewhat over the Plains by the weekend but may still stay somewhat above normal. Colder than average temperatures will prevail over the Northeast on Friday into the weekend. Expect Saturday to be the coldest day with highs 10-20F below normal. Rausch/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 Upper/Middle Mississippi Valley, and the Great Lakes, Fri, Jan 14. - Flooding occurring or imminent across portions of the Lower Mississippi Valley and the Pacific Northwest. - High winds across portions of the Plains, the Northeast, the Central Appalachians, the Mid-Atlantic, the Great Lakes, and the Ohio Valley, Fri, Jan 14. - Much below normal temperatures across portions of the Mid-Atlantic, the Northeast, and the Great Lakes, Sat, Jan 15. 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