Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Wed Feb 16 2022 Valid 12Z Sat Feb 19 2022 - 12Z Wed Feb 23 2022 ...Overview... The medium range period will begin Saturday with generally quiet weather, besides a clipper system bringing snow to the Great Lakes region. Then as next week begins, troughing is forecast to develop in the West and slowly track eastward along with a strong frontal system. Precipitation chances should increase in the West with this pattern and spread into the central U.S. once again by next Monday through Wednesday, with the possibility of northern tier snow and southern U.S. rain. ...Guidance Evaluation/Predictability Assessment... Recent model guidance shows good agreement overall with the large scale pattern even through the middle of next week, with some typical differences in the smaller scale details. To start the period, the surface low/clipper over the Great Lakes and upper-level energy supporting it have good consensus among 12/18Z models. A less certain feature during this timeframe is a compact shortwave tracking into the West ahead of the main larger scale trough. Overall recent models have trended stronger with this initial energy, with increasing consensus for a closed low likely centered just west of California on Saturday. The GFS was the slowest model to come to this conclusion (the 12Z had its low displaced east and the 18Z run showed an open trough), but the 00Z GFS does show a closed low in line with other guidance. Though there is better agreement now, considering the small scale of the low rounding the Pacific ridge, additional shifts in the forecast are possible. Then there is good agreement for energy to spill into the West and develop troughing as next week begins, while much of the central and eastern U.S. shifts to zonal flow and then ridging. 12/18Z GFS runs remain among the strongest, specifically with closing off a low within the trough even by early Sunday sinking into the Pacific Northwest, while the 12Z CMC was slightly east with its trough axis by around Tuesday compared to consensus. The phasing differences with potential stream separation are causing minor model differences that could continue to be an issue with the evolution of the troughing. The ECMWF has been more consistent and favored among the deterministic guidance, though both the 12Z and new 00Z runs may be a bit slow with lingering energy across the West by Wednesday. Despite these model differences, the theme of troughing developing in the West for the first half of the week slowly shifting eastward as well as sending northern stream energy across the north-central U.S. by midweek is consistent. The WPC forecast utilized a multi-model deterministic blend of the 12/18Z guidance for the early part of the period, slightly favoring the ECMWF and CMC. Phased in some GEFS and ECMWF ensemble mean guidance for the latter part of the period, ending up with about half deterministic models and half means by day 7, mitigating the individual model eccentricities. The main difference from the previous WPC forecast was a continued trend northward with the axis of heaviest QPF across the Mid-South Monday-Wednesday of next week. ...Weather Highlights/Threats... Lingering snow is forecast on Saturday across the Great Lakes region with the clipper system, with generally light to perhaps locally moderate amounts. Mainly dry conditions are expected elsewhere on Saturday other than a few showers possible in Florida, except that precipitation will be increasing in the Pacific Northwest and Northern Rockies with the upper trough coming in. Coastal and valley rain and mountain snow are likely over the Pacific Northwest spreading into California, the Great Basin, and the Rockies through the early part of next week. Snow could also spread farther east into the northern High Plains Sunday and into the rest of the northern tier states as the first half of the week progresses. The confidence in the axis of heaviest snow and snowfall amounts remains somewhat low. Farther south, moist inflow is forecast to return to the south-central and southeastern U.S., increasing chances for rainfall that could become heavy over the Mid-South in particular by Monday and Tuesday. Temperatures over the weekend are expected to be above normal for parts of the West into the Plains, with the largest anomalies of highs 20+ degrees above average over South Dakota and Nebraska. Meanwhile, cooler to near average temperatures over the eastern third of the country Saturday will warm Sunday. As the pattern amplifies, the south-central U.S. to the East Coast will further warm through the first half of next week, with widespread highs 10-20F and lows 20-30F above normal. Meanwhile, a cold Arctic high is forecast to shift into the north-central U.S., leading to well below average temperatures initially across the northern High Plains and spreading southward through midweek. Temperatures in some places could be 30 or more degrees below normal, and highs in the single digits are expected for Montana and the Dakotas Monday and Tuesday. 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 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