MID-WINTER ARCTIC AIR IS LURKING AROUND THE CORNER

January is considered the heart of winter across most of the country. Average temperatures are at their coldest for most locations during this month. Average highs are generally in the 20s and 30s in the North, with some 10s close to the Canadian Border. Highs are generally in the 40s and 50s in the South, with some 60s and 70s in the Desert Southwest and Florida. However, daylight hours start to slowly increase with 9-10 hours across the north and 10-11 hours across the South.

Widespread cold impacted the Central/Eastern US during the first week of December, with the most significant cold targeting the Midwest and the Great Lakes. This cold would relent during the second week of December across the South, particularly in the Southern Plains, but the cold pattern was reinforced across the Midwest into the Northeast through mid-December. The most potent cold shot occurred between December 12-15 in the Midwest where cold anomalies as much as 20-30 degrees below normal occurred. This would briefly bring the coldest air of the season to date into the Southeast early in week three before moderating. As this occurred, above normal temperatures were prevalent across the West beginning late in week one and continued through mid-December with the warmest anomalies in the Interior West. This warmth would expand through the South Central US during the third week of December before engulfing the Southeast by week four. Temperatures reaching 15-30 degrees above normal became routine in these regions by this period and many record highs were broken. Salt Lake City broke six separate record highs this December, including four consecutive days of record highs between December 22-25. Denver also set six daily record highs in December, all between December 15-25. Some of this warmth would reach the Midwest during the fourth week of December, but a trough over eastern Canada prevented the Northeast from experiencing much of this warmup. December did end with a cold shot sweeping across the Central/Eastern US over the final 2-3 days of the month. There were significant precipitation departures in December across the South Central US through the Mid-Atlantic/Southeast, with much of the region seeing totals at least an inch below normal, if not greater. Several clipper systems that impacted the Midwest through the Northeast, but with one exception early in the month and one exception late in the month, the pattern was not supportive of large impactful systems. The most active part of the country throughout December was the Pacific Northwest, which saw well above normal precipitation. After a dry start to December, this wet pattern expanded through the Southwest by the final 7-10 days of the month.

January should begin with a ridge building across the Central US during the first week of the month, providing above to well above normal temperatures to the Interior West and the Plains with more modest warm anomalies in the Midwest and Southeast. However, a -NAO ridge near Greenland will keep a trough stationed near eastern Canada, keeping a colder overall pattern in place the first week of January. An uptick in tropical forcing across the Maritime Continent should briefly amplify ridging over the Southeast, creating some warmer temperatures across the region that should also allow for the cold in the Northeast to moderate. By the end of week two, however, a -EPO ridge is likely to form near Alaska. This will shut off the flow of milder Pacific-based air into the US and create a gateway for Arctic air to gather across western Canada and eventually spill into the US. The brunt of any cold surge should focus across the Midwest into the East, likely during the third week of January and potentially lingering into the fourth week of the month. This period between January 15-25 may very well end up being the coldest stretch this winter, particularly across the Midwest where the most anomalous cold is most favorable to occur. For this cold shot to reach its full potential, it will be necessary to build up more snowpack than is currently in place across much of the Midwest. The limited snowpack in the Midwest would allow for the airmass to moderate more quickly as it extends southward. There will also be remnants of the Southeast ridge attempting to hold on early in week three. Due to these factors, the better opportunity for cold to impact the South should hold off until late in week three and into week four. The West should avoid the bulk of the more organized cold during this period. The Alaska ridge should diminish over the final few days of January. This should allow for temperatures to warm across the South late in the month. A reduction in cold should also occur across the Midwest and the Northeast, but with the lingering presence of a ridge near Greenland, it will be difficult for sustained warm anomalies to become established across the Northeast and through the Upper Mississippi Valley through the end of the month.

There will be a continuation of the wet end to December across the West moving into the first ten days of January. Multiple systems are likely to crash into the Pacific Coast, spreading rain and mountain snow through the region. This will include multiple rainfall events across Southern California. This should transition to a drier overall pattern by mid-January that should linger through much of the month. It will be a quieter start to January or most across the Central/Eastern US aside from occasional clipper systems producing light snow from the Upper Midwest towards the Northeast, as well as lake-effect snow off the Great Lakes. The storm track may turn more active during week two and the initial stages of week three across the Midwest through the Northeast. This will be the best opportunity to increase snowpack across the Midwest in advance of the expected cold surge. The best chance for a more impactful storm should be later in the period, especially for the Northeast. In the warm sector, this could bring increased chances for thunderstorms ahead of any systems across the Southeast/Gulf Coast. The storm track should shift southward later in week three and into the fourth week of January. This window will carry the highest risks for potential snow/ice impacts from Texas through the Southeast. A very dry airmass should settle in with the cold across the Midwest into the Northeast for most areas, but the influx of cold could lead to the potential of significant lake-effect snows off the Great Lakes. The winter threats should begin to fade across the South late in the month as the storm track slides northward, most likely from the Central Plains towards the Ohio Valley and the Mid-Atlantic.