Plain-language summary:
It is relatively mild today with snow showers throughout the region, though with steadier and heavier but still modest snow from southern Vermont to eastern Maine through tonight. Another modest snow will fall from southern Vermont to southeastern Maine Sunday night. Light snows will fall in northern areas on Monday, Wednesday, and possibly Friday, with heaviest in the Laurentians. It then turns extremely cold but likely drier for several days or more, in contrast to stormier expectations a few days ago, with moderation possible toward the end of January.
Meteorological discussion:
Snow showers and relatively mild throughout the region today, heavier and steadier from southern Vermont to eastern Maine, with another modest snow for southern Vermont to southeastern Maine Sunday into Sunday night
A broad upper-level trough is dominating eastern North America downstream of an upper-level ridge in western North America that has returned (+PNA). It briefly turned very cold after a storm that brought heavy snow to southern and eastern Ontario (much farther northwest than model projections in days prior) on Thursday, but now, several disturbances picked up relative warmth and moisture from the Great Lakes and have pulled the arctic air out of our region temporarily. One disturbance is centered on the northern shore of Lake Huron but is very broad, with snow showers extending from Minnesota to Maine, but nothing very heavy or organized. This is the disturbance that is bringing southwesterly flow that routed out the arctic air. With the low stability of the air modified by the Great Lakes, some of the snow showers will be convective and briefly heavy through tonight from Ontario to Vermont and Quebec, though total accumulations will be light. Another disturbance is just getting going to the south and will bring somewhat heavier and steadier snow to southern Vermont to eastern Maine through tonight, though few if any will get more than a few inches or 10 cm. Yet another system will round the base of the upper-level trough Sunday and try to come up the East Coast at the last second Sunday night, but the overall weather pattern is too broad with too many disturbances for the East Coast storm to really develop into a full-fledged Nor'easter, a classic scenario of recent winters. However, the storm will still clip southern Vermont to southeastern Maine with modest snow.
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| Source: TropicalTidbits |
Clippers brings light snow mostly in northern areas Monday and Wednesday, then arctic cold returns
Right after the late-forming East Coast storm, another clipper will move into western Quebec, to the northwest of our region again, on Monday, bringing southwesterly flow that is still modestly cold but not arctic cold. This will lead to light snow mostly along and northwest of the Appalachians, with the most and steadiest in the Laurentians except lake-enhanced snow off Lake Ontario streaming northeastward along the St. Lawrence Valley into southern Quebec. Arctic air will come in from the northwest behind the cold front until yet another clipper tracks into the Great Lakes on Wednesday and brings southwesterly flow with light snow mostly north of the U.S./Canada border again, though northern Maine could also experience snow. All these clippers are basically disturbances in the polar jet rotating around the polar vortex over Hudson Bay that is displaced southward by all the high-latitude blocking (-AO), and that is also allowing for the arctic air to descend into the mid-latitudes. Interestingly, the NAO is positive, which could be why systems are still moving rather quickly with a strong north-to-south temperature gradient. The really cold air will get more and more entrenched into the weather pattern with the passing of each clipper.
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| Source: TropicalTidbits |
Possibly one more clipper on Friday, then extreme cold but drier, contrary to prior expectations
Details become murky after Thursday, but there could be one more clipper on Friday before the most extremely cold arctic air that will have covered almost all of Canada descends into our region directly from the north, instead of from the west being modified by the Great Lakes. A few days ago, models showed the upper-level trough axis shifting to the Rockies with a southeast U.S. ridge developing, allowing storms to finally eject out of the Rockies and into our region, but now, most models agree on a very broad upper-level trough and arctic air mass extending from the Rockies eastward, which would suppress all of the moisture southward. It has been difficult to get a storm track from the central or southern Plains northeastward this winter and also last winter except for February. It is somewhat surprising during a La Niña winter, but it seems like there just is never a trough digging sharply into the Plains without other disturbances interfering to enable such a storm track. The NAO turning negative for a time will also help suppress storminess to the south, and barring some major shifts in the synoptic-scale weather pattern, it looks like a very dry and extremely cold several days starting next weekend into the following week for almost all of eastern North America. Some parts of our region could drop below -22F (-30C)! In fact, all of North America could be dry with almost no storminess coming in from the Pacific Ocean and a massive upper-level ridge connecting from Alaska to Greenland. It is amazing that the vast majority of the U.S., including southeastern parts of our region, will likely still have below average snowfall after all the arctic air, similar to last winter. Perhaps it is still too early to completely rule out a shift back to a more amplified upper-level trough over the Rockies that would allow a system with Gulf of Mexico moisture to push northeastward into our region, as shown by a few rogue outlier models and ensemble members.
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| Source: TropicalTidbits |
Possible moderation for end of January
There are some signs that toward the end of January, the Pacific jet will strengthen, breaking down the Alaskan upper-level ridging and allowing more Pacific air to move into North America, leading to a milder early February that could be less suppressive, but how this evolves is still quite uncertain. Though the way this winter is going, I would still bet on some amount of southwest U.S. upper-level ridging preventing the juicy southern storms to reach our region, with either cold high-pressure still dominating our region or clippers tracking to our north. It has been the warmest winter on record in the western U.S., a testament to how difficult it has been to get upper-level troughs in that region.
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| Source: TropicalTidbits |
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| Source: Climate Prediction Center |
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