Plain-language summary:
It will be extremely cold and sunny through Monday before moderating for the rest of the upcoming week. A burst of snow Tuesday afternoon and evening is likely, with lingering snow showers occur on Wednesday before likely drying out for the rest of the week with typical February cold. There is a slight chance for a snowstorm for following Monday, but it is more likely to be dry with a warming trend, with a thaw and modest rain likely for the middle of the following week especially in southern areas. It will likely turn colder again afterward, perhaps accompanied by more storminess.
Meteorological discussion:
Extremely cold and sunny through Monday
A very cold arctic air mass is in place now, with the air coming straight from the north-northwest with minimal modification over cold snow-covered ground, with even highs struggling to get above 5F (-15C) along and northwest of the Appalachians. This is despite almost full sunshine, as clouds from yesterday's clipper have cleared for most. These sunny days typically become more common in February as the arctic air masses become really dry with all the lakes and rivers frozen and not able to add moisture into the air to form clouds. Despite the cold air mass, the wind caused by the pressure gradient between the surface high-pressure to the west and the broad low-pressure over Atlantic Canada that is very slow to move away due to the high-latitude blocking (-NAO) will prevent ideal radiational cooling and temperatures from dropping very quickly at night, perhaps except for eastern Ontario and northwestern New York, which will be closer to the surface high-pressure center and therefore experience lighter winds.
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| Source: TropicalTidbits and HYSPLIT |
Gradually turning milder later in week with burst of snow Tuesday afternoon and evening and snow showers Wednesday
This will be the last very cold arctic air mass for at least a couple of weeks, or perhaps even until next winter. For the first time in weeks or perhaps this whole winter, the upper-level ridge in western North America will break down for a prolonged period, possibly more than a week, as the Pacific jet becomes stronger and pushes storms into the western U.S. This will relieve at least slightly the incredible snow drought in the warm and dry winter they have had so far. The more active Pacific jet will also cut off access to the arctic air for a while, with the AO turning neutral for a while after being strongly negative for almost a month. The upper-level troughing in western North America will promote upper-level ridging farther east across the central and southern U.S., but high-latitude blocking, especially over Greenland (-NAO), will trap a broad upper-level low or trough across Atlantic Canada which will stop any push of truly mild air from the southwest into our region for the upcoming week. Instead, the arctic air will just grow stale, and a low-pressure system in northern Ontario and the northern Great Lakes will push into our region, with its push of milder air into the low-level cold air in our region leading to a burst of at times moderate to heavy snow Tuesday afternoon and evening. The low-pressure system will then slide east-southeastward into Atlantic Canada Wednesday into Thursday, reinforcing the broad upper-level low there, with lingering snow showers and near average temperatures in our region. A widespread 2-5" (5-12 cm) is likely for most of the region, perhaps up to 6" (15 cm) in eastern Ontario where the dynamic forcing looks a little stronger.
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| Source: TropicalTidbits |
Likely dry with typical February cold Friday into next weekend, with slight chance of a snowstorm more likely for southern areas for following Monday
Multiple disturbances in the southern jet will travel west to east from the West Coast to the East Coast later in the week, being largely separate from the polar jet that will have retreated way to the north and weakened as the arctic air gets scoured out. The more active southern jet, which we have not seen much of this winter so far, could be a symptom of the La Niña weakening. Fittingly however, the blocking pattern and associated suppressive west-northwesterly flow will likely just squeeze the disturbances in a way that prevents them from strengthening and also shunts them out to sea well to the south of our region, leaving our region to gradually dry and clear out as surface high-pressure approaches, though there is a chance of a weak northern branch disturbance bringing a bit of snow some time over the weekend. The surface high-pressure will only be modestly cold, with the arctic air being locked to the north. Some model guidance is showing one of the southern jet disturbances ejecting out of the Rockies next weekend just as the Atlantic Canada upper-level trough pulls away to the northeast as the high-latitude blocking weakens for a while. If this scenario is correct, the disturbance could gather moisture from the Gulf of Mexico, causing latent heating and strengthening the storm as it heads northeastward, leading to a snowstorm across at least southern parts of our region for the following Monday as the air is still likely cold enough for snow at this point. This would have little or no boost from interaction with the polar jet given the polar jet's retreat, and would also require the disturbance to almost cut-off in the southwest U.S. and then move slowly enough to wait for the Atlantic Canada trough to pull away but yet remain strong and consolidated enough and just far enough north to feel a bit of the northern jet. Most models are currently showing the disturbance being too weak or far south to feel any connection with the northern jet and just gets shunted underneath the Atlantic Canada trough. However, models are notoriously poor at resolving the timing and intensity of these kind of slow-moving systems in a split flow, and have been varying wildly run-to-run, so it is too early to rule out any scenario.
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| Source: TropicalTidbits |
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| Source: TropicalTidbits |
At least brief thaw likely later in following week, especially in southern areas, with modest rain
For the following week, there is increasing multi-model ensemble agreement on at least a brief thaw occurring, especially in southern areas, even if is still too early to guarantee this scenario. The frozen Great Lakes, cold ground, and extensive snow cover do not appear sufficient to fight an overwhelmingly amplified western U.S. upper-level trough that will promote a strong eastern U.S. upper-level ridge and promote a storm track cutting into the Great Lakes and then into Quebec for at least one storm. The high-latitude blocking weakening (AO turning positive) and lack of arctic air preceding this storm also favors this type of storm track and a thaw with the first rain in several weeks. There are not indications of a particularly heavy rain for now given the broadness of the low-pressure system and lack of concentrated areas of forcing for ascent. It is worth noting though that this scenario is not guaranteed yet, and there are still some ensemble members with a less amplified scenario and/or an antecedent cold shot timed just right to avoid a thaw and lead to the storm producing at least some snow and/or ice for our region.
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| Source: TropicalTidbits |
Likely turning colder afterward with possible storminess
Beyond the thaw, colder air appears likely to return for late February as the weather pattern de-amplifies slightly. The continued -PNA will likely promote more upper-level troughiness and storminess in western North America, which would still favor some upper-level ridging in eastern North America, but it looks weaker, allowing some cold shots to come in especially for our region on northward, even though the core of the cold air looks to set up in western Canada instead. If it sets up right, there could be an active storm track from the Rockies into the Great Lakes or New England, a favorable track for storminess and snowiness for our region, with the storms able to pick up Gulf of Mexico and western Atlantic moisture, unlike the clippers that have been more dominant this winter so far. This might be more likely given that we will mostly lose the -NAO that has tended to suppress these storms (though there have not been many to begin with given the +PNA and western North American upper-level ridging and dryness that has dominated this winter). There also appears to be just enough high-latitude blocking and cold feedbacks (frozen Great Lakes, widespread deep snow cover, and cold ground) to prevent most of the storms from tracking too far north and bringing thaws with mild rain. However, we might be sort of "playing with fire" in this scenario, with not a big separation between a big snowstorm vs a messy wintry mix vs mostly rain given the strong temperature gradient.
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| Source: TropicalTidbits |
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| Source: Climate Prediction Center |
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