Plain-language summary:
It will be very mild through Tuesday, marking the first true taste of spring for our region. Then, it will turn colder in northern areas as a major storm bring ice pellets and freezing rain to northern areas Wednesday into early Thursday, while southern areas stay very warm with some rain. A brief period of heavy showers or even a thunderstorm is possible early Thursday before turning much colder, possibly accompanied by a little snow. Winter weather will likely then dominate for at least a week, albeit the March sun angle will make the cold less intense but could also make any storms stronger with stronger dynamics and more moisture. Snow is likely, especially in northern areas, late Friday into Friday night, with a bigger storm possible the following Monday. It remains very cold for March afterward but perhaps drier before possibly turning milder later the following week.
Meteorological discussion:
Very mild and mostly dry through Tuesday
Right after the calendar flipped to March, the weather pattern has flipped completely from the cold, suppressive wintertime weather pattern, sort of like last year. A +EPO, +NAO, and +AO has scoured the arctic air out of the contiguous U.S. and southern Canada with an active storm track to the north leading to persistent mild westerly to southwesterly flow of Pacific or even Gulf of Mexico air. The upper-level trough in western North America (-PNA, rare this winter even if relatively modest) has also boosted the eastern North American upper-level ridge, with rain falling deep into Quebec yesterday with a storm tracking way to the north. Even the cold front behind it will only briefly turn the winds to northerly, and the air mass will still be warmer than average for this time of year. Southeast of the Appalachians, sunshine and downsloping westerly winds will actually make it warmer than yesterday, when that area was stuck in low-level cold air damming. Another clipper tracking well to the north on Monday will back the flow to southwesterly again, leading to Monday being even warmer with many lower elevation locations, especially in southern areas, reaching 60F (16C) or higher in lower elevations given the higher March sun angle, melting and degrading snow cover, and unseasonably warm air mass and upper-level ridging, and it will be dry as well.
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| Source: TropicalTidbits |
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| Source: Climate Prediction Center |
Low-level arctic air bleeds into northern areas with major storm Wednesday and early Thursday leading to ice pellets and freezing rain in northern areas, continued warmth and some rain in southern areas, possibly ending as a little snow everywhere
At the same time, a very cold arctic air mass will be pushing across central and eastern Canada on Tuesday and Wednesday behind the clipper's cold front, but like last week's arctic air mass, it will not be able to push south much due to resistance from the strong upper-level ridge. The front will be almost stationary as another elongated disturbance entering the northwestern U.S. will ride along the front. After a mild Tuesday, the front will slowly push through Northern Maine and areas north of the U.S./Canada border, allowing the low-level cold air to bleed in starting later Tuesday with northerly to northeasterly flow. The low-level cold air will be enhanced by terrain-induced channeling along the St. Lawrence Valley and even the Champlain Valley initially. However, areas to the south will get even warmer, possibly even breaking some daily records, and it will remain warm aloft everywhere due to the upper-level ridge.
The disturbance from the west will strengthen into a formidable storm in the Great Lakes on Wednesday, especially as it at least partially phases with and picks up a cut-off upper-level low in the southwestern U.S. This interaction has been a difficulty for models to predict, with models initially showing this phase creating a very strong storm cutting northwest of our region, then a couple of days ago showing a much flatter northwestern U.S. disturbance that does not phase with the cut-off low, leading to a weaker, farther south, and colder storm, and now the models have reverted back to at least a partial phase. Given the low-level cold air in northern areas, precipitation will likely at least start as ice pellets and/or freezing rain, possibly heavy at times, while southern areas will stay just rain, possibly south of the main precipitation shield. Some areas could see a real ice storm, most likely in eastern Ontario and southern Quebec and possibly parts of Maine, if the storm is more elongated, which would allow for the heavy precipitation and precipitation types to train over the same area as opposed to a stronger storm that would push everything north with time with stronger warm advection. If the storm is farther north and stronger, the unseasonable warmth will push into all of our region at least briefly, possibly with a dry slot, followed by a sharp cold front with a brief period of heavy showers or even a thunderstorm early on Thursday before turning much colder, perhaps with a brief period of light snow depending on how much energy is left dangling to the southwest of the main storm. Usually, such scenarios with a strong storm tracking to the north do not favor backside snow, especially in recent years. If the storm is farther south and weaker, wintry precipitation will continue for a full day in northern areas with a constant supply of low-level cold air from the northeast until the storm exits on Thursday. As I wrote in my blog post a week ago, it is ironic that the region was struggling to get good moisture with all the suppression, but now the suppression suddenly breaks and now the upper-level ridge is too strong for snow in most or all of our region.
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| Source: TropicalTidbits |
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| Old model runs showing alternative scenarios. Source: TropicalTidbits |
Winter returns late Thursday, snow likely Friday into Friday night especially in northern areas and major storm possible Monday
The flip back to winter weather is powered by the return of the western North American ridge (+PNA) and a weakening of the Pacific jet, though interestingly, the AO and NAO are expected to remain positive, so there will not be any appreciable blocking or push of arctic air deep into the southern U.S. This will maintain a stronger than the already typically strong temperature gradient at this time of year, acting as fuel for storms especially with the lower springtime stability. As such, the active weather pattern will continue afterward, with another clipper already approaching our region from the west-northwest on Friday. This clipper appears stronger than most from mid-winter, perhaps powered by the March sun angle making the air masses less stable and strengthening the warm air masses to the south clashing with the arctic air to the north. Given the cold air, albeit modified by the March sun angle, precipitation will fall as snow throughout the region at least initially later Friday, possibly mixing with and changing to scattered showers south of the storm track Friday night as warm advection occurs again. Given the dynamics, the favored locations north of the storm track could get rather heavy snow for several hours. The trajectory and strength are still in question this far out, but right now, it appears that the heaviest snow will likely target northern areas.
Another
arctic air mass follows behind it before another disturbance riding
along the temperature gradient has the potential to become a big storm,
colder than this upcoming week's storm, depending on how amplified the
weather pattern is. The position of the broad upper-level trough axis to
our west puts our region in a favorable spot for cyclogenesis and
moisture transport from the south straight into the arctic air,
something not seen often this winter. It has the potential to finally be
a widespread big snowstorm, especially given the strengthening warm and
humid air masses in March pushing into the storm, but it could very
well be too weak and suppressed like most of this winter, or even too
amplified and going too far north, leading to a change to rain.
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| Source: TropicalTidbits |
Staying unseasonably cold for March through most of following week, possibly drier mid-late week and then milder
After that, the upper-level ridge/trough pattern appears to shift east, with the upper-level trough axis pushing east of our region later the following week, likely leading to drier weather but perhaps still unseasonably cold for March. Throughout much of this period, highs could be at or below freezing on most days, with the occasional night at or below 5F (-15C), more typical of January or February. However, the lack of -AO or -NAO high-latitude blocking suggests we could see a warmup as well with dry west-southwesterly flow from the Rockies, which will likely be unseasonably warm by then, but it remains to be seen how much resistance the arctic air will provide in our region, especially given the abundant arctic air projected to remain across Canada.
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| Source: TropicalTidbits |
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