It's now the final month of meteorological winter. The days are getting longer and average high temperatures are now beginning to climb. Average highs across New England are about 5-7 degrees warmer by the end of the month than the beginning.
Summary: February will likely feature highly variable temperatures with multiple up and down swings as air masses to the north and south battle. Generally colder air may slip into New England more frequently heading into the second half of the month, depending on how a large trough to our west pans out. This month is looking to be on the active side storm-wise, especially here at the start of the month. Read below for the in-depth discussion.
TEMPERATURES
The end of January featured changeable temperatures for New England, and this will generally continue into the first week of February. February will be starting with a mostly zonal flow across the United States. This will allow troughs and ridges to trade places frequently over New England. This supports both changeable temperatures as the different weather systems (both low and high pressure) as well as active weather.
These changeable temperatures are also supported by battling air masses over the eastern United States. Continued strong and resilient ridging over Alaska is indicative of a negative Eastern Pacific Oscillation pattern. When this pattern is negative, a large ridge builds near Alaska, which typically opens the door for Arctic air to plunge southward farther east in North America.
While this continues through the week, a ridge will likely set up across the southeast United States. This southern ridge will attempt to advect warmer and moist air up the coast into the northeast. Without a highly amplified flow (large troughs and ridges in the jet stream) across the United States, neither the cold pushing south nor the warmth pushing north will dominate for an extended period of time. This sets up a baroclinic zone across the east, which is where a temperature gradient exists on a constant pressure surface.
Heading toward the second week of the month, the zonal flow across the United States may begin to break down and begin to show signs of amplification. A deeper trough looks to dig into the western United States and progress eastward. This will likely bring below average temperatures to the northwest, which could spread eastward as the trough shifts east.
Below: 500mb average height anomaly from February 10-17, showing a trough digging into the west. Depending on how this evolves, New England could see a colder start to week 2 with a milder finish. This will depend on the timing of the western trough and potential ridging in the east:
With continued ridging over Alaska, the door will remain open for cold air intrusions, so the entire northern tier will have a shot at colder air during this time. Chances are higher to the west as the trough will be centered there at the start of the week. How it evolves as it slides eastward is a higher uncertainty. Ridging will also likely continue over the southeast, which will continue to battle with the colder air mass, so the chances for below average temperatures in week 2 are lower for the east then they are for the west, as seen below.
Heading toward the second half of the month, the pattern could become more favorable for more frequent cold air intrusions into the northeast. La Nina has developed and the pattern is beginning to show its influence. That is to say, cold intrusions are likely across the northwest and north-central part of the country.
The big question will be how far east do the cold air intrusions push? There are mixed signals on just how cold (or not so cold) the second half of February will be. Arctic Oscillation will likely trend toward a negative phase, which would support colder air for the second half of the month. With the PNA Index expected to remain positive, this could send more frequent colder shots of air into New England in the second half of the month.
Overall, February is certainly a tougher call than January, but we're predicting it will end up slightly below average when looking at the month as a whole. Temperatures will likely be highly variable with above and below average days, but we're thinking the above average days won't be as high as the below average days are low. We're also thinking it will be colder in the second half of the month as opposed to the first half.
PRECIPITATION
The start of February will be active. A fast, zonal flow will support systems moving through the region every couple days here at the start. In the temperature section, we brought up the baroclinic zone, where a temperature gradient exists on a constant pressure surface. This zone will be set up across the eastern United States. Shifts to the north or south with this zone will play a large role in precipitation types during storms.
Currently, storms are favored to move through this Tuesday, Wednesday night to Thursday and Saturday night to Sunday. Overall, an active pattern is favored for much of February, though that doesn't mean the pace of storms will be every 2-3 days the whole month, of course. La Nina events often lead to a wetter northwest, Great Lakes and Ohio Valley with more average precipitation for New England. With La Nina's influence getting stronger, this is currently a favored scenario, as seen on the Climate Prediction Center's monthly outlook below.
With an active start to the month, and the potential for a more favorable storm track to develop in the second half of the month amid amplification, we're predicting an above average month for precipitation in New England. Whether that falls as rain or snow (or something in between) will be determined by smaller-scale factors that can't be predicted weeks in advance. We will say that the potential for more wintry storms may be there in the second half of the month, but a definitive certainly can't be given.
With the potential for an active month, drought conditions that developed in the fall will likely improve. Drought status across northern New England is expected to be removed this month. Southern New England's deeper drought is expected to remain in place, though this will hinge on how much precipitation can be mustered.
LOOKING BACK
January played out almost as expected. While no monthly outlook is truly straightforward, calling for persistent cold last month was a pretty easy call to make. As expected, the core of coldest air was generally to New England's southwest with New England more on the fringes, so it wasn't as cold (relative to average) as it was for much of the rest of the country.
There were two specific, elongated cold stretches for New England, one from January 4th to the 11th and the other from January 20th to the 25th. Warm-ups back to average or above average between these cold stretches moderated New England's temperatures as a whole for the month, so we didn't end up as far below average as expected. Southern New England was generally colder; Boston ended the month 1.1° below average. The farther north in New England, the more mild it was relative to averages; Caribou, Maine ended up over 3° above average for the month as a whole.
It may have seemed much colder across New England than what these numbers or the map shows, but that's likely because our last several winters have featured multiple big thaws, something that hasn't really happened so far this winter. We also predicted a below average month for precipitation, which did pan out.
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