The colder and snowier pattern that was projected for January has verified well, as much of the Mid-Atlantic and Northeast has had a few significant winter storms to deal with over the past several weeks. February got off to a busy start, as a long duration, high impact winter storm affected much of the country from the Midwest into the Northeast. We projected the month of February to flip back warmer after a colder January. So far, somewhat of a wintry pattern has held on a bit longer, but the pattern has broken down some, as a few warmer days have certainly been mixed in with the wintry weather. This has especially been the case during the week of Feb. 13th - 19th, as high temperature records were approached or even broken on February 17th. However, snow still fell in parts of northern IL with wintry mix in parts of Indiana and Ohio.
It looks like the warmer, rather snowless pattern will continue for much of the Midwest and Eastern US until around the 25th, when a quick snap back to winter likely occurs. It appears that tropical forcing (MJO) isn't the culprit for this (as was the case in early January), as it looks to continue to propagate into the warm phases near Indonesia:
Instead, a very strong cyclone will develop shortly in the western Pacific, which will really shake up the pattern. This cyclone was missed by computer guidance, which drastically underdid its strength over the last few days. It was originally projected to drop only down to ~990 mb, but will instead drop to ~960mb.
The development of this cyclone will lead to an extension of the Pacific jet, which will then encourage the development of a ridge of high pressure over Alaska and the West Coast:
As a result of the ridge over Alaska, cold air will eject out of Canada into much of the Continental US after the disturbance on the 25-26th, leading to a pattern that features temperatures much below normal into the Midwest and Eastern US:
Given the development of the ridging over the West Coast, the subtropical jet stream is able to slip underneath, leading to something called "split flow." Split flow is when the polar and subtropical jet streams become separated and then meet up over the central and southern US, where pieces of energy are then able phase back together. This increases the risk for larger systems impacting the eastern US:
There was another scenario similar to this in November 2014 when Typhoon Nuri took a similar path and led to the same kind of blocking near Alaska that we're likely going to see in the upcoming weeks:
The pattern that we're likely to see has also historically produced a good bit of wintry weather for the northern Mid-Atlantic compared to average. Here is a composite analog of Marches where NYC recorded over 10" of snowfall compared to the expected pattern:
Notice that both patterns feature the promient ridging over the West Coast and Alaska. One interesting feature is that there is no ridging near Greenland, which is often needed to produce large snowfall events south of New England. However, given seasonal changes, that feature isn't necessary to produce these events, and the two patterns end up remarkably similar. While we aren't forecasting a March that is incredibly anomalous for the Mid-Atlantic, it shows the potential for cold air pressing far enough south to produce wintry events. This type of pattern would also feature frequent cold shots into the Midwest, which ups the chances for monthly snowfall totals to reach or even exceed climatology.
Overall, what do we expect the rest of the winter heading into March?
- The warm pattern that much of the Midwest and eastern US is in will continue through the 25th or so with not much wintry weather to speak of.
- However, after the system around the 25th, which could prove quite wintry for most forecast regions, there looks to be a sharp drop off in temperatures to below normal. Overrunning snowfall events are favored, but coastal storms are also in the cards given the split flow pattern developing as we head into March.
What about snowfall in March and even April?
New England:
- Averages ~8" / year March-April. Note, the 5 & 10 years are slightly higher, closer to 10.0" / year for Hartford-Bradley Airport and Boston Logan
- It's quite rare to not see measurable snowfall. That has only occurred once in the last 15 years in both Boston & Hartford and twice in the last 30 years. Typically, the two locations see 1.0"+ about 75% of the time.
- Although not shown, the 15 year max for Boston and Hartford both are around 2 feet, so it certainly can snow a lot in March - April. It's not uncommon to snow decently into April (> 1.0"), as it occurs once every 2 to 3 years. But pavement issues are tougher.
- How do we feel about New England's snow chances in March and April? Climatology already favors some snow for all of New England, even in relatively snowless winters, so New England looks to see snowfall on the higher end of climatology given the cold pattern. Areas farther north are typically favored, but areas in southern NH could actually be a bit on the drier side if the cold air ends up pressing far enough south.
NY-NJ-PA:
- There's quite a bit of variability here, but Newark, NJ, Allentown, PA and Harrisburg, PA all average around 6" / year March-April. Obviously, Northwest NJ and Poconos are higher. Meanwhile, Philadelphia and Atlantic City are closer to 4.0" / year since 2007.
- While it's more common to snow than not, most locations have seen ~5 or 6 instances over the last 15 where it has failed to produce measurable snow and / or 1.0". Interestingly, the < 0.1" and < 1.0" are similar, suggesting it either snows decently or it doesn't at all (0.1 - 0.9" isn't very common).
- It's not shown, but the 15 year max is 15" - 25" across the board, so March - April can certainly snow well. Note, decent April snow (> 1.0") is rare, but not unheard of. It occurs about once every 5 years in northern areas of PA, NJ, and NY, and once every 10 years south.
- How do we feel about this region's snow chances in March and April? Some snow is the norm in March of late, and this March shouldn't be an exception. Given the pattern setting up, there is a heightened risk for snowfall events in the northern Mid-Atlantic, especially given the analogs shown above. More mixed events are favored, but overrunning snowfall could bring some salting/plowable snowfall events in the first couple weeks of March.
Mid-Atlantic:
- Average snowfall in Richmond is ~1.5", Baltimore is ~3.0", and interpolating from Baltimore to Philadelphia and Harrisburg, PA would suggest Northern MD is ~4.0". But the average is fairly misleading, as it's comprised of a lot of 0's and T's, and somewhat snowy seasons (3"+)
- There are still more seasons than not that have both measurable snow, and > 1.0". That is not the case further south into Virginia, as it's much more common to have < 1.0" (and unmeasurable) snow.
- The 15 year max in Richmond, VA is 6.3", Baltimore is 12.1". It takes quite an anomalous pattern for that.
- How do we feel about the Mid-Atlantic's snow chances in March and April? Although the snowfall averages this far south for March/April are often skewed high due to anomalous years, it does look like the pattern setting up gives areas in the Mid-Atlantic a decent shot to see some snowfall. Most events will produce wintry precipitation towards NYC and north, but if cold shots are on the stronger side, an overrunning event may be in the cards for DC and even Richmond, VA.
Midwest:
- Average snowfall in Chicago is ~5.0", Indianapolis is ~3.5" and Cincinnati/Dayton/Columbus is between 2.5 - 3".
- All of these cities have seen accumulating snowfall over the last 10 years in March, aside from a couple outlier years. Some years have close to and even upwards of 10" of snow, so March can be quite snowy if the pattern fits.
- The 10-year max in Chicago is 12.5", Indianapolis is 13.7", and Dayton is 11.7". It takes a relatively anomalous pattern for these amounts, and most months have between a trace - 5.0" of snow.
- How do we feel about the Midwest's snow chances in March and April? Although we don't expect a particularly snowy March, the colder than average pattern will provide snowfall chances during the first couple weeks of the month throughout the Midwest. Overrunning events are heavily favored rather than wrapped up and intense low pressure systems.
Overall, the colder pattern only looks to sustain itself for the first couple weeks of March. As we head into the third week of March and onward into April, expect the pattern to become more and more hostile to snowfall both in the eastern US and the Midwest. Climatology also becomes much less favorable (outside of northern New England) heading into April, so March seems to be out like a lamb as of now.
