Up and Down Temperatures

Last Updated (Friday January 25, 2008 11:30 AM )

Wednesday Update: The Cape is situated in no-man's land between two contrasting air masses today. Yesterday's push of milder air has been shoved offshore by a cold front but the true arctic air expected to move in for the second half of the week is still 24 hours away - lurking behind an arctic front to our north. As such, today's air mass is cool, but not cold and will result in a pleasant day by January standards with sunshine dominating and temperatures climbing well into the 30s. However, despite starting the day in the low to mid 30s - which is quite mild for this time of the year - we won't see a dramatic temperature rise as colder air will be spilling into the region higher in the sky, limiting our ability to warm. So while you might look at your thermometer at home this morning and think we are headed for the 50s, temperatures will be capped in the high 30s to near 40°F.

We are still expecting a storm system to develop off the Mid-Atlantic on Thursday as the arctic air meets the Eastern Seaboard. While most, if not all, of this system's moisture will remain to our south and east, the combination of high pressure building in to our west and the developing offshore storm will turn winds to the north beginning later Thursday afternoon and lasting through Thursday night. The resulting flow of cold northerly air should be enough to get some ocean effect snow bands cranking on the Mid and Outer Cape by later Thursday evening. Given the strength of the cold air, the presence of some upper level energy swinging by, and the well-aligned northerly wind, there could be some organized snow bands for a time Thursday night. Should this materialize some accumulation is possible, mainly east of Hyannis. Ocean effect snow is difficult to forecast so check in for updates.

One last thing, the late weekend / early next week time period is becoming quite tricky from a forecast standpoint. The overall jet stream pattern will be undergoing some changes and while the big picture is fairly clear, smaller scale features are not. There's a theme developing in some of the latest set of computer guidance of a stalling and strengthening low pressure area southeast of Cape Cod Sunday and Monday (and Tuesday?) thanks to a slowing, or blocking, upper level pattern. One of the best mid-range computer models is leading the way with this idea, so this will be something to watch closely over the next several days.

Tuesday's Post: A large cold high pressure area is pulling away from the Eastern Seaboard today and at the same time a low pressure center is advancing northeastward across the Great Lakes. The resultant southerly wind direction is allowing marine-modified air to work northward from the waters east of the Mid-Atlantic region and onto the Cape. Amazingly, after such a cold start, this influx of milder temperatures will push readings well into the 30s to near 40°F this afternoon.

With temperatures near the surface so mild, it will be tough for any precipitation that moves in this afternoon to fall in any form other than rain. However, outside of the surface warmth, overall the atmosphere is cold enough to support some snow, so should a heavier burst of precipitation move overhead a few flakes of snow or ice pellets could mix in now and then. Southwest winds will be rather gusty this afternoon as well thanks to the rush of milder air, and a few gusts to 40 mph are possible.

This system will pull away tonight allowing colder air to filter back in and skies to eventually clear out later tonight. After a reasonably quiet day Wednesday, we turn our attention to an arctic front expected to drop through the region on Thursday. We'll watch this front carefully as it will:

1. Continue our temperature roller coaster: After struggling to 25°F yesterday, reaching 40°F today, the mid 30s Wednesday, temperatures will remain in the 20s both Thursday and Friday. In fact, by late week, overnight lows will again be well down into the teens and a strong north-northwest wind will make for low wind chills Thursday night and Friday morning.

2. Spawn an ocean storm. As the arctic air reaches the Mid-Atlantic, it will induce low pressure development east of Virginia. Assuming the forecast track doesn't bend any further westward, this system's precipitation shield could clip the region with a touch of light snow later Thursday and Thursday night (not all that different from this past Saturday). A minor accumulation of snow would be possible. In addition, and perhaps more important, this ocean storm will turn our winds to the north (even NNE on some computer guidance) Thursday night into Friday morning which when combined with advancing arctic air could spell some ocean effect clouds and snow showers on parts of the Cape.

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