Posted by: splillo | February 13, 2012

Shortwaves galore

Alright, first let's define a term:

Shortwave (noun) -- An upper level trough with a wavelength on the order of 1000km. It's the upper level feature that is responsible for the more typical representation of storm systems we see drawn on weather maps with the surface low pressure center and fronts. These shortwaves can be identified on an upper level map as a depression in the jet stream and by another quantity called "vorticity" -- the spin in the atmosphere. To see how it all works together, refer to the crude idealized model I've drawn up on the left.

So as I have suggested, the upcoming week could get stormy for much of the nation. A bunch of these shortwaves will be pouring into North America from the Pacific. This makes the forecast very complicated, because the disturbances interact with each other and present a multitude of possible outcomes; a tribute to chaos. Below, I have included a single forecast model projection of upper level vorticity for Saturday morning. I have highlighted the shortwaves that will be players in the forecast for this weekend.

I won't go into the specific role of each of these shortwaves, but suffice it to say the evolution of each one and their interactions are crucial to the forecast.

So why do I bring this up now? Well beneath the colorful chaos on that map, there is a pattern that is climatologically supportive of east coast winter storms. The vortex over southeast Canada acts to suppress storms to the south, enforcing a cold airmass over the region.

That's all well and good, but the pattern itself won't make it snow; we need a storm.  Well, we have the interactions of shortwaves 2 through 6 to consider for the development of a storm this weekend. Shortwave #4 is our southern energy that will trigger the development of a fairly classic looking low on the Gulf coast. What happens from there is up in the air (excuse the pun).

I think that we have the makings for at least a moderate snow storm for the Mid Atlantic region (Virginia and Maryland perhaps), but we need some phasing to happen between those northern disturbances and the southern shortwave to produce a strong enough storm that can barrel up the coast toward New England. I'll be keeping a close eye on all of the ingredients being thrown into the mixing pot over North America this weekend.

Posted by: splillo | February 8, 2012

Everywhere but New England

The Mid Atlantic region is getting a nice taste of winter today, as a storm system slides to the south of New England. Weak low pressure developed well offshore the North Carolina coast, but was able to throw back some moisture into the cold air mass over New Jersey, Pennsylvania and Maryland. Accumulations are on the light side (a coating to 3 inches), but in this non-existent winter, it certainly is a welcomed sight for snow-lovers as Tom Thunstrom discusses in his blog (Updating This Evening's Light Snow Event). Our experience this year has been a far cry from the events of last winter...



In New England we are sitting in the cold, but without the pleasures of snow. As I discussed in my last post, we still have to watch another disturbance diving out of Canada and then developing to our southeast. It could produce some light snow for at least eastern New England, including Cape Cod and the Islands.

Forecast surface map for 7am Saturday morning

Looking beyond the snow "threats", a surge of arctic air will hit the Northeast on Sunday, and stick around through the first half of next week. You can see on the surface forecast map to the right that the disturbance driving the arctic front through the region is also the feature that is suppressing the coastal storm to our southeast. This winter, we just happen to need this fine balance of cold and energy in order to get snow ... what some refer to as "threading the needle."

Notice on this surface map the massive area of high pressure overtaking the northern Plains to the Great Lakes region. This feature is associated with the deep arctic air mass, and will be accompanied by clearing skies and daytime temperatures in the teens and 20's in New England on Sunday.

Posted by: splillo | February 6, 2012

Cold and dry

Step outside, and you'll definitely acknowledge that it feels like winter. Temperatures this past weekend were stuck in the 20's to low 30's during the day ...which is actually about normal for this time of year. An occasional wind gust might have made you stick your hands a little deeper into your pockets and hurry to the warmth of your destination. However, with high pressure in control, the sun was also out in full force which helped take the edge off the cold.

Today, a low pressure system tracking to our north will help draw some warmer temperatures into the region, and many areas could make it into the 40's, under sunny skies. Should be a beautiful day!  That same low will drag a cold front across the region on Tuesday, which could be accompanied by a flurry or two. Colder temperatures will filter back into the Northeast for Wednesday, followed by another warm up at the end of the week.

Next weekend poses a few questions. A low tracking to our northeast will open the gates to another blast of arctic air. Meanwhile, there are two disturbances to watch: a cutoff low in the Southwest and a storm diving south from Canada into the Midwest. The northern storm alone will likely produce a significant low in the western Atlantic next weekend, but it would pass well south of us out to sea. If the northern storm can dive far enough southwest initially, it could join forces with that cutoff low (called "phasing"), and produce a stronger system that would deliver a winter storm for the eastern U.S. I do not see this scenario playing out though. These cutoff lows have had the tendency to sit tight in the Southwest, not getting picked up by the northern stream. Forecast models are all in agreement on this one as well. So I expect the storm to pass well south of us ...another cold and dry weekend ahead.

Outside of New England, believe it or not, there is an early season tropical disturbance in the Gulf of Mexico! A wave of low pressure was producing a broad area of showers and thunderstorms yesterday from the Yucatan Peninsula to Florida. The National Hurricane Center acknowledged the area of disturbed weather this morning. However the reason that you don't see hurricanes developing in February is because the jet stream is further south than in the summer, and literally shreds these storms apart. The disturbance in the Gulf should pass harmlessly out into the Atlantic today, just giving southern Florida a little rain.

Elsewhere around the world, arctic cold has plagued Europe in the past week. Below freezing temperatures and snow have made it as far south as the northern coast of Africa! Heavy snow has slammed much of Europe, not just in the mountains but also tapping into moisture from the Black Sea and unleashing over Istanbul, Turkey and Rome, Italy! It would appear that winter is visiting everywhere except for New England.

Posted by: splillo | February 1, 2012

Welcome! ...Where's Winter?

Welcome everyone to a blog dedicated to discussing the weather! Everyday I'll discuss the local conditions first, then launch into the global weather pattern. I'll mention significant weather events around the world. Finally, I'll provide a summary of the forecast for the week ahead. Some of the discussion may get technical at times, but I'll try to explain as much as possible.

So without further ado,

Today was just one more day of above normal temperatures across the region in this record-warm winter. Southern New England soared into the 50's and a few areas even broke into the 60's! This was just a few degrees below daily record highs. Plymouth, NH was stuck under clouds for much of the day, which held temperatures back in the 30's through the afternoon. However, a warm front surged north in the evening, and we have actually continued to warm into the 40's after sunset.

Meanwhile, to our north and east, a light wintry mix made the streets a little icy through the day, with temperatures stuck in the 20's ... so a huge range in temperatures across New England today!

Otherwise, as most of you have probably noted, snow has been scarce so far this winter for New England, as well as much of the contiguous United States. The two inches of snow that we saw in Plymouth on Tuesday whitened the campus and painted a nice wintry scene. Any other year, two inches in January would be no big deal, but this was almost a rare sight. Following the historic October blizzard that dumped 20 to 30 inches of snow across central New England (5" in Plymouth ... still remarkable), temperatures have averaged well above normal and storms have been primarily rain. Concord, NH recorded an incredible 23.0" in October. Since then, they have received a meager 13.6" ... in other words, more snow fell in the one October storm than in November, December, and January combined!

So where has winter been? While much of the Lower 48 have been looking out their windows at bare lawns, residents of Alaska can't see out their windows past the 10 feet of snow! So far this winter, Valdez, AK has recorded 330.4" of snow. When it's not snowing, Alaska has been in the deep freeze, with temperatures bottoming out as low as -50F. In Fairbanks, January 2012 went down as the fifth coldest on record with an average temperature of -26.9F. 

Will we ever get a taste of any of that? Winter is far from over in New England. We usually have to get past at least April 15th before dismissing the possibility of snow. However, in the short term, there isn't much hope of anything. Actually this next week looks fairly dry, with storms sliding well to our south. Expect some clouds tomorrow followed by a beautiful sunny weekend! Temperatures will generally be in the 30's during the day. A storm system will approach us early next week with temperatures rising into the 40's on Monday, followed by a few light rain or snow showers possible on Tuesday.

For Alaska, blizzard conditions from the latest storm will persist through tonight.

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