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Posted at 4:45 AM ET, 01/ 8/2008

Where's All the Snow?

By Matt Ross

Outside of the December 5 "clipper storm" that brought 3-5" to most of the DC metro area, the metro region has seen little to no snow. And it's been warm. December finished over two degrees above normal at Reagan National Airport (DCA) for DC's eighth consecutive month with at or above normal temperatures. As we approach what is statistically our coldest period of winter (January 9th - January 23rd), we are basking in spring-like conditions with temperatures in the 60s. Will it ever snow again?

Before we assume we'll cruise to a relatively snow-free winter based on the paltry snow totals to date, let's consider our climatology. Historically, the DC area does not receive a whole lot of snow in November and December. November and December combined only average 2.2" of snow per winter, or only about 15% of the area's seasonal norm of 15"-16". As the clipper storm on December 5th officially dumped 2.6" at Reagan National Airport, we actually slightly exceeded our average for the early winter season. Sitting here in early January, we still have nearly 80% of our snow statistically ahead of us, so snow lovers should actually be encouraged, right?

Well, we know that statistics rarely tell the whole story when it comes winter. For most folks, experience trumps statistics, and as snow lovers who have seen nary a flake in over a month, we are frustrated. It doesn't matter that we are performing OK by the numbers. We are roasting in early January for the fourth year in a row, and prospects seem grim. The only thing that will save us is not statistics, but a change in the pattern.

We are in the midst of a moderate La Nina event, our first moderate event in eight years (1999-2000 winter). La Nina is an oceanic phenomenon in which the sea surface temperatures in the equatorial Pacific Ocean run 1-2 degrees C below normal. This is the opposite of the more widely known El Nino, when such temperatures run above normal.

La Nina produces some predictable effects on our weather here on the East Coast, and this winter is performing according to form. While weak La Nina events are more amenable to snow and cold, and strong events to little snow and warmth, we are in a battleground during most moderate events. This La Nina event has maintained its strength heading into early 2008. One of the telltale signs of La Nina, the southeast ridge, has been a sometimes dominating factor through early winter.

The southeast ridge is a ridge of high pressure off of the southeastern coast, often centered over Bermuda, which is responsible for warmer than average weather in the Southeast up through the Mid-Atlantic. The southeast ridge has kept our region a battleground between cold and warm weather regimes during the early part of winter. Places that are very susceptible to the influence of the ridge include Raleigh, N.C., which recorded a December that was almost six degrees above normal with no snow. On the flip side, the ridge's warm air has not reached locations well to the north in southern New England, while steering storms in that direction. Boston, for example, recorded one of its snowiest Decembers on record. So what does that mean for us and the prospect of snow?

Well, first we need the southeast ridge to relax. While its presence in a weaker form can help force snow-producing storms up the coast, so far the ridge has been too powerful. While cold air has occasionally beaten down the ridge enough to make it down here from Canada, storm tracks have mainly been north and west of us, giving plenty of snow to the interior northeast and New England, but mainly keeping us in the warm sector with cold rain. The relaxation of the ridge will allow even more penetration of cold air and potentially shift the storm track to our south and east, a traditional snow maker for us during winter. What else do we need to happen?

It is probably pretty evident that in our area, we need several ingredients to come together to usher in a snowier pattern, not just one. This isn't New England. Nobody panics at the prospect of snow quite like Washingtonians, and that is partly due to its relative rarity. Some other ingredients, but not all, that make up the classic snow pattern for the region include the North Atlantic Oscillation (NAO), the 50-50 low, and the Polar Vortex.

While you don't need every ingredient in place to get snow here, the more you have in place the better. Let's start with the NAO. The NAO is traditionally measured by the difference in pressure between Iceland and the Azores. When this index is negative it is often indicated by a block of high pressure over Greenland. When this block is strong and well-placed, it tends to lock the cold air in place over the East Coast, which is critical for snow in our region. The negative NAO often operates in conjunction with another helpful snow ingredient, the 50-50 low.

The Newfoundland, or 50-50, low, so named because it often occurs at 50N latitude and 50W longitude, is an upper level low pressure system with closed circulation that spins off the coast of Newfoundland. Coupled with the Greenland block as described above, the 50-50 low keeps cold high pressure from sliding out to sea and helps force storms to cut below our area and up the coast, often resulting in whiter rather than wetter conditions for our area. But what if we don't have any cold air in place to lock in? This is where the polar vortex, essentially our cold air supplier, plays a major role.

The polar vortex is an upper level area of low pressure which often resides near Hudson Bay in Canada. The closer it gets to the U.S., the more cold air it brings from Canada. A strong polar vortex diving south towards the U.S. provides critical cold air for a snowy pattern in our region. But when the vortex is really weak or far away (displaced on the other side of the north pole), there is not enough cold air to support snow in our region. So far this winter, the polar vortex has not been well positioned to consistently provide the necessary cold air for lots of snow.

While snow lovers are certainly frustrated that a snowy pattern with the potential to bring several storms to the region has yet to materialize, there is hope. In our last moderate La Nina event (1999-2000) we saw a 2-3 week period of lots of snow and cold (despite an otherwise warm, snow-lacking winter). There are indications that toward the middle to end of January, the ingredients for a snowier pattern may come together, although snow lovers in our area will always be better off keeping expectations low. There is plenty of winter left to get a more snow favorable pattern in place, but the truth remains a lot needs to come together for a snowy pattern in the metro area. Let's just hope it isn't in late March or April when it happens. I think we all can agree that the last thing we want is a delayed spring.

By Matt Ross  | January 8, 2008; 4:45 AM ET
Categories:  Winter Storms  
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Generally well-written, Matt, but with one significant error. January thaw from mid-winter Bermuda highs, as we are seeing now, is not just an aberration, something La-Nina produced, or even part of the so-called (and mostly incorrect at that) global warming. It s a normal part of the average East Coast winter, and occurs regularly during most winters here.

Posted by: Mike | January 8, 2008 6:12 AM | Report abuse

Mike, Welcome and thanks for the feedback. Matt doesn't really say the southeast ridge (or Bermuda high) is an aberration produced only during La Nina winters (and makes no mention of global warming). He just implies you tend to see them a lot during La Nina winters. We all realize this pattern is a normal part of our climatology.

Posted by: Jason, Capital Weather Gang | January 8, 2008 7:12 AM | Report abuse

Finally, a bunch of guys who are as passionate about the weather (and snow?) as I am! And they're from around here! No more stalking the forums and blogs at (in)accuweather or wunderground. Great to have you guys.

Posted by: hobbes | January 8, 2008 7:46 AM | Report abuse

hobbes: Welcome. Thanks for commenting.

Posted by: Jason, Capital Weather Gang | January 8, 2008 7:52 AM | Report abuse


I am a retired meteorologist and have been an east coast weather enthusiastic since 1956.

I'd like to get your comment on something I have noticed through the years, and that is the contribution of the Pacific/North American Index (PNA)to major snow events on the East coast. In the winter I have found the PNA seems to add to and enhance precipitation events in winter on the east coast. This is verified by looking at the precipitation anomaly over the Mid-Atlantic and SE U.S. with which is negatively correlated to the PNA index. For us it generally reflects an enhanced subtropical jet in the SE and lower Missippi River valley. When this jet merges with the Polar Jetover over the SE or Missippi River, we tend to get a major snow event from a subsequent coastal low.
If the polar jet is not merged with the subtropical jet I have observed a warm, wet pattern over the SE. I believe a negative PNA reflects in winter a stronger, moisture laden subtropical jet along which short waves form either the west coast or Gulf of Mexico travel and feed on.

W. S.

Posted by: Warren Spaeth | January 8, 2008 8:03 AM | Report abuse

Warren: Welcome. The PNA is definitely another important factor. I agree with your observations. Matt may have thoughts as well.

Posted by: Jason, Capital Weather Gang | January 8, 2008 8:13 AM | Report abuse

Mike....agree with you...We have seen 60s in January for 7 consecutive years now.....

Warren...perhaps in the future I will do a post focused on the North Pacific...I kind of avoided it here, but no doubt it is an important driver of our pattern....

Posted by: Matt Ross, Capital Weather Gang | January 8, 2008 9:37 AM | Report abuse

I tend to put more confidence in the NAO (North Atlantic Oscillation) than in the PNA. Apparently it helps to have both the NAO and PNA negative to max us out for snow around here. But the best years for snow and winter precipitation around here seem to be the "neutral" or "La Nada" years. We havent had one of those in a while. It seems as though we tend to "flip" from El Nino to La Nina and back nowadays.

Posted by: John Andre (El Bombo) | January 8, 2008 9:55 AM | Report abuse

Jet stream overview: Right now the jet is primarily to our northwest. It seems to be holding a stationary boundary from TX to IL in place and this is causing training of thunderstorms through and just to the SE of Chicago. There's a lot of flood risk over parts of IN and MI (Lower Peninsula) at this time. Fort Wayne is in the middle of the flood risk area. There have also been severe thunderstorms and unusual January tornadoes as far north as southeastern WI. Elsewhere, the jet is strong over Japan and the Pacific, and the only hints of a split jet are over western Europe and the Himalayas (the mountains there are high enough to cause a split jet this time of year). In the Southern Hemisphere, the summer jet is primarily to the south of most continental areas, passing over Patagonia and touching the southern tip of Africa. The only major land mass south of the jet stream down there is Tierra del Fuego. The jet is primarily to the south of Australia and even Tasmania is north of the circumpolar Antarctic jet.

According to the GFS (Unisys chart) the jet stream may not reach us by 0Z tomorrow. This means the frontal passage and accompanying rain could be delayed to some extent.

Posted by: John Andre (El Bombo) | January 8, 2008 10:14 AM | Report abuse

Matt, Jason
Congrats! Matt great write up on the antecedent requirements for DC snow. All the stars need to line up and some yaers they do, this year still has a great deal of time left for snowlovers to rejoice. I'm rooting for you, great blog guys.

Posted by: Ginx | January 8, 2008 10:47 AM | Report abuse

Ah, now this is the sort of post I come to capwx for - thanks, Matt! But why, oh why, am I not out taking advantage of the SE Ridge by sailing today??? It's not as if this is the first you've mentioned it, so I've no excuse.

Posted by: ~sg | January 8, 2008 11:41 AM | Report abuse

Nice job, Matt.
Congrats on the move.

Hey Hobbes, check out if you like guys passionate about weather.

Posted by: YHBrooklyn | January 8, 2008 11:48 AM | Report abuse

Thanks for the glimmer of hope. I remember January 22-23, 2000 we had a good dumping of snow. It was my first winter in the region, and I went in late to work just to go sledding on my birthday. LOL. So, I will keep my fingers crossed we will get the same this year.

Posted by: kim in Manassas | January 8, 2008 1:12 PM | Report abuse

Well we still have a lot of winter to get through, as Matt says. I'm pretty sure we'll see more white stuff again this winter. :)

Posted by: Josh, Capital Weather Gang | January 8, 2008 2:32 PM | Report abuse

Wow!!! This is my first time on the blog and I learned more about meteorology and weather reading this than I have in the past 45 years. This could become addictive.

As an avid skier who gets things tuned up locally every year from December through February before heading out to Colorado or Utah for two weeks in March I am really disappointed in the lack of snow and the temperature. At least with consistent sub-32 degree nights and moderate days you would see Whitetail and Liberty making snow, but the conditions are pretty miserable. Snowshoe looks pretty good, but still has not opened all of its terrain.

The local ski areas have a tough time getting 80 days per year in a typical winter, but it is doubly hard when the grass at home is green and you are thinking about breaking out the golf clubs in January.

Posted by: Lester Burnham | January 8, 2008 3:50 PM | Report abuse

Good stuff Matt, hope to see more stuff from you here other then just once a week!

Posted by: Mike from the Blue Ridge | January 8, 2008 4:27 PM | Report abuse

Hope this new location turns out as an asset. Another day of shorts & t shirts.

Posted by: VaTechBob. | January 8, 2008 6:11 PM | Report abuse

How much for Mebane?

Posted by: MebaneManiac | January 8, 2008 7:06 PM | Report abuse

Very informative, Matt! We truly enjoyed reading, and learning, about weather in general, and snow in particular, in our region. Thanks for doing this and continued good luck to all of you.

Posted by: Judy and Av Hecht | January 9, 2008 3:15 AM | Report abuse

I am only in the 8th grade, and wow have I learned a lot! Anyway, I live in georgia,do you forsee any chances of getting snow here before spring? just wondering, I would love to have an actual snow day from school! lol

Posted by: chase | January 30, 2008 7:45 AM | Report abuse

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