Desierto norte de Chile

Friday, February 24, 2012

Warm and blustery, or cool and drizzly?

Today's weather will be very interesting. A warm front is located about 200 km south of Annapolis, and the NWS predicts it to come north of us today (so high temperatures near 70F), then a cold front passing later this evening with rain and thunderstorms. I'm more skeptical, as temperatures in the upper 40s now (at 9:30 a.m.) and drizzle indicating the cool, stable layer is still well entrenched over us. Will be interesting to see what happens, as the severity of the afternoon precipitation strongly depends on the position of the surface warm front. My afternoon bicycle ride home could be quite interesting!

Sunday, February 19, 2012

That was likely our last chance at snow...

The weak surface low slowly intensifying in eastern NC this afternoon will likely be our last chance at appreciable snow this winter. For us in the mid-Atlantic, the large majority of our snow comes from interacting upper-tropospheric vorticity maxima that phase to promote strong surface cyclogenesis. Cold air from our north is advected in at the surface while moist air from the south is advected aloft. The last week of NWP forecasts have bounced all around with how they treat today's low, but ultimately the phasing between vorticity centers didn't happen, so the slowly intensifying low will move essentially east from N. Carolina later this afternoon. Had it moved northeast (driven by a more amplified upper-troposphere wave), it would likely have brought us snow today/tonight. However we'll be lucky now to see even flurries. All in all, a disappointing "flourish" to a throughly non-snowy year. Since July 1, BWI has received 1.8" of snow: 0.4" on 09 Jan, 0.9" on 21 Jan, and 0.5" on 11 Feb. The total is 17.7" below the median annual snowfall value of 19.5". If it stands for the year (a reasonable outcome), it would be the 3rd least snowy winter in Baltimore since 1883 (1949-50 with 0.7", and 1972-73 with 1.2", are the 1st and 2nd least snowy, respectively).

Thursday, February 16, 2012

Snow on Sunday?

It seems like an eternity has passed since my previous post (in reality, it's been only 36 hours!) The many model initializations since Tuesday and this morning have all had varying solutions for the coastal low, ranging from a dry, cirrus-y day to a heavy rain and thunderstorm type of day. The latest couple of model runs have seemed to converge on a solution that looks snowy. Still many questions regarding rain/snow for Annapolis - given our very warm winter and associated warm surface temperatures that will need to be overcome. But the predictions are encouraging, and point to snow during some point of the event (right now at the end, once the surface low begins to move away and the surface layer can cool enough to support frozen precip). Here's the GFS forecast for 10 a.m. Sunday.

Tuesday, February 14, 2012

Happy Valentine's day: will it snow over the weekend?

Happy Valentine's Day to all! After following the NWP models nearly daily for the past 2+ months, we finally have a couple of solutions that indicate a potential for a snowstorm over the weekend. Will be worth following over the next couple of days- to see whether the major upper-troposphere players (various amplitude shortwave troughs in the north and south) phase together to promote surface cyclogenesis that moves up the coast, or whether they stay separate and result in a weak low that moves essentially east into the Bahamas. Here's a forecast of MSLP, 6-hr precip, and 850-hPa temp from the GFS.

Monday, February 06, 2012

I'm guilty, too

In a blog post in the Spanish daily newspaper El País (of Madrid), there's a nice series of articles about traveling. This figure caught my attention more than most: the mean number of vacation days earned by citizens of various countries, and the number of vacation days actually taken (and, naturally, the number of unused days). My country, USA, comes in 3rd to last in the group, only ahead of work-a-holic Japan and South Korea. Even Mexico and India earn - and take - more paid vacation days than we do. I wonder why it is, that we both earn few, and take even fewer, vacation days?

I admit it, though: I'm guilty, too, of not using all of my 'precious' vacation days. Perhaps because the academic semester is so loaded, that taking vacation during the teaching term is frowned upon. Equally likely is that because the summer schedule is so flexible, that I don't feel the same need to take vacation days because I already am resting when compared with the other 3/4ths of the year. Those are probably my reasons, but I'm curious the justification of the rest of the country.

Wednesday, February 01, 2012

Warm and snow-less

This winter continues its warm and snow-less march to spring. The current temperature here in Annapolis is 67F, and today's high temperatures here and to our west might top out at 70F! For the first day of February, warmth like that is impressive.

What is governing this warmth? While the atmospheric system is incredibly complex, it often can be diagnosed effectively through the use of climate indices: two that are popular are the El Niño-Southern Oscillation (ENSO) index, and the North Atlantic Oscillation (NAO). ENSO measures sea surface temperatures in the tropical eastern Pacific ocean and NAO measures sea level pressures between Iceland and the Azores islands. While the causality of both remains debatable, the effects of each are pretty well known: both affect the frequency, amplitude, and translation of planetary waves, which in turn affect cloud cover, precipitation, and temperature.

The NWS Office in Sterling, VA (who forecasts for us here in Annapolis) has put together a great brief on the combined effects of ENSO & NAO on snowfall in Washington, DC. Their presentation is found here (which came from the media agenda here), and at the Washington Post here.  The years with above-normal snowfall (>15.5" in a year) almost always occur during a negative phase of the NAO, and the majority of the snowy years occur when ENSO is either neutral or warm. The combination of those two yields upper-level troughing and below-normal temperatures over the eastern 2/3rds of the U.S.

The current ENSO Index is -0.979, and the NAO index is around +0.25. On the phase-space diagram from the NWS, that puts us in the upper-left quadrant- the one with the least snowy years. Furthermore, and even less encouraging, is the ensemble NAO forecast, which calls for mostly +NAO for the next 2 weeks. By the time the NAO goes negative again, we'll be heading toward spring!

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