Thursday, December 21, 2006

Happy Solstice!


Cloudy, cool. Winter solstice is at 7:22pm tonight. A few peeks of sun and a southerly breeze were no match for a mid-level overcast and a few minor sprinkles of rain on one of the shortest days of the year in the Washington metro area. The temperature in most places stayed below 50°; the highs were 46° at National, 47° at Dulles, but 53° at BWI. Clouds will become thicker and showers will develop through the day tomorrow.

Tonight and Tomorrow

Showers developing, cool. Tonight will be overcast with a 40% chance of showers by dawn; lows will be in the low 40s in town, a couple of degrees cooler in the 'burbs. Tomorrow will be cloudy with showers likely, especially in the afternoon and earlier west of the mountains, with highs in the upper 40s.

For the outlook through the holiday weekend and beyond with Larson's Long-Range, scroll down to Josh's post below.


If you've been with us since last year (if so, thanks; if not, welcome!), you may recall we did some fun-with-numbers analysis of the relationship between December and January in Washington. Considering the amount of wailing and gnashing of teeth going on lately in the Comments section about the End of Winter As We Know It, this is probably a good time to take a second look at the data. The gist of the results is that, despite any amount of wishcasting, guessing, golden childhood memories, El Niño, NAO, or EIEIO, snow in Washington is enough of a random event that there is almost no connection whatsoever between the amount of snow in December and the amount in January. Anyone who tells you differently should be closely examined for controlled substances. In fact, the nearly microscopic amount of correlation (¼%) which does exist is actually slightly negative.

Since this December is well on its way to the "bust" category for snowfall, it's relevant to look more closely at the data points huddled along the y-axis in the original chart. The January snowfall for the 30 winters with December snowfall of 0.1" or less is shown in the chart above. Included in that set are 2 Januaries with over 20" each. The average amount of 5.6" is not very far from the January average of 6.6" for the entire period of record.

Although Mr. GW may have his greasy carbon-bloated thumb on the scale over at Momma Nature's Weather Grill and Deli, reports of winter's demise are certainly premature. (Before you fire up the political flamethrowers, please note that "GW" refers to "global warming", not a certain person's initials, but you knew that anyway, didn't you? ) chart from NWS data, photo © Kevin Ambrose

Clarification: In the interest of full disclosure, we should point out that a site visitor noted that the Union of Concerned Scientists climate projection map posted yesterday was based only on summer heat index. A projection based on the entire year would show a smaller geographic change.

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