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Posted at 11:30 AM ET, 12/ 7/2009

The snowy legend of Dec. 5 continues

By Andrew Freedman

* Two more wintry threats: Full Forecast | Climate e-mail interviews *
* Report your snowfall total to CWG | View submitted snow totals *


A snow-lined sidewalk on Saturday in the District. By CWG's Ian Livingston. How much snow did you get?

December 5th came through again for D.C. area snow lovers.

As Frank Roylance of the Baltimore Sun noted on his blog on Nov. 29, before this year it had snowed in five of the last seven years on Dec. 5 in the Baltimore/Washington region, as measured at BWI Airport. True to recent form, the Washington area's first snowstorm of the 2009-10 winter season occurred on Saturday, Dec. 5, with area accumulations ranging from less than an inch in parts of D.C. and some spots south and east of the city, to between 6 and 8 inches in far northern Montgomery County and well west of town.

Memo to the staff of the Old Farmer's Almanac: start forecasting snow on Dec. 5, instead of "rain[y] and mild" as they did this year.

I have no doubt that CWG would have been laughed at and viciously criticized in our comments section had we issued an official forecast for "a dusting to 8 inches." But that's pretty much how the accumulations worked out across the area, with the lowest amounts recorded in urban centers such as downtown D.C. and Baltimore, and higher totals in more rural locations and higher elevations.

Some spots, like Harrisonburg, Va., out west in the Shenandoah Valley and home to James Madison University, did better than most, with eight inches recorded according to the National Weather Service. Compared to that, D.C.'s official reading of .2 inches at National Airport was downright pathetic. The proximity of the relatively warm waters of the Potomac River didn't help the airport's effort at recording a respectable snow total, but that doesn't make it less lame.

According to our reader-submitted snow totals, a jackpot of 9 inches was reported near Front Royal, Va., and Herndon and Vienna did quite well too, with about 5 to 6 inches. A reader in Bethesda submitted a measurement of 3 inches, and readers confirmed that amounts declined to a sloppy trace downtown and to the southeast of D.C.

Why such a huge disparity in accumulations, you ask? As CWG forecasters noted several times throughout the event, the accumulations at each location were heavily dependent on the snowfall rate and temperatures at/close to the ground. The heavier it snowed, the easier it was to overcome initially warm temperatures. Subtle differences in temperature mattered a great deal.

Heavier bands of snow set up just to the west and north of the District and took a while to get into the city, and temperatures in the concrete jungle of urban areas remained just above freezing for much of the event, precluding much lasting accumulation.

Oh well. D.C. snow lovers still have the rest of this winter to look forward to (officially it's not winter yet anyway, although meteorological winter started on Dec. 1). And if we don't get any more snowstorms, don't fret too much. There's always next December 5th.

By Andrew Freedman  | December 7, 2009; 11:30 AM ET
Categories:  Freedman, News & Notes, Winter Storms  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   Del.icio.us   StumbleUpon   Technorati   Google Buzz   Previous: Forecast: Two more wintry threats to watch
Next: PM Update: Next storm arrives late tomorrow

Comments

This weekend's GFS: The storm center appears to form well to our south, off Myrtle Beach/Savannah, though the precipitation field seems to extend well north into the Mid-Atlantic. We should see at least some light to moderate snow up here.

If the storm moves offshore to the east, any precipitation may end quickly.

BTW all remaining Redskins games this year are late-kickoff events, with one Monday night game. No more of this 1 PM stuff, and no postseason for us.

Posted by: Bombo47jea | December 7, 2009 12:46 PM | Report abuse

There was actually measurable snow (ignore "trace" in 2006) in just 4 out of the last 7 years on December 5th (trace amounts are hardly meaningful to so snow fans).

If one forecasted measurable snow based on a coin toss coming up heads on each of those seven Dec 5ths, there would be a 27% chance it would snow four of those years. The chance for snow on the 8th year (this year) on Dec 5th (5 out of 8) was 23%. Not bad odds especially if the forecast were long range.

There is a 16% chance the trend will continue with snow on Dec 5th 2010. Before building up hopes for a repeat, this also means there's an 84% chance of no snow on Dec 5th next year

Posted by: SteveT-CapitalWeatherGang | December 7, 2009 2:15 PM | Report abuse

Can anyone explain why DC official precip totals and temps are recorded at National, where it is always a little warmer and almost always gets less snow?

Posted by: lilymama | December 7, 2009 3:27 PM | Report abuse

SteveT, I think what you wrote is correct if you were predicting the run before its beginning seven years ago... but using the coin flip method (assuming we have a fair coin), next year would still be 50%. In other words, how past years' coins turned out shouldn't impact next year's metaphorical toss.

Posted by: spgass1 | December 7, 2009 4:49 PM | Report abuse

spgass1

Your are correct if next year were totally independent (50/50). The probabilities I gave are CONDITIONAL on the SEQUENCE of 4/7 continuing to 5/8!

Posted by: SteveT-CapitalWeatherGang | December 7, 2009 5:11 PM | Report abuse

Trying to downplay the snow, Andrew?

This is almost too embarrassing to watch.

Mr. Q.

Posted by: Mr_Q | December 8, 2009 9:14 AM | Report abuse

SteveT: I agree with spgass1. If you've already observed 4/7, then going to either 5/8 or 4/8 should have the same probability distribution as 1/1 versus 0/1 _unless_ there is some physical reason to believe that you are "depleting" December 5th snow days. (eg, if you are drawing from a bag that starts with equal numbers of black and white marbles, if you pull several black marbles in a row, the probability of a white marble increases)

Posted by: marcusmarcus | December 8, 2009 4:13 PM | Report abuse

I am no fan of Dr. Tracton. Point of fact, I don't hold a very high opinion of him. Quite the contrary. I have made that excruciatingly obvious for anyone who is a regular of this blog. But I am a HUGE fan of truth and clarity.

Dr. Tracton stated,
... in just 4 out of the last 7 years on December 5th ...
and
... based on a coin toss coming up heads on each of those seven Dec 5ths ...
and
The chance for snow on the 8th year (this year) on Dec 5th (5 out of 8) was 23%.

After making it abundantly clear that he was referring to the odds in a serial/cascading manner, he then made the following unfortunate statement,
--begin quote--
There is a 16% chance the trend will continue with snow on Dec 5th 2010. Before building up hopes for a repeat, this also means there's an 84% chance of no snow on Dec 5th next year
--end quote--

Clearly, his poor choice of words and lack of punctuation not withstanding, he obviously meant -
--begin quote--
There is a 16% chance the trend will continue with snow on Dec 5th 2010 (6 out of 9). Before building up hopes for a repeat, this also means there's an 84% chance of no snow on Dec 5th next year (the opposite/inverse odds of 6 out of 9)
--end quote--

I hope we can all put down our extremely anal book making program if only for the evening, and welcome Dr. Tracton with the good grace both he and we deserve. ;)

Mr. Q.

Posted by: Mr_Q | December 8, 2009 11:47 PM | Report abuse

The comments to this entry are closed.

 
 
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