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Posted at 10:30 AM ET, 02/15/2011

D.C. area snow chances decreasing, not done

By Ian Livingston

CNN reports from the National Mall on March 2, 2009. Photo by CWG photographer Kevin Ambrose.

In the middle of a milder period with more warmth to come and no real snow threats on the horizon, all while leaving the "peak" of winter behind, local snow lovers are probably feeling a bit depressed. Perhaps day after day of a Snow Potential Index of 0 has not helped matters much.

Following above average snowfall in December and January, much of the area has managed 8 to 18 inches of snow so far this season, including 9.5" at Washington and 11.9" at both Dulles and Baltimore. A vast majority of the snow came during Commutageddon. February has been quiet so far.

While near average seasonal snowfall is still within reach in many spots, we may need some help getting there as we chew away at available winter days. However, it may be that a year such as this (moderate to strong La Nina) offers more tail-end hope than others.

Before getting started, let's put to rest the idea that a warm-up in mid-to-late February is the end of winter. Plenty of snow has fallen after that period (see: 2/22-23/87, 3/13/93, 3/9/99, 3/1-2/09), and after a significant warm-up (see: 2/22/87, 3/8/93, 3/3/99, 2/27/09). It is also true that factors like increasing temperatures and sun angle play prominent roles in diminishing snow potential, but late-season storms can be quite explosive thanks to growing temperature contrasts and plenty of cold air to the north still to be tapped.

When examining the last 30-season average ending 2009-10, the final accumulating (.1"+) snowfall at Washington came during March or April exactly 50 percent of the time. The final two weeks of February account for an additional 20 percent of final snowfalls. So in 70 percent of years, there has been measurable snow following mid-February.

Number of instances of final accumulating snowfall in each month during a 30-season period beginning 1980-81 and ending 2009-10. Washington as reported at National Airport (DCA), Dulles (IAD), and Baltimore as reported at Baltimore-Washington International (BWI).

If you live away from National Airport (most people), your odds of getting more snow are even better. A brief comparison to other local NOAA observation locations shows 70 percent of final snowfalls have happened in March or later at Dulles compared to 67 percent at Baltimore. Add in another roughly 10 percent at Dulles and 17 percent at Baltimore for the second half of February.

Though I painted a positive picture (for snow lovers) above with high percentages of additional accumulating (.1"+) snowfalls to come, when looking at events that dropped snow greater than 1" at National, the 30-season (1980-81 thru 2009-10) average for each major snowfall month is 18.7 percent in December, 39.2 percent in January, 31.4 percent for February, and a measly 8.8 percent in March. November barely scraped by with 2 percent, and April was a no show.

So we are, of course, running out of time with every day that passes. The raw trend line from February through March is decidedly downhill [DCA | BWI], as the peak [DCA | IAD | BWI] of snow generally occurs from late January through mid-February at all area climate locations though there may be a secondary peak heading into March.

Enjoying the snow after the Storm of the Century in March 1993. Photo from "Blizzards and Snowstorms of Washington, D.C."

Loyal readers of CWG are aware that La Nina has been underway this winter. Some folks find it helpful to base future projections on similar ENSO (i.e. either El Nino or La Nina) phases of the past. Just beware the sample of La Ninas is small* (also, for some years prior to 1950, whether it was a La Nina and the strength are subject to debate). It also leaves out some years "close" to Nina but not quite there. Still, there is some semblance of an image in the fog. The chance of late season snow during La Nina, particularly into March, is seemingly higher than during a "typical" winter around here.

The full La Nina sample -- 14 weak seasons / 14 moderate to strong seasons -- for Washington in the list at the bottom produces a similar snow peak result when compared to "normal," with 1"+ events most likely in January. However, the sample features a more even distribution through the end of the season with 23 percent of such events occurring in February and 17.7 percent in March. In moderate-to-strong La Ninas, the events are even more "tail heavy" with the February-April period picking up a total of 46 percent of the 1"+ snows.

Number of events dropping more than 3" of snow in Washington, D.C. as recorded at National Airport by La Nina strength. There are 28 seasons in total (14 weak, 7 moderate, and 7 strong) not including any numbers from the current La Nina.

Examining 3"+ and 5"+ inch events, the idea that La Nina March may contain greater-than-normal snow opportunities appears again, though the overall sample of events is increasingly small, and many of the bigger snows were long ago (pre-1950). Not to mention that strong Ninas appear to have less "big" snow overall than other types.

During the 30-season period ending 2009-10, 3"+ snowfalls during March made up 9.6 percent of all snowfalls for any month and 5"+ March snowfalls made up 12 percent of all 5"+ snowfalls. Moderate-to-strong La Nina March runs 31.6 percent (tied with January for most) on 3"+ events and 28.6 percent (tied with Jan. and Feb.) for 5"+ events.

Recent moderate and strong La Ninas have proven either futile for late season snow or abundant. In the moderate La Nina of 2007-08, D.C. recorded its final snow on February 20 with 1" at DCA. The strong La Nina of 1999-2000 concluded with .4" on February 18. Another moderate La Nina, this time in 1998-99, brought 8.9" to D.C. during 3 events from late February through mid-March with the majority (8.4") falling on March 9.

If there are any immediate conclusions to be drawn, it seems the odds are historically quite good to see the ground whitened again, especially if you live at an elevation greater than National (which is pretty much everybody!). How white the ground ends up is another matter entirely.

What do you think? Does the recent trend of less snow at the end of the season hold or does La Nina try to send some late-season magic our way?

* La Nina events in the overall sample: 28, 14 of which are moderate or strong. Weak: 1903-1904, 1908-1909, 1910-1911, 1924-1925, 1938-1939, 1950-1951, 1956-1957, 1962-1963, 1964-1965, 1967-1968, 1971-1972, 1974-1975, 1995-1996, 2000-2001; Moderate: 1909-1910, 1933-1934, 1942-1943, 1954-1955, 1970-1971, 1998-1999, 2007-2008; Strong: 1916-1917, 1949-1950, 1955-1956, 1973-1974, 1975-1976, 1988-1989, 1999-2000.

By Ian Livingston  | February 15, 2011; 10:30 AM ET
Categories:  Latest, Local Climate  
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Next: Amazing U.S. snow cover retreat in six days


"So in 70 percent of years, there has been measurable snow following mid-February"

*nods head, waves shovel*

Posted by: FIREDRAGON47 | February 15, 2011 11:01 AM | Report abuse

Nice work!

Posted by: wjunker | February 15, 2011 11:09 AM | Report abuse

The information in this article was very comforting. Thanks!

Posted by: Snowlover2 | February 15, 2011 11:23 AM | Report abuse

Oh well...I'm just waiting for tornado to "officially" open on the plains for the season and reading Reed Timmer's/TVN's tweets.

Thanks for keeping the snow hope alive however.

Posted by: kygurl94 | February 15, 2011 11:26 AM | Report abuse

*licks crumbs up off the floor and looks up for more*

thanks ian. lots of reason for hope there - at least in a generic sort of way. i think that data also supports the idea that march gets disproportionately big snows - even in nina years.

Posted by: walter-in-fallschurch | February 15, 2011 11:27 AM | Report abuse

I'm done with winter, so I decline your offer. Thanks, anyway.

Posted by: oldtimehockey | February 15, 2011 11:53 AM | Report abuse

Here are the issues I see...not counting Punxsatawney Phil(!):

1] It IS past the peak of winter...and this warm spell may have spoiled the "Holy Grail" of a cold meteorological winter across the board from December 1 to March 1. We could actually have a WARMER THAN AVERAGE February!

2] We still need about 6 to 10 inches of snow to reach AVERAGE snowfall for the season [something predicted by CWG in their winter outlook last November].

3] Presidents' Day weekend figures to be snow-free, always a bummer in my book.

4] Finally, although accumulating snow in March does happen, it's harder to achieve; the temperature rarely stays below freezing during the day, the ground is usually above freezing and even if we're lucky enough to get something like the 1993 Superstorm, it never stays all snow if you are too close to the Potomac. There's just too darned much warm air advection! People forget that, during the Superstorm, we in Arlington County got several hours of sleet and nasty cold rain at the height of the storm, cutting accumulations dramatically.

It is true however that thundersnows can happen more often in March if the setup is right. We're on the cusp of spring and occasionally thunderstorms move north and west of the rain/snow line, leading to heavy bursts of thundersnow or thundersleet in favored areas.

Posted by: Bombo47jea | February 15, 2011 12:01 PM | Report abuse

Posted by: KRUZ | February 15, 2011 12:04 PM | Report abuse

Apparently the EURO is showing a warmer than average March as well. And even has the rain snow line for next weeks storms much further north than the GFS has it at I 80.

I guess technically we could say snow chances arent done until sometime in april as we have had snow in april. But at this point, it seems unlikely to me. If we make it out of next week without snow, i personally think we are doneski!

Next weeks late storm looks huge on the models but just like most storms this winter it looks like a storm for the north. Much the way early weeks storm looks.

I would love to hear CWG's thoughts on all the latest EURO outputs, apparently they are looking mighty warm!

Snow chances will be around until april but that doesnt mean it will actually snow any amount worth mentioning.

Posted by: KRUZ | February 15, 2011 12:30 PM | Report abuse

I don't care if we see any snow the rest of the year. Ian, that is the best article I have read this year. You guys at CWG continue to impress. Just kidding about no snow, I want 10 feet!

Posted by: dannythe357 | February 15, 2011 1:23 PM | Report abuse

Don't see anything thru the rest of this month but mostly above average temps & below average prec. Once March arrives I'm done with winter, even if it does snow in March it quickly disappears.
Really need a wet spring or we could be looking at another drought this summer. Rivers r already experiencing below average flows, & unfortunetly, as long as, La Nina remains mod-strong the dry conditions will probably continue.

Posted by: VaTechBob | February 15, 2011 1:53 PM | Report abuse

Kruz, I don't totally disagree with your sentiments. In my mind winter (or the snow part of winter) is pretty much done in D.C. at least once we hit March. That said, I think there is reason for "hope" based on the numbers. There is a big difference between March and April. April has not produced anything of real note in some time.

Posted by: Ian-CapitalWeatherGang | February 15, 2011 1:56 PM | Report abuse

dannythe357, thanks for the comment.

Posted by: Ian-CapitalWeatherGang | February 15, 2011 1:58 PM | Report abuse

Well I guess i'm going to probably make the snow haters' day. These numbers are great and obviously a good tool to look at BUT the problem with the numbers are that in a normal La Nina year the storm track is different and the pattern is different than what we have seen for most of the winter. Over the last 2 weeks, we have finally seen a La Nina flow and thus if we make it out of next week without seeing a secondary low pressure form a long a stalled front to the south. Most likely though, the Bermuda high will continue to rear its head and significant snow is over south of the Mason-Dixon line.

Posted by: wb1313 | February 15, 2011 2:15 PM | Report abuse

Apparently there was one year in which no measurable snow at National fell after December. When was that?

On the other side of that graph, I can't recall ever having a truly measurable snow in this area in April. Whatever is in the graph must have been "traces", "dustings", or whatever they're called, which, in my personal opinion, don't really count.

Posted by: mkarns | February 15, 2011 2:32 PM | Report abuse

mkarns, 1997-98 had the only accumulation at DC in December of .1". There were 17 other days with a trace of snow that winter. Anything listed as accumulating snow is at least .1" which does not include traces.

Posted by: Ian-CapitalWeatherGang | February 15, 2011 2:46 PM | Report abuse


on these other La Nina years what were the temps like dec thru feb?... because we were well below average much of this winter even as far back as dec 1. i could believe there is hope for snow if the past couple of months werent as cold as they have been.

did any of those years resemble this one temps wise?... because i cant recall a winter in the past 10 years or so where it was below average cold for so long (daytime highs in the 20s). if we were goin into march with average or even above average temps this winter i could buy into a
snowy march but with as cold as its been up until this week it just seems to me the pattern will change to a warmer one, not colder as it has been since dec 1.

Posted by: KRUZ | February 15, 2011 3:09 PM | Report abuse

As much as I like snow, at this point, as long as something wet falls, I'll take it. Otherwise, the "d" word (drought) will begin to be heard throughout the area. Another summer like last year and I'm going to have to reconsider my 30-year vegetable gardening streak.

Posted by: petworthlad | February 15, 2011 3:21 PM | Report abuse

are you saying that because it was colder than normal earlier in the winter, it won't be cold in march? as if the winter is "trying" to "even itself out"?

it doesn't work that way.

but, a more convincing argument, unfortunately against snow, is the recent "flip" in the jet stream (see jason's awful-for-snow next post) to apparently a more la nina-like path.

Posted by: walter-in-fallschurch | February 15, 2011 3:44 PM | Report abuse

KRUZ, I'll have to look at the temps and report back this evening. I don't have all the data on my current computer right now. When I last looked (about a week ago) at how we were running for "general cold" rather than extreme cold etc, we were about even with 00-01 which was a weak Nina.

As a snow lover I would rather have seen this flip warm a few weeks ago instead of now. Usually it seems these flips last about 10-14 days if not longer. Obviously looking for a cooldown that produces a lot of snow is more difficult in March than February.

However, Nina often has more blocking (-NAO) at the end of the season than during most of the season.. tho this year we had plenty of blocking early that did not necessarily help too much on the snow front at least. Right now there are no major signs that a prolonged -NAO is on the way back though it could show up here than there.

Posted by: Ian-CapitalWeatherGang | February 15, 2011 3:56 PM | Report abuse


from my understanding the jetstream will be all over the place next week because of how unstable the atmosphere will be. cold up north, hot down south.

im not saying that winter is trying to even itself out, im just basically saying that the best of what winter had came and went faster than it should and theres just not much left. winters back is broken as HM said.

Winter in a way pre-mature EJ@$^&**%# ;)
I think you get my drift!?!

But yeah, i know theres really no particular method to weathers madness but i think the snow train has ran its course for us.
Its been hard getting snow all winter long here in DC, and now with the cold air lost to our south its gonna be even harder to get snow now and considering we havent gotten very much so far this winter:/

Posted by: KRUZ | February 15, 2011 6:09 PM | Report abuse

well, here's to the jet stream flipping again next week - or at least varying wildly...

Posted by: walter-in-fallschurch | February 15, 2011 6:38 PM | Report abuse

Topper Shutt just uttered the sweet sweet words.... "It could be over, we'll see" After he gave presidents days forecast of mid 50s and possible rain showers!

Posted by: KRUZ | February 15, 2011 7:23 PM | Report abuse

Nice analysis....looks like biggest March storm you have listed was "storm of the century" in 1993, which certainly was an outlier as far as March storms go. So historically, we are looking at chances for a significant storm for the next 2-3 weeks at best. Could always snow after that, but my experience in 25 years of living here is any snow after that does not amount to much and quickly melts--sometimes the same day. Seems like the weather pattern would have to flip pretty dramatically now for a big, or even moderate snow by end of February.

Posted by: weatherdude | February 15, 2011 8:35 PM | Report abuse

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