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Posted at 11:00 AM ET, 12/27/2010

Weather Checker: "False Alarmageddon"?

By Jamie Yesnowitz

Weather Checker is an outsider's analysis of CWG's forecast accuracy. See previous Weather Checker posts.

Snowfall totals in D.C. metro region on Dec. 26 from NOAA. Capital Weather Gang initially forecast 3-6" (Saturday afternoon) for immediate metro area, before lowering to 1-3" (Sunday morning) and ultimately a trace to two inches (midday Sunday)

After the historic snow last season, it seemed too good to be true (for snow lovers, at least) that yet another significant snow event was going to hit the DC area yesterday. And ultimately it was, defying the predictions of most forecasters, including the Capital Weather Gang.

First, there is no disputing that CWG expended an amazing amount of energy in covering the storm that ultimately lacked energy inside the Beltway. Their less than accurate prediction certainly couldn't be attributed to lack of effort. Technical guidance from Wes Junker, the CWG's new winter weather expert, and real-time updates from Jason Samenow late into the night on the two days prior to the storm while watching new model runs come out, showed the seriousness with which CWG performs its mission, and added significant color to the story.

Likewise, the continual chatter in the comment boxes by all of the members of CWG supplementing Jason and Wes' commentary was very helpful. If the content produced by CWG on this particular storm is anywhere close to representative of what future storms will bring, then Washingtonians will be treated to top-of-the line analysis that simply cannot be found in other cities. Of course, additional analysis from CWG leads to an enhanced risk that something said will be amiss, and may lead to over-thinking the result of a storm by twisting with each model run, which seems to have happened here.

The genesis of "False Alarmageddon" on the long-range models was picked up by CWG at least one week before the storm. The Snow Lover's Crystal Ball on Dec. 19 contained the following quote from Wes Junker regarding the models: "This is a rare storm where we can have 50% probability five days in advance of at least 1 inch of snow falling. Models are in unusual agreement."

Forecasts on Dec. 20 and Dec. 21 pegged the likelihood of an accumulating snow (1" or more) on Saturday into Sunday at 55%, with a 20% chance of a significant snow (4" or more). The probabilities did not appreciably change on Dec. 22 (50-60% of an accumulating snow, and a 20-30% chance of a significant snow, except that the timing of the storm was pushed back to a Sunday to Monday event. On Dec. 23, CWG's measured probability of snow actually fell considerably, to 30-40% for an accumulating snow, and 10-15% for a significant snow. The SLCB on Dec. 24 tweaked these percentages to 30% and 15% respectively. So less than 48 hours prior to the start of the storm, the analysis seemed to be "dead on," suggesting that a miss to the east was very likely.

If the forecast had stayed the same from that point on, I think that the CWG would have been universally commended for its call. The problem was that several of the models looked considerably more promising from a snow perspective on each run, and Jason gradually pushed the odds of accumulating snow to 60-65% and the odds of significant snow to 35-40% by 1:20 a.m. on Saturday. Still not an indefensible call considering the result - a miss on the accumulating snow prediction, as by and large, places inside the Beltway did not receive an inch of snow, but not necessarily a miss on the significant snow prediction (less than 50% likelihood means the event still is a no go). My thought was that if a snow map were issued at that time, a 1-3" prediction would have been supportable.

By 10:30 am on Saturday, however, the odds of accumulating snow were raised to "better than 70%" and the odds of significant snow crossed the 50% threshold. At 1:15 pm on Saturday, a snow accumulation chart was formulated, and basically suggested that anything from a dusting to a snowstorm was possible, with 3-6" the most likely result.

The original snow map, which was released at 3:55 p.m. on Saturday, again suggested that the entire DC metro area would receive 3-6" of snow, with lesser amounts north and west, and greater amounts north and east toward the other major I-95 cities.

With respect to the timeline, CWG expected that there was a fair (40%) chance of light snow on Saturday night, and that light to moderate snow would last practically all day Sunday. When the forecast timeline was originally released with details on the intensity of the storm, I was somewhat concerned that it is normally very difficult to get 3-6" of accumulating snow during the daytime in this area with marginal temperatures (even in December, when the sun angle is at its lowest) without a fair amount of moderate or heavy banding, especially when starting without any snow cover.

On Saturday evening, seeing that the snow was not going to start until Sunday morning at the earliest and that some of the models were backing off amounts, CWG noted that the snowfall amounts were likely to be on the low end of the 3-6" range.

However, the accumulations for the storm were not lowered until after 9 a.m. on Sunday, when it was clear that the storm was only going to brush the D.C. metro area, at best. The revised accumulation map put the D.C. metro area in the 1-3" range, with higher amounts a few miles east of DC and Baltimore, and practically nothing west of Warrenton and Charlottesville. While many of the snowfall amounts well away from D.C. verified (Eastern Shore, Delmarva Peninsula), the snowfall in the immediate D.C. metro area did not reach the 1" threshold.

So overall, not a good result, even though CWG walked back the optimistic 3-6" prediction by Sunday morning. On the positive side, it should be noted that CWG never raised its confidence level on the storm above "low-medium," and plenty of cautionary language was used whenever the potential for large accumulations was raised. In the CWG frequently asked questions section following the issuance of its team forecast, the significant possibility of lower and higher snowfall totals than forecast was discussed early and often. And it might provide cold comfort that none of the media outlets called this one correctly for D.C. But this storm really calls into question the reliability of the models, and one question that CWG might want to consider in their internal post-mortem on the storm is how much weight CWG should put on these models in the future.

About the author: Jamie Yesnowitz has been interested in the weather since he rooted for school-closing snowstorms while growing up in Brooklyn and East Rockaway, N.Y. After graduating from Dartmouth College with a bachelor's degree in economics and government, his focus on the accuracy of weather predictions took hold when he moved to Coral Gables, Fla., to attend the University of Miami School of Law. Class was scheduled to begin on August 24, 1992. Hurricane Andrew had other ideas, however, shutting down the school for weeks. But what stuck in Jamie's mind was the final unpredicted swerve of the eye that saved those living in Miami and points north, and completely devastated areas about 20 miles south of Miami.

Undeterred by the hurricane, Jamie ultimately served as editor-in-chief of his law school newspaper, and earned both a juris doctorate and master's degree in taxation. Following law school, Jamie practiced corporate and securities law in New York before shifting to the state and local tax consulting world. Jamie moved from New York to the Washington area in 2003, and he is presently a state and local tax senior manager at a major accounting firm. Jamie lives in Potomac with his wife, Sandra, and their two daughters, Sarah and Carly.

By Jamie Yesnowitz  | December 27, 2010; 11:00 AM ET
Categories:  Capital Weather Gang, Latest, Weather Checker, Winter Storms  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: No-mageddon: The Washington, D.C. snow hole
Next: Blizzard blasts coastal cities from Va. to Mass.


Honestly I think the forecast was right on. I personally think the CWG did a great job predicting the storm's overall behavior. Asking them to predict with accuracy the amount of snow that one particular location on the very edge of the storm would get is frankly not realistic.

From the very beginning we were told by the CWG that we were going to be right on the edge of the storm. If the storm track was a few miles west we would get buried, but if it was a few miles east we could get nothing.

And that is exactly what happened. The storm track was a few miles east, so DC got a dusting, while locations no more than 50 miles east of DC got several inches of snow.

I'm not an expert, but I would think that predicting where exactly is that edge going to be is pretty tough since it requires an amount of precision that today's instruments simply cannot provide.

Look at other places like Boston or NYC, the forecasts for them were really accurate.

Just my two cents anyway.

Posted by: dantebouchot | December 27, 2010 11:15 AM | Report abuse

Thanks to jaybird926 for the poll idea - which I adapted and inserted into Jamie's post.

Posted by: Jason-CapitalWeatherGang | December 27, 2010 11:16 AM | Report abuse

And by the way, I voted None. It is what it is. Eventually the models got it right. The day we invent a time machine we can drop the models and complain about time travelers not being 1005 accurate in their predictions. For now we will just have to deal with the fact that Nature is unpredictable.

Posted by: dantebouchot | December 27, 2010 11:21 AM | Report abuse

Am I a bit disappointed in the outcome? Yes.

Am I impressed with the work and analysis that was done? Yes.

If one thinks about the limits of precision of models in general, then the information of the ensemble models provided, the analysis they allowed, and the "fit" to the actual progression of the storm was really quite good.

The CWG staff and the community members do amazing things. I'm hard pressed to name another weather resource as comprehensive as CWG (including Weather Underground).

Posted by: scory | December 27, 2010 11:28 AM | Report abuse

Anyone disappointed with the coverage of this storm by CWG was not reading carefully enough. From the beginning, CWG cautioned that it was just about impossible to have any confidence in a sure forecast. The edge of the storm would be too close to call.

Those who changed travel plans did so to prevent a possible problem, but it was a gamble all along, as was cautioned frequently by CWG staff when questioned about projected travel conditions. I can remember repeatedly seeing "use your own judgment" in the comments.

I, for one, know that the most accurate and up to date information is right here at CWG. I am a devoted follower-- this site is first to be opened as I boot up each morning. Thanks, CWG, for your dedication and passion for the weather. You are awesome.

Posted by: scienceteacher3 | December 27, 2010 11:28 AM | Report abuse

CWG is by far the most informative and valuable weather source in the Metro area. The other posts are correct if you read from the beginning. Confidence is key in gauging the weather that will actually come to bear.

My relatives ended up staying an extra day or two because of the possible weather issues (not my number one choice) but better than driving down I-95 to dig them out.

Looking forward to the 50s, now that is the way to ring in the New Year! Thanks again and I will keep reading. pap

Posted by: papoling | December 27, 2010 11:40 AM | Report abuse

To echo what I said in a previous thread, if you watched Mosaic on Saturday evening, the low was not on a track that would bring a big snow to Washington. As the low moved almost due eastward across the northern Gulf, towards NE Florida it was too far south by about 50-75 miles. Historically, the big storms often move across southern Alabama and Georgia and then blow up when they reach the Atlantic Ocean. This one arced too far to the SE.

The Sunday a.m. Wash Post print edition was equivocal and in doing so called it right.

Posted by: JerryFloyd1 | December 27, 2010 11:40 AM | Report abuse

Poll is a good idea, but none of the options are for me. It's more complicated than that. On one hand I understand the variability in forecasting certain storms, but on the other hand this storm really opened my eyes to the stubbornness in short term forecasting which is what ultimately upset people with this storm. Once totals were put out by many stations, especially local TV stations and the NWS, they were reluctant to change, for reasons I hope aren't dissonance or media hype.

So for me I feel the same but different.

Posted by: bbirnbau | December 27, 2010 11:48 AM | Report abuse

I think the CWG did a great job in keeping us up-to-date every time a new model or forecast was released, with plenty of information on both the uncertainties and caveats of the wildly fluctuating forecasts. In the end, the only thing they may have erred on was that they leaned on the high-end of the snow forecast in the 24 hours leading up to the event, but then again, nobody in the meteorology business really had a handle on this system. If anything, this storm may help improve the way models forecast explosive Nor'easter development and tracks.

Posted by: marklandterrapins | December 27, 2010 11:52 AM | Report abuse

Oh and I want to reiterate what other people have said; this is BY FAR the best place to receive information in the metro area. No where else does a forecasting team provide information that is so in depth, catering to weather novices as well as us geeks out there who demand scientific discussion. No matter the outcome of this storm, the intentions are there. Good job guys.

Posted by: bbirnbau | December 27, 2010 11:53 AM | Report abuse

This no-storm did change my opinion of local snow forecasting.
It has turned out to be even more hilarious than previously suspected.

So sorry everyone's holiday weekend was in some way hosed by weather.

Posted by: FIREDRAGON47 | December 27, 2010 11:55 AM | Report abuse

It did snow almost continuously from mid-morning until nightfall...only problem: the snow here was so light that little accumulation occurred.

I'm still putting some blame on my light dance schedule...possibly a dance at Glen Echo for New Year's Eve, another dance a week later on Jan. 7 at the Elks Lodge. Next Tuesday night dance, as I posted separately, isn't until the 11th. The much-unneeded bad weather crowd is always around whenever I have a big dance event on the agenda. Look for our first big wintry-mix threat the evening of Tuesday, Jan. never fails on Clarendon Ballroom night!

Posted by: Bombo47jea | December 27, 2010 11:59 AM | Report abuse

@bbirnbau - I agree.

Hey, Here's an idea: Let's start a POLL!!
In your opinion, what is the best weather information resource in DC?

C) Capital Weather Gang

Please - - I urge everyone to vote!!!

Posted by: BobMiller2 | December 27, 2010 12:00 PM | Report abuse

If I was to grade you on your snow forecasting, it would be an A+. Why? Because it wasn't your fault that this storm was hard to predict and besides that, you even mentioned that there's a high probability of getting nada (which is what we ended up with.) Some of the people that comment on this blog have the biggest sense of entitlement I've EVER seen. They expect that you will give them a 100% accurate forecast whenever THEY want. Well I've got a news for them: CWG worked as hard as possible, day and night, and ON CHRISTMAS FOR CRYING OUT LOUD and you dare criticize them?!

Anyway, like I said, A+ for CWG!!

Posted by: BobMiller2 | December 27, 2010 12:08 PM | Report abuse

bbirnbau - I thought you were done posting here? ;-)

Posted by: FIREDRAGON47 | December 27, 2010 12:10 PM | Report abuse

In situations like this weekend, I barely even read the actual post. The real news is in the comments where the forecast is critiqued and tweaked in real time. Instead of beating yourselves up about the lack of snow inside the beltway, I really would like to know WTF would cause DC to get stuck in a snowless donut hole. I have never seen anything like that before. It's freakish. That NOAA map is almost comical.

Posted by: AdmiralX | December 27, 2010 12:15 PM | Report abuse

Jamie (a.k.a. Weather Checker) provides valid criticism, as have many of our fantastic commenters over the past day or so. And anytime forecasters predict accumulating snow (no matter how little or much) and basically don't get more than a dusting, they're going to be subject to and deserving of criticism. But one important point, I think, is that during the whole week leading up to this storm, including the final day and hours, we were mostly consistent in downplaying the chances for a major storm of 6" or more here in the metro area (at the same time some, though certainly not all, other outlets were much more bullish). -Dan, CWG

Posted by: CapitalWeatherGang | December 27, 2010 12:41 PM | Report abuse

i was as excited as anybody to return from the in-laws to see that accumulation map showing us in the 3-6" range. but...even according to that post (which referenced the previous post's "snow accumulation potential" chart) the chance of less than 1" was listed as 25%.

correct me if i'm wrong, but i don't think there was EVER a CWG prediction saying we would for sure get over an inch. keep in mind that even a 90% chance of 1" also means 10% chance of less than an inch.

Posted by: walter-in-fallschurch | December 27, 2010 12:59 PM | Report abuse

Hind sight is always 20/20. Knowing all the varibles in predicting any storm, people have 2 realize that 4casting isn't a prefect science. CWG was always consistant in stating that his storm was a tough one 2 get a handle on, & stated that they were tending 2 the light end of the amounts.
It would b great if very 4cast was prefect, but that's not the case now. The 4cast was off, but that's no reason 4 some 2 act like it was a personel affort 2 them.
The only things quarented in life r death & taxes.

Posted by: VaTechBob | December 27, 2010 1:02 PM | Report abuse

From early on when Wes Junker said that this would be a particularly hard storm to forecast and then on a continuing basis with both the relatively low confidence indicators and with the extensive discussion of disagreement between the models I had a clear sense that the final outcome would not be known until just before. On the other hand, if there hadn't been any snow at all in DC (it snowed all day at my place), I would have been disappointed with the forecast.

We are very lucky to have a dedicated weather team for DC: it even got me back to reading the Post.

Posted by: easyenough | December 27, 2010 1:06 PM | Report abuse

I would like another option on the poll:

"Not at all. As always, I will only believe it when I see it."

Posted by: ah___ | December 27, 2010 1:09 PM | Report abuse

Three post-mortem comments from me.

First, and (for me) most important. I think that the CWG coverage was superb. When the calls were made, or changed, it was always based on some reasoning that to me seemed quite plausible (note: I am a sci-tech person, and I am familiar with computational fluid dynamics, but not of the meteorology type). Extra brownie points for the dedication, *many* brownie points.

Second, the almost unanimous hopes for a massive snowfall were not my cup of tea. Although I didn't express it to avoid spoiling the general mood, I was cheering for a miss, and happy when it happened. Anyway, that's my problem, and it's not a big deal: I enjoyed the commentary anyway.

Third, maybe it's my impression, but there was more trolling going on than usual. For some stretches the conversation seemed to be monopolized by 2-3 individuals, who didn't try to contribute to the technical discussion, and whose comments did not seem to me especially witty in such large amounts. Obviously the definition of "troll" and "witty" is highly subjective, but I wish the poster's nick was placed at the top of the post, rather than the bottom, so we could skip reading as needed. Something CWG might want to think about. I'm not advocating moderation, though, or limits to how frequently someone may post.

Posted by: MikeinDC2 | December 27, 2010 1:18 PM | Report abuse

VaTechBob, you said,
"Hind sight is always 20/20."

yeah... or 50/50 if you're steve spurrier.

Posted by: walter-in-fallschurch | December 27, 2010 1:21 PM | Report abuse

@MikeinDC2 --

I concur with your third point. One person in particular, whom I had not seen here before this weekend, was posting remarks such as "I'm going to fix breakfast now!" and "What should I fix for breakfast?" as if this were a chat room. Tiresome indeed.

Posted by: natsncats | December 27, 2010 1:28 PM | Report abuse

@natsncats and @MikeinDC2

During major weather events, the comment area can become a bit like the Wild West and due to the volume, it becomes tough to moderate especially when we're trying to do rapid updates (and post stuff to Twitter, Facebook etc) and coordinate coverage.

Having said that, we do have a big team, and we'll try to do better with this next time.

Posted by: Jason-CapitalWeatherGang | December 27, 2010 1:40 PM | Report abuse

As someone who's followed storms for several years now, I can say this was a toughie. I think we needed a Jan 2000 track for this storm to verify. Instead, it was judge NE enough to spare central md from significant snows. This was also a very compact storm. You'd also want to see more overruning out ahead of it when the storm was in Texas...instead it seemed to dry out from the disturbance to the north. It did seem like the models towards the end trended enough east to really spare us...I think the NAM painted a pretty clear picture of the potential for "bust" here (which basically had the bulk of the QPF confined to the coastal areas)...although it did overestimate the QPF here (that's probably what caused the busted forecasts). What can ya do??? Live and learn, at least until the computer models can catch these subtleties

Posted by: swishjobs | December 27, 2010 2:08 PM | Report abuse

One thing I greatly appreciate is the honesty from the CWG team and an explanation of how forecasts are derived (some of the users have helped as well). It is curious how things were all over the board on Friday/Saturday.

All of your efforts on the holiday were greatly appreciated even if in the end the storm did not deliver what might have been expected.

I also appreciate the honesty in the post-mortem regarding your forecast. You guys were pretty clear that this storm was clearly giving you a lot of challenges with regard to the modeling and you were clear in articulating this.

Thanks again for your efforts, now if you guys can just get these winds to calm down!

Posted by: jcurrin | December 27, 2010 2:14 PM | Report abuse

...and one more thing, I find this blog to take a while to post's slow on my home and work computer. Just a heads up, although I'm sure you guys know that by now.

Posted by: swishjobs | December 27, 2010 2:16 PM | Report abuse

Honestly I had a blast following all the information you guys posted for us snow lovers. I felt kind of bad for you guys because it was a holiday, but your site was without a doubt the go to place for information on this storm. I really like the way you translate the technical stuff for us and explain your thoughts on what it means. I get lost on some of the other weather sites because I'm a novice, but when you explain it I learn something. I think you guys did a fantastic job and I really appreciate your efforts.

Posted by: alpal3 | December 27, 2010 2:26 PM | Report abuse

Thank you for your diligent work, CWG. Your forecasts conveyed an adequate level of doubt in this storm's path while fully expressing the storm's potential. It's a tough line to walk, and you did it admirably.

Posted by: mason08 | December 27, 2010 2:47 PM | Report abuse

I concur with your third point. One person in particular, whom I had not seen here before this weekend, was posting remarks such as "I'm going to fix breakfast now!" and "What should I fix for breakfast?" as if this were a chat room. Tiresome indeed.

No more tiresome then another regular poster commenting about their "dance" schedule - or does that somehow contribute to the technical discussion?

Posted by: Axel2 | December 27, 2010 2:57 PM | Report abuse


Thanks for including the poll, and the mention.

Posted by: jaybird926 | December 27, 2010 3:29 PM | Report abuse

Your forecast was great CWG, I think this storm was pretty hard to predict, and you stayed on top of things throughout the situation, even thought it was Christmas.

I would give you an A+ for effort, a B- for overall forecasting, because even though you were off your mark I'm willing to put some of the blame on the models and you guys were definitely stressing the point that you were uncertain about your forecast.

Great job CWG, I'll still be looking to you guys for your forecasts :).

Posted by: DelMarVaStormTracker | December 27, 2010 6:02 PM | Report abuse

Said it before, I'll say it again. This is the only hype free site out there. The forecasters here take it seriously, they admit when they're wrong and they continue to try to improve their forecasting.

Despite the computer models and all the other advances, forecasting is still a crap shoot. Mother Nature does what she will. And if you're disappointed by the weather outcome, don't blame the messengers here.

Thanks for your hard work during the holiday season!

Posted by: concepcion611 | December 27, 2010 7:22 PM | Report abuse

Having watched all the posts about the impending storm I never felt misled at all since so much of the commentary revolved around how uncertain and tough to call it was. By the time the final call was made with the caveat that totals were likely to be at the low end it was spot on for my neighborhood. The accumulation forecast map put this area at a trace to 1" (I think), and we got a trace. My respect for CWG has only grown over the past week. Thanks for the all the hard work guys!

Posted by: Chip_M | December 27, 2010 7:42 PM | Report abuse

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