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Posted at 11:45 AM ET, 01/18/2011

Reviewing a slippery forecast & photos

By Jason Samenow

An icy road in Fairfax, Va. Submitted by Rich.

Another difficult to predict winter storm in 2010-11 has come and gone. So how would I evaluate our forecast effort?

I actually think we did pretty well with this one. Yes- we missed some important details - mainly underestimating the extent and duration of cold air at the surface. But we identified the potential for a wintry mix of precipitation well in advance and correctly characterized the timing and evolution of the storm.

Keep reading for a self-evaluation of our forecast and enjoy the photos submitted by CWG readers and Twitter followers....

A frozen lamp post in College Park. Submitted via Twitter by garthmoore.

* On Friday, Wes wrote about how the overall pattern was bad for snow but did not rule out a wintry mix. He wrote: "...enough residual cold air may remain across the region to allow for a brief period of snow, sleet and/or freezing rain when the precipitation begins early Tuesday morning, particularly west of the city." At the time, he indicated it was likely the mix would change to rain - which turned out not be true - but none of the models at the time showed a coastal low forming to our south (and that it would pass to our east) which turned out to be key helping keep the cold air in place

A frozen weather station in Lorton, Va. Submitted by Jamie, aka LortonWeather on Twitter.

* By Saturday, recognizing the coastal low may keep the colder air in place longer, Ian wrote: "As precipitation chances increase, cold air could hold on long enough to keep parts of the area near or below freezing into the night. All precipitation types are in play, though a transition from brief light snow to sleet and rain (or freezing rain) seems possible." That was pretty spot on.

* On Sunday, I did an analysis of the situation and wrote: "the stale cold air that's in place Monday will be slow to erode Monday night and Tuesday as long as winds remain from the north." I concluded: "The bottom line is that models suggest light to very light amounts of precipitation, but enough cold air may stick around for a frozen mix Monday night into Tuesday morning, especially north and west of the District." Of course, precipitation amounts ended up being more in the light to moderate range and cold air was more pervasive than I anticipated. But I was on the right track.

* On Monday, I prepared a detailed forecast of what to expect by geographic zone. In the north and west zone (Zone 3), I pretty much got it right - indicating some accumulating snow followed by substantial ice. In the central zone (Zone 2), I got the amount of snow right (dusting to 1") and correctly predicted a change over to ice. However, I initially (at 1:30 p.m.) incorrectly indicated the ice would change to rain overnight. At 5 p.m., I did post an update indicating precipitation may end up remaining ice through morning. Also, in all of our evening updates (starting at 7:30 p.m.), Dan indicated that would be the case. Our biggest failing was in the eastern zone (Zone 1). Although we correctly indicated little or no snow there and said there would be freezing rain and sleet, our prediction for a fairly rapid changeover to rain did not occur, except perhaps right along the Bay. My forecast that "a few icy spots can't be ruled out in normally colder locations if temperatures are stubborn to warm overnight" was clearly an understatement. Across all the zones, we got the start and end time about right.

* In summary, the forecast was about right with the important error of underestimating the extent and duration of the cold air. While it's true the models didn't simulate the extent/duration of cold air, we can't use that as an excuse. We knew very well from the past models that don't handle these kind of events well. We did account for that, but not enough.

So that's my take. How would you grade us? Vote below...

By Jason Samenow  | January 18, 2011; 11:45 AM ET
Categories:  Capital Weather Gang, Latest, Recaps, Weather Checker  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Forecast: Very icy morning, unsettled week
Next: Snow/mix chance returns Thurs. night & Fri.


Constructive criticism welcome -- let us know what you think!

Posted by: Camden-CapitalWeatherGang | January 18, 2011 11:59 AM | Report abuse

even though i live in zone 1 (where there's still no sign of melting) i gave you a "B" for admitting the underforecasting for that zone and being pretty accurate for the others, please keep the zones going for tonite/tomorrow morning!

Posted by: luvhh | January 18, 2011 12:01 PM | Report abuse

You all did very well with this storm. There are some folks on here who will try to be disruptive say it was a bust and why didn't it rain and yada yada yada. I for one think you forecasted this storm better than any other media outlet in the DC area.

PS the photos are great too!

Posted by: BobMiller2 | January 18, 2011 12:03 PM | Report abuse

I give you credit for knowing last night that it wasn't going to warm up and change over to rain during the nightime (post midnight - 3 a.m.)
A forecaster on NBC actually said by 3 a.m. it would all change to rain and rush hour would be fine.

Posted by: tryingtochill | January 18, 2011 12:09 PM | Report abuse

As a zone 1 resident I gave you guys a B on this tricky forecast(because an A- isn't an option here). The only reason it wasn't an A was instead of coming out and finding a wet car to get into this morning,I spent a good deal of time unexpectedly chipping the ice away. But hey, this is mother nature...all we mere mortals can do is guess at what she is up to!

Posted by: ftwash | January 18, 2011 12:18 PM | Report abuse

I'm guessing the one vote for F was from the sourpuss in the last thread...

Posted by: natsncats | January 18, 2011 12:20 PM | Report abuse

My primary interest in a weather forecast is to know what conditions I'll see when I go outside. From that perspective, this forecast missed the mark. Zone 1 ice was supposed to be long gone by 7am, and it's still in place now. It may have only been one factor that didn't verify (late rain), but it made an enormous difference in conditions.

That constructive criticism aside, I also enjoy CWG for the detailed discussions about all the factors that go into the final analysis, and it appears you got a lot of these right. I also echo luvhh's appreciation for the zone forecasts -- keep them coming. Thanks.

Posted by: mmurphy70 | January 18, 2011 12:20 PM | Report abuse

I see the temputure is struggling to get to the frezzing mark, but I'm curirous tonight second round are we going to see more mess or this time it will will be RAIN??

What's the deal on end of the week storm??

Posted by: Michael_Nguyen | January 18, 2011 12:23 PM | Report abuse

I gave you a B because I expected there be rain when I woke up, but there was none, just a lot of ice. But the coverage was great and so was the zone forecasting idea. Keep up the great work!
Thursday Night-Friday storm-Snow lovers crystal ball any time soon? :)

Posted by: cubscapsfan | January 18, 2011 12:25 PM | Report abuse

Not bad. The evil of an ice storm cannot be hyped enough. So wish we had gotten the predicted morning spell of rain above freezing temps.
CLEAN YOUR CARS. Nearly died getting to work this last hour because of flying spinning sheets of hood ice from fellow commuters.

Posted by: FIREDRAGON47 | January 18, 2011 12:28 PM | Report abuse

I gave an A. Probably a bit overrated, but then again the weather forecast and especially the graphics were spot on. Zone 2 was pretty icy but you never know whether the govt will have a 2 hr delay or not

Posted by: mkbf26 | January 18, 2011 12:41 PM | Report abuse

I think this storm was hard to predict and you guys did a good job with the information you had.

Posted by: Anonymous123451 | January 18, 2011 12:52 PM | Report abuse

I give this one a solid B. Very good forecast in my view. Timing was spot on, as was the evolution from S to IP to ZR. The only thing that was off was the changeover to R. CAD is one of the most difficult phenomena to predict in an area that's full of difficult prediction. Models do often underestimate how long CAD will hold on - but that being said, it's almost impossible to know to what extent they've underestimated it in advance.

I had a feeling CAD might hold on a good long time for this event, simply because we don't have a transient shot of cold air in place - instead, we've had a long term cold regime in place. But that's just a layman's gut feeling and not a reliable forecasting tool :).

Posted by: jahutch | January 18, 2011 12:55 PM | Report abuse

This is neither kudos nor criticism, but rather a question. It seems to me that many of the computer models typically underestimate the strength of cold air masses in these "cold air damming" situations, in that they frequently show faster surface warming than actually takes place. Was this the case for this event as well, or did the models catch on to the slower erosion of the cold air mass as the event neared?

Posted by: afreedma | January 18, 2011 1:00 PM | Report abuse

CWG, I gave you a D. I love you guys and all but this storm was confusing to follow. You guys never predicted a full-out ice storm. It was suppose to be sleet/snow then changing to rain/freezing rain. It was mostly all freezing precip and the storm over-performed which is something you guys weren't expecting either. You guys played it to be a minor event and it wasn't. Things started changing when you started NOWcasting. I didn't feel confident about your forecasting this time around. Sorry.

Posted by: lll1424 | January 18, 2011 1:01 PM | Report abuse

Thanks for all of the feedback so far. Much appreciated.

Posted by: Jason-CapitalWeatherGang | January 18, 2011 1:03 PM | Report abuse

Tricky or not, not one forecaster called for an ice storm. THere was 1/2 of ice in Burke, VA, and the temperature was still at 27 F at 0800. When it takes an extra 30 minutes to get out the door when forecasters predict rain will be washing the snow and sleet away, you cannot get a passing grade---D from me. Other posters here are way too kind, and for some reason feel that not even getting half of the story right is worth a B.

Posted by: Russtinator | January 18, 2011 1:09 PM | Report abuse

you guys did a great job as usual. like just about everyone else, i think the "zone system" is the way to forecast this area - there's always such a contrast between what happens east of the city and west of the city, and i'm sure the zones will shift from forecast to forecast.

one suggestion: on that zone map you should show the beltway and maybe some of the other major roads - 50, 66, 95 etc... many people know where they are on the map based on their relation to those major roads.

Posted by: walter-in-fallschurch | January 18, 2011 1:10 PM | Report abuse


The models slowly caught (trended colder) on but never really got there. Temps were colder than modeled (at the surface) across the board.

Posted by: Jason-CapitalWeatherGang | January 18, 2011 1:14 PM | Report abuse

This was an ice storm. I'm in Zone 2, and I think that the basic prediction as far as precip was right until the change to rain. It's STILL not melted, even on the walk I salted heavily before I went to bed last night. People driving in around 10 am were doing so on pure ice - around a quarter inch on the road, and it didn't start melting until close to noon. And those driving in were going way too fast, I might add. I was tempted to pull up a lawn chair and watch idiots skid through the stop sign at the bottom of our hill, but it seemed morbid given the risk. People need to exercise a whole, whole lot more caution and sense in conditions like these.

I'll take snow over ice any day. It would have been good to feel prepared for what I woke to find, but the dreaded vampire cloud did give me some idea that there might be ice.

Posted by: BadMommy1 | January 18, 2011 1:20 PM | Report abuse

Methinks a calm, rational, carefully weighed approach to the weather will never satisfy some readers. What would satisfy them would seem to be a prediction with 100% accuracy, a task I'd like to see them perform themselves.

Posted by: mensan98th | January 18, 2011 1:25 PM | Report abuse

I rely on you guys when there's extreme weather. I know you all are always honest and you keep us up to speed while these events are happening. I think you did very well!

Posted by: Pat_E | January 18, 2011 1:30 PM | Report abuse

Reposting my comment from previous thread here, since it's really more relevant to this discussion:
This CAD setup (whether "traditional CAD" or not) is exactly what several of us were trying to point out yesterday. Seems like we always get one of these a year, after which we're more receptive to the possibilities of CAD. I think that's what was behind Doug Hill's "feeling in my gut" comment last night. I know it's hard to mix "feeling" with model science, but sometimes you got to go with feeling!

Posted by: petworthlad | January 18, 2011 1:32 PM | Report abuse

I think you guys did an outstanding job with the forecast. The only issue was the back and forth between temperatures to determine the extent of the icing.

Probably not the spot for this question, but what are temperatures predicted to be tonight? Will the commute be a rough one tomorrow is all of this stuff refreezes? If so, I'll need an early start to beat traffic.

Posted by: PoorTeacher | January 18, 2011 1:34 PM | Report abuse


Thanks for the feedback. But do note that late afternoon yesterday and especially into the evening, we communicated that west of DC it was looking likely to stay ice into the morning.


Thanks for the feedback. If we were wishy-washy it was because it was really difficult to know how long the cold air was going to hang on (except in zone 3, were it was clear). The models were eroding it too soon... We knew it was too soon, but just didn't know how far.

Posted by: Jason-CapitalWeatherGang | January 18, 2011 1:34 PM | Report abuse

By the way, in upper NW DC, the temperature has finally made it above freezing at 1:30pm. We never had any non-freezing rain at all. I gave you a "C" on this one, but I've always been a strict grader ;)

And I'd have to give the NWS the same grade too.

Posted by: petworthlad | January 18, 2011 1:37 PM | Report abuse

Please someone reassure me that the temps will stay above freezing tonight. Don't want this half inch deep slushy mess to re-freeze.

Posted by: FIREDRAGON47 | January 18, 2011 1:38 PM | Report abuse


Forecasting can be as much art as science. And it's also about experience. I knew from past cases that with a north wind temperatures were unlikely to warm up as fast as the models indicated. But sometimes it's tough to stray from the models too far. We did stray from them a bit- but didn't go far enough out on the limb. And I think you could criticize us for maybe not highlighting prominently enough the chance that it would be worse than expected. I'm pretty sure we did say it, but probably not loudly enough.

Posted by: Jason-CapitalWeatherGang | January 18, 2011 1:41 PM | Report abuse

I've spent much time cold air damning. CWG did a great job, as usual. Thank you.

Posted by: hawknt | January 18, 2011 1:41 PM | Report abuse

I love CWG and the calm, rational approach you guys take to forecasting the weather. But in this case I have no problem grading the forecast as a solid C. I like how you usually provide some percentages to your predictions of snow and would have liked to see some odds of the ice persisting in areas such as mine. I am firmly in Zone 1, down toward Mt. Vernon in Alexandria, and we still have plenty of ice, although it is finally disappearing now. The school cast was one apple and I would loved to have known that there was 25%, or whatever, chance that the rain would be freezing into the morning, hence resulting in school cancellation.

But hey, you guys rock no matter how the storms actually turn out.

Posted by: rightsaid | January 18, 2011 1:43 PM | Report abuse

Fine job on the forecast. I posted a short video and a couple of photos if interested.

Looking forward to reading about the next events...

Posted by: spgass1 | January 18, 2011 1:46 PM | Report abuse


According to this NWS map, the forecast lows across the region should be between 33° and 35°. I recall you mentioning that you're in Centreville, so expect a low of about 33°. If it manages to drop a bit lower than expected, there could be some re-freezing.

Posted by: BobMiller2 | January 18, 2011 1:46 PM | Report abuse

And all those that complain about the unexpected (for them at least) ice this morning would be complaining of "overreaction" if there were LOUD warnings of dangerous ice and it didn't show.

Posted by: hawknt | January 18, 2011 1:46 PM | Report abuse

I gave you an A, mainly because as early as late last week, you guys were calling for a wintry mix that could spell havoc for the Tuesday morning commute. To get the timing that close and so far ahead deserves an A in my book, even if the amount of rain that you thought might happened did not materialize. Nice job!

Posted by: Dougmacintyre | January 18, 2011 1:47 PM | Report abuse

One of the interesting things about this thread is the variability in the responses. It shows how differently people can interpret and take action on the same information. Communication scholars and psychologists could have some fun with this.

Posted by: Jason-CapitalWeatherGang | January 18, 2011 1:52 PM | Report abuse

Usually I would give this forecast a D but considering that you guys did stray from the models which were projecting significantly warmer temps I gave a B. Yes, the storm was more severe than projected, but you guys went against the grain where as most local forecasters were siding far more towards the models with this one.

33 degrees in Ellicott City today. NO WAY we get to our projected high of 38. Maybe some snow showers tonight? Hoping for Thursday night.

Posted by: bbirnbau | January 18, 2011 1:56 PM | Report abuse

You'all were spot on. It's nice to have a single-source "go to" weather location, as opposed to spending time going to four different sites, studying trends & systems, and trying to figure it out for myself (unless that's my Fun for that day). When I NEED TO KNOW, it's CWG for sure! And, you make it fun. Thanks!

Posted by: wwwwonderwhiskers | January 18, 2011 2:06 PM | Report abuse

I'd say a B. I think it would be difficult for anyone to get an "A" forecast, because this area is just not that predictable. CWG is great. Your blog gets me through every winter, ever since I moved here from Houston four years ago.

Posted by: jms8 | January 18, 2011 2:10 PM | Report abuse

Solid B as far as I'm concerned. There were errors in the initial forecast and you guys definitely understimated the cold air damming and wet bulb temp issue; but you quickly came around and explained why. Looking forward to your thoughts on Friday...there's now a general consensus of 3-6+ out there for DC/MD.

Posted by: DLO1975 | January 18, 2011 2:15 PM | Report abuse

@hawknt: I call BS.

The forecast for the last "under performing" snow storm had plenty of indication that there was a significant chance that there might be only a dusting. So, while disappointing (to snow lovers), it wasn't a surprise.

I'm just saying I like the CWG approach to providing percentage chances for various levels of potential snowfall and would like to have seen the same thing for an ice event.

Posted by: rightsaid | January 18, 2011 2:18 PM | Report abuse

I don't know how hard it was to get this right, but from a pure information consumption perspective what I read all the way up until about 11 PM was that I shouldn't worry about the weather in zone 2 because it would be warm and raining by morning. Instead, I got an ice storm with hard ice covering everything through 10 AM at least. Just on a decision-making basis, the forecast was not useful and doesn't deserve more than C.

Posted by: easyenough | January 18, 2011 2:19 PM | Report abuse

I know you updated your forecasts later on Monday to allow for all ice, but when you posted the 3-zone map and the 1.5 apple schoolcast, and said there would be a change to just rain overnight, I relaxed. Now, this morning, schools are closed, and even at noon it is barely above 32F and I have a big ice-chipping job on my driveway and steps. I was counting on the rain to do that for me! I wish you had emphasized the potential for this outcome more, even if it was a slim chance.

Posted by: pxl4 | January 18, 2011 2:23 PM | Report abuse

I give CWG an A when graded on a curve. As jms8 said, getting a flat "A" forecast is pretty difficult with any storm. But, when compared to everyone else, CWG provided the most insight, fair predictions, and critical counter arguments. I also don't believe that I would characterize this as an "ice storm" so much as a lesser "ice event," which is consistent with the CWG forecast.

Last night, when a neighbor told me that "they're predicting rain will wash everything away by rush hour," I countered that the CWG said that the cold may hold on longer and keep the ice around. You may not be perfect, but you are my most trusted weather forecasting resource for the DC Metro.

Posted by: figgy_va | January 18, 2011 2:28 PM | Report abuse

31.3 here in my part of Ashburn.

Still anxiously awaiting topping 32 degrees. And really worried about tonight.

Posted by: ThinkSpring | January 18, 2011 2:32 PM | Report abuse

Jason just posted a Snow Lover's Chrystal Ball update for Friday.

Posted by: BobMiller2 | January 18, 2011 2:42 PM | Report abuse

Jason just posted a Snow Lover's Chrystal Ball update for Friday.

Posted by: BobMiller2 | January 18, 2011 2:43 PM | Report abuse

Sorry for the double post and for the typo.

Posted by: BobMiller2 | January 18, 2011 2:47 PM | Report abuse

Is what's on the ground likely to refreeze tonight to make tomorrow's commute tricky?

Posted by: kersl | January 18, 2011 3:06 PM | Report abuse

kersl & ThinkSpring - Jason is aiming for ~330pm to post an update on tonight's temperature expectations. Downtown it is doubtful there will be a re-freeze, but well outside the Beltway there could be some isolated spots of trouble--yet some of this is evaporating slowly. It won't be as impactful as this morning's treacherous conditions, at least. Glad most of you are poking above 32!

Posted by: Camden-CapitalWeatherGang | January 18, 2011 3:28 PM | Report abuse

I gave you guys an "A". I don't believe anyone can perfectly predict the weather but you guys do a fine job of taking as many factors as possible into consideration. I checked last night and saw that Zone 2 (where I live) was to expect ice in the morning so that's what I was prepared for. I wasn't necessarily expecting 0.5" of ice (which gives me some work to do to get to the main road) but once I managed to get out to the salted roads I didn't have any problems maneuvering my way to work. Despite a two-hour delay for the federal government, I made it in early. Thanks for working so hard to keep us up-to-date with the weather in the DC metro area!

Posted by: jbrickey | January 18, 2011 4:34 PM | Report abuse

I wish I'd seen your forecast rather than believing the National Weather Service that things wouldn't get bad until 10 pm. I decided to go to a movie that started around 7, figuring by the time it was over around 9 I'd have plenty of time to get home and safe before things got going. Instead, I found white stuff all over my car and the parking lot treacherous to navigate.

Posted by: kevinwparker | January 18, 2011 7:48 PM | Report abuse

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