Network News

X My Profile
View More Activity
The new Washington
Post Weather website
Jump to CWG's
Latest Full Forecast
Outside now? Radar, temps
and more: Weather Wall
Follow us on Twitter (@capitalweather) and become a fan on Facebook
Posted at 10:00 AM ET, 03/ 4/2009

CWG Gets Credit For a Correct Forecast, But...

By Capital Weather Gang

Weather Checker

* Warming Up, Slowly but Surely: Full Forecast | CWG Grades Itself *


Near whiteout conditions Monday morning in D.C. -- the perfect time to jog on the Mall. By CWG photographer Kevin Ambrose.

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

By Jamie Yesnowitz

Well, Washington finally got a real winter storm, and in the end, CWG's Saturday prediction of several inches of snow across the area late Sunday through early Monday did verify. But the devil truly was in the details, particularly in the coverage several days out, and the late-breaking change in prediction on Sunday night.

Keep reading for the Weather Checker's full review...

Prior to the Storm

The long-range forecast starting about a week out was poor. CWG's Monday forecast (by Jason Samenow) did not hint at significant winter weather, predicting with medium confidence seasonably cool high pressure over the coming weekend, with highs in the 40s on Sunday. The Tuesday forecast (by Matt Rogers) did note the potential for a "wildcard" over the weekend, but in looking at the prevailing pattern of the winter, dismissed it as "a minor worry, and something just to monitor in the days ahead."

By midweek, CWG's Wednesday forecast (by Dan Stillman) predicted with low-medium confidence a wintry mix over the weekend, with temperatures that "may be warm enough to favor rain and limit the impact of any snow or sleet." If this prediction was solely related to the brief period of mixed precipitation that came through Saturday night, then it came true, but it was unclear whether the forecast specifically applied to Saturday night or the whole weekend. Then, the Thursday forecast (by Camden Walker) missed, expecting with low-medium confidence that any precipitation Saturday night and Sunday would wind down Sunday night with partial clearing, and with medium confidence that Monday would be mostly sunny. A similar forecast was issued by Ian Livingston that afternoon. The Wednesday and Thursday forecasts incorrectly viewed the Saturday night and Sunday night storms as one discrete event.

On Friday, the forecasts came into much better focus. The Friday morning forecast (by Josh Larson) was the first to directly address the two-storm potential, noting that while there was a chance for wintry weather on Sunday night and Monday, there was a decent chance of a miss to the south and east. A midday Snow Lover's Crystal Ball (by Dan Stillman; updated that evening), noted with low confidence a 50-50 chance of snow, and also mentioned the possibility of a miss to the south and east.

By late Saturday morning, it became apparent that a storm was likely to affect the Washington area. That day's Snow Lover's Crystal Ball and Saturday night update (both by Jason Samenow) were spot on with respect to expected accumulations, including the potential for bigger accumulations south and east of the city.

Timing as Storm Approached

CWG's Sunday morning Team Forecast timeline, which called for accumulation to start between 4 and 8 p.m., was accurate for areas several miles south and east of the city. But it was way off for D.C. and points north and west, where there was little or no accumulation until after midnight, thanks to light and spotty precipitation along with temperatures substantially higher than forecast.

This first part of the storm proved yet again that a 20-mile miss can make all the difference in the world. While one can hope that long-range forecasts (e.g., several days to a week out) can improve as models and meteorologists advance, I'm not sure that errors as small as 20 miles will ever go away.

The Backtrack

The Sunday night backtrack in the forecast was a bigger mistake. I've never been a fan of nowcasting. And as the first half of the storm came and went with little fanfare and not much accumulation northwest of the city, the team changed its forecast, lowering snow amounts substantially for locations north and west of the Beltway.

One question from my end is whether, prior to the change in forecast, CWG considered that the energetic upper-level area of low pressure -- which overnight into Monday morning delivered the accumulations originally predicted -- could possibly draw energy out of the surface low pressure responsible for the first half of the storm.

Also, did the negative comments that streamed in when the first part of the storm fizzled in any way contribute to CWG's decision to change its forecast? I would hope not. In any event, the flaw in adjusting the forecast, in my view, was more egregious than the flaw in timing.

Overall

Ultimately, CWG was correct in its initial take of what proved to be an oddball storm, both in terms of its higher accumulations south and east of the city, and the fact that it occurred in early March. In high school math class, I got some credit for getting the answer right, but only got full credit if I could show the teacher how I got to the answer. Likewise, while CWG's initial forecast was correct, the way it verified was not ideal.

About the Weather Checker...

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 Capital Weather Gang  | March 4, 2009; 10:00 AM ET
Categories:  Weather Checker  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   Del.icio.us   StumbleUpon   Technorati   Google Buzz   Previous: Forecast: Warming Up, Slowly but Surely
Next: Snowstorm Comments: Best of...

Comments

Fair assessment, Jamie, but disagree on your point about nowcasting. As a forecaster, you've got to be willing to do it despite its potential pitfalls. As an analogy, say you buy a stock and it starts tanking and there are indications it could go lower. Do you sell some of your shares or risk losing everything? Yes, you've got be careful of the emotional risk and selling low, but you've got to also protect yourself from financial disaster if, in your expert judgment, the downside is real. If you're a smart investor (or good forecaster in the case of weather), you make the right adjustment more often than the wrong one. In this case, we made the wrong one...but in the past mid-term adjustments have served us well.

Posted by: CapitalWeatherGang | March 4, 2009 11:02 AM | Report abuse

I appreciate the feedback. Particularly apt analogy considering how the markets are doing lately :)

I guess my problem with nowcasting is that one can claim accuracy well after the event has started. I'm not saying that CWG does that at all (these post-mortems are proof of that!), but many forecasters out there would have.

To use another analogy, nowcasting is like putting down $100 on a blackjack hand and pulling $50 back when the dealer shows a 10 and you have 16. Obviosuly, the casino won't allow it. And there's always the chance you hit and get a five.

Obviously, forecasters should comment on what's going on during the storm (i.e., this could end up on the low side of accumulation prediction), but changing the official forecast right around "halftime" left CWG open to a double miss.

I think that what we can learn from this snowstorm is never underestimate the second pulse of energy in a two-punch storm. I know that we had an underperforming storm make up for lost time back in 2006, and am wondering whether the set-up for that storm was similar to the other night.

--Jamie

Posted by: JamieYPotomac | March 4, 2009 11:49 AM | Report abuse

There were some similarities to the storm of Feb 11-12 2006 as well as one in 2005 (which was even more similar -- where once again the upper low bailed out the forecast).

Posted by: CapitalWeatherGang | March 4, 2009 12:06 PM | Report abuse

My evaluation: It was a 'bonus snow' occurring just after the end of meteorological winter [though I refuse to end met. winter on specific dates. Actually I begin 'met winter' when it's cold enough to kill the hardiest singing crickets, as late as New Years or later some years and end 'met winter' with the beginning of Lent on Ash Wednesday, which also varies year by year. The choice of Mardi Gras as the last day of 'met winter' is somewhat arbitrary, but is usually an accurate indicator of the beginning of spring.]

It was not what I'd consider an 'optimum snow' since the "sweet spot" of maximum accumulation was to my south and east. To qualify as an "optimum snow" the 'sweet spot' max. accumulation and thundersnow, if any, MUST occur along Carlin Springs Road in the corridor from Baileys Crossroads to Ballston. Very few snowstorms qualify for such a distinction! It's possible that the thunderstorms feeding into the freeze line over the Eastern Shore early Sunday evening actually stole moisture from us west of I-95 during the early phases of the storm. There probably was thundersnow over the Northern Neck and parts of Southern Maryland.

Posted by: Bombo47jea | March 4, 2009 12:40 PM | Report abuse

Weather forecasting seems a thankless task in this area. Running a blog like the CWG does is like painting a big red target for all the local weather hostilities and frustrations to aim their darts (and other stuff).

I'll give the gang a "B" for their forecast on this storm. They shouldn't have backtracked their forecast in the middle of the event, but the initial forecast was pretty much spot on. That being typed, I understand some the EXTREME negative comments left Sunday night when the storm was tardy with accumulations especially to the north & west of the city. Perhaps one reason a few people went mental is that they were watching the same local weather radar loops that I was, showing precip overspreading the area, when in fact nothing was reaching the ground. For hours.

False radar images on top of being teased with double digit snow accumulation forecasts after hardly any snow at all for a long long time made for some bitter postings late Sunday night.
Hopefully everyone enjoyed this one, as it will be a long time before the next decent DC metro snowfall. Spring is coming.

Posted by: FIREDRAGON47 | March 4, 2009 3:44 PM | Report abuse

Either way - thank you so much for doing the post mortem.

There is nothing - I repeat NOTHING more aggrivating than watching a weather forecaster whiff on a forecast for an event, and then go on the next day without little more than passing reference to the prior days events.

It is because of these post mortems that cause me to turn to you guys as my #1 weather source. You strive for accuracy because you know you will be accountable. Keep up the excellent work!

Posted by: fishman1 | March 4, 2009 3:52 PM | Report abuse

The comments to this entry are closed.

 
 
RSS Feed
Subscribe to The Post

© 2012 The Washington Post Company