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Posted at 11:00 AM ET, 12/ 1/2008

Weather Checker: When Is a Miss a Miss?

By Capital Weather Gang

* Afternoon Shower? Full Forecast | Radar & More: Weather Wall *

A rainbow seen from Oakton, Va., on Saturday Nov. 15. By Capital Weather Gang photographer Kevin Ambrose.

Welcome to the first installment of Weather Checker, an outsider's analysis of CWG's forecast accuracy.

By Jamie Yesnowitz

We had some wild weather to deal with on Saturday Nov. 15. As warm air surged from the south and pushed highs into the mid 70s (they haven't made it past the low 50s since), cold air approached from the west. The clashing of cold and warm, along with ample moisture and energy in the atmosphere, was volatile enough to prompt a Tornado Watch from the National Weather Service, though only heavy showers and a few thunderstorms materialized. By late afternoon, a rainbow could be seen as skies began to clear.

All in all, these were rare but not unheard of conditions for November in the D.C. area. Did CWG get the forecast right? Let's review the predictions heading into this intriguing weather day.

Keep reading for the Weather Checker's verdict...

To refresh the memory, let's go over the official observations Friday Nov. 14 and Saturday Nov. 15. At Reagan National, the temperature stayed in the 50s most of Friday, then moderated and held steady at an unusually warm 56 most of Friday night with intervals of fog, mist and light rain, and rose steadily through the 60s on Saturday morning when the rain stopped. At 12:52 pm, gusty winds from the south pushed the temperature to 70 as a low-pressure area and associated cold front advanced toward the region. An hour later, the temperature spiked to 74 as cloud cover briefly broke, bathing the D.C. area in glorious late-fall sunshine. By 2:52 p.m., the heavy rain came as winds shifted to come out of the west, knocking temperatures down to 65. Similar conditions were recorded at Dulles, with a high temperature of 75.

On Thursday Nov. 13, CWG's morning forecast (by Josh Larson) predicted with medium confidence highs in the mid 60s on Friday followed by a rainy Saturday morning with highs near 60 and turning colder later in the day. In hindsight, we can clearly call this forecast a miss with a nearly 10-degree bust on Friday -- temperatures only made it to the mid 50s because a vaunted wind from the south did not arrive in time -- and a nearly 15-degree bust on Saturday. CWG's Thursday afternoon forecast (by Ian Livingston) for Friday similarly busted from a temperature perspective.

The Friday morning forecast (by Camden Walker) did somewhat better on temperatures, calling for Friday "highs near 60, with a 70-degree reading not out of the question" on Saturday. Still a moderate miss, however, when considering the mention that showers would be "likely throughout the day" on Saturday, when in fact much of Saturday was dry but for a few stormy moments.

CWG's Friday afternoon forecast (by Ian Livingston) for a possible batch of heavier rain on Saturday morning might be considered correct if one counts the rain in the pre-dawn hours. The predicted highs in the mid-to-upper 60s, however, were too low.

Finally, CWG's same-day medium-confidence forecast (by Jason Samenow) nailed the timing of the weather for most of the day. Though the predicted high of "near 70" was still a few degrees off, and precipitation was out of the immediate metro area by 4 p.m., a few hours before the "by around 7 p.m." predicted departure.

Was the 5-to-15-degree miss for Saturday a miss, even though the outlier temperatures only took hold for a couple of hours? I think you have to say it is given the magnitude of the error. Fortunately, it's not as grievous as missing the track of a winter storm by 10 to 20 miles, which can be the difference between a foot of snow and an inch of disappointment (for snowlovers, that is).

Interestingly enough, had the cold front arrived three to six hours earlier, rather than waiting until the height of daytime heating, it's unlikely temperatures would have made it to the mid 70s.

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  | December 1, 2008; 11:00 AM ET
Categories:  Weather Checker  
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Next: Update: Band of Heavy Showers, Some Thunder


A hearty welcome to Jamie, our straight-shooting weather checker. Great job on this debut effort.

Posted by: Dan-CapitalWeatherGang | December 1, 2008 12:30 PM | Report abuse

"warm air surged from the north"?

Sounds like the definition of a miss . . .

Posted by: weathergrill | December 1, 2008 12:45 PM | Report abuse

good catch weathergrill... fixed.

Posted by: Dan-CapitalWeatherGang | December 1, 2008 12:49 PM | Report abuse

Jamie, welcome to CWG! Will you please consider documenting and discussing the methodology and criteria you use to judge forecasts - and, the scale you use for characterizing your results? (For example, how far off does a forecast have to be to earn a rating as a 'miss'? Is there a 'near-miss'? A 'bullseye'?) I'm especially interested to hear how the confidence level provided for each individual forecast is taken into account. Is a medium confidence forecast 72 hours before the event worth the same value as a high confidence forecast 24 hours in advance?

Thanks for your work and for whatever information you can share on your approach!

Posted by: --sg | December 1, 2008 1:49 PM | Report abuse

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