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Posted at 10:30 AM ET, 08/12/2009

Checking the Forecast for a Rare August Day

Weather Checker

* Staying Humid: Full Forecast | Climate Change & National Security *

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

By Jamie Yesnowitz

Until the recent searing heat, this summer has been strangely mild, and probably the most tolerable of my seven years in the D.C. area. Still, it's a novelty when an August day passes with temperatures that don't surpass 80, as was the case this past Thursday (Aug. 6) for many areas downtown and to the south and east of D.C.

So, I thought it might be instructive to look back and see how CWG fared in its forecast for this rather rare August day.

Keep reading for what the Weather Checker has to say...

To review, Thursday's weather at Reagan National (DCA) consisted of 0.12 inches of light rain in the early morning, followed by consistent cloud cover with temperatures in the low 70s, until late afternoon when the clouds broke and the high made it to 79 just after 4 p.m. BWI and Andrews Air Force Base (ADW) only reached 78 and 75, respectively, while IAD spiked to 83 (the sun came quicker north and west of town as clearing skies moved in from northwest to southeast). IAD and BWI reported only .04" and .05" of rain, respectively, with .22" at ADW.

Jason Samenow's Monday forecast picked up on a cooling trend for Thursday (from low 90s to near 90 earlier in the week), and predicted with medium confidence that Thursday temperatures would moderate to the mid-80s with a mix of clouds and sun and the potential for an isolated storm in the afternoon. While Jason got the trend right, the temperatures were still overstated, and it turned out to be be a showery morning with no afternoon storms.

Tuesday's forecast by Matt Rogers correctly predicted, with low-medium confidence, the Thursday morning showers and significant cloud cover, but again overshot (for many parts of the area) on highs being "in the 80s."

Likewise, Dan Stillman's Wednesday forecast accurately noted with medium confidence the potential for morning showers and the eventual change to partly sunny skies in the afternoon. Predicted highs of mid-80s or low 80s, depending on the timing of clearing skies, verified for the north and west suburbs, but not for locations in D.C. and to the south and east. In addition, the forecast headline "Typical Summer Stuff, Then Real Heat?" failed to characterize Thursday's weather, which in fact was quite atypical for August.

Ian Livingston's Wednesday afternoon forecast finally raised the potential of Thursday temperatures remaining in the 70s all day and noted the challenge of predicting when the rain and clouds would depart.

Finally, Brian Jackson's same-day forecast (medium-high confidence) initially overestimated the intensity of rain as "moderate to heavy," before a mid-morning forecast change to "light to moderate." As for temperatures, it was a little less clear: The "Express Forecast" at the top of the post predicted highs of 75-79 degrees, correct for DCA and BWI, but too low for IAD and other spots north and west of town.

The quibble from my perspective was Jackson's more detailed forecast narrative, which said, "...temperatures will struggle and we'll spend the majority of the day in the mid-to-upper 70s. If our wave [of low pressure] gets some giddy-up and moves out sooner than expected, some afternoon and evening sun may be able to push the mercury above 80."

While I liked the use of the term "giddy-up," I'm not sure mid-to-upper 70s was an accurate characterization of the day, as many locations saw temperatures no higher than the low 70s through early-to-mid afternoon.

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  |  10:30 AM ET, 08/12/2009

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