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Posted at 11:00 AM ET, 11/17/2009

Ida's remnants play havoc with last week's forecast

Weather Checker

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

By Jamie Yesnowitz

It's rarely easy to predict the path and timing of a tropical system once it makes landfall. This was especially true with the remnants of what was once Hurricane Ida. Conflicting model predictions -- some taking Ida's remains almost due east after coming ashore along the Gulf Coast, others suggesting a more northerly track with impacts further up the East Coast -- challenged CWG and other forecast outlets early last week.

The end result for the D.C. area was almost 48 hours of uninterrupted rain and some gusty winds on Wednesday and Thursday of last week -- though it was nothing like the pasting received by southeast Virginia and the Maryland/Delaware beaches -- followed by lingering clouds and showers on Friday and Saturday and, finally, a beautiful Sunday.

Let's see how CWG fared forecast-wise...

Brian Jackson's Sunday forecast was the first on CWG to note that Ida's leftovers could impact the Tuesday night into Wednesday period and that Tuesday night, the forecast would become "a bit tricky" depending on Ida's path. He was right on that assessment. Unfortunately, Brian missed badly when he predicted with medium confidence that a trailing cold front would push Ida's moisture out with clearing skies on Wednesday afternoon. His predicted Wednesday highs in the mid-to-upper 50s technically verified just after midnight on Wednesday. However, a more accurate description of the day would have been "a windswept inch of rain with temperatures falling into the upper 40s."

Jason Samenow's Monday forecast was not much better. At least Jason tacitly admitted that an unpredictable event was upon the D.C. area, as he outlined three potential scenarios for Tuesday night (30% chance of steady/heavy rain, 30% chance of showers, and 40% chance of mainly dry weather) at low-medium confidence. In fact, that type of forecast probably should have been classified as low confidence. Jason did lean "towards a more pessimistic, wet scenario" of lingering rain over gradual clearing for Wednesday, and that call was correct. But the forecast did not mention the inch or so of rain that ended up falling on Wednesday, or temperatures that stayed in the upper 40s most of the day. Likewise, predicted sunshine and warmer temperatures for Thursday and Friday (at medium-high confidence) did not come to be.

By late Tuesday morning, Matt Rogers' medium-confidence forecast mentioned the possibility that the storm system would stick around well past Wednesday. However, Matt seemingly underplayed the likelihood of significant rain, only noting a 50% chance of showers on Wednesday and not providing detail on how much would fall.

Later that afternoon, Ian Livingston's update covered what would happen on Wednesday more accurately, with the forecast being "rainier tomorrow than first advertised."

Finally, Dan Stillman's late-morning Wednesday forecast was largely correct, both from a precipitation and temperature perspective, for the Wednesday-through-Sunday period.

Bottom line: CWG failed to pick up on the duration and intensity of the event until very late in the game.

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  |  11:00 AM ET, 11/17/2009

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