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

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

By Capital Weather Gang

Weather Checker

* Our Full Forecast | Fall photos in D.C. | Sesame Street weather *


Brittany Thompson wades across Worcester Street in Ocean City, Md. (Laura Emmons/Associated Press)

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 Capital Weather Gang  | November 17, 2009; 11:00 AM ET
Categories:  Weather Checker  
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Comments

Yes, "CWG failed to pick up on the duration and intensity of the event until very late in the game".

For perspective, to the best of my knowledge neither did any other outlet, including the National Whether Service - and for explicable reasons.

Jason got it exactly right on Monday, namely that all were dealing with an unpredictable event. That should translate to anything was possible and nothing more than a "stay tuned", rather than trying to parse the outcome with what were indeterminate probabilities.

It's important and scientifically justified to acknowledge those situations and circumstances when one just does not, really cannot know what lay ahead even at short ranges. What's critical is being able to discriminate - as CWG forecasters generally do - between these cases and those that are more predictable and coupled with reasonable estimates of confidence.

For the weather geeks out there it appears the Ida event resulted from the serendipity of Ida merging and interacting (phasing) with two low-latitude troughs, one approaching from the west and the other from the east. Without going into details, it's not surprising that model forecasts did very poorly.

Posted by: SteveT-CapitalWeatherGang | November 17, 2009 12:13 PM | Report abuse

SteveT: Any chance of getting you to go into details as to why Ida behaved as it did, and why all forecasting outlets missed it? That's the kind of weather geekery for which so many of us turn to CWG. Forecasts may not always verify, but the analysis never fails us. :-)

Posted by: --sg | November 17, 2009 10:00 PM | Report abuse

@sg

If you (or anyone) would like more details, it's probably best to get in touch with me directly (s.tracton@hotmail.com), since I don't know the degree of geekiness you can tolerate. Be assured I'll not reveal your identity and email address.

Posted by: SteveT-CapitalWeatherGang | November 17, 2009 10:55 PM | Report abuse

Please note that "Bombocast" posted a possible impact almost a week in advance...based on my interpretation of the weekly GEM prediction which had a potent nor'easter developing from Ida's remnants near Cape Hatteras...while Ida was moving up the Yucatan Channel at the time.

At the same time NHC predicted that Ida would move across Alabama and Georgia while fizzling out inland...GFS didn't reach agreement with GEM until rather late in the game. As I recall, NAM missed the nor'easter altogether.

Posted by: Bombo47jea | November 18, 2009 2:00 PM | Report abuse

You did note it early on Bombo, and I would have to say, so did I -- even if not as an official CWG forecast. (I'm off on the weekends!) ;-)

Posted by: Ian-CapitalWeatherGang | November 18, 2009 4:23 PM | Report abuse

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