The Washington Post

Behind the busted forecast: the wedge wimps out

Temperatures at 3 p.m around 70 in D.C., but only in 50s and cooler from northern Delaware and to the north and northwest

What happened? A very shallow wedge of cool air was supposed to envelop the region, capping temperatures despite strong flow from the south.

But the push of southerly air prevailed, and the wedge only reached southeast Pennsylvania and northern Delaware. It’s currently just 51 in Philadelphia with a wind from the east.

The exact location of these wedges give forecasters fits every time they’re a possibility. And models are horrible at simulating them.

Models forecast temperatures in the low 50s this afternoon compared to actual readings in the 60s to around 70.

Related: Behind the busted forecast: the wedge always wins

That recent experience probably influenced us too much, resulting in a overly conservative temperature forecast today. CWG forecaster Matt Rogers, sensed forecast highs might be too low this morning, posting the following comment just after 7 a.m.:

I was very attentive to [the Jan 12-13 track record in my forecast] ... Based on what I can tell, the forcing ahead of this front is considerably stronger than that weekend. And already, we are detecting some southerly wind components in the DC area. That fateful Saturday the 12th had us stuck in easterly to northeasterly flow instead. In fact, I am worried given the earlier start here that today could be warmer than expected around the city and south.

Matt was right...

Sometimes, we say “the wedge always wins”. Maybe that should be revised to “nobody can predict the wedge”.

Jason is the Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science, and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association.


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