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Posted at 02:40 PM ET, 09/21/2011

Worst D.C. September weather in memory?


Rainfall forecast today through Saturday morning indicates 1.5-3” of rain is likely over the D.C. metro region. (NOAA)
Summer has come and passed
The innocent can never last
Wake me up when September ends

- Green Day, “Wake me up when September ends”

Although the above Green Day lyric is so 2005, it probably has entered more than a few minds during this depressingly dim September. So far this month, we’ve had at least a trace of precipitation on 12 of 20 days. And dismally, we’ve had only four days with more than 50% sunshine.

Last year through September 20, we indulged in more than twice as many blue-sky days. I looked back at the previous five Septembers and none match 2011 in the gloominess category (although 2006 and 2009 were close)

The short-term outlook for sunshine is grim. A slow moving front complemented by a plume of tropical moisture surging north means more showers tomorrow and Friday, possibly heavy.

Making matters worse, a cutoff low is forecast to develop this weekend over the Ohio Valley and stagnate over the Northeast well into next week.


Cutoff low simulated by the GFS model for Monday of next week, centered over the Ohio Valley. (NOAA)
Why is this bad? These lows often bring frequent clouds and showers and take a long time to depart. Remember my post about cutoff lows from April 2009?

By far the best description of a cutoff low I’ve seen comes courtesy Chick Jacobs at the Fayetteville Observer:
Think of a cutoff low as a drunk relative at the family reunion who just won’t go home.
The National Weather Service’s technical definition clarifies why this description is so apt:
A cut-off low is an upper-level low which has become completely displaced (cut off) from basic westerly current, and moves independently of that current.

The good news with this particular cutoff low is that the cloudiest, dampest weather will likely be to our north, but we’re going to have at least some spotty shower chances daily through the middle of next week.

On those rare occasions when the sun does come out, savor it. This September, sunshine is sacred.

Can you remember a worse September?

Related: What is Washington, D.C.’s weather like in September? Breaking down norms and extremes

By  |  02:40 PM ET, 09/21/2011

Categories:  Local Climate, Latest

 
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