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Revenge of the Inverted Trough

Carson revisits his biggest forecast bust ever; while trying to avoid a repeat tonight.

MAINE, USA — My Norlun Trough forecast of 2010 shall live in local weather infamy. 

I had painted in a very localized zone of 6-10" of snow with an inverted (Norlun) trough likely to just sweep through York County. It was a pin point forecast attempt.

You want to know how much snow we got?


Literally nothing.

It was actually sunny.

Since I'm a pretty fun guy to mock and rag on (I think it's my face); I still get tweets and messages about that forecast every time someone mentions an inverted trough.


Now back into the belly of the beast as an inverted trough threatens tonight.

Credit: ncm

Above is the NAM model depiction of the inverted trough tonight. Now typically the NAM is a real piece of trash computer model; but it has value when it comes to this really mesoscale short range kind of stuff.

What makes inverted troughs so difficult to forecast is pretty well illustrated in that map. Notice how thin but heavy the snow band is? It's only 50-75 miles wide but it's showing moderate banding which would equate to several inches.

So little wiggles in placement have a huge net impact.

To that end, compare the position of the trough on the NAM to that of the EURO and GFS:

Credit: ncm
Credit: ncm

The differences are subtle, but they mean the world when it comes to "IMBY" snow amounts.

So tuning the models based on my experience, leaning a bit more NAM on the position of the trough, and a bit more euro on total moisture gives me this:

Credit: ncm

It ain't pretty but I think it's going to be in the ballpark. The only thing I WILL say is within that 2-4" band along the coastline there's a chance someone gets 6" of fluff by tomorrow morning. But it didn't make sense to draw a contour that is under 10 miles wide...asking for trouble.

Timing-wise the snow starts after sunset and wraps up after 2 a.m. tomorrow morning.

The story on Thursday will be full barney cold.

Welp, wish me luck on this forecast and even if it's dead on you can still heckle me because...well, it's my face:

See ya


https://www.instagram.com/keithcarsonweather

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