Wow! GFS vs NAM

A little side note for you. Two of the main models we use for forecasting (there are more, but these are two of the big hitters) are the GFS and NAM, both run by the U.S. NWS. We can get point-specific forecast for airports (which we then extrapolate or apply to the surrounding area), and the latest from these two for BWI show what we’re up against.

The models give a precipitation forecast for the airport, but in liquid equivalent (we’ll assume a 10::1 ratio for snow, so you take the liquid as snow and multiply by 10 to get snowfall)… here are the details of the two for BWI.

NAM
Total Precip: 0.267″
Pcp as Rain: 0.120″
Pcp as Snow: 0.145″ (1-2″ of snow)

GFS*
Total Precip: 0.648″
Pcp as Rain: 0.0″
Pcp as Snow: 0.648″ (6-7″ of snow)
* Some — but not much — of the GFS snow is with a light snow it has forecast for the end of next week, which is less than 0.1″ (1.0″ of snow)

Wow. Talk about a difference. The NAM was what rolled in first last night, and what made me pull the plug. If the GFS is right, that was a bad call on my part. Huh… curious to see where this goes. Obviously, the NWS didn’t like what they were seeing either cos they pulled the plug too. How ironic would it be if the GFS verified…

GFS pcp fcst for BWI


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