Model to model consistency is often something we use to measure confidence in a specific feature.   Sometimes it works… and sometimes it doesn’t… like today.    In today’s forecast I should have stuck with my original hunches from last night with a late day SW surge for the North Coast of MA, however this morning’s outputs showed a distinct delay in the offshore Low shifting north to allow the southerlies to fill in.

Knowing it was a tricky forecast I did put some bulleted hedges in:

 •  Generally the cool sea breeze won’t want to give up to the warmer south and SSW flow hence it it’s going to happen, it probably won’t be until the sea breeze is retreating late in the day. Southerlies lucky to fill in before dusk.

 •  Watch trends to the south and west as the SSW flow is likely to come on from that direction. Sooner it fills in the stronger it should get.

Here is a quick synoptic setup of the day:   Panel 1 is the morning, Panel 2 is the afternoon.   Note the area of Low pressure sliding north and right behind it is a tighter pressure gradient zone that slips over MA by the evening and hence a stronger SW flow incoming…. but when?

12z nam morn

12z nam

Here’s what happened:

Check out the latest graph for Deer Island (Boston Harbor) and snapshot of the area’s winds:

snap 830pm deer island graph

Note that in the very pretty graph above you can see several models overlaid.  Which one got it right?    Looks like WRAMS got the speeds the closest but the 5km NAM did a little better on the timing.   Note that the box on the graph is the NWS Marine forecast that didn’t catch the surge at all.

The graph is cool at showing the latest models and how they did compared to reality, but what model got it right from the morning?

Using our newest features on our professional data viewer, I can go back several model runs to see which model I should have listened to.

Here are those same models but in their mapped versions both 06Z runs out to the same time:

wrams06z Nam5km06z

It looks like WRAMS 06Z was the best choice for today.   Go WRAMS!

-Matt Corey
Meteorologist, etc….
WeatherFlow