Prepared by Meteorologist: Matt Corey

These Spring days in New England often see healthy areas of Low pressure the sweep off to the north into Nova Scotia.  Computer models have improved over the years but still struggle to handle the post storm winds because rarely does a straight West wind prevail.   More common is a morning NW then afternoon “troughing” along the Cape Cod Canal axis which turns winds to the WSW for southern RI and Cape Cod while sometimes enhancing the WNW flow north of Boston.

This particular day was tricky because the cool front dragging behind the northern Low was slowing down but there was some serious cool air advection behind this front.   It was only a matter of time for that front to clear out and the cool and gusty wind to fill in.

avnsr2.12hr

Here is the 8am forecast chart.  I highlighted New England here to show what cool air advection looks like.  Notice how the height lines (height is determined by the temperature of the layer) are perpendicular to the isobars.   Since the wind flows with the isobars (mostly), you can deduce from this type of chart that cool air is moving into the region.  The smaller the “boxes”, the faster the cool air advection.

 

 

 

 

 

 

avnsr2.24hr2

Here is the 8pm forecast chart.  Note that the model is hinting at a trough (I colored it red) developing over the Canal.  This is a good hint to a forecaster that the canal trough is likely and to be alert because sometimes these can really kick up WSW in the south and east and WNW in the north and west.   This day though, the synoptic forcing behind the front is kind of strong so the trough effects aren’t as dramatic.   Still… it’s this trough that keyed me in that a backside surge of cool air is likely, especially Boston and Northwards.

 

 

 

 

 

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Another good item to look at is the forecasted profile.   Here the model gives it’s estimate for what might be happening aloft during the day.  I highlighted the gusty winds predicted but notice the model output doesn’t put much winds on the surface through the afternoon….. hmm… Think that’s right?

 

 

 

 

 

 

6am

Here is what I woke up to:  Rain.  Well, it was predicted to clear out but one thing rain can do is stabilize the boundary layer which can sometimes delay winds because it takes longer for that layer to break down and scour out.    The am update I pushed the stronger winds back a bit based on the model trends and this persistent rain.

 

 

 

 

What happened?-  Well, as we predicted, the winds came on, and quite strong.   That cool air surged into the region and mixed very well to the surface.   One area that we cover that sees some intense post frontal action is Newburyport, MA.   Notice that our sensor is on a peninsula with good open fetch over the Bay:

newburyport

Plum Island, MA wind graph:  Notice the afternoon surge with gusts over 30mph once the rain cleared out.Plum Island

 

Here is the graph for Dread Ledge located off of Nahant, MA.   Note how the wind came up and down around the morning showers then the gusty WNW flow pushed up past midday.dread ledge