At the time of this post (evening on the 13th) a very strong cold front is traversing the region.  This is the same cold front that brought record snows to Montana, severe storms to Minnesota and at times allowed it to be warmer in parts of Alaska than parts of Texas!!   As this front continues to push offshore high pressure will assume command of our weather for the next few days.  We all like images so I created one to illustrate what is currently occurring.

The cold front will continue it’s march off the East Coast this evening; taking with it all of the clouds and showers and making way for the general wind direction to turn to be out of the northwest.  This will allow much cooler and drier air from Canada to enter the region.  This cooler and drier air is symbolized by the very large area of high pressure centered around the Great Lakes.

This area of high pressure will be our weather for the next 5 days or so.  We can expect lots of sunshine and more reasonable temperatures for the month of November.

7 Day Forecast

Tonight: Cold front pushes offshore. Skies clear and cooler temperatures move in.  Winds shift to the northwest allowing Canadian air to move in.  Overnight lows in the lower 30s.

Wednesday:  Clear skies as high pressure is in total control.  Highs slightly above 45.

Thursday:  High pressure is still in control. Afternoon highs around 45.

Friday – Sunday:  Partly cloudy skies with highs ranging from 45 to 50.

Monday:  Chance of an isolated shower.  Highs around 50.

Extended Forecast:

I teased it in the title of this post, but there appears to be stormy days on the horizon.  The longer range computer models continue to advertise a system forming off of the East Coast  sometime around mid-week for the week of Thanksgiving.   A similar pattern to the one that allowed both Sandy and the nor’easter that followed appears to be making a return.

In the Meteorology community there are a number of devised products called teleconnections that have been created to help describe the large scale pattern in the atmosphere.  These teleconnections and subsiquent large scale patterns tend to produce somewhat repeatable results and are helpful when it comes to forecasting.  Here in New England, possibly the most important teleconnector for our weather pattern is called the North Atlantic Oscillation or simply, the NAO.

The NAO deals with the interaction of two large scale, semi-permanent features over the Northern Atlantic.  These two features are the Icelandic low and the Azores High.  The value of the NAO depends on the strength of these two features.  If the two features are strong, then the NAO is said to be positive, but if they are weak, then it is said that the NAO is negative.

For a more detailed explanation of the NAO, go here.

The pattern that allowed Sandy and the nor’easter to impact us was one that featured a negative NAO value.  It is this negative value of the NAO that promotes blocking in the atmosphere over the North Atlantic ocean.  When this blocking pattern forms, storm systems are allowed to curl up the East Coast and impact New England.

Well looking ahead to the time frame of next week, it looks like a negative NAO is going to make a return.

The above image is the Ensemble forecast from the GFS forecasting model and it shows that all of the members dip below zero sometime around the 17th and stay negative through at least Thanksgiving.  The GFS isn’t the only longer range model predicting the NAO value to become zero.  The ECMWF is also forecasting for this value to become negative around the same time frame.  Looking below at the column on the far right, we can see that the value of the NAO is very near zero by hour 162 (day 7) and is below zero by hour 192 (day 8).  This negative value of the NAO combined with the continued advertisement of a storm system by the computer guidance give me the confidence that a storm system is going to form off the East Coast sometime next week.  How close it comes to New England is the question to be answered at a later date.

 2012111312z ECMWF RUN NAO Values
 NAO value for forecast hour 000:  115.784065
 NAO value for forecast hour 024:  89.1970596
 NAO value for forecast hour 048:  134.995956
 NAO value for forecast hour 072:  140.430328
 NAO value for forecast hour 096:  164.703491
 NAO value for forecast hour 120:  146.786713
 NAO value for forecast hour 144:  69.299469
 NAO value for forecast hour 168:  0.320800781
 NAO value for forecast hour 192: -78.2510376
 NAO value for forecast hour 216: -100.020218
 NAO value for forecast hour 240: -108.136703
 NAO value for Day 1-5:  135.222717
 NAO value for Day 6-10: -43.3575363

-Chris

Posted by in Forecast