Monday, March 09, 2015

More details on the record cold and snowy February for Northern & Eastern Maine, updated 3/7

February 2015 was a month to remember across New England and the greater Northeast U.S. in general.   It was one of the coldest Februaries on record with average temperatures 9 to 15 degrees below normal.  Caribou, Maine had its all-time coldest February on record with an average temperature of just 2.8 degrees, which surpassed 1993 when the average temperature was 4.1 degrees.  Even more impressive, Bangor set an all-time coldest month record.   The average temperature of 6.1 degrees smashed the previous record for February of 11.3 degrees in 1993.  It also broke the all-time coldest month record by more than 2 degrees. The old record of 8.4 degrees was established in 1994.

Across New England there were some other impressive monthly temperature records. Portland, Maine observed its coldest February on record, and the 2nd coldest month of all-time.  Boston, Massachusetts  and Providence, Rhode Island each had their 2nd coldest February and 2nd coldest month of all time.  Hartford, Connecticut had its coldest month ever on record.  Below is a map (Fig. 1) of the departure from normal temperatures (F) during the month of February from the Northeast Regional Climate Center.   Fifteen of the 35 airport climate sites had a record cold February (Fig.2)

In addition to the cold, many areas, especially coastal New England had record snowfall, with totals up to 4 ½ feet above normal (Fig.3).  Seventeen of the 35 airport climate sites had a top 10 snowy February.   Two sites (Boston and Worcester) had their all-time snowiest month on record.

The remainder of this article hopes to explore the upper air and surface weather patterns that produced the persistent cold weather across all of the Northeast U.S., and the snowy weather that was observed across much of coastal New England.  In order to do this, a reanalysis of upper air and surface patterns was examined using NOAA’s Earth System Research Laboratory’s reanalysis tool.  In the near future, plans are to examine in more depth the causes of this pattern with an examination of several climate indices.

First, we will examine the composite mean 500 millibar geopotential heights across the northern Hemisphere during the month of February (Fig.7).  One will note the persistence of the low 500 millibar heights across central Siberia, northern Canada, and into the Great Lakes and Northeast U.S.   If one takes a closer look at the 500 millibar composite anomalies (1981-2010 climatology) (Fig.8) negative anomalies on the order of 90 to 120 millibars are noted across the northeast U.S. including all of New England.  At the same time, strong positive height anomalies were noted west of the continental divide.  The persistence of the upper air pattern led to well below normal temperatures at the surface (Fig. 9) that corresponded well with the upper air anomalies.

Next, we will examine the surface pattern during the month of February.   A persistent surface trough was evident just off the Northeast U.S. coast (Fig. 10).  When one compares the composite mean surface sea level pressure to the 1981-2010 climatological mean (Fig.11) it becomes evident that surface pressures were lower than the climatlogical mean just off the Northeast U.S. Coast.   There were a number of surface lows that moved toward the Northeast U.S. coast from the west and intensified across the Canadian Maritimes.  The persistence of this pattern led to favorable conditions for significant snowfall along and near the New England Coast.

In the near future the NWS Caribou hopes to examine in more depth the causes of this pattern with an examination of several climate indices.


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