Wednesday, December 29, 2010

2010: Jacksonville Weather Year in Review

From the continual arctic blasts of cold air to start the year, to the long standing oppressive heat of the summer, and the lack of any substantial rainfall during the latter half of the year, the weather in 2010 will be remembered mainly for the extreme variations in temperature and lack of precipitation that were experienced across northeast Florida and southeast Georgia.  Overall, despite a record summer heat wave, the quick return to much colder than normal weather in December will help make 2010 one of the coldest years on record across the area.

The cold start to 2010 can be partially explained by the dramatic shift in the mid-latitude jet stream configuration associated with the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO). The switch began on New Year’s Day as an arctic air mass entered the region and started what would be the coldest 2 weeks in climate history across the forecast area. Most of the climate sites across the area set new all-time records for consecutive days with minimum temperatures at 32 degrees or less.
  • RECORD BROKEN: ≤ 32°F  Consecutive Day Streak
    -Old Record: 8 days (January 17-24, 1977)
    -New Record: 12 days (January 2-14, 2010)

The cold start to 2010 not only set records in the first 2 weeks of January, it ended up being the coldest start to the first four months of the calendar year (January through April) of all-time.
  • RECORD BROKEN: January to April 2010 Average Temperature
    -Old Record: 55.6°F in 1983
    -New Record: 55.2°F (4.1°F below normal)

The weather turned sharply warmer in May as it usually does in this region, due to a large ridge of high pressure that extended from the Western Atlantic Ocean across the southeast United States. This pattern remained in place over the entire summer season from May through September and was the cause of a heat wave that lasted longer than most ever have across the region.  Almost all of the climate sites in southeast Georgia and northeast Florida set new all-time consecutive day streaks of maximum temperatures greater than or equal to 90 degrees.
  • RECORD BROKEN: Consecutive # of Days Max Temp ≥90°F -Old Record: 44 days (Jul-Aug 1992)
    -New Record: 50 days
Indian summer conditions persisted after the heat wave broke in August and lasted well into September.  Although no official statistics are kept on Heat Index values during the summer months, normally during June, July and August heat index values top out around 100 degrees each day, but this summer the lack of afternoon convection to cool temperatures off and the high levels of relative humidity allowed for the heat index to reach 105 degrees or more on 60 days this summer, while the heat index actually reached an extremely dangerous 110 degrees or more on 13 separate days this summer. In fact, the summer of 2010 (May through September) will go down as the warmest on record.
  • RECORD BROKEN: May to September 2010 Average Temperature -Old Record: 81.2°F in 1957
    -New Record: 81.4°F (2.9°F above normal) in 2010

 The dry weather continued into December, but in addition to the severe drought conditions was the return to a negative phase in the (NAO) and (AO) which also allowed for early season arctic air masses to plunge into the region.  This will likely result in one of the coldest Decembers on record as average temperatures will run almost 10 degrees below normal.  
  •  RECORD BROKEN: Total # of Freezes
    -Old Record: 38 in 1977
    -New Record: 43 in 2010
  •  RECORD BROKEN: # of December Freezes
    -Old Record: 12 in 2000
    -New Record: 18 in 2010

Other Records
2010 Average Temperature
(Departure from Normal)

Jacksonville, FL (JAX)
Normal:  68.0°F
2010:  67.0°F 
(1.0°F below normal)
[3rd coldest year on record]

 Given the cold latter portion of the 2009-2010 winter and the near record cold we have seen in December, it is tempting to conclude that our area may be in for a brutally cold winter…but that is not necessarily the case. Most winter seasons see pattern shifts at some point, and recent events bear that out…December of 2009 was actually 1.4 degrees warmer than normal in Jacksonville with 10 days reaching 70 degrees or higher.  Despite the early season warmth, the rest of the winter turned abruptly colder, as noted in Table 2. A similar turnaround was noted in the winter of 1989-1990…after a record cold December averaging 7.7 degrees below normal, January and February turned almost balmy, averaging 4.4 and 6.5 degrees above normal, respectively.  The bottom line is that what happens early in a season is not necessarily an indicator of what the rest of the season will be like.

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