I sent this email out to my customers eary this morning
At the 300-500 mb levels, upper air winds (jetstream) which
involve a series of longwave troughs and blocking ridges are
interconnected and interrelated all around the globe, this is called a
teleconnection. Part of this teleconnection is the North Atlantic
Pressure Oscillation (NAO).
The NAO has positive, negative and neutral phases. A positive
phase positions a warm upper air ridge in the eastern third of th U.S.,
a negative phase a cold upper level trough and a neutral phase a mean
upper level zonal flow.
During the winter of 1998-99 the NAO was in a positive phase
and coupled with a strong La'Nina pattern, a mild to warm winter in
Florida.
In the winter of 1995-96 the NAO stayed in a prolonged negative
phase, the end result a cold December through February in Florida.
In December 1989 the NAO moved into a month long negative
phase and we all remember the 100 year Christmas freeze. I was living in
rural Sumter County in North Central Florida and saw a max/min temp. of
40/32 on 12/22, 28/22 on 12/23, 32/16 on 12/24 and 49/8 on 12/25 with 58
consecutive hours below 32, unbelievable! During the past two
weeks the Northern Hemispheric global upper air wind pattern has been
retrograding(backing up westward) and long range global
models(ECMWF,UKMET,CGBL) in varying degrees forecast this trend to
continue.
Starting around the beginning of December the NAO will in
all probability move into a negative phase. As the retrograde of the
upper air pattern continues it's very slow movement, this will mean a
persistent and entrenched longwave trough setting up in the eastern
third of the U.S. including, Florida for 2-3 consecutive weeks!!! That
will result in repeated Polar and Arctic air outbreaks in the eastern
third of the U.S. including Florida.
Therefore we are updating our December weather outlook to
below normal temperature, from the slightly below normal temperature, we
first issued in the third week of October.
The official winter forecast from NOAA/NCEP for the SE U.S.
is for above normal temperature, tied to the La'Nina pattern hanging
tough but La'Nina is much weaker this year and a possible negative NAO
pattern overlooked. January and February 2000 may be slightly on the
mild to warm side here in Florida but we have to get through December
first.
Though December 1989 was brutally cold for Florida, the
following January and February of 1990 was mild as the NAO moved back
into a positive phase.
Sincerely,
Thomas Giella Weather And Consulting Services
Plant City, Fl.
Main Weather Site URL-
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http://kn4lf.tripod.com/index-31.html
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http://kn4lf.tripod.com/index-5.html
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http://kn4lf.tripod.com/index-10.html
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