AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
308 AM EST Mon Jan 21 2013
.NEAR TERM [Through Today]…
Based on overnight obs, dropped min temps 1-2 degrees for this
The large scale longwave pattern is highlighted by expansive H5
trough anchored from elongated vortex over Hudson Bay with axis into
Ern Conus and a ridge along west coast from Yukon to CA. Flow across
the SE region remains largely zonal with limited cirrus moving ewd
across mainly Srn portions of CWFA. At surface, one ridge of high
pressure extends Atlc across much of Gulf Coast and a second from
Cntrl Canada into Cntrl Plains across OH Valley. In between low
across St Lawrence Valley Canada with cold front down Wrn Atlc then
Swd to a low over SC the wwd to another low over AR. Locally this
translates to weak high pressure, light winds and mild temps south
During today, the trough will amplify and nudge ewd. This will drive
cold front Swd and thru our area during the aftn and into the Nrn
most Gulf of Mex by sundown. In its wake, mid continent high
pressure will expand ESE towards Gulf region. Some light fog may
linger past sunrise. With little lift and no dynamics, this will be
a dry front. Offshore winds will modestly increase in wake of front.
Strong Canadian high pressure will build in behind front but cold
air advection will initially lag so expect aftn high from upper 60s
north to low to mid 70s south.
.SHORT TERM [Tonight Through Wednesday]…
Winds will remain elevated overnight in the wake of the
aforementioned dry cold front. However, cold air advection will be
rather minimal by the time the front clears the Tri-State area.
Thus, have trended on the warmer side of the guidance envelope,
with low to mid 40s along the coast and across much of north
Florida. The coldest spots will be across southeast Alabama
and southern Georgia, where what is left of the CAA will drop
temps as low as the middle 30s.
On Tuesday, expect a much cooler afternoon than in recent days,
with highs in the middle to upper 50s across much of S.E. Alabama
and S. Georgia, and lower 60s across the Florida Panhandle. This
is warmer than most of the raw models would suggest, however, an
analysis of 850 mb temps would suggest that the warmer statistical
guidance is most likely the better solution in this case.
Tuesday night will be the coldest night of the week. The calm
center of high pressure will move closer to the Tri-State region,
though likely not move directly overhead until later in the
afternoon on Wednesday. Nonetheless, calm winds and clear skies
will promote optimal radiational cooling locally. Expect
temperatures near the 30 degree mark area wide, with the typically
cooler spots dipping into the upper 20s. Patchy frost may be
possible come Wednesday morning.
Wednesday`s forecast scenario will be similar to Tuesday, only
slightly warmer, with low to mid 60s expected area wide.
.LONG TERM [Wednesday Night through Sunday]…
After a transitional period on Wednesday and Thursday, the mid and
upper level flow pattern is expected to amplify once again with a
high-amplitude trough evolving over the eastern CONUS by Friday
and Saturday. The 20.12z runs of the ECMWF and GFS differ slightly
on the timing of the cold front associated with the developing
cyclone, but there should be a good chance of rain sometime from
late Thursday into Friday. The surface high, and shallow cold air
mass, that settles into the Southeast region in the wake of the
front next weekend is projected to originate from far NW Canada.
At the very least this looks like a recipe for another widespread
light freeze, with a small chance for the first hard freeze of the
season depending on the eventual strength of the cold front.
.AVIATION [Beginning 08Z Monday]…
VFR conditions will remain the norm through the period, with the
exception of perhaps patchy fog/haze for a few hours around sunrise
this morning (mainly near KVLD).
A dry cold front will pass over our Gulf of Mexico waters tonight
through tomorrow. With it, an increase in winds to cautionary
levels is expected. Thereafter, winds will fall to below headline
criteria until the end of the week when another front is expected
to bring cautionary, and possibly advisory level, winds and seas to
the northeast Gulf.
A dry cold front will move south across the forecast area today. In
its wake…cooler and much drier air will overspread the region into
mid week. Later today inland humidities will drop to around 25
percent but critical ERC and dispersion levels are not expected.
However on Tuesday afternoon…min RH will plummet to around 20
percent and dispersions and ERC values will likely reach critical
levels across portions of north FL. Therefore a watch was issued for
these areas. Red flag conditions are likely again on Wednesday
before the airmass begins to moisten up.
Meaningful rainfall is not expected in or around local basins,
rivers, or streams. Thus, there are no flooding concerns through