AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
416 AM EST Fri Dec 14 2012

.NEAR TERM [Through Tonight]…
The 03 UTC regional surface analysis showed a 1028 mb high pressure
system centered over northeast GA, helping to provide northeast
winds across our forecast area. Vapor imagery and upper air data
showed a ridge from Mobile to the lower Great Lakes, and a trough
over CA. A strong subsidence inversion was located at about the
940 mb level (roughly 2300 ft) at 00 UTC at Tallahassee, helping to
“lock in” the low clouds below. Little change in the inversion is
likely today given our proximity to the 500 mb ridge, so the clouds
will once again be problematic today. On the one hand, the cloud
layer is thin (1000 ft or less), which would argue for quick
dissipation after sunrise. On the other hand, the strong inversion
and low sun angle will limit mixing (and subsequent cloud
dissipation). Based on these competing factors, and the latest
consensus of NWP guidance, we expect the sun to finally break
through this afternoon. As is usually the case in these scenarios,
the various MOS are quite warm, with highs well in the 60s. If the
clouds don`t dissipate (which is possible), highs will remain in the
50s all day…just like Thursday. To account for this uncertainty we
adjusted our high temperature forecast down by about 5 degrees. If
it appears that the clouds are lifting by late morning or sooner,
the next shift will need to adjust our temperatures back toward the
warmer MOS.

&&

.SHORT TERM [Saturday Through Sunday]…
The 500 mb flow pattern over the CONUS will be more progressive than
we`ve seen for a while, but the storm track will still be a bit far
to the north to significantly impact our region with significant
severe weather threats or arctic air outbreaks. The trough currently
over CA will quickly shear out to the northeast and buckle the
Southeast U.S. 500 mb ridge a bit on Saturday, but very weak Q-G
forcing and limited deep layer moisture will keep our PoP at 10% or
less. Our next chance of rain will begin Sunday as a cold front
approaches from the northwest. The PoP will range from 40% around
Dothan and Albany to less than 20% at Cross City. Temperatures will
be back to being above average, but not as warm as what we observed
leading up to this current “cool” snap. Lows will be in the mid to
upper 40s Saturday, and in the 50s Sunday. Highs will be in the
lower to mid 70s. Our high temperature forecast is a few degrees
cooler than the MOS consensus, as there is some question about how
long any fog/low clouds that develop overnight will linger into the
day (a problem we often have to address this time of year when
temperatures are warm).

&&

.LONG TERM [Sunday Night through Friday]…
The period begins with a frontal system moving into the region.
While several prior model runs have indicated a more energetic
system, the latest GFS and Euro runs from 14/00z take the bulk of
the energy well to the north of the region. Nevertheless, moderately
fast mid level wind fields could support a strong storm or two on
Monday before the surface frontal boundary moves through the
forecast area. There is fairly good consistency here between the
available guidance so high end chance to likely pops will be used
into Monday.

By Tuesday afternoon high pressure will begin to build over the
region. While there will be a cool shot of air behind this system,
it certainly doesn`t appear to be terribly cold air. In fact, it may
be a challenge to even get temperatures Wednesday morning to drop
into the mid 30s. As the pattern across North America is expected to
remain quite fast, the weather pattern will shift from high pressure
on Wednesday and Thursday to the next storm system arriving by
Friday. There is a lot of uncertainty with the temperature forecast
Friday and beyond with the guidance flipping back and forth between
a more temperate frontal passage (this cycle) and an arctic blast
(last cycle). For now, will trend temperatures several degrees below
climo at the end of the forecast period.

&&

.AVIATION [Through 12Z Saturday]…
Extensive low ceilings that persisted over TLH/VLD on Thursday
have moved back in to all terminals producing at least MVFR
conditions and many areas of IFR level cigs. While this is a very
shallow saturated layer, expect the low clouds to last well
through the morning and possibly into the afternoon hours at
TLH/VLD where VFR conditions may not return until as late as 20z.
VFR conditions are anticipated thereafter with the potential for
some restrictions returning by sunrise on Saturday at VLD/TLH.

&&

.MARINE…
As of 06 UTC winds were in the 10-15 KT range, which is generally
where they will stay through the weekend. (Though the direction will
veer from northeast today to south by Sunday).

&&

.FIRE WEATHER…
Relative humidity is expected to remain above critical levels
through at least Wednesday.

&&

.HYDROLOGY
Despite widespread rain amounts of about one half to one inch over
the eastern third of our forecast area, river stages remain well
below action stage. This is likely to continue at least through this
weekend.