Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
228 PM EST Tuesday Dec 10 2013
Short term (tonight - thursday)...
models this afternoon are in relatively good agreement with
synoptic scale features during the short term period...so will
use a blend. A short wave trough moving through the Appalachians
this afternoon will exit east off the middle Atlantic coast tonight.
An attendant cold front now nearing the Florida Big Bend region will
move into the Nature Coast later this afternoon and evening then
into west central Florida overnight...before stalling out across the
south Central Peninsula on Wednesday as it becomes parallel to the
upper level flow. Limited moisture and weakening convergence along
and ahead of the front will limit rain chances with highest probability of precipitation
(20 percent) likely to reside over the Nature Coast this
evening...otherwise just expecting an increase in clouds and
perhaps a few sprinkles overnight.
During Wednesday and Wednesday night the aforementioned front will
stall out and become ill-defined close to Lake Okeechobee as
surface high pressure over the Ohio/Tennessee valleys is reinforced by a
stronger ridge building southeast from the Central Plains.
Adequate low level moisture and weak overrunning may produce some
low topped showers especially in the vicinity of the stalled
front...but at the moment think overall coverage will be too low
to include a pop mention...so for now will word for sprinkles
On Thursday strong high pressure (1038mb) advancing east toward
the middle Atlantic with an increasing northeast flow should help to
push the remnant frontal boundary south of the region during the
day with slightly cooler and drier air filtering in from the
north. May see some lingering showers or sprinkles across southern
most zones through early afternoon...otherwise skies should become
partly sunny across central and northern zones during the day as
the drier air filters in. The cooler/drier air in the wake of the
front will allow overnight lows and daytime high temperatures to
return to more seasonal levels first across the Nature Coast
tonight and Wednesday and then across the remainder of the region
during Wednesday night and Thursday.
Long term (thursday night - tuesday)...
extended forecast period will begin on Friday with long wave
troughing exiting the eastern Seaboard into the Atlantic. Global
operational runs and their ensembles are in good agreement showing
a more zonal or even slightly ridged middle/upper level pattern
developing in the troughs wake through at least Saturday morning
for our region of the Continental U.S.. this setup along with high pressure
parked to our north should provide seasonable temperatures and generally
rain-free conditions for the end of the week.
The pattern and forecast become more complex over the upcoming
weekend as the next piece of energy ejects eastward from the
Southern Plains and toward the southern Appalachians. It is with
this system that we begin to see divergence in the reliable long
range model solutions. The GFS ensemble members and their ensemble
mean seems to be a reasonable blend between the GFS and European model (ecmwf). The
operational GFS is a bit faster and more aggressive with its frontal
passage through Florida late Saturday into Sunday. Once again...a
blend is likely to be the more appropriate forecast in terms of
frontal timing and pre-frontal potential for precipitation.
Behind this system for the early portion of next week...some degree
of surface ridging looks to build to our north over GA/Carolinas.
The GFS is stronger with this feature providing more of a gradient
over the Florida Peninsula and rougher conditions over the eastern Gulf
compared to some of the other guidance members. Will use the GFS
pattern...but taper winds back somewhat...and await a better
guidance consensus in future forecast packages. Overall no
significant hazards are foreseen in the extended forecast time
period...with the risk of severe weather with the front appearing
low...and no significant risk of freezing temperatures at this
VFR conditions will continue through the rest of the day as a cold
front moves into the northern Florida Peninsula. Most shower
activity associated with the front should dissipate before reaching
the Tampa Bay area taf sites...with winds turning to the northeast
and then northwest behind the front. MVFR ceilings will fill in
behind the front early Wednesday morning...then begin to burn off
by middle morning.
pre-frontal southwest flow will shift into the northwest and north
and increase to cautionary levels and small craft range across the
near shore and offshore Gulf waters from Venice north to the
Suwannee tonight through early Wednesday as the front moves south
through the waters. Given these expected trends will hoist exercise
caution and small craft headlines for near and offshore waters
mentioned above in the 430 PM coastal package. Winds will become
northeast to east and diminish below headline criteria on Wednesday
as the front settles into the central Gulf waters. This decrease in
winds though will be short-lived as winds and seas will again
increase to cautionary or small craft late Thursday through Friday
as the pressure gradient tightens in response to strong high
pressure building toward the middle Atlantic coast. Winds will remain
elevated Friday night into Saturday as they veer into the southeast
and south as the aforementioned surface high to the north shifts
eastward into the Atlantic and low pressure develops over the lower
MS valley. During Saturday night into Sunday a stronger cold front
will approach from the west with southwest winds Saturday night
shifting into the northwest and north on Sunday as the front moves
south through the waters...with additional cautionary or small craft
headlines a good possibility.
drier air will filter into the region from the north on Thursday.
This drier air will produce several hours of humidity values below
35 percent across Levy and Citrus counties during the afternoon.
Despite these long durations though 20 foot winds and erc values
are expected to remain below critical levels...so no red flag
conditions are expected at this time. As the low level flow veers
into the northeast and east Friday into the weekend a slow increase
in moisture is expected which will keep humidity values above
critical levels with no other fire weather issues expected at this
Preliminary point temps/pops...
tpa 62 80 64 76 / 10 10 10 10
fmy 65 84 66 80 / 10 10 10 20
gif 60 80 62 74 / 10 10 10 10
srq 63 82 65 76 / 10 10 10 10
bkv 56 79 61 73 / 10 10 10 10
spg 64 79 65 74 / 10 10 10 10
Gulf waters...Small Craft Advisory from 7 PM this evening to 10 am EST
Wednesday for Englewood to Tarpon Springs out 20 to
60 nm-Tarpon Springs to Suwannee River out 20 to 60
Short term/marine/fire weather...57/McMichael