Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
335 am EST Thursday Nov 27 2014
08z water vapor and h4 rap analysis shows an amplified upper level
pattern across the Continental U.S. Consisting of longwave ridging over the
inter-mountain west...and downstream longwave troughing to the east
of the Continental Divide. Most of the inclement weather associated
with this eastern Continental U.S. Trough is now off the eastern Seaboard or
exiting the New England area. The trough axis is now passing our
longitude pushing the plume of deep tropical moisture further to our
east with time. Deep layer subsidence/drying has now overspread the
northern and central portions of the Florida Peninsula. One final
shortwave impulse to impact our region is clearly visible in WV
imagery as it rounds the trough base through the Tennessee Valley. This
impulse will propel a secondary cold front through the eastern Gulf
and Florida Peninsula today.
We saw an incredible drying of the column on Wednesday between the
26/12z ktbw sounding which had a precipitable water value over 1... the
27/00z sounding where the precipitable water value had dropped all the way down to
0.17". Huge dewpoint depressions greater than 40c were sampled from
almost the surface up to nearly 300mb. This 0.17" precipitable water value is near
(within a few hundredths of an inch) an all time low for late
November. In fact...it is a rare occasion that we see precipitable water values
lower than this at any time of year. The only clouds to speak of
this early am are some very thin high level cirrus streaming over
the southern peninsula on the periphery of the upper trough and
within the rrq of an impressive upper jet along the eastern
As mentioned above...another cold front is quickly approaching the
region from the northwest. The front as of the issuance of this
discussion was passing into the Florida Panhandle on its way toward
our region. Temperatures across the region under mostly clear skies
range from the middle 40s to lower 50s south...to the upper 30s and
lower 40s north. Not expecting much more of a temperature drop over
these cooler Nature Coast zones as the thermal ridge ahead of the
approaching front begins to arrive in the coming hours.
Short term (today through friday)...
upper trough axis will move to the eastern Seaboard through the day
while a secondary cold front makes a dry passage across the eastern
Gulf and Florida Peninsula. Generally speaking this front will be
accompanied by a wind shift...and a quick increase in winds over the
eastern Gulf and along the coast. Those with plans near the beach
should expect winds to become rather gusty from the northwest for
the afternoon hours. Have hoisted an elevated risk of rip currents
for the second half of the day in response to this increasing
onshore flow for the beaches of Pinellas...Manatee...and Sarasota
counties. Despite the cold frontal passage...temperatures today will
be seasonable with 60s north and upper 60s to around 70s south. The
developing gusty wind will make it feel cooler this afternoon...
especially near the coast. Conditions will turn much cooler this
evening as the sun begins to set.
a chilly night setting up in the wake of the front. High pressure
will still be well off to the northwest of the region which will
keep the gradient tight and at least some wind blowing through the
night. With the forecast high position...it will be difficult to
decouple the boundary layer...for even our far northern zones. With
this in mind...radiational cooling will not be much of a factor
tonight...but rather will be looking at an advection/drainage event
from the north. Generally speaking the MOS is biased too cold for
advection night...and kept temperatures at or just above the MOS ensembles
for low temperatures. This results in low temperatures ranging from
around 32 over inland Levy County...to the upper 30s and lower 40s
for the I-4 corridor and southward. Normally warmer spots under
northeast flow such as Pinellas County and the Sanibel region will
stay in the middle to upper 40s. If things work out this way then
freeze products will not be necessary...however it is a close call
up toward Levy County and will need to be monitored closely with
future guidance runs. Did include a mention of patchy frost for
portions of the Nature Coast where temperatures in the Lower/Middle 30s are
forecast. Conditions are even borderline for frost with a light wind
and dewpoint depressions of 3-5 degrees late at night. However...a
few more sheltered area could still realize a touch of frost toward
dawn. Wind chills will be a concern with widespread readings in the
30s early Friday morning...and even some upper 20s for the Nature
high pressure at the surface builds into northern Florida while the
upper level pattern begins to further flatten out overhead. Friday
is looking to be a dry and cool day with high temperatures
recovering by middle afternoon to around 60 for Chiefland...lower 60s
along the I-4 corridor and middle/upper 60s down toward Fort Myers.
However...should be looking at lots of sunshine and a bit less wind
to help the overall temperature feel for the second half of the day.
Have a safe and Happy Thanksgiving everyone!
Long term (saturday through next wednesday)...
the period begins with an upper trough across western Canada...an
upper ridge over the U.S rockies...a shortwave trough aloft
northwest Mexico...and a trough over Atlantic waters. At the surface
a frontal boundary stretched from the Pacific northwest to the
northern U.S. Plains while high pressure sprawled from the central
and eastern Gulf of Mexico to the lower Great Lakes.
With time the Canadian trough rotates down across the Pacific
northwest then over the northern plains while the Mexican short wave
trough tracks east. In response the upper ridge flattens and slides
along the Gulf Coast region through the southeast U.S. And out over
the Atlantic by the middle of next week. Meanwhile the frontal
boundary shifts eastward...strung out from the western Gulf Coast to
New England for the start of next week as high pressure builds over
the Central Plains. The high pressure originally from the Gulf to
the Great Lakes tracks out over the Atlantic but continues to ridge
back through the east and central Gulf Coast. During the early part
of the week the plains high moves east...bridging the by now
decaying frontal boundary...and reinforcing the ridge from the
The upper ridging moving by will be the dominate factor with a
dry airmass keeping the forecast rain free. Temperatures initially
near or just below normal gradually warm to normal to slightly
above. Surface high pressure north of the area will maintain a tight
enough pressure gradient for northeasterly and easterly
winds...robust at times especially on the Gulf.
VFR conditions are expected through the forecast period with winds
generally northwest to north.
a secondary cold front will quickly pass through the region this
morning and early afternoon. Winds and seas will quickly build to
advisory levels in the wake of this front for later this afternoon
through Friday morning. A few wind gust approaching gale force can
not be ruled out tonight as well. Winds and seas will gradual
subside on Friday as high pressure build to the north of the region.
This ridge of high pressure will remain in place to our north
through the upcoming weekend and keep winds across the eastern Gulf
of Mexico from an offshore east to northeast direction.
another cold front will make a dry passage across the region today
and be followed by high pressure building to our north for the
duration of the forecast period. Relative humidity values are
forecast to approach or briefly drop below 35 percent for much of
the region this afternoon...and once again on Friday afternoon.
Erc values are currently all below 27 which will keep red flag
conditions from being achieved both days.
No significant fog is expected to impact the region the next couple
Preliminary point temps/pops...
tpa 68 42 63 47 / 0 0 0 0
fmy 72 44 68 51 / 0 0 0 0
gif 68 40 64 47 / 0 0 0 0
srq 70 43 65 48 / 0 0 0 0
bkv 66 34 61 39 / 0 0 0 0
spg 66 48 62 53 / 0 0 0 0
Florida...rip current risk from noon EST today through this evening
for coastal Manatee-coastal Sarasota-Pinellas.
Gulf waters...Small Craft Advisory from 1 PM this afternoon to
1 PM EST Friday for Bonita Beach to Englewood out 20 to
60 nm-Englewood to Tarpon Springs out 20 to 60 nm.
Small Craft Advisory from 1 PM this afternoon to 10 am EST
Friday for Bonita Beach to Englewood out 20 nm-
Englewood to Tarpon Springs out 20 nm-Tarpon Springs
to Suwannee River out 20 nm-Tarpon Springs to
Suwannee River out 20 to 60 nm.
Small Craft Advisory from 4 PM this afternoon to 7 am EST
Friday for Charlotte Harbor and Pine Island Sound-
Tampa Bay waters.
Synopsis/short term/marine/aviation/fire weather...mroczka