Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL
FXUS62 KTBW 080128
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
828 PM EST Wed Dec 7 2016
01Z water vapor H4 RAP analysis shows most of the CONUS under a
very broad longwave trough. This trough is anchored by a large
cut-off low spinning to the north of the Great Lakes region.
Closer to home we find the Florida peninsula under a moisture axis
associated with the southern stream jet...and this feature has
kept the presence of some high level cirrus over our northern
zones through the afternoon/evening hours.
At the surface...we find weak high pressure nosing into our region
from the north...with a trough/weakness in the pattern to the
south of the Florida peninsula and across the SE Gulf of Mexico.
Weak but persistent isentropic upglide/WAA over this boundary is
responsible for a band of clouds...mainly above 5KFT across the SE
Gulf and extending into far south Florida. These clouds are
currently just south of the Fort Myers area...but all NWP
indications are that the axis of upglide/moistening will shift
north and northeast overnight and these clouds will begin to
overspread areas to the south of the I-4 corridor. The further
south...the more likely skies are to be mostly cloudy or cloudy by
the time the sun rises.
Further north...the increase in clouds will hold off until during
the day Thursday. With more clear skies late tonight and light
winds under the ridge...will be expecting areas of shallow ground
fog to develop across the Nature Coast...and extending down into
Polk/Hillsborough Counties. The SREF/NARRE are in good agreement
on the placement of this fog and inherited forecast is also in
good agreement. Some patches of dense fog are always
possible...but in general not anticipating a widespread dense fog
Low temperatures by sunrise ranging from the upper 40s north of
Brooksville... to the 50s through the middle of the
peninsula...and lower 60s down toward Fort Myers.
Forecast discussion for Thursday fore earlier today below still
.AVIATION (08/00Z through 09/00Z)...
VFR through 06Z for all terminals. Strong agreement in the
guidance that we will see fog/low cigs developing north of the I-4
corridor and drifting southward late night. Best potential to see
a period of MVFR/IFR vis will be at KLAL. Lower potential but
still possible for a brief MVFR/IFR cig to reach KTPA/KPIE between
10-14UTC. General VFR conditions for much of Thursday...with
increasing clouds above 5KFT through the day. Further
south...increasing clouds through the overnight for
KPGD/KFMY/KRSW...but generally above 5KFT...and no significant
restrictions expected through TAF period.
.Prev Discussion... /issued 622 PM EST Wed Dec 7 2016/
SHORT TERM (Tonight - Thursday)...
The main concern for the first 24 hours of the forecast will be
fog development overnight. Low-level moisture will remain
plentiful, and surface winds will generally be a light drainage
flow. The only question is whether or not increasing cloud cover
will curtail radiational cooling. Visible satellite imagery
already shows some over-running cloudiness lifting northward from
the stationary frontal boundary to our south. Model guidance is in
good agreement that this will continue overnight, but there are
differences in extent and timing. Areas south of Tampa Bay are
the most likely to see too much cloud cover to allow for
significant fog overnight. From the Bay area north, clouds will be
slower to increase and should allow better radiational cooling.
With this in mind, will have patchy fog overnight around the Tampa
Bay area, then areas of fog for the Nature Coast. There is also a
fair chance that some areas will see dense fog, and advisories may
be needed later tonight.
Clouds will lower and thicken on Thursday with light rain and
showers developing over our southern zones in the morning, then
spreading northward into the Tampa Bay area during the afternoon.
I don`t expect to see measurable rain make it much farther north
than Tampa before sunset. Clouds and rain may keep temperatures a
bit lower than currently forecast.
LONG TERM (Thursday Night - Wednesday)...
A closed upper low sits over central Quebec with troughing
extending through the Great Lakes region. The trough moves slowly
eastward through Friday and deepens over northern Florida. The
upper flow over Florida becomes more zonal on Saturday with a 160
knot jet max over the mid- Atlantic region. On the surface, models
are in good agreement with the weather pattern through the
weekend. A disturbance develops along a stationary frontal
boundary extending over southern Florida and into the Gulf of
Mexico. This will bring our highest rain chances through the
period with 20-30 POPs from Tampa northward and 40-50 POPs south
of Tampa. This boundary moves south of Florida by late Friday as a
1037 MB high pressure center over the central U.S. moves eastward
and takes control of the weather over Florida. The gradient
between the boundary over southern Florida and strong high
pressure up north will produce Small Craft Advisory winds and seas
over the coastal waters by Friday morning and lasting through
Saturday morning. This will also allow for some of the coolest air
we`ve seen this season to advect into the region. The high and low
temps on Friday and Saturday will be 6-10 degrees below average
for this time of year. The high pushes east over the western
Atlantic by Sunday morning, which will cause a veering of the
winds to the east- southeast, allowing for the temps to rebound to
near normal for Sunday and into next week.
On Sunday is when the models begin to diverge. GFS is developing
a 1006 MB low pressure system and frontal boundary near the Great
Lakes. ECMWF is also developing a system as well, but not nearly as
strong keeping it around 1017 MB. The movement is also slower with
the ECMWF. Leaning more toward the GFS solution which would bring
the front through early Monday, which will prompt our next rain
event. Due to the uncertainty at this time, will keep POPs in the
20-40 percent range region wide. High pressure to the north moves
southeast and will bring clearing conditions by late Monday into
early Tuesday morning. Temperatures next week will be right around
Benign conditions will continue for about another 18-24 hours then
northerly winds increase to 20 knots or so behind a cold front
beginning late Thursday into Friday. Enhanced northeast flow will
continue through Saturday followed by decreasing easterly flow on
Sunday as high pressure moves by to our north. Small Craft
Advisories will likely be needed by Thursday night.
Very dry air will be in place on Friday with relative humidities
falling below 35 percent over portions of the nature coast. Winds
could exceed 15 mph, but ERC values are forecast to remain low
enough to preclude red flag conditions.
.Preliminary Point Temps/PoPs...
TPA 60 73 54 63 / 0 20 30 10
FMY 65 78 59 67 / 10 30 40 30
GIF 57 75 53 63 / 0 10 30 10
SRQ 60 72 56 65 / 0 30 30 10
BKV 50 72 49 61 / 0 10 20 10
SPG 61 72 55 63 / 0 20 30 10