Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tallahassee Florida
839 PM EDT Thu Sep 18 2014
Near term [through tonight]...
isolated convection has diminished for the evening. A steady
stream of mid and high level clouds is likely overnight with
lows ranging from the mid 60s to the lower 70s.
[through 00z saturday] mainly VFR conditions are expected through
the period at the terminals. There is a chance for a brief period
of MVFR to possibly IFR conditions around vld for a few hours
around sunrise. Isolated to scattered convection is also expected
during the afternoon hours on Friday with the best chance around
vld where a thunderstorms in the vicinity was included.
Prev discussion [344 PM edt]...
Short term [friday through Saturday night]...
A relatively low-amplitude wave currently near Arkansas should
continue digging southeast, leading to the development of a broad
mid-upper level trough centered just east of our area by Friday
afternoon. Models indicate that this may close off into a low
briefly on Saturday near the northeast Florida coastline. Either
way, our forecast area is expected to be on the back side of the
mid-upper level trough axis. Because of this, isentropic descent
is noted at most layers (295-315k), associated with weak
subsidence given our position relative to the trough axis. We
will, however, remain in a low-level easterly flow regime near the
base of a surface ridge axis. With pwats close to September median
values at tlh, this is a flow pattern that can lead to some
isolated to scattered showers from the mid afternoon to evening.
Given negating factors for large scale vertical motion, we opted
to keep pops closer to the low end of guidance both Friday and
Saturday (20-30%, with 40% far east). While model guidance does
indicate some convective instability, these sort of patterns tend
to favor low-topped convective showers versus thunderstorms, so
the forecast wording reflects a lower chance of storms.
The expanding low-level surface ridge and east to northeast flow
should lead to some cold air advection in those layers. Model consensus 850mb
temperatures are forecast to decrease about 3-4c from this
evening through Saturday evening. The result should be a gradual
cooling trend through the period, with highs on Friday from the
upper 80s to around 90, and highs on Saturday in the mid 80s. It's
Worth noting that Tallahassee has not observed a day with below
normal temperatures (by avg temp) since August 1st, and that may
finally occur during this forecast period (especially saturday),
although it will likely be very close.
Long term [sunday through thursday]...
There is a little uncertainty in the models regarding the exact
evolution of the mid-upper level flow pattern next week, although
it has been a consistent trend to show significant amplification
over North America. The one consistent trend has been the
establishment of a persistent easterly low-level flow regime
across our area as another strong surface high builds into the
northeastern US. This should keep isolated to scattered showers in
the forecast (mainly in the late afternoon and early evening),
with temperatures moderating close to seasonal normals.
Much of the forecast period will be dominated by a surface high
pressure ridge over the eastern US, which will place the coastal
waters in an easterly flow regime on most days. Several periods of
enhanced easterly flow seem likely: (1) from Friday to Saturday
with scec winds possible offshore -and- (2) beginning Wednesday
with scec winds likely.
Relative humidity values and other parameters are not expected to approach red
flag levels during the next several days.
Generally light rainfall amounts are expected for the foreseeable
future, except in very localized instances. Therefore, we are not
expecting any significant flooding issues over the next week.
Preliminary point temps/pops...
Tallahassee 69 90 68 86 67 / 10 40 30 30 20
Panama City 72 89 71 87 70 / 10 30 30 20 20
Dothan 66 89 68 85 65 / 10 20 20 10 10
Albany 68 88 68 85 65 / 10 30 20 20 10
Valdosta 69 87 66 84 66 / 10 40 30 40 20
Cross City 70 87 66 86 66 / 10 40 30 40 20
Apalachicola 71 87 72 84 71 / 10 30 30 30 20