Scientific Forecaster Discussion
fxus62 ktae 150034
Area forecast discussion
National Weather Service Tallahassee Florida
734 PM EST Thu Dec 14 2017
Near term [through tonight]...
A large, positively-tilted upper level trough lies across most of
the eastern and central conus, with the axis of the trough
stretching from the Great Lakes down to northwest Mexico. A +pv
anomaly at the base of the trough well to our west is helping
amplify the feature this evening. Locally, however, the flow is
mostly zonal with the southern stream upper level jet stretching
along the northern Gulf Coast, keeping US under a thick ribbon of
upper level cloud cover. At the low levels, our area has a vaguely
defined pressure pattern in place with weak low pressure
(~1016mb) along a dry cold front to our northwest (across northern
Alabama and central ms) and weak high pressure (~1020mb) well to our
east over Bermuda. Surface winds are calm to light and variable.
Overall, the forecast remains on track for mild conditions
tonight, with cloudy skies, calm winds, and low temperatures in
Previous discussion [629 PM est]...
Short term [tonight through saturday]...
Zonal flow aloft will prevail through much of the period as the
eastern Continental U.S. Trough lifts north and an east/west subtropical ridge
lifts northward across the Florida Peninsula. An area of +pv that will
mostly cutoff across northern Mexico and southern Texas tomorrow, will
move northeast through the Southern Plains and middle Mississippi
Valley Saturday through Saturday night. In advance of this wave, the
ridge will amplify a bit over the southeast on Saturday. At the
surface, a dry cold front associated with a shortwave moving off the
northeast coast today will gradually move through the southeast
through Friday afternoon on the nose of a building surface ridge. No
rain is expected over land with this front, though there may be some
across the northeast Gulf as a weak southern stream wave passes over
the front. Highs will generally be in the lower to middle 60s, with
overnight lows ranging from the upper 30s to the middle 40s. These
forecast highs and lows remain very close to seasonal norms.
Long term [saturday night through thursday]...
The extended range forecast becomes a bit more complicated due to
the lack of agreement on some details between the global models. In
general, a transition to a wetter pattern is expected. The 00/12z
gfs' differs from the 00z European model (ecmwf) in that they fail to cutoff the
southern half of the northern stream longwave trough as it moves
through the Pacific northwest. This essentially results in
differences as to how progressive the system is and just how dynamic
it is locally once it arrives. As of the 12z model cycle, the
Canadian has come into better agreement with the GFS on the more
progressive side. Regardless of the exact details, expect shower and
possibly thunderstorm chances to begin ramping up Sunday night. The
big question will be whether this system clears out of the southeast
by Wednesday morning, or if it lingers through the end of the week
when another front will approach from the northwest. Expect both
highs and lows to be above average until the frontal system clears
Aviation [through 00z saturday]...
In general, we're expecting VFR conditions with light and variable
winds that become northwesterly tomorrow in the wake of a dry cold
front. GFS shows some weak isentropic ascent around 295 k over
parts of North Florida and south central Georgia with model soundings
showing a moist cloud layer starting around 20kft- 25kft.
Therefore, cannot rule out some scattered MVFR cigs near ecp,
tlh, and vld this morning around 08-10z and lifting around 12-15z.
Patchy fog will be possible in this area as well, but confidence
was too low to include in the taf package.
Winds and seas are forecast to remain below cautionary conditions
through the weekend. A brief uptick in winds to around 15 knots is
expected behind a cold front tomorrow through tomorrow night.
Winds will likely be around 15 knots on Sunday as well; otherwise
relatively light winds are forecast.
No meaningful rain is expected through much of the weekend. Late
Sunday through early next week, there's the potential for average
rainfall amounts of 1-3" with isolated higher amounts. The quantitative precipitation forecast early
next week remains uncertain as models differ significantly regarding
the details of the evolution of the frontal system. These rainfall
estimates are subject to change in either direction. Based on the
current amounts forecast, flooding is not expected to be a concern.
Spotter information statement...
Spotter activation is not requested. However, spotters are always
encouraged to safely report significant weather conditions when they
occur by calling the office or tweeting US @nwstallahassee.
Preliminary point temps/pops...
Tallahassee 46 65 41 60 46 / 0 0 0 0 0
Panama City 50 61 43 60 52 / 10 0 0 10 0
Dothan 42 54 34 56 43 / 0 0 0 0 0
Albany 41 58 35 57 42 / 0 0 0 0 0
Valdosta 44 64 40 59 44 / 0 0 0 0 0
Cross City 49 71 45 65 48 / 10 0 0 0 0
Apalachicola 53 67 46 61 54 / 10 10 0 0 0
Florida...high rip current risk until 1 am EST /midnight CST/ Friday for