Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tallahassee Florida
431 am EDT Tuesday Apr 21 2015
Near term [through today]...
A split flow regime continues across North America this morning
with a highly amplified trough dominating the eastern 2/3 of the
continent. The subtropical jet is quite strong across Dixie with a
140-knots jet at 250 mb centered over la, MS and Alabama. Surface analysis
shows a cold front bisecting the area from about Albany to Panama
City as of 06 UTC. This front will continue to inch across the
remainder of the forecast area this morning and bring some much
overdue drying to the area. Probability of precipitation will be none today with afternoon
dew points dropping into the middle to upper 40s across our northern
zones with middle to upper 50s near the coast. Afternoon highs will
actually be a bit below normal across the northern 2/3 of the
forecast area with middle to upper 70s expected there. The Florida Big
Bend will reach the lower 80s.
Short term [tonight through thursday]...
Tonight should be a cooler night than we have seen in awhile with
drier air arriving from the north behind the cold front.
Tallahassee has not recorded a low temperature below 60 degrees since
April 5th, unless we briefly hit that mark this morning, despite
our normal low for this time of year being 53. However, lows in
the 50s seem likely across at least the northern half of our area,
with a good chance elsewhere away from the beaches.
Wednesday will be our second consecutive day with relatively low
humidity and seasonably warm temperatures as high pressure
controls the regional weather. Changes begin on Wednesday night as
the high quickly erodes. Rain chances will return to the forecast
after midnight on Wednesday night and into Thursday. Models are
focusing most of the quantitative precipitation forecast on Thursday in the southern half of our
area, closer to the higher thetae air mass lurking just offshore,
as moisture return will just be beginning. A few stronger storms
can't be ruled out - more on that pattern in the long term section
of this discussion.
Long term [thursday night through tuesday]...
From Friday into Saturday, our forecast area will be positioned on
the southern periphery of a strengthening band of middle-level
westerlies that should help reinforce a plume of steeper lapse
rates along the Gulf Coast region. When combined with more
substantial low-level moisture return, instability should be
building along the entire Gulf Coast in that time frame while the
stronger westerlies will contribute to moderate-strong wind shear.
This should set up a favorable environment for strong to severe
storms across the region once again. Models differ somewhat on the
timing of the largest waves of convection, but the main message is
that we will likely see some thunderstorms from Friday into
Saturday, and that there's a chance of some severe weather. Stay
tuned as the forecast details get further refined.
For Sunday into Tuesday, models are suggesting a bit more
northwest flow aloft on the backside of an East Coast trough which
could lead to lower rain chances, a slightly drier air mass, and
seasonably warm conditions.
[through 12z tuesday] a relatively brief period of IFR ceilings is
expected ahead of a cold front this morning at tlh and vld.
These ceilings should clear shortly after 12 UTC with VFR and
light winds prevailing thereafter across the region.
After a brief period of scec winds this morning, winds and seas
should diminish through Thursday due to high pressure. Winds
should veer around to a more southerly direction on Friday and
Saturday and could reach scec levels this weekend.
Relative humidity will actually drop below 40% each of the next two afternoons
across much of the forecast area. Fuels remain quite moist.
About the only fire weather concern is that dispersion indices
will be high both days, over 75 in some areas.
Minor flooding is occurring along parts of the Choctawhatchee
River and is expected to continue. Bruce is forecast to
eventually reach moderate flood stage in a couple of days. Minor
flooding is also predicted by the middle of the week on the
Kinchafoonee creek at Dawson. Increased releases from the Woodruff
dam will result in the Apalachicola rising above flood stage at
Blountstown tonight. With the expected releases to peak near
60kcfs, the river level at Blountstown will be near 19 feet by
Wednesday, still in the minor flood category.
Preliminary point temps/pops...
Tallahassee 81 57 85 64 83 / 0 0 10 20 40
Panama City 76 63 79 67 79 / 0 0 10 30 40
Dothan 75 56 82 61 80 / 0 0 10 30 40
Albany 75 56 84 61 79 / 0 0 10 20 30
Valdosta 79 56 85 62 82 / 0 0 10 20 40
Cross City 83 58 86 63 82 / 0 0 10 30 40
Apalachicola 78 64 81 68 80 / 0 0 10 30 50