Scientific Forecaster Discussion
fxus62 ktae 200100
Area forecast discussion
National Weather Service Tallahassee Florida
900 PM EDT Tue Sep 19 2017
Rather than diminishing at sunset, as one would expect in late
Summer, this evening's showers and thunderstorms have become
stronger and more numerous across south al, where an outflow
boundary has developed. This mesoscale feature separates a pool of
relatively cool air and higher pressure to its north (across
central al) from a warm, moist airmass to its south (across our
forecast area). Additionally, based on the 8 PM EDT Tallahassee
raob, the airmass across our region has moistened and destabilized
considerably. We added evening pops for much our forecast area
(through 2 am) based on the expectation that at least scattered deep
moist convection may continue to be sustained along the slowly-
advancing boundary, which the recent rap runs has moving
southeastward. Our pop forecast is somewhat based on the latest
hrrr runs, except we had to extend the higher pops farther south
to account for the hrrr's incorrect storm initialization.
Aviation [through 00z thursday]...
We will update the kdhn taf to account for a greater potential
for thunderstorms and rain early tonight. Otherwise our previous thinking holds:
We expect mainly VFR conditions through Wednesday. As deep layer
moisture increases Wednesday, we expect more rain showers/thunderstorms and rain than what
we've had recently, especially across the Florida Panhandle. Scattered
to numerous thunderstorms and rain will develop along the sea breeze front Wednesday
afternoon, affecting kecp and ktlh at times. Elsewhere thunderstorms and rain will
be isolated, and have not been forecast at the other terminals in
this taf package.
Previous discussion [715 PM edt]...
Near term [through tonight]...
Isolated to scattered showers will diminish with the loss of daytime
heating this evening, giving way to partly cloudy skies and
continued muggy conditions. Given moist boundary layer conditions,
light patchy fog is not out of the question across portions of the
region, particularly in locales that see rainfall this afternoon.
Overnight lows in the low 70s are expected across the region
Short term [wednesday through Thursday night]...
A train of southern stream shortwaves will come crashing into the
southeast Wednesday and Thursday. These waves will eventually
consolidate as upper-level winds become north-easterly when broad
low pressure forms over the mid-Atlantic and northeast influenced
by Jose and a northern stream trough. A resultant surface trough
is likely to form across the southeast and force scattered
convection each afternoon. Pops will generally hover around 40%,
with highs around 90 degrees.
Long term [friday through tuesday]...
While the consolidating shortwave will remain trapped over the
southeast by Maria, deep-layer dry air will be funneling into the
region from the north/northeast. Thus, pops will remain rather low
beginning this weekend, with highs in the upper 80s.
Light winds and low seas will prevail through the remainder of the
week. By the weekend, easterly flow could result in some nocturnal
wind surges at or above 15 knots.
Low dispersion values below 20 in the afternoon expected Wednesday
and Thursday afternoons. Patchy fog is possible in the early morning
Average rainfall totals over the next several days are expected to
be less than a half of an inch. Area river levels are continuing
to fall across much of the region, and have crested near or in
action stage across the Suwannee. Thus, there are no flooding
concerns over the next several days.
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 72 90 71 89 71 / 20 40 20 40 20
Panama City 76 86 74 86 74 / 20 40 20 40 20
Dothan 71 89 71 90 70 / 50 40 20 40 20
Albany 71 90 71 90 70 / 40 20 20 40 20
Valdosta 70 89 71 88 70 / 20 20 20 40 20
Cross City 69 91 70 89 70 / 10 10 10 20 20
Apalachicola 74 87 74 87 74 / 10 30 10 40 20