Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 170830
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
430 AM EDT Thu Apr 17 2014
...Heavy Rain Likely on Friday with Widespread Flooding Possible...
.Near Term [Through Today]...
Water vapor imagery and model analysis indicate a broad upper level
trough over much of the CONUS this morning with a short wave moving
from the Southern Rockies out into the Southern Plains. Surface
analysis shows high pressure centered over New England ridging
southwestward to the northern Gulf of Mexico with a front stalled
over the southeastern Gulf and Yucatan Peninsula. Satellite imagery
indicates low clouds encroaching on the forecast area from the east
and south. This trend is forecast to continue through the day as
isentropic ascent on the 295-300K surfaces steadily increases and
pressure falls commence in the central Gulf as the upstream short
wave approaches form the northwest. PoPs will be confined to our FL
zones this afternoon and will mainly be in the slight chance
category. Any precipitation that falls will be in the form of light
stratiform rain. Despite the increase in cloud cover, temps will be
a few degrees warmer than yesterday with highs ranging from the
upper 60s north to mid 70s southeast.
.Short Term [Tonight Through Saturday Night]...
The entire short range forecast will revolve around a Gulf low
forecast to bring heavy rain and flooding throughout the Tri-State
region. The good news from a forecast standpoint is that models
are coming into a better consensus regarding the track and
intensity of the low; the bad news is that our confidence is
increasing that widespread heavy rains will overspread our local
area, further aggravating ongoing river flooding with potentially
By tonight, an elongated southern stream +PV anomaly will have
merged with a northern stream anomaly, consolidated and
strengthened across the Southern Plains and Lower Mississippi
Valley. As this feature moves over an enhanced low-level
baroclinic zone across the northeast Gulf, surface cyclogenesis
will begin. By early Friday morning, a closed circulation will
have formed just south of New Orleans, with a large stratiform
rain shield spreading across the northern Gulf. As the surface low
intensifies under the large area of stratiform rain, so too will
the upper level anomaly, though it will begin to cutoff from the
northern stream flow as -PV advection occurs aloft atop the large
rain shield. As the upper anomaly strengthens and cuts-off through
the first part of the day Friday, the forward propagation of the
surface low will slow, with the system becoming more vertically
stacked by Friday night. Luckily, another southern stream anomaly
will be propagating eastward into the western Gulf overnight
Friday, keeping a rather steady west wind aloft and allowing the
system across the Southeast to gradually drift away from land into
the western Atlantic by mid-morning Saturday.
A very moist maritime tropical airmass will be in place across the
Tri-State region on Friday with PWAT values nearing 2 inches
across north Florida. That is approaching +3 standard deviations
above the norm. Further, synoptic ascent will be maximized locally
with the proximity of the surface low and the deep layer ascent
provided by the split flow regime. This will result in widespread
heavy rainfall nearly all day on Friday. At this time it appears
as though 3 inches of rain will be common across southeast
Alabama, south Georgia, and north Florida. With average amounts
that high, confidence is increasing that isolated locations could
pick up anywhere between 3-6 inches. That being said, this
rainfall will likely fall over an extended period of time
resulting in, for the most part, slow water rises. For that
reason, have opted for a more general Flood Watch as opposed to a
Flash Flood Watch. However, the flash flooding potential is non-
zero and will be highest near rivers currently running at high
levels and in our more urban locations.
Severe weather is not anticipated with this system, though a few
thunderstorms may be possible across the extreme southeast Big
Bend of Florida on Friday afternoon.
One last thing to mention is that afternoon "highs" will be quite
low across most areas on Friday with prolonged rain and
cloudiness. Portions of south Georgia and southeast Alabama will
struggle to reach 60 degrees while most other locations will top
out in the middle 60s.
By Friday night, the heavy rain threat will have diminished,
though light showers will continue on the back side of the
departing low pressure until it has moved far enough east. Most
areas should be rain free by Saturday afternoon, possibly Saturday
evening closer to the Suwannee River Valley.
.Long Term [Sunday Through Thursday]...
By Sunday, slight ridging will begin to settle in the area allowing
for a break from precipitation. The next chance of rain occurs
Tuesday when the flow will become more zonal and a shortwave to the
north of our area will bring a slight chance of rain and isolated
thunderstorms to the northern counties. Throughout the entire period,
temperatures will be near climatology with highs in the lower 80s,
and lows in the upper 50s.
[Through 06Z Friday]
MVFR ceilings will overspread the aerodrome from southeast to
northwest during the 08-12z time frame and then remain in place
for the remainder of the period. Exceptions include VFR ceilings
AOB 4 kft at DHN and ABY during the afternoon and early evening
hours and IFR possibly setting in toward the end of the period at
ECP with the commencement of a steady rain.
Advisory level conditions will continue through this evening for
the northern Gulf at the base of strong high pressure stretching
down the eastern U.S. coastline. Late tonight a strong surface low
will near our waters and may bring gale conditions through Friday
for waters west of Apalachicola. To the east Advisory conditions
will likely prevail through the passage of the low pressure. The
possible gale conditions will subside by Friday night, with
advisory conditions diminishing by Saturday evening.
Low level moisture will quickly increase across the region with a
wetting rain expected across the entire region from late tonight
through Friday night. Drier and breezy conditions will then arrive
for most of the weekend. However, it does not appear that RH will
get low enough to be concerned about red flag criteria, especially
with the wet fuels.
Heavy rains across the FL Panhandle on Tuesday resulted in sharp
rises on the Chipola River where the Altha gage crested about 2 ft
above moderate flood stage. Only minor rises occurred on the
Choctawhatchee, Apalachicola and Ochlockonee Rivers. Most of
the area rivers have crested and are falling slowly, but steadily.
More heavy rain is expected Friday. Rain totals of 1 to 3 inches are
possible with 2 to 4 inches possible in the Florida Big Bend region.
Isolated higher totals are possible. This will reverse the
aforementioned recessions and likely return some rivers to flood
that had dropped below in the interim. Also, stages continue to
steadily rise on the Suwannee River and flooding is expected early
next work week.
As rain rates should be more gradual with this system than the last,
and with the above rainfall totals expected to fall over 12-24
hours, the flooding threat with this next round of rain should be of
the areal/river variety. The flash flooding threat should be lower.
In other words, areas of existing high water or flooding may
worsen... and areas of high water could also develop in places like
fields or low-lying areas. River flooding will also be possible,
particularly in rivers around the Florida Big Bend and Apalachee Bay
The most up-to-date river forecast information can always be found
on our AHPS page (below):
.Preliminary Point Temps/PoPs...
Tallahassee 73 56 65 52 70 / 20 90 100 60 30
Panama City 72 57 65 55 73 / 20 90 100 40 10
Dothan 71 52 60 51 73 / 10 90 100 50 30
Albany 70 52 59 50 68 / 10 80 100 60 30
Valdosta 72 56 66 52 65 / 10 70 100 60 30
Cross City 75 62 73 59 69 / 20 70 90 50 20
Apalachicola 70 61 67 55 71 / 30 90 100 40 10
FL...Flood Watch from late tonight through late Friday night for
Calhoun-Central Walton-Coastal Bay-Coastal Dixie-Coastal
Franklin-Coastal Gulf-Coastal Jefferson-Coastal Taylor-
Coastal Wakulla-Gadsden-Holmes-Inland Bay-Inland Dixie-
Inland Franklin-Inland Gulf-Inland Jefferson-Inland Taylor-
Inland Wakulla-Inland Walton-Jackson-Lafayette-Leon-Liberty-
GA...Flood Watch from late tonight through late Friday night for
AL...Flood Watch from late tonight through late Friday night for
GM...Small Craft Advisory until 2 AM EDT Friday for Apalachee Bay-
Coastal waters from Suwannee River to Keaton Beach FL out
20 NM-Coastal waters from Apalachicola to Destin FL out 20
NM-Waters from Apalachicola to Destin FL from 20 to 60 NM.
Small Craft Advisory until 8 PM EDT Friday for Coastal waters
From Ochlockonee River to Apalachicola FL out to 20 NM-
Waters from Suwannee River to Apalachicola FL from 20 to 60
Gale Watch from late tonight through Friday evening for Coastal
waters from Apalachicola to Destin FL out 20 NM-Waters from
Apalachicola to Destin FL from 20 to 60 NM.