Area Forecast Discussion
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FXUS62 KTAE 171314

914 AM EDT Thu Apr 17 2014

...Heavy Rain Likely on Friday with Widespread Flooding Possible...

.Near Term [Through Today]...
The 12z KTAE sounding this morning reveals that a dry airmass
remains in place, although some increase in mid-level moisture was
noted compared to the previous sounding. Overall, it should be
mainly dry today with increasing clouds ahead of an approaching
Gulf low. Isolated light showers could develop towards the end of
the day close to the coast. Only made a few minor changes to the
PoPs from the previous forecast.


[Through 12z Friday] MVFR ceilings will overspread the aerodrome
from south to north and remain in place for most of the day.
Exceptions include VFR ceilings AOB 4 kft at DHN and ABY during
the afternoon and early evening hours. IFR will set in with the
commencement of a steady rain which will overspread the region
from southwest to northeast.


.Prev Discussion [430 AM EDT]...

.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
significant impacts.

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.


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.

.Fire Weather...

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 /  10  90 100  60  30
Panama City   72  57  65  55  73 /  10  90 100  40  10
Dothan        71  52  60  51  73 /   0  90 100  50  30
Albany        70  52  59  50  68 /   0  80 100  60  30
Valdosta      72  56  66  52  65 /   0  70 100  60  30
Cross City    75  62  73  59  69 /  10  70  90  50  20
Apalachicola  70  61  67  55  71 /  20  90 100  40  10


.TAE Watches/Warnings/Advisories...

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-
     Madison-South Walton-Washington.

     High Rip Current Risk through late tonight for Coastal Bay-
     Coastal Franklin-Coastal Gulf-South Walton.

GA...Flood Watch from late tonight through late Friday night for
     Baker-Ben Hill-Berrien-Brooks-Calhoun-Clay-Colquitt-Cook-

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.



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