Flash Flood Warning 10, NWS Tallahassee, FL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
429 PM EDT SAT AUG 1 2015

.Near Term [Through Tonight]...

A northeast to southwest oriented surface trough extended from near
Destin across Tallahassee to near Valdosta at 18Z, and will remain
generally stationary through tonight. A wave of low pressure is
discernible over TLH. Deep layer southwesterly flow will continue
to funnel tropical moisture into the eastern FL Big Bend south of
the boundary. It is this area that is most vulnerable for flash
flooding. Radar estimates anywhere from 7 to 11 inches of rain has
already fallen across western Dixie County since yesterday. Our CAM
guidance continues to be bullish with potential storm total
rainfall. Probabilities of 6 and 9 inches are around 60% and 40%
respectively. With increasing confidence that the heaviest rains
will occur over the eastern FL Big Bend, we will trim out a row of
counties from the northwest edge of the flash flood watch. We won't
shave it any closer than that though as PWs are quite high and
precipitation efficiency should be as well. Therefore, even areas
north of the trough could get some localized flooding.

.Short Term [Sunday Through Monday Night]...

The area will remain under the eastern edge of a mid-upper level
ridge while the stalled surface front bisecting our forecast area
from Destin to Valdosta will slowly shift eastward through the
period. Models are in good agreement that dewpoints along and
ahead of the surface front will be in the mid-upper 70s during the
daytime hours with PWs around 2-2.5" (about 30-40% above normal
during the time when annual values peak) and CAPE values that will
peak around 1500-2000 J/kg ahead of the front during the day as
well. With all of the ingredients in place, high coverage of
thunderstorms is expected along and ahead of the front, with more
isolated convection behind it. Wind shear will be quite weak with
the high pressure aloft, so storm motion will remain slow to
almost static. With lots of environmental moisture and little to
no storm movement, we expect periods of heavy rainfall will
continue in the Florida Big Bend and south central Georgia through
Sunday and therefore have extended the watch out in time for the
zones still expected to receive the most rain. By Monday night, we
expect the front to have shifted eastward enough such that the
highest chances will be mostly southeast of a line from
Apalachicola to Madison, with the highest rainfall totals expected
to be south and east of our area.

.Long Term [Tuesday Through Saturday]...

There is some model discrepancy with how quickly the stalled front
will exit our forecast area, so kept chances highest (around 40%)
along the Big Bend through Wednesday. Although the front will begin
to decay or completely exit the area by mid-week, another
disturbance to our northwest will begin to slowly sweep through the
area and increase coverage of convection beyond what we would
normally see with our late-season sea breeze. Thus, rain chances
will be high (40-50%) across the area Thursday through the weekend.
Highs will return to the low 90s and lows will stay in the mid
70s.

&&

.Aviation...
[Through 18Z Sunday] Scattered to numerous showers and thunderstorms
will occasionally reduce cigs/vsby down to MVFR or IFR with the best
chances of this happening at VLD and TLH. Overnight, another round
of IFR ceilings is now in the forecast at ABY, VLD and TLH from
roughly 08-13Z.

&&

.Marine...

As a stalled frontal system crosses the northern Gulf coast, a
tightened pressure gradient in place ahead of the front will keep
winds and seas at advisory levels through Sunday. By Sunday night,
the gradient will weaken and winds and seas will quickly return to
normal levels.

&&

.Fire Weather...

No fire weather concerns through next week.

&&

.Hydrology...

Rainfall amounts on Friday were locally heavy across
the Southeastern Florida Big Bend and across portions of
Southwestern Georgia. With the very moist air mass still in place
across far Southern Georgia and into the Florida Big Bend, a flash
flood watch remains in effect through Sunday. Model guidance
indicates the heaviest rain amounts will be across the Southeastern
Florida Big Bend, where 3 to 5 inches of rain should be common
through Sunday night.

With the bulk of the heavy rainfall expected to fall across the
Southern portion of the area, and the lower part of the river
basins, the potential for river flooding in the days ahead is low.
Only the Steinhatchee River is anticipated to reach flood stage at
this time based on the latest QPF forecasts. The Suwannee at Fowlers
Bluff will reach action stage due to heavy rainfall and above normal
tides.

With the flash flood watch in effect, the primary concern will be
flooding in slow drainage areas, as rainfall rates should easily
exceed 3-4 in/hr with many of the storms through Sunday.

&&

.Climate...

The average temperature at Tallahassee International Airport in July
was 85.4 degrees. That makes this July the hottest month on record
at the TLH location. In Apalachicola, the average temperature was
also 85.4 degrees making it the hottest month on record at that
location as well.

&&

.Preliminary Point Temps/PoPs...

Tallahassee   75  93  75  95  74 /  50  40  50  40  20
Panama City   77  90  77  90  78 /  50  30  30  40  30
Dothan        74  95  74  96  74 /  30  20  20  20  10
Albany        74  95  74  97  74 /  40  20  10  20  10
Valdosta      74  91  74  95  74 /  60  50  30  40  20
Cross City    74  86  74  88  74 /  90  90  70  60  30
Apalachicola  78  90  77  91  77 /  70  40  50  50  30

&&

.TAE WATCHES/WARNINGS/ADVISORIES...

FL...FLASH FLOOD WATCH through Sunday evening FOR Coastal Dixie-
     Coastal Franklin-Coastal Gulf-Coastal Jefferson-Coastal
     Taylor-Coastal Wakulla-Inland Dixie-Inland Franklin-Inland
     Gulf-Inland Jefferson-Inland Taylor-Inland Wakulla-
     Lafayette-Leon-Liberty-Madison.

     HIGH RIP CURRENT RISK until 10 PM EDT /9 PM CDT/ this evening
     FOR Coastal Franklin-South Walton.

GA...FLASH FLOOD WATCH through Sunday evening FOR Brooks-Lanier-
     Lowndes.

AL...NONE.

GM...SMALL CRAFT ADVISORY until 8 PM EDT Sunday FOR Coastal waters
     from Suwannee River to Keaton Beach out 20 NM-Waters from
     Suwannee River to Apalachicola FL from 20 to 60 NM.

&&

NEAR TERM...WOOL
SHORT TERM...MOORE
LONG TERM...MOORE
AVIATION...WOOL
MARINE...MOORE
FIRE WEATHER...FOURNIER
HYDROLOGY...WESTON