Area Forecast Discussion
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FXUS62 KTAE 200527

Area Forecast Discussion
National Weather Service Tallahassee FL
1227 AM EST Fri Jan 20 2017

.AVIATION [Through 06Z Saturday]...

Widespread area of RA continues to move eastward across the
region, with RA expected to clear at DHN and ECP within the next
few hours. All other TAF sites will see RA prior to daybreak. TLH
and VLD are currently seeing the development of low CIGS and fog
respectively at this hour, with these conditions expected to
persist until RA moves through later tonight. Low CIGS are
expected and areas of fog may redevelop as showers clear the area
from west to east through daybreak. VFR conditions to resume by
late morning.



.NEAR TERM [Through Tonight]...

A line of storms stretches along central AL and the western FL
Panhandle. With the loss of daytime heating, instability ahead of
the line of storms has fallen greatly. The 00Z RAP analyzes MLCAPE
values to be around 250 J/kg in southeast AL and southwest GA,
with values approaching 500 J/kg along the northern Gulf waters.
Our 00Z sounding reflects these paltry values with SBCAPE of 225
J/kg and mid-level lapse rates around 5 C/km. The low level jet
that was featuring values up to around 60 kts earlier has weakened
to around 35-45 kts. RAP forecasts for 0-1 km shear have fallen to
15-20 kts, though 0-6 km shear remains fairly high at around 50
kts. Overall, these storms and the environment are looking less
and less favorable for severe thunderstorms overnight, though
there remains a marginal risk for some isolated damaging wind
gusts or a brief tornado.

Timing for the storms however, still appears to be on track, with
our western zones beginning to see showers and thunderstorms over
the next few hours, then storms dissipating as they head further
east through the night.

.SHORT TERM [Friday Through Sunday]...

The aforementioned trough will be moving through the Tennessee and
Ohio valleys through tomorrow afternoon with southerly flow
prevailing at the surface on the western edge of high pressure. A
scattering of light to moderate showers are expected on Friday as
weak low-level (300K) isentropic ascent sits over the region.
These showers should come to an end by the evening.

The main concern in the short term period will be for the
potential for severe weather over the weekend. The northern stream
longwave trough will continue to amplify and move eastward across
the central CONUS in response to a few shortwaves; most notably a
strong shortwave moving through the Four Corners region. As the
broad longwave forcing moves along the Gulf Coast, a coastal
trough/low is expected to develop; thus increasing low-level
forcing and the low-level wind field. Deep layer shear will be
plenty from the northern stream trough and very steep lapse rates
are expected to be in place as well. This will favor discrete
storm development through the day across the Tri-State region with
all modes of severe weather possible. Saturday night into Sunday,
the potent shortwave that was over the Four Corners will move into
the southern Mississippi Valley and result in even more low-level
and upper-level forcing across the region. Lapse rates will still
be quite steep, though dampening a bit. However, a decent increase
in low/deep layer shear should compensate for the slight reduction
in lapse rates. With this second wave, a more organized squall
line is expected with the primary threats being tornadoes and
damaging winds, though severe hail can`t be ruled out along the
line as well. The local area currently resides under a Slight Risk
by the SPC for Saturday, and have a 15-30% risk on Sunday. Those
type of outlooks that far into the future tend to indicate a fair
amount of confidence in severe weather unfolding across the
region. The main variable will be the timing of the waves of
severe weather and whether the first will end up interfering with
the evolution of the squall line. Folks are urged to pay close
attention to the forecast over the next 24-36 hours. For
information on expected rainfall totals, see the hydrology
discussion below.

.LONG TERM [Sunday Night Through Thursday]...

As the system moves away from the region, some showers may
linger into Monday but the chance of severe weather should begin
to diminish. Also, fast offshore winds (20-30 kt) are expected
to decrease by Monday night. Afterwards, a cooler and dry air
mass filters in and stays over the CWA for a few days allowing temps
to cool down closer to the seasonal average. On Wednesday night
into Thursday, a low pressure system moves over Michigan into
the Northeastern seaboard while its corresponding cold front moves
into our area. There is some disagreement between the global models
as to the timing of the frontal passage. The ECWMF has the front
moving through the region by the end of Thursday which is quicker
compared to the GFS. However, both bring rain to the CWA beginning
Wednesday night.


Winds will begin to ramp up to Advisory levels late Friday night
ahead of a strong low pressure system. Advisory levels will
prevail through early next week, with Gale force gusts and
possibly sustained winds Sunday night through Monday. Seas could
climb as high as 15 feet well offshore by Monday afternoon.


No concerns.


Beginning tonight, 2 to 4 inches of rain are expected to fall
across the Tri-State region through Sunday night. Isolated amounts
around 6 inches will be possible as well. These amounts will most
likely fall over a long enough period that flash flooding wont be
a concern. While rises are naturally expected on area rivers, with
widespread average amounts probably wont force area rivers into
flood stage. Should the locally higher amounts fall over
Kinchafoonee Creek or the Choctawhatchee River minor flooding
could be possible there.



Tallahassee   77  64  74  64  76 /  40  50  80  80  70
Panama City   73  67  73  66  71 /  40  60  80  80  70
Dothan        76  63  74  61  71 /  40  60  90  80  70
Albany        77  63  74  62  74 /  50  50  90  80  80
Valdosta      77  63  75  64  76 /  30  40  80  80  80
Cross City    77  63  76  65  76 /  20  30  80  80  80
Apalachicola  73  67  73  67  73 /  30  50  80  80  70






SHORT TERM...Harrigan
LONG TERM...Harrigan/Chaney
HYDROLOGY...Harrigan is the U.S. government's official web portal to all federal, state and local government web resources and services.