Area Forecast Discussion
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114
FXUS62 KTAE 131939
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
339 PM EDT Sun Apr 13 2014

.Near Term [through Tonight]...
As the influence of the ridge of surface high pressure that has been
in place across our area continues to be eroded, boundary layer flow
should increasingly veer to a S-SE direction. This should enable
greater low-level moisture to be advected N-NWwd around the
perimeter of the high pressure. 0-1km mixing ratios are projected to
increase from around 9 g/kg at 18z this afternoon, to around 12 g/kg
by 12z Monday (based on a consensus of NAM, GFS, and ECMWF). Most
model guidance shows a corresponding surge of higher low-level RH
from the S-SE overnight tonight. This will lead to an increase in
cloud cover - stratus building in mainly after 06z, combined with
cirrus. The greater cloud cover should lead to above normal low
temperatures tonight in the lower 60s. The cloud layers and winds
around 4-5 knots overnight may prevent much fog formation, but we
still included a mention of patchy fog. NAM forecast soundings show
some moderate vertical motion fields in the low stratus layer as it
arrives, so some sprinkles or drizzle can`t be ruled out. However,
that is really the only model that indicates that, so we have opted
not to include any mention of RW- or DZ at this time.

&&

.Short Term [Monday Through Tuesday Night]...
The recent stretch of fair and seasonably warm weather that we have
experienced during the past several days will be coming to an abrupt
end by Monday night and Tuesday, as the next system in a series of
shortwaves digs SE towards the NE Gulf Coast. This upper level
system is expected to develop a weak Sfc low which will race
northeastward towards NY and New England on Tuesday. This low will
drag a fairly strong cold front through the CWA on Tuesday and clear
the region on Tuesday night, with much cooler and drier air to
follow. Out ahead of the cold front, there will be some threat for
severe weather, mainly across SE AL and western portions of the FL
Panhandle where the Storm Prediction Center has placed its eastward
extent of a Slight Risk. However, both wind shear and instability
appear to be more limited for this event than the more significant
one last week, and this is becoming apparent in many of the Hi-res
mesoscale model runs which are now coming into temporal range for
our region. Nevertheless, still have a period of Isolated Svr Storms
in the grids in and around the Slight Risk area, with potential
damaging wind gusts being the primary threat. As for rainfall
amounts, which clearly caused the most widespread problems with the
previous system, the prognosticated situation continues to gradually
improve. While bands of heavy rainfall are still likely with this
developing low, it now appears that the models are in good agreement
that it will likely be too progressive to be an extreme rainfall
producer for our area, with the heavier rain bands propagating very
quickly to the east. Nevertheless, parts of SE AL could still see
1.5" to 2.0" of storm total rainfall (with locally higher amounts),
but most areas across the CWA should generally see between 0.75" and
1.5" of rain before all is said and done. See the Hydrology section
below for potential riverine impacts. Finally, with this upper level
shortwave digging so far to the south for this time of year, it will
be accompanied by a quick burst of some unseasonably cold air. Temps
on Tuesday will likely fall from west to east during the day, and
lows on Tuesday night could reach the mid to upper 30s over the
interior.


.Long Term [Wednesday Through Sunday]...
Given the latest more progressive Global model runs where the ECMWF
has come into very good agreement with the GFS, the overall fcst
confidence has increased substantially across our CWA. This should
result in a quick hitting, but quick exiting low pressure system as
the very progressive upper level synoptic pattern should have
swept any lingering showers or storms well off to our east by the
beginning of the period. In fact, this progression now appears to be
rapid enough to allow plenty of the cooler and drier air to become
quickly established over much of the CWA by Wednesday morning, with
the majority of the numerical and raw model guidance now showing low
temperatures dipping down into the mid to upper 30s across the
western half of the region. A mostly sunny and unseasonably cool day
will follow on Wednesday, with a gradual warming trend expected for
the end of the week and into next weekend. As for rain chances by
the latter part of the period, the models have begun to diverge
significantly once again, with the GFS still indicating the
potential for a possible two-pronged rainfall event, while the ECMWF
shows a split in the jet stream flow, which would allow one
shortwave to pass to our north and another to pass to our south.
This would leave most of the CWA protected with fair and seasonable
conditions, but it is clearly too far in advance to buy solely into
one of these solutions. Therefore, will plan on a compromised
resultant for the end of the period, using our statistically
verified blend of GFS/ECMWF/HPC guidance which has shown to be quite
difficult to beat over the long haul.

&&

.Aviation...
[through 18z Monday] VFR conditions with S-SE winds will prevail
today. Lower CIGS may build in overnight from the south or
southeast, particularly at TLH and VLD. MVFR CIGS seem most likely,
with IFR possible especially at those two terminals. A gradual
improvement in ceilings is expected on Monday morning. Some patchy
fog is possible.

&&

.Marine...
Winds and seas will begin to gradually increase out of the south
then southwest ahead of the approaching cold front on Monday night
into Tuesday reaching cautionary levels. After the cold front passes
through later from west to east on Tuesday, winds will quickly
increase out of the northwest to Small Craft Advisory levels over
the waters, with headline conditions lingering into Wednesday
morning. Furthermore, only a brief respite in the elevated winds and
seas is expected, as a tight pressure pattern is expected to keep
conditions fairly difficult for small craft for much of the week.

&&

.Fire Weather...
Relative humidity levels will remain above critical thresholds for
the next several afternoons. The next wetting rains should arrive
Monday Night and Tuesday.

&&

.Hydrology...
While a few of our area rivers remain in minor flood stage (except
for the Choctawhatchee river near Bruce which is at moderate flood
levels and will likely remain quite elevated for several days), most
have crested and begun to slowly recede. However, yet another batch
of rainfall on Monday night into Tuesday may cause some of these
rivers to return to minor flood stage. The good news is that the
models continue to come into better agreement that the low pressure
system which will be responsible for the coming rains will be very
progressive. Therefore, with the rain expected to come to an end by
late Tuesday afternoon or evening, now expect lower storm total
rainfall amounts across the CWA. These should generally range from
0.75" over the SE FL Big Bend to generally 1.0" to 1.5" elsewhere. A
few locations over SE AL could still see closer to 2.0" before all
is said and done, so expect any concerns caused by this system to be
minor.

The most up to date, specific river forecast information can be
found on the AHPS page at

http:/water.weather.gov/ahps2/index.php?wfo=tae.


&&

.Preliminary Point Temps/PoPs...

Tallahassee   63  82  62  73  39 /  10  20  50  70  10
Panama City   65  77  62  65  44 /  10  30  70  70  10
Dothan        62  82  57  65  36 /  10  40  90  60  10
Albany        63  82  62  66  38 /  10  30  70  70  10
Valdosta      63  85  63  73  40 /  10  20  50  70  20
Cross City    63  85  63  76  42 /  10  20  30  70  30
Apalachicola  66  77  65  69  46 /  10  20  50  70  10

&&

.TAE Watches/Warnings/Advisories...

FL...None.
GA...None.
AL...None.
GM...None.

&&

$$

NEAR TERM...LAMERS
SHORT TERM...GOULD
LONG TERM...GOULD
AVIATION...LAMERS
MARINE...GOULD
FIRE WEATHER...LAMERS
HYDROLOGY...GOULD






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