Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 032013
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
313 PM EST Mon Mar 3 2014
.Near Term [Through Tonight]...
The cold front has picked up some forward momentum this afternoon,
as the mid/upper shortwave has finally caught up to it. A thin, but
solid band of showers has redeveloped along the front as the entire
system has become more vertical. Thunder, or any sort of widespread
convection is not anticipated as dry mid-level air is capping deep
moist convection, and the upper wave is forecast to lift northeast
into the Mid-Atlantic through the remainder of the afternoon taking
away any forcing removed from the surface front.
The area of low pressure that has remained fairly stationary along
the NC/SC line will begin to weaken and drift southeast as the upper
wave moves away and the warm sector gets shunted southeast ahead of
a backdoor cold front. As the low drifts south it will aid in
increasing the forward speed of the cold front and subsequent,
temporary clearing. As the low dissipates and moves into the western
Atlantic, moist northeasterly flow will force a stable, saturated
layer under a substantial deep layer dry airmass. This will result
in an area of low cloudiness spreading southwest over the Tri-State
region through the night.
Expect overnight lows to fall into the mid 30s across most of south
Georgia and southeast Alabama, with temperatures increasing from
near 40 degrees along a line from Valdosta to Tallahassee, up to
near 50 degrees in Cross City.
.Short Term [Tuesday Through Wednesday Night]...
Expect an unsettled weather pattern thru the period. The large
scale pattern begins with weak troughing exiting Ewd into the Wrn
Atlc with the next disturbance amplifying over the Plains. A series
of H5 srn stream impulses (vorts) eject Ewd from this disturbance
and across SE region thru the period. The lead impulse/vort max should
move across LWR Ms Valley by Tues eve providing increased lift
further south. However as trough deepens...a second impulse drops
south across Nrn Gulf region Tues night and into Atlc on Wed. This
leave CWFA in weak WSW steering flow on Tues but deeper SW flow
Tues night into Wed. By Wed night...next and more impressive
trough develops over mid- continent and aided by third and Srn
most impulse...rapidly deepens SEWD to Wrn Gulf.
At surface...By Tues morning, Monday`s front will have advanced
to Wrn Atlc SEWD thru S/Cntrl FL into adjacent Gulf of Mex where it
stalls as it becomes parallel to SW flow ahead of the next UPPER
system. In its wake..cool wedge builds down Atlc seaboard yielding a
cool overcast dreary day especially for the Nrn tier of GA
counties. Max Temps Tues will be tricky depending on strength of
wedge/cold air advection with notable NE-SW temp gradient. However
coldest air remains well north of CWFA. By Tues night...wedge
begins to breaks down as above Gulf shortwave begins to travel
along stalled frontal boundary enhancing isentropic lift north of
it...inducing cyclogenesis and a developing low on front just east
of FL. Low then lifts Newd likewise lifting front Nwd increasing
local isentropic lift. This will support increasing RA from SW-
NE Tues night ahead of shortwave with rain exiting from NW-SE thru
Wed as second shortwave crosses Nrn Gulf of Mex. By Wed
aftn...third shortwave develops cyclogenesis off TX coast with
cold front extending SSW in gulf and warm front extending Ewd
across extreme Nrn Gulf. By 12z Thurs...low has advanced to
E/Cntrl Gulf (father south and weaker than previous guidance) with
rain ahead of low overspreading local region from SW-NE. Will
leave out Tstms from GRIDS except for extreme offshore waters
where instabilities decent Wed night .
Expect Highs Tues from near 50 ne tier GA counties to upper 60s SE
Big Bend rising on Wed to mid-upper 50s northern GA counties to upper
60s south. Lows Tues night from near 40 north to upper 40s south...
and Wed night mid 40s north to around 50 south. 40-20% W-E aftn POPS
on Tues...80-50% NW-SE Pops Tues night...30-60% NW-SE POPS on Wed
increasing to 50-70% NW-SE Pops Wed night.
.Long Term [Thursday Through Monday]...
The main focus will be Thursday when the next round of shortwave
energy...strongest of the week...moves from LWR MS Valley to near
east coast. H5 cut-off low forms near base of shortwave deepening
trough over Gulf region. Each of the recent runs less pessimistic
and new 12z GFS now develops Surface low well south of 00z position
which was just south of AL/FL coast. New track places low trajectory
well south of our land area across N/Cntrl FL thru Thurs eve
with cold front remaining south of our area. Such a track would
put all of our forecast area in the cool sector. Will insert isold
Tstms only across extreme offshore waters which may be dropped if
next run consistent with current one. (NAM even drier and a bit
faster) Still with isentropic lift aided by passing waves...rain
chances remain high.
On Thursday night..as trough moves offshore and low exits into Atlc
rain decreases then ends from SW-NE. Ridging builds in aloft and
high pressure at surface with deep layer dry air on Fri but
progressive pattern develops quickly next Wrn trough which begins
to move quickly Ewd progressively flattening Ern ridge with
steering flow becoming increasingly SWLY with rising temps. This
trough reaches Gulf region by Sun eve with some model differences
mainly in timing with GFS more progressive. The GFS drags a weak
cold front across Sun eve the ECMWF keeps front to our west thru
Will go with 50-70% POPs on Thurs..0-30% SW-NE Thurs night...0-30%
Fri...NIL POPS rest of period except 40-20% NW-SE POPs on Sun with
the front. Highs upper 50s north to near 70 south Thurs...upper
60s Fri...70 to 75 Sat thru Mon. Lows Thurs night around 40 north
to near 50 south...40-45 Fri night...near 50 Sat and Sun nights.
[Through 18Z Tuesday] Generally, widespread MVFR ceilings prevail
across the region, with some scattering to VFR out ahead of a cold
front. Behind the front gradual scattering to VFR is possible,
though at least a brief period of low-end MVFR should be expected
in the wake of the front at KABY and KDHN. Later tonight, IFR
ceilings will likely spread southwest into the region, though the
southward extent is a bit uncertain at this time. KVLD, KABY, and
KDHN will almost certainly be affected by dawn.
Winds will continue to shift to the northwest at 15 to 20 KT
behind the cold front this afternoon, mainly over the Panhandle
coastal waters. Winds will become north around 15 KT over the
entire coastal waters overnight. Winds will be northeast to east
10 to 15 KT Tuesday and Wednesday. In the wake of a low moving
across the Gulf of Mex on Thurs..winds will veer and increase to
exercise caution then possibly to low end advisory levels well
offshore into Thurs night.
Relative humidity levels will remain above critical thresholds for
the foreseeable future. The only notable item is that dispersions
will remain quite low over the next couple of days.
Although several rivers still exhibited above-normal stage/flow,
those that were recently at flood stage were continuing to decline.
Today`s basin average rainfall totals will be less than a quarter of
an inch, which should not have much of an impact. The QPF for
Tuesday night/early Wednesday will likely be even less. Totals for
Thursday`s system will be 1 to 1.25 inches. The latest GFS
ensemble-based hydro forecast (MMEFS) does not forecast any of our
rivers to reach flood stage this week.
.Preliminary Point Temps/PoPs...
Tallahassee 41 60 45 62 50 / 0 20 60 50 60
Panama City 42 58 47 62 52 / 0 20 70 40 60
Dothan 36 54 41 62 47 / 0 30 70 30 50
Albany 36 52 40 59 46 / 0 30 70 40 50
Valdosta 41 57 42 60 48 / 20 20 60 50 60
Cross City 50 67 49 68 51 / 20 20 50 60 70
Apalachicola 45 60 48 61 54 / 0 20 60 50 60