Small Craft Advisory 40, NWS Tallahassee, FL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
301 AM EST Tue Nov 12 2013

...Blast of Arctic Air to Arrive Later Today...

.NEAR TERM [Through Today]...
Early this morning, the local forecast area remains in a weak
spot in the surface pressure gradient between relatively lower
pressure in the Gulf and near the Bahamas, and an anomalously
strong high pressure building south over the central Plains. The
result is relatively weak flow, and some locally dense fog has
developed in parts of south-central Georgia near Valdosta. This
will be monitored in case an advisory is needed. The main story
will be the approach of the strong cold front from the northwest
today. We remain far enough out ahead of the front currently such
that our highs should be fairly warm - around seasonal normals in
the mid-70s in most locations. The latest HRRR and local 4km WRF-
ARW show the front arriving in the northwest part of our area
around 18-19 UTC, with temperatures beginning to sharply fall
between 20-00 UTC. Therefore, we did not follow the usual diurnal
temperature curve in all areas. The frontal passage looks to be a
dry one, with most of the effects occurring behind the cold front.
More on that below.

&&

.SHORT TERM [Tonight Through Thursday]...
Aforementioned arctic front will blow through the forecast area
this evening as a sharp upper trough digs into the Deep South. A
shallow, but much colder air mass will pour into the forecast area
tonight on very gusty northerly winds, as a 1040mb surface high
slides south to the Missouri Bootheel. Winds are expected to gust
to near 35 mph this evening as the cold air advection kicks in.
However, current forecast keeps the winds just below wind
advisory criteria (gusts 40mph or higher or sustained 26mph or
higher).

Outside of the wind, the other concern overnight will be the
potential for a light freeze for southeast Alabama. Statistical
guidance as well as most raw numerical guidance shows portions of
southeast Alabama dropping below 32 degrees for an hour or two
around sunrise. While a pure advection freeze would be somewhat
unusual for early November, the agreement in the guidance has
convinced me to go with a Freeze Watch tonight for southeast
Alabama. The next shift can refine the numbers and make the
decision on whether or not to upgrade to a Freeze Warning. With
temperatures approaching freezing in this area and the strong
northerly winds, wind chill values will reach the lower 20s as
well.

The intense low-level cold advection will continue through the day
on Wednesday as the surface high slides east to the southern
Appalachians. High temperatures Wednesday afternoon are unlikely
to get out of the 50s for all of the region, except perhaps a
portion of Dixie County.

For Wednesday night, the 1033mb surface high is forecast to settle
over the Carolina Piedmont, with the gradient relaxing for the
forecast area. This ridge position is not ideal for radiational
cooling in the TAE CWA. However, give the arctic nature of the
airmass, winds should diminish enough to allow for a widespread
light freeze away from the coast. Lows are generally expected to
be between 29 and 32, but a few colder values are possible in well
sheltered areas. Will issue a freeze watch for most of the area
away from the coast.

&&

.LONG TERM [Thursday Night through Monday]...
Weak upper ridging returns on Thursday. The ridge slides east
Friday becoming centered over or just south of the Bahamas through
the weekend placing the local area in deep moist southwest flow.
The ridge is forecast to flatten Monday as the next trough moves
east from the Central Plains. A few embedded upper level
disturbances combined with increasing deep layer moisture will bring
an unsettled weather pattern with rain chances Friday through the
weekend. Then more rain is expected on Monday with the approach and
possible passage of the next cold front. After chilly mid week
temperatures, we will see a gradual warming trend through the
period. Min and max temps will be below seasonal levels through
Friday recovering to near or just above climo for the weekend and
the first day of next week.

&&

.AVIATION [through 06 UTC Wednesday]...
Despite high clouds encroaching on the area, some fog has developed
over SC-SE Georgia, with VLD roughly on the western periphery of the
area of fog. Latest observations have dipped below airfield minimums
(1/4SM visibility, and 100 foot CIGS). Therefore, we included a
temporary condition for dense fog through 11 UTC, although this may
need to be extended based on trends. At the other terminals, VFR
should prevail, and fog at VLD should dissipate by mid-morning. NW-N
winds will increase in the afternoon. Most gusts will be around
20-25 knots after 21 UTC, but peak gusts could reach as high as
30-35 knots - especially in the evening (after 00 UTC).

&&

.MARINE...
Conditions over the coastal waters will deteriorate rapidly late
this afternoon into the evening in the wake of a strong cold
front. Northerly 30 knot winds are expected by mid-evening over
the waters, with frequent gusts to gale force. The frequent gusts
to gale force necessitate a Gale Warning for the waters by mid-
evening lasting through early Wednesday morning. Thereafter, a
tight pressure gradient will keep Small Craft Advisory conditions
in place into much of Thursday. Conditions should drop below
headline levels by Friday into the weekend.

&&

.FIRE WEATHER...
Relative humidity levels today will remain above critical levels,
but we should see gradually increasing winds and high dispersion
values. Fuels will continue to dry today. Over much of the area,
the last ten days have not had any wetting rains. Tomorrow
(Wednesday), a much drier air mass will surge into the area behind
a cold front. The combination of low relative humidity and breezy
winds could create red flag conditions over much of our Alabama
and Florida zones. Despite earlier concerns about ERC values in
Florida, the latest ERC forecast for today has all zones at least
at 24, and with another day of drying it's at least conceivable
that any zones could reach the minimum threshold of 26 for red
flag criteria. Therefore, we expanded the Fire Weather Watch to
include all Florida zones. Relative humidity levels rebound
quickly by Thursday.

&&

.HYDROLOGY...
With minimal rain chances in the forecast, there will be no
hydrological concerns over the next several days.

&&

.PRELIMINARY POINT TEMPS/POPS...
Tallahassee   76  40  57  32  65 /  0   0   0   0   0
Panama City   74  40  57  40  65 /  0   0   0   0  10
Dothan        72  32  54  30  62 /  0   0   0   0   0
Albany        73  33  54  29  63 /  0   0   0   0   0
Valdosta      76  38  55  33  64 /  0   0   0   0   0
Cross City    76  42  60  35  69 /  0   0   0   0   0
Apalachicola  75  42  58  40  64 /  0   0   0   0  10

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...FIRE WEATHER WATCH Wednesday afternoon for Calhoun-Central
     Walton-Coastal Bay-Coastal Dixie-Coastal Wakulla-Holmes-
     Inland Bay-Inland Dixie-Inland Wakulla-Inland Walton-
     Jackson-Lafayette-Leon-South Walton-Washington.
     FREEZE WATCH from late Wednesday night through Thursday
     morning for Calhoun-Central Walton-Gadsden-Holmes-Inland
     Bay-Inland Jefferson-Inland Walton-Jackson-Leon-Liberty-
     Madison-Washington.
GA...FREEZE WATCH from late Wednesday night through Thursday
     morning for Baker-Ben Hill-Berrien-Brooks-Calhoun-Clay-
     Colquitt-Cook-Decatur-Dougherty-Early-Grady-Irwin-Lanier-
     Lee-Lowndes-Miller-Mitchell-Quitman-Randolph-Seminole-
     Terrell-Thomas-Tift-Turner-Worth.
AL...FREEZE WATCH from late Wednesday night through Thursday
     morning for Coffee-Dale-Geneva-Henry-Houston.
     FREEZE WATCH from late tonight through Wednesday morning for
     Coffee-Dale-Geneva-Henry-Houston.
     FIRE WEATHER WATCH Wednesday afternoon for Coffee-Dale-Geneva-
     Henry-Houston.
GM...SMALL CRAFT ADVISORY from 4 PM this afternoon to 9 PM EST this
     evening for Apalachee Bay or Coastal Waters From Keaton
     Beach to Ochlockonee River Fl out to 20 Nm-Coastal Waters
     From Ochlockonee River to Apalachicola Fl out to 20 Nm-
     Coastal waters from Suwannee River to Keaton Beach out 20
     NM-Coastal waters from Apalachicola to Destin FL out 20
     NM-Waters from Suwannee River to Apalachicola FL from 20
     to 60 NM-Waters from Apalachicola to Destin FL from 20 to
     60 NM.
     SMALL CRAFT ADVISORY from 7 AM Wednesday to 1 PM EST Thursday
     for Coastal Waters From Ochlockonee River to Apalachicola
     Fl out to 20 Nm-Coastal waters from Apalachicola to
     Destin FL out 20 NM-Waters from Suwannee River to
     Apalachicola FL from 20 to 60 NM-Waters from Apalachicola
     to Destin FL from 20 to 60 NM.
     GALE WARNING from 9 PM this evening to 7 AM EST Wednesday for
     Apalachee Bay or Coastal Waters From Keaton Beach to
     Ochlockonee River Fl out to 20 Nm-Coastal Waters From
     Ochlockonee River to Apalachicola Fl out to 20 Nm-Coastal
     waters from Suwannee River to Keaton Beach out 20 NM-
     Coastal waters from Apalachicola to Destin FL out 20 NM-
     Waters from Suwannee River to Apalachicola FL from 20 to
     60 NM-Waters from Apalachicola to Destin FL from 20 to 60
     NM.
     SMALL CRAFT ADVISORY from 7 AM Wednesday to 4 AM EST Thursday
     for Apalachee Bay or Coastal Waters From Keaton Beach to
     Ochlockonee River Fl out to 20 Nm-Coastal waters from
     Suwannee River to Keaton Beach out 20 NM.
&&

NEAR TERM...Lamers
SHORT TERM...Camp
LONG TERM...Barry
AVIATION...Lamers
MARINE...Camp
FIRE WEATHER...Lamers
HYDROLOGY...Camp