Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 120841
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
341 AM EST Tue Dec 12 2017

...FREEZE WATCH IN EFFECT FOR MUCH OF INTERIOR TONIGHT...

.NEAR TERM /Through Tonight/...
Warmer temperatures were observed across the region this morning
due to southwesterly winds ahead of the next cold front moving
across the Southeast. A dry cold front will push to near the FL/GA
border by the early afternoon and through the region by mid
afternoon. Breezy to windy westerly winds will prevail today,
with wind speeds 15-20 mph with gusts to 25-35 mph. Will hold off
on a Wind Advisory at this time due to winds remaining generally
below 35 mph in gusts, but there could be a few isolated gusts to
35 mph this afternoon. Temperatures will warm to above normal
across northeast Florida, due to cold air advection lagging behind
the frontal boundary passage, with highs in the upper 60s to
lower 70s. Highs across interior southeast Georgia will be near
normal in the low to mid 60s, with upper 60s along the coast due
to the westerly flow.

Strong cold air advection is expected behind the cold front
tonight, with temperatures falling to around the freezing mark
across most of the interior. Across northeast Florida and
coastal areas, temperatures will fall to the mid 30s to near 40
degrees. Wind chills will be in the mid 20s across much of the
interior, and around 30 along the coast. A Freeze Watch has been
issued for all of southeast Georgia and much of interior northeast
Florida late tonight into Wednesday morning.

.SHORT TERM /Wednesday through Thursday Night/...
Negatively tilted troughing aloft over the Mid-Atlantic States and
New England will slowly pivot northward as a pair of shortwave
troughs dive quickly southeastward from the Canadian Prairies
early on Wednesday into the Great Lakes States and Ohio Valley by
early Thursday. These shortwaves will pivot eastward into the
Mid-Atlantic States and New England on Thursday as the next
shortwave trough diving southward from Canada sharpens over the
Plains states on Thursday night. As the negatively tilted trough
lifts northward and further away from our region on Wednesday,
heights aloft will begin to slowly rise locally by Wednesday
evening as flow aloft gradually becomes more zonal in nature.
Surface ridging will continue to build eastward from Texas early
on Wednesday, allowing our local pressure gradient to gradually
loosen during the day. A cold and dry air mass will prevail on
Wednesday as deep northwesterly flow prevails. Despite full
sunshine, highs will only climb to the mid and upper 50s, which is
about 8-12 degrees below mid-December climo.

Surface ridging will settle over the Florida peninsula on
Wednesday night as a clipper system races southeastward through
the Ohio Valley. The subtropical jet stream will also lift
northward from the Florida peninsula during the overnight hours,
which could advect a mid and high altitude cloud deck over north
central and possibly northeast Florida from the Gulf of Mexico
during the overnight hours, potentially interfering with the peak
of the Geminid Meteor Shower. Clear skies should prevail
overnight across southeast Georgia. A developing southwesterly low
level wind will likely level off temperatures during the overnight
hours, with lows in the mid to upper 30s at inland locations
likely occurring right around midnight, with coastal lows
generally around 40.

A dry cold front will push into the southeastern states on
Thursday, with periods of mid and high altitude cloudiness
traversing our region from west to east as the fast subtropical
jet stream remains over our area. Zonal flow aloft and west-
southwest surface winds of 10-15 mph during the afternoon hours
will help temperatures rebound to near climo, with low to mid 60s
expected in southeast Georgia and mid to upper 60s for northeast
and north central Florida.

The cold front will lose support by Thursday evening as troughing
over the Plains states digs into the lower Mississippi Valley,
causing heights aloft locally to rise slightly. This digging
trough will also sharpen the subtropical jet stream that will be
in place along the northern Gulf coast, with deepening moisture
values advecting northeastward from the Gulf of Mexico into north
central Florida during the overnight hours. Mid and high altitude
cloudiness will increase during the evening hours across north
central and northeast Florida, with isolated light showers
possible towards sunrise on Friday for north central Florida and
southern portions of the Suwannee Valley. A dry low and mid level
air mass will prevail over southeast Georgia, where a cirrus cloud
shield should gradually thicken overnight. Increasing cloudiness
and light low level south to southwesterly winds will result in
above climo lows, with mid to upper 40s over inland southeast
Georgia and 50-55 expected elsewhere.

.LONG TERM /Friday through Tuesday/...
A potent shortwave trough will pivot eastward from the lower
Mississippi Valley across the Tennessee Valley and southeastern
states on Friday, driving a cold front through our region. 00Z GFS
ensembles continue to be wetter than the ECMWF with this frontal
passage, and model blends yield scattered to numerous coverage of
showers across north central Florida, with high-end scattered
coverage over northeast Florida and slightly lower chances for
southeast Georgia. Cold air advection will likely begin during the
afternoon hours over inland southeast Georgia, where highs will
only reach the upper 50s to near 60, while highs elsewhere reach
the mid to upper 60s. The last shot of arctic air for the long-
term period will plunge over our region on Friday night as high
pressure quickly builds into the southeastern states. The 00Z
ECWMF keeps the subtropical jet and associated mid and high
altitude clouds in place over northeast and north central Florida,
while the GFS and MOS guidance indicates temporary clearing
overnight, which would allow lows to fall to the mid/upper 30s
inland and around 40 at the coast. Cool high pressure will prevail
over the southeastern states on Saturday and will only slowly
progress eastward off the southeast U.S. coast by Saturday
evening. Highs on Saturday will only climb to the mid/upper 50s,
except lower 60s for north central Florida. Lows Saturday night
will range from the upper 30s/lower 40s inland to the mid/upper
40s at the coast.

Southwesterly flow aloft will develop and strengthen towards the
end of the weekend and early next week as the next shortwave
trough dives into the lower Mississippi Valley and southeastern
states. Long-term guidance remains in disagreement on the
amplitude and speed of this shortwave trough, but dry weather
should prevail through at least Sunday evening, with highs on
Sunday rebounding to the mid/upper 60s, except lower 70s for north
central Florida. Rain chances should gradually increase from west
to east from Sunday night through early next week, with
subtropical ridging in place over the Bahamas and south Florida
boosting highs into the low/mid 70s by Monday, except perhaps
upper 60s for inland southeast Georgia, where cloudiness should be
thicker. Milder Pacific air and zonal flow aloft are progged
towards the mid portions of next week, with a minimal and brief
cool-down possible by Tuesday in the wake of the departing
shortwave trough and associated cold front.

&&

.AVIATION...
VFR conditions expected through the period. Southwest winds 5-10
knots overnight will become westerly during the day on Tuesday and
increase to 15-20 knots with gusts of 25-30 knots ahead of and
behind a cold front. Winds will diminish to around 10 knots this
evening.

&&

.MARINE...
Small Craft Advisories are in effect for the offshore coastal
waters beginning this morning for westerly winds increasing to
around 20 knots and this afternoon for the nearshore waters. Winds
will increase to around 25 knots this afternoon offshore, and a
few gusts to gale force are possible. Seas will also build to 5-7
feet offshore this afternoon and continue through tonight. High
pressure will then build over the Florida peninsula on Wednesday,
with lighter winds. The ridge will build SSE through Thu in
advance of yet another cold front expected to cross the waters
late Fri or Sat with a low chance of rainfall with the potential
for marginal advisory conditions over the outer waters.

Rip Currents: Low risk today. Moderate risk highlighted for Tuesday.

&&

.FIRE WEATHER...
Southwesterly surface winds will quickly increase during the mid
and late morning hours today, with westerly sustained winds near
20 mph this afternoon with frequent gusts of 30-35 mph. Minimum
relative humidity values will fall to around 35 percent this
afternoon, and low ERC values will preclude Red Flag Conditions
today. A colder and dry air mass will then plunge into our region
tonight, with surface winds shifting to a northwesterly direction
and remaining breezy in coastal locations. A long duration of
relative humidity values below critical thresholds is expected on
Wednesday, with minimum values falling to around 25 percent during
the afternoon hours area-wide. Northwesterly surface winds of 5-10
mph during the morning hours will become westerly during the
afternoon, and these lighter winds and low ERC values will again
preclude Red Flag conditions.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  61  31  54  35 /   0   0   0   0
SSI  68  36  52  43 /   0   0   0   0
JAX  71  35  57  37 /   0   0   0  10
SGJ  72  37  56  40 /   0   0   0  10
GNV  71  33  58  38 /   0   0   0  10
OCF  72  34  59  38 /   0   0   0  10

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Freeze Watch from late tonight through Wednesday morning for
     Alachua-Baker-Bradford-Clay-Columbia-Gilchrist-Hamilton-
     Inland Duval-Inland Nassau-Suwannee-Union.

GA...Freeze Watch from late tonight through Wednesday morning for
     Appling-Atkinson-Bacon-Brantley-Charlton-Clinch-Coffee-
     Echols-Inland Camden-Inland Glynn-Jeff Davis-Pierce-Ware-
     Wayne.

AM...Small Craft Advisory from 7 AM this morning to 9 AM EST
     Wednesday for Waters from Altamaha Sound GA to Fernandina
     Beach FL from 20 to 60 NM-Waters from Fernandina Beach to
     St. Augustine FL from 20 to 60 NM-Waters from St. Augustine
     to Flagler Beach FL from 20 to 60 NM.

     Small Craft Advisory from 1 PM this afternoon to 5 AM EST
     Wednesday for Coastal waters from Altamaha Sound to
     Fernandina Beach FL out 20 NM-Coastal waters from
     Fernandina Beach to St. Augustine FL out 20 NM-Coastal
     waters from St. Augustine to Flagler Beach FL out 20 NM.

&&

$$

Kennedy/Nelson



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