Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 201904

Area Forecast Discussion
National Weather Service Jacksonville FL
304 PM EDT Thu Oct 20 2016

...Strong Cold Front to Blast through our Area on Friday...

Afternoon surface analysis depicts a weak coastal trough moving
onshore along the northeast Florida coastal counties. High
pressure (1019 millibars) was slowly settling southward into the
Carolinas and Georgia. Meanwhile, low pressure (1004 millibars)
was moving northwestward over the Bahamas. Aloft...a strong
shortwave was pivoting through the Upper Mississippi valley, which
was pushing a cold front eastward into the lower Mississippi
Valley as well as the Tennessee/Ohio Valleys. Ridging aloft
prevails downstream of this trough over our area, while troughing
remains positioned east of our region over the Bahamas. The
coastal trough is producing a few showers over the coastal
counties of northeast Florida and the adjacent coastal waters,
with activity moving southwestward at 10-15 mph. A healthy cumulus
field prevails elsewhere, with inland temperatures climbing
into the low to mid 80s, with coastal temperatures around 80.
Dewpoints range from the lower 60s across inland southeast Georgia
to the lower 70s at the northeast Florida beaches.

.Near Term /this Afternoon through Friday/...
Surface ridging will shift directly over our region this evening
as the strong cold front moves across the Appalachians and
approaches the Florida panhandle. Showers over coastal northeast
Florida will quickly fade after sunset, with skies rapidly
clearing as a dry air mass prevails aloft. Expect a period of
radiational cooling through the predawn hours, with some increase
in westerly winds and mid-level cloudiness possible over inland
southeast GA in advance of the front during the predawn hours on
Friday. Patchy fog should develop over the eastern half of
northeast Florida as well as north central Florida and the coastal
counties of southeast Georgia, with some locally dense fog
possible. This fog will likely dissipate towards sunrise as
northwesterly flow just off the surface strengthens in advance of
the approaching front. Lows will generally fall into the low to
mid 60s.

The cold front will be on the doorstep of the Altamaha/Ocmulgee
Rivers and the western Suwannee Valley on Friday morning. Expect
only mid and high level clouds along and ahead of the front, as
deeper moisture pivoting north of our region, which will preclude
shower development. The front will progress quickly eastward
during the morning hours and should move into the coastal waters
during the early afternoon hours. Northwesterly winds will rapidly
increase in the immediate wake of the front, with significant cold
air advection lagging the front by about 6 hours. Skies will clear
from northwest to southeast during the afternoon hours. Highs will
be held to near 80 across inland southeast Georgia, with mid to
upper 80s expected over much of northeast and north central

.Short Term /Friday Night through Saturday Night/...
The upper level trough will push towards the east coast, with the
trough axis east of the region. The surface cold front will be
moving across south central Florida Friday evening, with very dry
air filtering southward through the region overnight through the
day on Saturday. The surface ridge will then build across the
region through Saturday night, providing light winds. Dewpoints
will fall into the 40s across the region by daybreak Saturday, and
into the 30s across much of the interior by Saturday afternoon.

Lows Saturday morning are forecast to be 5 to 15 degrees cooler
than Friday morning, with lows in the upper 40s to near 50 across
much of the interior and the mid to upper 50s along and east of
the St Johns River. Sunny skies are forecast for Saturday behind
the front, and highs will be slightly below normal in the low to
mid 70s. Clear skies with high pressure overnight Saturday night
will allow for excellent radiational cooling and temperatures will
fall into the low to mid 40s across much of the region, except low
50s near and east of the St Johns River.

.Long Term /Sunday Through Wednesday/...
An upper ridge will stretch across the northern Gulf through the
middle of the country, with a trough over the northeastern conus
and off the east coast. A reinforcing shortwave is forecast to
move across the Great Lakes and into the northeast Monday into
Tuesday morning. Surface high pressure over the region will break
down on Monday, with another ridge pushing southeast across the
Great Lakes and Ohio Valley and into the southeast. This ridge
will then remain northeast of the area through the middle of the
week. Low level flow will turn more easterly, and low level
moisture will increase. A few coastal showers are possible by
Wednesday. Temperatures will moderate back to the upper 70s to low
80s by Monday, and then continue through the middle of the week.


Isolated showers may impact CRG and SGJ, creating brief periods
of MVFR ceilings around 2500 ft. Otherwise, VFR conditions will
prevail at the regional terminals. Northeasterly sustained surface
winds around 10 knots will diminish towards 00Z. Patchy fog may
develop during the late evening hours at the TAF sites, with sub-
MVFR visibilities possible after 06Z. Fog should dissipate around
or before 12Z as a dry cold front approaches our region from the
west. VFR cigs will accompany this frontal passage, with
northwesterly winds increasing in the wake of the front after 16Z.


A weak inverted trough will persist over the coastal waters this
afternoon, creating a broken band of showers over the waters
adjacent to the northeast Florida coast that will shift southward
late this afternoon. Activity will quickly diminish this evening
as high pressure settles over our area. Seas are still in the
exercise caution range of 4-6 feet offshore, and these seas will
linger through tonight. A fast moving, strong and dry cold front
will race eastward through our waters on Friday morning, followed
by an abrupt surge of northwesterly winds on Friday afternoon. A
small craft advisory will be required for the offshore waters from
Friday afternoon through Saturday as wind speeds exceed 20 knots
and seas build into the 6-8 foot range. Winds and seas will
gradually diminish Saturday night and Sunday as high pressure
builds into our region from the west.

Rip Currents: High risk continues at the northeast Florida beaches
due to the combination of a lingering long period easterly swell
and onshore winds. A moderate risk is expected at the southeast GA
beaches. Expect an elevated risk to persist through Friday.


Coastal Flood Advisory will remain in effect through tonight as
onshore winds keep minor tidal flood conditions in place during
times of high tide across the St. Johns River Basin, mainly for
locations south of downtown Jacksonville. Offshore winds
developing on Friday should allow this flood event to end after 2
weeks that began with Matthew.


AMG  62  80  48  73 /   0  10   0   0
SSI  65  82  54  71 /   0  10   0   0
JAX  64  86  49  73 /  10  10   0   0
SGJ  66  87  58  73 /  20  10   0   0
GNV  61  86  49  75 /   0  10   0   0
OCF  62  87  52  75 /  10  10   0   0


FL...High Rip Current Risk through late tonight for Coastal Duval-
     Coastal Nassau-Flagler-St. Johns.

     Coastal Flood Advisory until 5 AM EDT Friday for Clay-Coastal
     Duval-Flagler-Inland Duval-Putnam-St. Johns.



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