Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 190248
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
948 PM EST Thu Jan 18 2018

...HARD FREEZE WARNING IN EFFECT THROUGH MID-MORNING ON FRIDAY...

.UPDATE...
Late evening surface analysis depicts arctic high pressure (1032
millibars) blanketing the Tennessee and lower Mississippi Valleys.
Aloft...zonal flow has developed locally in the wake of deep
troughing that is progressing off the U.S. east coast. A weak
shortwave trough embedded within the zonal flow pattern is
progressing eastward across Deep South Texas. The evening
soundings at Jacksonville and Tallahassee continue to display near
record dry conditions for mid-January, with precipitable water
vapor (PWAT) values at both locations at 0.20 or less continuing
during the past 24 hours. Skies are clear and winds are calm at
most locations, allowing for radiational cooling and temperatures
falling below freezing by 02Z at most inland locations. Dewpoint
temperatures have risen substantially this evening into the 20s,
so we added widespread frost to the forecast grids for the
overnight through the early morning hours. We also adjusted the
onset and expiration times of the Hard Freeze Warning to account
for the expected long duration of 27 or below degree temperatures
overnight, with temperatures not expected to climb above freezing
until the mid-morning hours on Friday. Lows will generally fall to
the low and mid 20s inland, with upper 20s expected along and east
of the Intracoastal Waterway in northeast Florida and at the
immediate beaches in southeast Georgia by the predawn hours.

High pressure will begin to slowly weaken as it builds directly
over our region on Friday. A dry air mass and plenty of sunshine
will prevail, allowing temperatures to quickly rise, with highs
reaching the upper 50s to lower 60s inland, which is only about 5
degrees below mid-January climo. Our loose local pressure gradient
will allow a weak sea breeze to move across the coastal
communities during the afternoon hours, with water temperatures in
the upper 40s and lower 50s keeping highs in the mid 50s for our
beach communities. Thin cirrus may increase towards the evening
hours in our western locations as the aforementioned moisture-
starved shortwave trough migrates eastward along the Interstate
10 corridor.

&&

.AVIATION...
VFR conditions will prevail at the regional terminals. Light west
or northwesterly surface winds will develop by the mid-morning
hours, with a weak sea breeze moving across SGJ and CRG by 19Z.
Surface wind speeds will remain below 10 knots on Friday.

&&

.MARINE...
Strong high pressure centered over the lower Mississippi Valley
this evening will continue to build over into our region on Friday
and will linger over the coastal waters through early Sunday while
slowly weakening. Light offshore winds will prevail tonight, with
seas continuing to gradually diminish, but still at caution levels
of 4-6 feet in the offshore waters. Our local pressure gradient
will also continue to loosen, with morning offshore winds on
Friday and Saturday becoming onshore at 10 knots or less during
the afternoon hours. Seas will fall below caution levels offshore
on Friday morning. High pressure will slide off the Carolina coast
on Sunday, with light onshore winds developing. A cold front will
move into the lower Mississippi Valley by Sunday night and will
progress eastward across our local waters by early Tuesday.
Southwesterly winds will develop on Monday and will gradually
strengthen on Monday night ahead of the front, but speeds and seas
are expected to remain below caution levels at this time.

Rip Currents: Wave heights will continue to decrease on Friday,
with a lingering long period northeasterly ocean swell perhaps
keeping a low-end moderate risk in place at the northeast Florida
beaches on Friday. Low risk expected this weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  23  58  31  61 /   0   0   0   0
SSI  29  56  37  57 /   0   0   0   0
JAX  24  59  33  60 /   0   0   0   0
SGJ  28  56  38  61 /   0   0   0   0
GNV  23  61  33  64 /   0   0   0   0
OCF  23  62  35  67 /   0   0   0   0

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Hard Freeze Warning until 10 AM EST Friday for Alachua-Baker-
     Bradford-Clay-Coastal Duval-Coastal Nassau-Columbia-Flagler-
     Gilchrist-Hamilton-Inland Duval-Inland Nassau-Marion-Putnam-
     St. Johns-Suwannee-Union.

GA...Hard Freeze Warning until 10 AM EST Friday for Appling-Atkinson-
     Bacon-Brantley-Charlton-Clinch-Coastal Camden-Coastal Glynn-
     Coffee-Echols-Inland Camden-Inland Glynn-Jeff Davis-Pierce-
     Ware-Wayne.

AM...None.
&&

$$

Nelson/Peterson/Corless



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