Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 212140
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
440 PM EST Mon Jan 21 2019

...LIGHT FREEZE AND FROST FOR INLAND SOUTHEAST GEORGIA TONIGHT...

.Currently...

Late afternoon surface analysis depicts Arctic high pressure
(1038 millibars) building southeastward from the Ohio Valley.
Meanwhile, low pressure (998 millibars) was emerging from the lee
side of the Colorado Rockies. Aloft...deep troughing is
progressing slowly eastward along the New England coast, which is
allowing heights to gradually rise locally downstream of a deep
trough that is digging from the Rockies into the Desert Southwest.
Visible satellite imagery shows that cold air marine
stratocumulus clouds are beginning to move onshore along the
Flagler and St. Johns County coasts from the Atlantic waters, as
low level winds have veered to northeasterly, which is signaling
the end of cold air advection over our region. Skies elsewhere are
clear, and temperatures range from the upper 40s to mid 50s,
except around 60 degrees in north central Florida. A very dry air
mass persists over inland southeast Georgia, where dewpoints
remain in the upper teens and 20s, while dewpoints in northeast
and north central Florida are climbing through the upper 20s and
30s as of 21Z.

.Near Term (this Evening through Tuesday)...

The very dry air mass in place over southeast Georgia will combine
with clear skies and gradually decoupling surface winds this
evening to promote radiational cooling and a light
freeze/widespread frost overnight for inland locations. Marine
stratocumulus clouds will continue to make more inland progress
during the predawn hours into north central and eastern portions
of northeast Florida as low level flow continues to veer and
becomes east-northeasterly before sunrise. Lows at coastal
locations will likely occur before midnight as onshore winds
strengthen a little during the predawn hours and stratocumulus
increases in coverage, while steady or slowly rising temperatures
occur across the rest of inland northeast and north central
Florida before sunrise as warm air advection begins. Areas of
frost are expected over the northern Suwannee Valley overnight,
where lows will fall to the low and mid 30s, while lows in
coastal northeast Florida fall to the the mid 40s this evening
rise into the low to mid 50s by sunrise.

Positively tilted troughing will continue to dig southeastward
into the southern Plains States on Tuesday, allowing heights
locally to continue to rise as deeper south-southwest flow
develops aloft. Low level flow will become southeasterly as the
strong surface ridge shifts towards the Virginia coast, and our
local pressure gradient will continue to slowly tighten, resulting
in extensive stratocumulus coverage advecting northwestward over
much of our area. Breezy onshore winds and plenty of low
cloudiness will keep highs in the upper 50s for coastal southeast
Georgia and low to mid 60s for coastal northeast Florida. Highs
will climb to around 60 for inland southeast Georgia and the mid
to upper 60s for inland locations in northeast and north central
Florida. Isolated coastal showers could develop over southeast
Georgia towards sunset, but dry conditions will otherwise prevail.

.Short Term (Tuesday night through Thursday)...

Low pressure over the Southern Plains States on Tuesday will
quickly lift northeastward into the Great Lakes region on
Wednesday, pushing a cold front through the lower Mississippi and
Tennessee Valleys by Wednesday afternoon. This evolution of the
weather pattern will veer our local winds to south-southeasterly
on Tuesday night and then southerly on Wednesday. Model soundings
continue to suggest that extensive stratocumulus cloudiness will
persist over our region on Tuesday night through Wednesday
morning, which may limit fog formation. Lows will continue to
trend warmer as warm air advection continues, with inland lows
generally 50-55 and upper 50s at the coast on Tuesday night.
Veering low and mid level winds may advect isolated showers over
portions of coastal northeast Florida on Tuesday evening, with
some increase in coverage through Wednesday morning in southeast
Georgia as a weak warm front develops north of Interstate 10. This
front will quickly lift northward on Wednesday, and some peaks of
sunshine and breezy southerly winds should boost highs into the
70s for all but coastal southeast Georgia, where upper 60s are
forecast.

The positively tilted trough will then progress across the
eastern U.S. from Wednesday night through Thursday. Secondary
cyclogenesis is still progged along the cold front over coastal
Louisiana on Wednesday, and this feature will accelerate
northeastward across Georgia on Wednesday night. Guidance is
still suggesting that a convective line will accompany the cold
front as it crosses our region during the predawn and morning
hours on Thursday. Strong unidirectional southwesterly flow could
bring a few stronger thunderstorms onshore from the Gulf of
Mexico by late night or predawn Thursday, but this convection will
likely encounter a stable nocturnal boundary layer over north
central Florida and the Suwannee Valley that will tend to weaken
convection as it progresses quickly eastward. Lows will remain in
the 60s for most of northeast and north central Florida on
Wednesday night ahead of the front, while temperatures may drop
back into the 50s for the western Suwannee Valley and southeast
Georgia towards sunrise on Thursday behind the frontal passage.

Showers and a few embedded thunderstorms will then push offshore
by early Thursday afternoon, with low stratus ceilings possibly
overspreading southeast Georgia in the wake of the front as cold
air advection develops. Some clearing may be possible late in the
day from west to east for northeast and north central Florida, and
highs will generally climb to the 60-65 range, except upper 60s in
north central and coastal northeast Florida as winds shift to
westerly. Rainfall totals with this system may average out to
around an inch region-wide given the impressive dynamics and
highly diffluent flow aloft that will accompany the passage of
this trough through our region. Locally higher totals may be
possible in the Suwannee Valley and north central Florida if
convection traversing the northeast Gulf of Mexico maintains
itself more than currently forecast.

.Long Term (Thursday night through Monday)...

Deep troughing will then become established over the eastern U.S.
late this week and into next weekend, with long term models still
differing on details of reinforcing shortwave troughs that will be
diving through our region. The highest threat for widespread
freeze locally appears to be on Friday night and early Saturday as
surface ridging builds into the southeastern states behind the
departing cold front. Highs will certainly remain below
climatology into early next week, and low temperatures over the
weekend will be dependent upon cloud cover, which may increase
as one possible shortwave digs into the Gulf of Mexico and potentially
results in cyclogenesis. Chilly rainfall may may into our region
late this weekend if current ensemble guidance trends continue.

&&

.Aviation...

VFR with SKC this afternoon and evening with light NE flow. After
06z expect E-NE flow to begin to push MVFR CIGS from Strato-Cu
deck over the Atlc Coastal Waters into the coastal areas, with
possible CIGS around 2500 ft at SGJ by 09z, then rest of the TAF
sites by 12z, with widespread MVFR CIGS and possible OVC conds by
15z area-wide. E-NE winds increasing by 15z Tue with 12-16G18-24
knots possible with strongest winds at the coast /SGJ/.

&&

.Marine...

Strong high pressure will gradually shift southeastward from the
Ohio Valley this afternoon and will move off the Virginia/North
Carolina coastline by Tuesday evening. East-northeast winds will
remain at Caution levels tonight offshore and just under Caution
levels near shore. Winds will then shift to east-southeasterly on
Tuesday, with speeds reaching Caution levels near shore and seas
remaining in the 4-6 foot range offshore and 3-5 feet near shore.
Winds will then shift to southeasterly on Tuesday night, and Small
Craft Advisory conditions will develop offshore. Meanwhile, low
pressure emerging over the Southern Plains states on Tuesday will
move northeastward through the Great Lakes states on Wednesday,
pushing a cold front into the southeastern U.S. by the afternoon
hours.

Small Craft Advisory conditions will then develop near shore by
Wednesday evening as southerly winds strengthen in advance of this
front, which will bring an increasing coverage of showers and
thunderstorms to our waters by late Wednesday night and Thursday
morning. The front will move through our waters by Thursday
afternoon, with northwesterly winds developing in the wake of this
front on Thursday night. Winds and seas will fall below Small
Craft Advisory levels by early Friday as high pressure gradually
builds over the southeastern states.

Rip Currents: High-end moderate risk will continue at all area
beaches through midweek as onshore winds persist and strengthen.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  31  59  49  71 /   0  10  20  20
SSI  38  58  53  67 /   0  20  20  20
JAX  36  63  54  74 /  10  10  20  10
SGJ  44  64  57  73 /  10  10  20  20
GNV  37  68  53  77 /   0   0  10  10
OCF  39  69  54  78 /   0   0  10  10

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...Freeze Warning from 1 AM to 8 AM EST Tuesday for Appling-
     Atkinson-Bacon-Brantley-Charlton-Clinch-Coffee-Echols-
     Inland Camden-Inland Glynn-Jeff Davis-Pierce-Ware-Wayne.

AM...None.
&&

$$

Nelson/Hess/Wolf


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