159 
FXUS62 KJAX 210110
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
810 PM EST Sun Dec 20 2020

...AREAS OF DRIZZLE/FOG TO DEVELOP AS RAINFALL TAPERS OFF TONIGHT...

.UPDATE...

Forecast remains on track as low pressure will track along
stationary frontal boundary along the I-10 corridor near the
FL/GA border this evening and into the SE GA coastal waters after
midnight. This will continue scattered to numerous showers this
evening with a slight chance for a brief thunderstorm across NE FL
but severe weather is not expected. In the wake of the low
pressure system, cool and damp airmass will filter in on NW winds
and expect areas of fog and drizzle to take over as the rainfall
tapers off. Widespread visibilities of 1 to 3 miles can be
expected with some patchy dense fog/drizzle with vsbys of 1/2 mile
or less not out of the question, but the NW flow at 5-10 mph
should keep the fog/stratus mainly as a low cloud deck at 100-200
ft and dense fog not expected to become organized/widespread for
advisories. Temps will slowly fall into the upper 40s SE GA and
lower to middle 50s for NE FL by sunrise Monday Morning. This low
clouds/drizzle/fog will slowly dissipate and break-up by the mid
to late morning hours as Northwest winds increase to 10-15 mph and
drier airmass filters in during the afternoon hours. Enough
sunshine should break through in the afternoon to push Max Temps
to around 60 degrees SE GA and mid/upper 60s for NE FL.

&&

.PREV DISCUSSION [632 PM EST]...

.Near Term.../through Monday/...

Low pressure center will track east across NE FL this evening. Most
convective activity will be ahead of the low its self associated 
with a prefrontal trough and upper short wave energy. The warm front
ahead of this low will stretch east across area near the GA/FL line.

The best chance for stronger storms will be in the warm sector 
between the warm front and cold front, over NE FL. Current timing 
puts main area of storms off the coast around 01z. The cold front
itself will cross NE FL during the evening, and may produce a few
more storms over NE FL, but expect the atmosphere will be fairly 
stable at that point with loss of diurnal heating and better 
energy will have been with the prefrontal trough. The low will 
track further to the east during the overnight hours, with a few 
wrap around showers anticipated through the night.

High pressure will build from the west during the day Monday, with 
skies clearing.

Temperatures will trend above normal Tonight. Readings will then be 
below normal for Monday, as northwest flow advects in cooler air.


.Short Term.../Monday night through Thursday night/...

High pressure will continue to build east toward the region Monday 
night, then become centered to the north on Tuesday, and northeast 
on Tuesday night. The high will move further toward the northeast
Wednesday. Due to subsidence associated with this high, the period 
from Monday night through Wednesday is expected to be dry. 
Temperatures will trend near normal through Tuesday night, then 
above normal Wednesday on southeast flow. 

The high will move more toward the northeast Wednesday night, as a 
cold front approaches from the west northwest. With warm advection
Wednesday night, temperatures and dewpoints moving across area 
waters will exceed sea surface temperatures. This will result in the
potential for sea fog, especially over FL coastal waters, with this 
fog possibly expanding over land through the night into early 
Thursday. 

Longer range models vary about 6 hours or so on timing of this 
frontal passage. GFS forecasting this front to enter western 
counties around dawn Thursday, then track to the east of forecast 
area around sunset. ECMWF about 6 hours slower than this. With the
GFS timing best support for stronger storms will be over eastern 
counties where airmass will have additional help from diurnal 
instability. The slower ECMWF would allow much of the forecast 
area to destabilize prior to frontal passage. At this point, will 
be forecasting using an average of the model forecasts, yielding a
stormy day throughout the day Thursday, with the potential for 
the activity to stretch into the evening hours. Temperatures are 
expected to trend well above normal Wednesday night into Thursday,
then near to a little below Thursday night. If a faster solution,
such as the GFS happens, temperatures would likely trend a little
cooler Thursday.


.LONG TERM.../Friday Through Sunday/...

The region will be between departing high pressure to the northeast,
and building high pressure from the west northwest Friday. This will
result in an enhanced pressure gradient over the area, and elevated 
winds for much of the day, as skies clear. A few showers will be 
possible early in the day. Cold advection on west northwest flow 
will yield highs on Friday that will in general be about 10 degrees 
below average, with readings topping out in the 50s. 

As high pressure builds to the northwest, winds will subside for 
Friday night, with the northwest flow advecting in cooler air on 
mainly clear skies. Lows are expected to fall to around freezing or 
below across inland areas, with a widespread front anticipated. The 
cold air will push all the way to the coast, with readings even 
falling into the 30s at beach communities. 

The region will be under the influence of high pressure for 
Saturday, with mainly sunny skies, but temperatures will remain on 
the cool side, with highs once again only in the 50s. 

The high will build more toward the northeast Saturday night through
Sunday. While the dry weather is expected to continue, clouds will 
increase as the flow trends more onshore, which will provide better
moisture. Another cold night is expected for Saturday night, but not
as cold as Friday night. A few inland locations may get close to 
freezing Saturday night with patchy frost, but much of the area will
begin to see a trend toward milder air. Highs on Sunday will be a
little milder, but still below normal.


.AVIATION...
[Through 00Z Tuesday]

Mostly MVFR CIGS and VSBYS in off/on rainfall at all TAF sites at
00z, but as low pressure passes on by, expect rapidly lowering
CIGS through the evening hours to IFR by 02-04z with light to 
moderate rainfall continuing, then by 04-06z range as the low 
pressure departs and low level winds become light NW, expect CIGS 
to lower to LIFR below 500 ft at all TAF sites with drizzle and
fog lowering the VSBYS into the 1-3 mile range and possibly lower
at SSI/VQQ locations. These LIFR conds remain in place until
lifting back to IFR with increasing NW winds to 10-12 knots
around 12z, with CIGS breaking up in the 14-16z time frame with
VFR conds returning to all locations by 16-18z time frame.


.Marine...

Low pressure will track east across area this evening into Tonight.
Thunderstorms will be possible as this system tracks through, along 
with the potential for a few strong storms. Fog will be possible 
Tonight. High pressure will build from the west Monday night, 
then northwest Tuesday. The high will build toward the northeast 
Tuesday night through Wednesday night. A potential for sea fog 
will exist Wednesday night into Thursday morning. A strong cold 
front will move east across area Thursday into Thursday night, 
with potential for strong thunderstorms. High pressure will build 
to the northwest Friday into Friday night, then north Saturday, 
and northeast Saturday night and Sunday. 

Small Craft Advisory headlines Tonight into Monday, and are expected
again for Thursday night into Friday.

Rip Currents: SE GA - Low through Monday
              NE FL - Low through Monday


.Fire Weather...

RH levels approach critical levels Friday and Saturday afternoons. 
However, at this time winds are expected to be on the light side, so
headlines are not forecast.

&&

.PRELIMINARY POINT TEMPS/POPS...

AMG  48  62  38  64  38 /  80   0   0   0   0 
SSI  52  62  45  64  47 /  80   0   0   0   0 
JAX  52  64  42  65  45 /  70   0   0   0   0 
SGJ  55  65  45  65  50 /  60  10   0   0   0 
GNV  53  65  42  66  41 /  40   0   0   0   0 
OCF  55  67  43  67  42 /  50   0   0   0   0 

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...Small Craft Advisory from 11 PM this evening to 3 PM EST Monday 
     for 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 4 AM to 10 AM EST Monday 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-Waters from Altamaha Sound GA to 
     Fernandina Beach FL from 20 to 60 NM.

&&