Weather

949 
fxus62 kchs 060540 
afdchs 


Area forecast discussion 
National Weather Service Charleston SC 
1240 am EST Tuesday Jan 6 2009 


Synopsis... 
a weak cold front will continue to approach from the west and 
stall just north of the area tonight. High pressure to the 
southeast will provide above normal temperatures through Tuesday 
night. A cold front will advance through the region 
Wednesday...then a secondary cold front will cross the area 
Thursday. Cool high pressure will build over the area through 
Friday night..before moving offshore Saturday. Another cold front 
is expected Sunday...with high pressure returning north of the area 
Monday. 


&& 


Near term /until 6 am this morning/... 
a surface analysis this evening depicts a northeast-southwest 
orientated cold front extending from the southern Appalachians 
into the north Gulf Coast region...while another east-west 
oriented cold front extends near the North Carolina/Virginia 
border. The front to the west will become stationary tonight as it 
becomes parallel to the middle level flow...while high pressure 
moving toward the middle-Atlantic coast will drive the front near the 
North Carolina/Virginia border southward. This front will 
eventually stall north of the area later tonight. 


The region will remain within a warm and moist southerly flow 
tonight. A tightening surface pressure and strengthening low level 
jet ahead of the cold front will result in an increase in winds 
overnight. These stronger winds will be enough to prevent any 
widespread fog from becoming a concern. Although some light patchy 
fog could not be ruled out...visibilities should not be low enough 
or last long enough to warrant inclusion in the forecast. 


Precipitation chances appear minimal at best tonight...as the 
deepest moisture and best lift remain north and west of the area 
closer to the frontal boundaries. The forecast will reflect a 
slight chance of showers for the remainder of the night...mainly 
north of the I-16 corridor. 


A good amount of middle level cloud cover over the area...except for 
perhaps north coastal Georgia...combined with a strengthening 
southerly flow will prohibit temperatures from falling much below 
the middle to upper 50s away from the immediate coast tonight. 


&& 


Short term /6 am this morning through 6 am Wednesday/... 
as deepest moisture shifts to the north with the warm front...cloud 
cover may become more scattered and allow for periods of sunshine 
on Tuesday. Combined with persistent warm southwest flow...temperatures 
on Tuesday will approach record highs for several locations. 
Expect afternoon temperatures to range from the middle to upper 70s 
on Tuesday. If more clearing occurs in southeast Georgia...high 
temperatures could approach near 80 degrees as indicated by the 
thickness scheme. 


Have kept conditions rain free on Tuesday after the early morning 
hours. Winds will gradually increase as the pressure gradient 
tightens ahead of another frontal system to the west. 


&& 


Long term /Wednesday through Monday/... 
Tuesday night through Monday...fairly good model agreement into 
Saturday leads to above normal forecast confidence. More uncertainty 
begins Saturday as models diverge with respect to another cold front. 


The area will remain in the warm sector of a storm system Tuesday night 
into Wednesday before a cold front pushes through Wednesday afternoon. Still a 
potential for a few thunderstorms late Tuesday night into Wednesday. The main hazard 
looks to be damaging winds with strong low-level winds in 
place...however instability will be the main limiting factor. Rain 
chances will end west to east late Wednesday as the front pushes offshore. High 
pressure will then build in from the SW while another reinforcing 
cold front pushes through the area late Thursday. High pressure will then 
slide north of the area into Sat before another cold front approaches 
from the west. Generally followed the slower HPC/European model (ecmwf) timing with the 
frontal passage...which slows the frontal passage down until sun. 
High pressure then returns Monday. 


Above normal temperatures through Wednesday with near normal temperatures Wednesday night 
through Friday night. Above normal temperatures return Sat/Sat night ahead of 
the next front with near normal temperatures sun and below normal temperatures 
thereafter through Monday. 


Lake winds...a lake Wind Advisory will likely be needed Tuesday night 
through Wednesday night for Lake Moultrie as winds increase in association 
with the passage of a cold front. 


&& 


Aviation /06z Tuesday through Saturday/... 
short wave moving through the area will push east-northeast of the terminals 
before daybreak...allowing for broken-overcast altocumulus ceilings around 15k 
feet to give way to clearing. Low stratus and a little mist will 
affect ksav between 10-13z...otherwise with increasing low level 
wind fields the risk of fog is substantially less than recent 
mornings or downright non-existent. As a result...our forecast 
shows VFR weather to prevail through 06z Wednesday. 


The main issue this forecast period is in regards to winds. There 
is enough of a difference between surface winds at ksav and those 
at 1500 feet to produce wind shear from for a few hours either side 
of sunrise this morning. At kchs the difference is not great 
enough to include wind shear...but pilots should still be alert 
for winds at between 1-2k feet that will be between 25 and 30 knots 
through middle morning. From late morning until about an hour before 
sunset the surface winds will increase enough to negate any wind 
shear. But with increasing mixing heights tapping into 20-30 knots of 
winds in the boundary layer...we have included gusts to 20 knots or 
greater for several hours during peak heating today. Wind shear is 
possible again tonight and will reassess the situation with the 
12z tafs. 


Extended aviation outlook...periods of MVFR and/or IFR conditions 
into Wednesday...with VFR weather to return thereafter. Wind shear 
and/or strong surface winds will impact the terminals through 
Thursday. 


&& 


Marine... 
high pressure over the southwest Atlantic will keep a 
south/southwest flow in place over the coastal waters 
tonight...as a cold front stalls north and west of the area. A 
strengthening low level flow and tightening surface pressure 
gradient will cause wind speeds to increase over the coastal 
waters tonight...with the strongest winds over the outer Georgia 
waters where mixing profiles are best due to warmer sea surface 
temperatures. Winds could reach as high as 15-20 knots with seas 
building up to 3 or 4 feet throughout the waters. 


Southwest winds will steadily increase through the day on Tuesday 
as low level jetting increases to 30 to 40 knots over the southeast 
states. Have gone ahead and issued a Small Craft Advisory for the 
nearshore waters north of Edisto Beach and the offshore Georgia 
waters beginning Tuesday afternoon...as confidence is fairly good 
that winds and seas will come into criteria late in the second 
period. 


Tuesday night through Saturday...deteriorating conditions expected 
at the beginning of the period ahead of a cold front...which is 
expected to push through the waters late Wednesday afternoon. Strong small 
craft conditions expected over all waters by late Tuesday night with the 
potential for gale conditions as well...mainly over the outer Georgia 
waters where better mixing is possible and over the northern SC 
waters where the better pressure gradient is expected. However...due to 
the uncertainty in the frontal passage timing...have held off on any 
gale watches for now. Conditions improve slightly Thursday before another 
reinforcing cold front pushes through late in the day. 
However...advisory conditions will likely be continuing over the northern 
SC waters and outer Georgia waters. Improving conditions then expected 
late in the week as high pressure builds back in from the north Friday...then 
slips offshore Sat. 


&& 


Climate... 
record high temperatures for January 6th 


Charleston Airport...78 
downtown Charleston...76 
Savannah Airport...78 


&& 


Chs watches/warnings/advisories... 
Georgia...none. 
SC...none. 
Marine...Small Craft Advisory from 5 PM this afternoon to 6 am EST 
Friday for amz350-374. 


&& 


$$ 


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