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FXUS62 KCHS 221113

Area Forecast Discussion
National Weather Service Charleston SC
713 AM EDT Sat Jul 22 2017

Atlantic high pressure will extend west into the southeast
coast through this weekend while a surface trough remains
inland. A weak cold front will approach the area during the
middle of next week. Low pressure should then develop over the
area and linger through late week.


Today: A broad mid level weakness will extend along the lower 
Gulf coast to Northern Florida while deep subtropical ridges 
remain anchored over the Atlantic and from the Carolinas west 
into the southern Plains. Sunny skies early on, will result in 
temps rising into the lower 90s by early afternoon. Across 
southeast and coastal SC, we think substantial upper ridging and
very dry air between 500 MB and 250 MB should be enough to keep
diurnal convection isolated at best and across several zones 
including Charleston, we decided on silent POPs today even 
though a spotty and brief shower/tstm is certainly possible.

Over south GA, a weak mid level vort is noted close to the Florida
state line and moisture is certainly deeper not far to the south
of our forecast area. Many models suggest an active Gulf Coast 
sea breeze this afternoon and 700 MB flow turns southwest with 
time. Some of this late day convection to the south of the 
Altamaha could send out some late day mesoscale boundaries that 
bisect the far south GA sea breeze. This may result in isolated
to locally scattered showers and storms close to the Altamaha 
region. We have a small area of late day low-end chance POPs in
our far southern GA zones, otherwise we maintained slight chance
POPs in southeast GA.

Hot and humid weather, typical for this time of year will persist.
Highs will reach the mid 90s with perhaps a few upper 90s adjacent
to the CSRA and southeast Midlands. Forecast heat indices reach
the 105-107 degree range later today but windows of any 
potentially higher indices appears very small in areal extent. 

Tonight: If any early evening convection lingers over southeast
GA, it should diminish rather quickly prior to 03Z. Otherwise, 
skies will be mostly clear to partly cloudy. Lows will be in
the mid 70s most areas. Beaches will remain around 80.


Sunday: High pressure will gradually retreat over the Western 
Atlantic while lee troughing develops over the Midlands early week. 
Guidance suggests that weak mid-lvl energy will pass just off the 
Southeast coast, perhaps spawning showers and thunderstorms near the 
beaches. However, additional precip activity should develop inland 
where max temps approach the mid 90s near the vicinity of the lee 
trough. Chances of showers/thunderstorms remain in the forecast 
during mid afternoon/evening hours. Activity should diminish within 
a few hours of sunset, but an isolated shower or thunderstorm can 
not be ruled out overnight. Low temps should range in the mid 70s. 

Monday and Tuesday: A southwest flow will advect deep moisture over 
the Southeast United States well ahead of a cold front approaching 
from the north/northwest mid week. Fairly unstable conditions will 
develop each afternoon, even as cloud cover expands over the region. 
PWATs around 2.25 inches along with max temps in the lower 90s 
support chances of showers and thunderstorms each afternoon, with 
greater precip coverage anticipated on Tuesday as mid-lvl energy 
shifts over the Southeast while a sfc trough persists inland.
Overnight lows will remain mild under some clouds, generally ranging 
in the mid 70s.


An unsettled weather pattern will persist through mid week while 
southwest flow advects deep moisture to the region ahead of a cold 
front approaching from the north/northwest. The cold front should 
struggle to push south into the region, likely stalling just north 
of the area as its parent mid/upper lvl trough of low pressure 
shifts off the Northeast coast. However, weak low pressure should 
develop near the stalled boundary on Wednesday and persist through 
late week until a second mid/upper lvl trough shifts over the 
Northeast and gradually amplifies, forcing some mid-lvl energy over 
the Mid Atlantic and Southeast states late week. The pattern 
suggests at least chances of showers and thunderstorms each day with 
greatest coverage occurring during peak diurnal heating hours. Temps 
will generally peak around normal mid week, but could approach the 
mid 90s by the upcoming weekend. Overnight lows will range in the 
mid 70s.


VFR at KSAV/KCHS through 06Z Sunday. Isolated late day showers
and tstms are possible along the southeast GA sea breeze corridor.

Extended Aviation Outlook: Afternoon showers/thunderstorms could 
provide brief flight restrictions each day. However, greatest 
chances of flight restrictions should occur on Wednesday as a cold 
front stalls just north of the area. Otherwise, VFR conditions will 


The pressure gradient is slowly strengthening between the high 
pressure centered south of Bermuda and a better defined Piedmont
surface trough well inland. Southwest to south flow is expected
to increase to a solid 15 kt later this afternoon and continue 
tonight, before decreasing toward daybreak. Seas will increase 
from 2 to 3 ft to 3-4 ft as winds build.

Sunday through Thursday: High pressure will prevail over the waters 
early next week while a trough of low pressure develops inland. A 
cold front will then stall just north of the area during the middle 
of next week before weak low pressure slides closer to the coast. In 
general, winds/seas are expected to remain below Small Craft 
Advisory levels through the period. However, we could see southwest 
winds gusting around 20 kts Sunday and Monday while the pressure 
gradient is somewhat enhanced over coastal waters. The gradient 
should then relax as low pressure gradually shifts near the 
Southeast coast mid week. Seas will generally range between 2-4 ft, 
with the exception of some 5 feet seas near 20 nm away from the 
South Carolina coast Sunday night and Monday night.


Elevated tide levels due to the lunar perigee and new moon will
result in the possibility for minor coastal flooding during the
evening high tides this weekend into early next week, especially
along the SC coast. This evening's chances for shallow coastal 
flooding look decent (similar to yesterday) and coastal flood 
advisories will likely be required later today.





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