953 
FXUS62 KCHS 211600
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1200 PM EDT Mon May 21 2018

.SYNOPSIS...
The region will remain between Atlantic high pressure and broad
low pressure to the west. This pattern should support south
winds through most of the week, yielding warm and moist
conditions. 

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Increased pops slightly across southwest zones, otherwise the 
forecast is on track. 


Subtropical ridging from the east will hold form today as weak
shortwave energy meanders along the eastern Gulf coast. Modified
forecast soundings are not overly unstable today with a well 
defined H7 theta-e minimum centered right over Southeast South 
Carolina and Southeast Georgia. This will essentially cap off 
the atmosphere and the potential for deep convection despite 
highs warming into the lower-mid 80s. The various CAMs are 
consistent in developing isolated, low-topped showers ahead of 
the sea breeze and with sufficiently deep low-level moisture in
place, this can not be completely discounted. A few coastal 
showers could move inland this morning, but activity over the 
Atlantic should diminish as low-level convergence shifts west 
to/ahead of the sea breeze. Plan to drop mentionable pops for 
the coastal counties and just include 20-30% pops across the 
interior. 30% pops along with a mention of a slight chance of 
tstms were clustered across the far southwest Georgia zones 
where guidance shows deeper moisture and weaker mid-level
capping.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
Tonight: Sfc high pressure centered over Bermuda will build across 
the forecast area tonight. In addition, slight increases in H5 
heights are expected as mid level low drifts west across the Deep 
South. Forecast sounding across the CWA indicate that a significant 
subsidence inversion will build around H850. Given little to no sfc 
instability and forcing, I will indicate decreasing values of SCHC 
PoPs overnight. Low temperatures should verify well in the upper 60s 
to around 70 degrees.

Tuesday through Thursday: The area will remain between Atlantic
high pressure to the east and low pressure to the west. A cold 
front will approach from the north Wednesday night before 
stalling out just north of the area. This pattern will maintain 
the tropical air mass in place and lead to higher than normal 
rain chances, especially each afternoon and evening. In general 
we think the highest chances will be inland near the better 
moisture, instability and forcing. Some spots could pick up over
an inch. No significant flooding or severe weather is 
anticipated at this time. Temperatures will generally be near to
above normal, especially lows.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
High pressure pushing southeast from the Ohio Valley/Mid-Atlantic 
region will combine with Atlantic high pressure as surface low 
pressure tries to organize slightly in the central Gulf of Mexico. 
The low should move toward the north-central Gulf coast and this 
will continue to feed tropical moisture into the local area leading 
to high rain chances especially each afternoon/evening. We continue 
to discount the GFS which indicates a secondary low move north along 
the Southeast U.S. coast as it remains an outlier. Temperatures 
should stay near to above normal.

&&

.AVIATION /16Z MONDAY THROUGH FRIDAY/...
VFR. Convection will remain west of the terminals. Similar to
this morning, shallow ground fog and patches of stratus will
redevelop after midnight. Probabilities for impacts at either
terminal are too low to justify a mention at this time.

Extended Aviation Outlook: A persistent tropical air mass will lead 
to higher than normal rain chances through the period, mainly each 
afternoon. Thunder chances will be low however given the limited 
instability.

&&

.MARINE...
Today: Large high pressure centered over Bermuda will gradually
build west over the region through tonight. Southeast winds 
will continue through today and tonight, speeds remaining 
between 10 kt or less. Wave heights are forecast to range from 
2-4 ft within 20 NM to 4-5 ft beyond 20 NM.

Tuesday through Saturday: The area will remain between low pressure 
to the west and high pressure to the east. No significant wind 
concerns, however seas will be elevated near Small Craft 
Advisory levels close to the Gulf Stream into Tuesday and again 
starting Friday night.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$