163 
FXUS62 KCHS 180817
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
417 AM EDT Wed Jul 18 2018

.SYNOPSIS...
A cold front will approach the region from the northwest today,
then stall over or nearby our area through Thursday night. The
front will slowly lift north on Friday. Another cold front
should approach from the northwest early next week. 

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 4 AM: Latest surface observations indicated that the sfc 
cold front was located near the I-85 corridor of the western 
Carolinas. The cold front is forecast to slide slowly east 
today. However, preferred guidance indicates that a frontal wave
will develop over the mid-Savannah River Valley late this 
afternoon, as a H7 trough ripples over the region. Once the wave
develops, the front will likely become nearly stationary 
upstream of the forecast area. Forecast soundings east of the 
front indicate deep instability, low LFC, and PW around 2.1 
inches. Deep convection is expected to easily develop once the 
convective temperature in the upper 80s is reached, forecast to 
occur by 18Z. Cool pools and sea breeze just inland of the coast
should serve as the primary focus for showers and 
thunderstorms. I will forecast a late afternoon to early evening
peak in convection coverage, high likely to low cate PoPs 
across the Lowcountry of SC. Using a blend of MOS, high 
temperatures should range from the low 90s across SE GA to upper
80s across Berkeley County.

Tonight: The weak front, aided by convective cool pools, should 
slowly drift SE across the forecast area. Convection coverage is 
expected to decrease through the overnight hours. However, given the 
position of the front and lingering instability, I will keep a 
mention of scattered showers/thunderstorms during the period. 
Temperature timing is difficult to pin down, largely dependent on 
the position and timing of thunderstorms. The temperature curve will 
reflect a diurnal trends with this package, but will refined with 
later updates. Low temperatures should range in the low to mid
70s. 

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
The mid levels will consist of a trough just off the East Coast 
Thursday morning. This trough will get pushed further offshore as 
ridging builds to our north during the day, generally leaving our 
area with semi-zonal flow. The ridging will be short- lived because 
Friday it will get pushed offshore as an amplifying trough centers 
itself from the Great Lakes Region down into the Deep South. This 
trough remains in roughly the same location into Saturday while 
amplifying further. At the surface, a stationary front is forecasted 
to meander across our southernmost counties Thursday and Thursday 
night. Friday the front will transition into a warm front and slowly 
lift northward across our area. It's forecasted to be just north of 
our area by Friday night. Saturday the warm front will continue it's 
slow progress northward, away from our area. Meanwhile, troughing 
will start to develop inland. Plenty of moisture will be in place. 
Models show PWATs exceeding 2.25" across our entire area Thursday 
and Friday. Though, their are hints of pockets up to 2.5" with the 
front itself. SPC climatology indicates these values would be in 
record territory for CHS for this time of the year. Values finally 
drop below 2" Friday night and Saturday as the front moves to our 
north. Given all the moisture in place, lift from the front, and 
good model agreements spitting out plenty of rain, we adjusted POPs 
higher, but kept them capped at likely Thursday and Friday 
afternoons. Saturday a vast majority of the area is in the chance 
category. Though, it must be stressed that these POPs are highly 
dependent on the exact location of the front. An unexpected shift 
further north or south would necessitate changes to the POPs. The 
severe threat remains low due to the limited instability. Models 
have changed quite a but, now showing less instability. Thursday and 
Friday GFS BLCAPEs struggle to reach 1,000 J/kg. They do increase to 
the 1,500-2,000 J/kg range on Saturday with pockets of higher DCAPEs 
approaching 1,000 J/kg. But this is highly dependent on the exact 
location of the front. We continue to forecast a chance of 
thunderstorms with a low severe threat. The main concern continues 
to be the rainfall potential. The deep moisture and slow storm 
motions resulting from light steering winds higher up should allow 
for periods of heavy rain Thursday and Friday. Local flooding is 
possible both of these days. High temperatures will be a few degrees 
below normal Thursday and Friday due to the showers/thunderstorms 
and cloud cover. Highs will rebound to normal on Saturday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
The models are in good agreement showing a strong trough over the 
East Coast Saturday night through Monday, with it weakening on 
Tuesday. However, they don't agree as much with the surface pattern. 
The models hint at a trough inland Saturday night into Sunday. 
Another cold front will slowly approach from the northwest Sunday 
into Monday. Then, they disagree over whether the front makes it to 
our area or stays to the north. Regardless, the end result will be a 
rainy weather pattern.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
KSAV and KCHS are forecast to remain VFR through sunrise
Wednesday morning. KSAV may see periods of FEW-SCT stratocu
<1 kft. A slow moving cold front will advance toward the Coastal
Plain from the Foothill this afternoon. A weak frontal wave is
forecast to develop across the mid-Savannah River Valley late
this afternoon and evening. Once the wave develops, the front is
expected to slow or become nearly stationary. Deep instability
and moisture on the east side of the front will favor
thunderstorms this afternoon and evening, highlighted with a
TEMPO from 19Z-23Z. Remnant showers and thunderstorms could
linger well into this evening. Storms motions are forecast to
range from 5-10 kts.

Extended Aviation Outlook: A series of fronts will bring unsettled 
weather to the region. Periodic flight restrictions are likely in 
convection, mainly during the afternoon and evening hours.

&&

.MARINE...
A cold front will approach the coast today, remaining inland through 
sunset. Scattered to Numerous thunderstorms are forecast to develop 
along a sea breeze early this afternoon, possibly drifting over the 
Intracoastal Waterway. Scattered thunderstorms should drift or 
develop over the marine zones from mid afternoon through this 
evening. Otherwise, the pattern will support SW winds between 10-15 
kts with gusts near 20 kts. Wave heights are forecast to range 
between 2-3 ft within 20 NM to 3-4 ft beyond 20 NM. The cold front 
is timed to slide off the SC coast tonight, tracking SSE. Winds will 
shift in the wake of the front from the north. Winds south the front 
should veer from the WSW and decrease to around 10 kts. Scattered 
thunderstorms are expected to linger through most of the night. Wave 
heights will generally range between 2-3 ft. 

A stationary front will meander over or nearby our area through
Thursday night. This front will transition into a warm front 
and slowly lift northward on Friday, becoming located to our 
north by Friday night. A trough will develop inland and prevail 
into Sunday. Meanwhile another cold front will slowly approach 
from the northwest early next week. Even with this active 
weather pattern, no Small Craft Advisories are expected.

&&

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

&&

$$
NEAR TERM...NED
SHORT TERM...MS
LONG TERM...MS
AVIATION...NED/MS
MARINE...NED/MS