Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 200435

Area Forecast Discussion
National Weather Service Charleston SC
1235 AM EDT Sat Apr 20 2019

A strong cold front will move offshore early tonight. Low
pressure over the Ohio Valley will prevail Saturday, followed
by high pressure Sunday through Wednesday or Thursday. The next
cold front may approach late next week. 


Skies will continue to clear through the early morning with
breezy conditions lingering. No major changes were made for the
early morning update.


Saturday: An unseasonably strong trough over the eastern half 
of the country in the morning with low pressure both surface and
aloft in the Ohio Valley will steadily begin to fill as they 
both lift off to the east-northeast. A strong short wave pin- 
wheeling around the base of a large trough will swing through 
the forecast district in the morning, then into the Atlantic 
during the afternoon. Given the lack of moisture with PWat no 
more than about 1/2 to 2/3 inches, suggests that it won't be 
able to generate anything more than scattered to broken 
cumulus/stratocumulus clouds. However, with the cold mid levels 
and steep lapse rates we'll have to consider mention of small 
PoP at a later time. The low heights and H85 temps that are just
2-3C will lead to temps below normal, with most highs only 65- 
70F. Deep mixing tapping into modest low level winds will 
produce some gusty west to southwest breezes that are still as 
high as 20-30 mph during the late morning and afternoon. This is
probably not strong enough to hamper any storm surveys or 
recovery efforts that might be necessary.

Saturday night: Clearing skies will ensue, and with continued 
advection of cooler air will allow for temps to get down to the 
mid- upper 40s by Sunday morning inland from US-17, and even to 
the lower 50s closer to the coast.

Sunday through Monday: A deep mid level cyclone near the 
Shenandoah of Virginia will reach near the Mason-Dixon line by 
00Z Monday, then becomes situated near Long Island by 00Z 
Tuesday. A dry west- northwest flow aloft on the back side of 
the low will encompass the local area, while at the surface 
initially over the northeast Gulf of Mexico on Sunday will 
expand overhead on Monday. The lack of any triggering mechanisms
plus the lack of moisture will allow for generally clear skies,
and with climbing heights and H85 temps, warmer weather will 
return, more noticeably on Monday.


High pressure over the Southeast Monday night will remain 
nearly stationary into Tuesday, bringing dry conditions and 
above normal temperatures. The high starts to shift offshore 
Wednesday as a front approaches from the north. Models have this
front weakening as it gets closer to us, meaning the rain 
threat should be low until maybe late in the week.


VFR. Gusty winds will linger at both KCHS and KSAV for much of
the period.

Extended Aviation Outlook: VFR.


All gales have been downgraded to Small Craft Advisories.

Saturday: Deep low pressure in the Ohio Valley will weaken 
through the day, but there remains a fairly tight gradient 
across the area. That along with the large seas that will take 
time to come down, will result in a Small Craft Advisories for 
all marine areas, including Charleston Harbor. 

Sunday through Wednesday: High pressure that initially builds 
in from the west on Sunday, will settle overhead Monday and 
Tuesday, before pushing southeast of the waters next Wednesday. 
This will generate quiet marine conditions through the entire 

Rip Currents: Although winds are offshore or parallel to the 
coast on Saturday, the wind speeds are still high enough to 
combine with small swells to result in a Moderate Risk of Rip 
Currents at area beaches.


MARINE...Small Craft Advisory until 5 PM EDT this afternoon for AMZ330-
     Small Craft Advisory until midnight EDT tonight for AMZ350.
     Small Craft Advisory until 2 AM EDT Sunday for AMZ374.
     Small Craft Advisory until 2 PM EDT this afternoon for AMZ354.