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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 192114
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
514 PM EDT Fri Apr 19 2019

.SYNOPSIS...
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. 

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
This evening and tonight: While the main line of convection 
that produced severe weather this afternoon has moved east of 
the forecast area, the actual cold front remains draped 
north/south across Georgia. With the cooling aloft with the 
upper low and forcing along the cold front, a broken band of 
showers and isolated thunderstorms has developed just to the 
west of the forecast area. This activity will continue to push 
eastward and across the forecast area this evening. The showers 
should begin to wane through the evening, but could produce 
scattered coverage. Thunder is possible, but the severe threat 
is low given the amount of convective overturning that took 
place today. The front will move offshore tonight and rain 
chances will come to an end. Skies should steadily clear through
the night as well. Lows are forecast to range from the upper 
40s to low 50s away from the coast, with mid to upper 50s at the
beaches. 

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
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.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
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.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
KCHS: Thunderstorms have moved east of KCHS and a period of 
light rain will continue for a few hours. MVFR ceilings could 
continue for another few hours as well, then go VFR this 
evening. There is a low end chance for MVFR ceilings to develop 
late in the period, but will keep VFR for now. Winds will be 
gusty once again on Saturday, frequently reaching the 25-30 knot
range. 

KSAV: Thunderstorms have pushed well to the east and all that 
is left is lingering light rain that will persist for another 
couple of hours. Thereafter, VFR conditions will prevail. Winds 
will become gusty again on Saturday, with just a low end chance 
of MVFR ceilings to develop. 

Extended Aviation Outlook: Gusty southwest winds will prevail 
on Saturday. Otherwise VFR will prevail into next week.

&&

.MARINE...
This evening and tonight: A sharp cold front will move eastward
across the waters tonight and winds will become increasingly 
west-southwesterly with time. Gales have ended across all waters
except for the Charleston County waters. Gales could continue 
there this evening, but should diminish to solid advisory level 
thresholds. Elsewhere, Small Craft Advisories have replaced the 
canceled Gale Warnings, and those will continue through the 
overnight. Winds will likely diminish late tonight, perhaps 
below advisory levels, but seas will remain elevated. By late 
tonight seas will subside to become 5-8 feet in the Charleston 
County waters, 4-6 feet further south, and 5-8 in the outer 
Georgia waters. 

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 
period. 

Surf zone hazards: A High Surf Advisory continues through this 
evening for the Charleston County coast. 

Rip Currents: A High Risk of Rip Currents continues through 8 
pm. 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.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ117-
     119-139-141.
SC...High Risk for Rip Currents until 8 PM EDT this evening for 
     SCZ048>051.
     High Surf Advisory until 11 PM EDT this evening for SCZ050.
MARINE...Small Craft Advisory until 5 PM EDT Saturday for AMZ330-352.
     Gale Warning until 11 PM EDT this evening for AMZ350.
     Small Craft Advisory until 2 PM EDT Saturday for AMZ354.
     Small Craft Advisory until 2 AM EDT Sunday for AMZ374.

&&

$$

NEAR TERM...BSH
SHORT TERM...33
LONG TERM...MS
AVIATION...BSH/33
MARINE...BSH/33