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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 251416
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1016 AM EDT Sat May 25 2019

.SYNOPSIS...
High pressure and unseasonably hot conditions will dominate
into late next week. 

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
No significant changes were made to the previous forecast.

Deep high pressure will persist today as a weak backdoor cold
front dissipates near the Santee River. This feature, along with
the sea/lake breezes and possible convective outflows from
nearby convection, could spark isolated showers and 
thunderstorms this afternoon across southeast SC/GA. However, we
decided to maintain rain chances only around 10 percent so no
mention in the forecast. Given downdraft CAPEs over 1000 J/kg
there is a very low risk of a stronger storm with gusty winds if
one can sustain itself in such a dry environment. Otherwise, 
mostly sunny skies should prevail with highs reaching near 100 
inland, generally west of I-95, with mid 80s along the coast. 
With dewpoints expected to lower during the afternoon inland it 
looks like heat indices will top out below Advisory levels of 
105 degrees. A Special Weather Statement has been issued to 
highlight the heat given how unusual it is for this time of year
as well as the fact that it's a holiday weekend.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
Tonight: Dry and warm conditions will occur tonight as the 
syntopic pattern remains stagnant across the Southeast. Similar 
to the past several nights, the boundary layer will decouple 
well inland during the mid-late evening hours, working east early
Sunday. Only the coast looks to remain weakly coupled. Lows 
will range from the lower 70s inland to the upper 70s at the 
beaches and Downtown Charleston with a few upper 60s possible in
some of the normally cooler spots.

Sunday through Tuesday: The mid-levels will consist of strong 
high pressure hovering over the Southeast Sunday, with the 
center of the high drifting southwards into the northern Gulf of
Mexico Monday and Tuesday. Heights over our area will slowly 
drop through the short term. But it won't matter given the 
unseasonably strong strength of the high. NAEFS shows 500 mb 
heights peaking at about 3 standard deviations above normal 
Sunday. It also shows above normal temperatures at almost all 
levels of the atmosphere. At the surface, areas of high pressure
will stretch from the western Atlantic into the Southeast 
states. Surface analysis indicates signs of weak thermal 
troughing developing inland each day. But strong subsidence and 
a very dry atmosphere will stop any convection from forming. The
only moisture will be fair weather clouds each afternoon. The 
heat wave will continue with temperatures forecasted to reach or
exceed record values throughout the short term. For the high 
temperatures, we once again went with a blend of models, 
thickness values, and accounted for the sea breeze (if any). 
Sunday, expect widespread upper 90s to lower 100s. Monday may be
the hottest day in the short term because the sea breeze may 
remain pinned to the coast for most of the day, allowing inland 
temperatures to bake. If so, most locations away from the 
immediate coast could reach at least 100 degrees for highs. 
Tuesday highs may only be a degree cooler. Though, the sea 
breeze may make it farther inland earlier in the day. Lows each 
night will only cool down into the 70s. Heat indices of course 
are forecasted to be above 100 degrees each day. Heat Advisories
could be needed, especially along the coast.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
The mid-level ridge will remain in place Tuesday night through 
Thursday, then finally flatten out Thursday night followed by zonal 
flow on Friday. Surface high pressure will continue to dominate our 
weather pattern. Models hint at a cold front approaching towards 
Friday. But they also show it dissipating as it runs into our 
persistently dry airmass. Temperatures should trend downward a few 
degrees each day. However, they are still forecasted to remain well 
above normal throughout the long term. Additionally, no rainfall is 
in the forecast. Heat advisories, poor air quality, and dry fuels 
that could increase the risk of wildfires are all concerns. But 
there remain too many variables this far out to get to deep into the 
details.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
VFR at KCHS/KSAV. Very low risk of shower/thunderstorm impact 
this afternoon, mainly at KCHS. 

Extended Aviation Outlook: VFR.

&&

.MARINE...
Through Tonight: Unseasonably strong high pressure will lead to
a summer-like pattern with mainly southwest winds 15 kt or less,
veering to more westerly at night and southerly during the day. 
Seas will average 1-2 ft.

Sunday through Wednesday: Atlantic high pressure will prevail. 
The sea breeze should develop along the coast each afternoon, 
bringing periods of gusty winds, especially to Charleston 
Harbor. However, no advisories are expected. Winds are then 
forecasted to ease into each evening. Waves will generally peak 
in the 3-4 ft range.

&&

.CLIMATE...
A significant, prolonged heat wave will challenge or break many 
of these records:

ALL TIME RECORD HIGHS FOR MAY:
KCHS: 99 set May 21, 1938.
KSAV: 101 set May 30, 1898 and May 31, 1945.
KCXM: 99 set May 21, 1938 and May 26, 1953.

RECORDS FOR SAT 05/25...

Station     Record High       Year(s)
-------     -----------       -------
KCHS            97            2000, 1953
KSAV           100            1953
KCXM            95            1962, 1953, 1912

Station     Record High Min   Year(s)
-------     ---------------   -------
KCHS            75            1953
KSAV            76            1878
KCXM            79            1998

RECORDS FOR SUN 05/26...

Station     Record High       Year(s)
-------     -----------       -------
KCHS            98            1953
KSAV           100            1953

Station     Record High Min   Year(s)
-------     ---------------   -------
KCHS            75            1998
KCXM            79            1998

RECORDS FOR MON 05/27...

Station     Record High       Year(s)
-------     -----------       -------
KCHS            98            1989
KSAV            98            1989, 1962
KCXM            95            1962, 1926

Station     Record High Min   Year(s)
-------     ---------------   -------
KCHS            76            1991
KSAV            77            1878
KCXM            78            1991

RECORDS FOR TUE 05/28...

Station     Record High       Year(s)
-------     -----------       -------
KCHS            97            1967, 1964
KSAV            96            1964, 1898
KCXM            93            2000

Station     Record High Min   Year(s)
-------     ---------------   -------
KCHS            76            2000
KSAV            76            1885
KCXM            80            2000

RECORDS FOR WED 05/29...

Station     Record High       Year(s)
-------     -----------       -------
KCHS            95            1945
KSAV            98            1945, 1898

Station     Record High Min   Year(s)
-------     ---------------   -------
KCHS            76            2018
KSAV            75            1885
KCXM            77            1998

RECORDS FOR THU 05/30...

Station     Record High       Year(s)
-------     -----------       -------
KCHS            95            2004
KSAV           101            1898

Station     Record High Min   Year(s)
-------     ---------------   -------
KCHS            75            1982
KSAV            75            1924
KCXM            78            1998

RECORDS FOR FRI 05/31...

Station     Record High       Year(s)
-------     -----------       -------
KCHS            98            1953 


Station     Record High Min   Year(s)
-------     ---------------   -------
KCHS            77            2004 
KSAV            75            2004

&&

.EQUIPMENT...
WFO Charleston will only conduct upper-air soundings at 12Z until
further notice due to a shortage of helium.

&&

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

&&

$$
NEAR TERM...RJB
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
CLIMATE...
EQUIPMENT...