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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 250750

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


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


GOES-E water vapor imagery shows a pronounced, deep layered
anticyclone in place across the Southeast U.S. this morning.
This feature will remain anchored across the region today with
the local forecast area positioned directly underneath the
925-700 hPa anticyclone. A weak, backdoor cold front sliding
south through eastern North Carolina at 25/07z will drop into 
the Pee Dee later over the next several hours, likely washing 
out near or just north of the Santee River later today. Despite 
this feature being nearby, strong capping aloft, deep-layered 
dry air and warm mid-level temperatures should prevent any 
meaningful convection from firing this far to the south. 
Modified RAP soundings do show the cap briefly breaking north of
the I-26 corridor by mid-afternoon, but the resulting CAPE 
profiles are long/skinny and any moist updrafts that are able to
initiate should quickly entrain dry air and dissipate. Will 
show gridded pops 5-10% north of I-26 with 0% pops elsewhere. 
Expect a shallow, high-based cumulus field to develop by early 
afternoon along and inland from the sea breeze. Otherwise, skies
will be sunny with only a few whips of cirrus passing through.

It will be another hot one today with H8 temperatures forecast 
to rise another 1-2C. A warmer start to the day coupled with 
warmer temperatures aloft should support highs a few degrees 
warmer than Friday, except at the coast where the resultant sea 
breeze should get a slightly earlier push inland with the lack 
of a strong downslope flow component. NAEFS analysis shows 1000 
hPA temperature rising to 2-3 standard deviations above the mean
for late May; a testament to how warm this airmass could become.
A number of sites reported highs 98-99 degrees away from the 
coast Friday afternoon and with warmer conditions expected today
anticipate some areas will see their first 100 degree reading 
of the year, especially over interior Southeast Georgia. Highs 
will range from around 100 far interior to the mid 80s at the 
beaches. Dewpoints will once again mix out into the lower-mid 
60s as temperatures peak, but will pool back into the lower 70s 
as the resultant sea breeze moves inland across the coastal 
counties. Max heat indices should peak in the 99-103 range, 
which is below the pre-July 1 Heat Advisory criteria of 105. A 
special weather statement will be issued to highlight today's 
heat given the holiday weekend is in progress.


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.


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 



Extended Aviation Outlook: VFR.


Through Tonight: South to southwest winds will dominate through
the period with winds 5-10 kt today increasing to 10-15 kt. 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.


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

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.


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


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

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


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


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


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


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


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

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


WFO Charleston will only release 12z upper air soundings until 
further notice due to a station helium shortage.