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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 260801
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
401 AM EDT Sun May 26 2019

...ALL TIME RECORD HIGHS FOR THE MONTH OF MAY COULD BE CHALLENGED
TODAY AS THE A PROLONGED, EARLY SEASON HEAT WAVE CONTINUES...

.SYNOPSIS...
High pressure and unseasonably hot conditions will persist most
of this week. Some relief from the oppressive heat is expected
by next weekend.

&&

.NEAR TERM /THROUGH TODAY/...
It will be another hot and oppressively hot day as the stagnant
synoptic pattern featuring anomalously strong deep-layered high
pressure will remain largely unchanged across the Southeast
States. Mid-level heights will fall about 10dm across Southeast
South Carolina and Southeast Georgia as the center of the mean 
anticyclone retrogrades ever so slightly to the south/southwest,
but H8 temperatures are forecast to rise another 1C through the
day. This will yield a modest westerly flow which will pin the 
sea breeze to the immediate coast until late in the afternoon. A
pinned sea breeze coupled with ongoing dry soil/drought 
conditions, warmer 1000-850 hPa temperatures and a slightly 
warmer start to the day, should allow highs to warm about 1-2 
degrees higher than what was observed Saturday afternoon. The 
warmest conditions look to occur the Metter-Reidsville-Savannah-
Springfield-Beaufort corridor where H8 temperatures are forecast
to reach 21-22C. Expect highs to range from from 100-103 inland
to the upper 80s/lower 90s at the beaches. It appears the all 
time record highs for May could be challenged at both KCHS and 
KSAV. NAEFS once again shows 1000 hPa temperatures peaking 2-3
standard deviations above the daily mean.

Dewpoints are expected to mix out in the lower 60s inland from 
the sea breeze, then pool back into the lower-mid 70s across the
coastal counties as the sea breeze moves inland. Heat indices 
are expected to peak 103-107F in a large corridor from 
Reidsville to Charleston with 100-103F at the beaches and 
locations well inland adjacent to the CSRA and Southern 
Midlands. A combination of an impact-based and criteria-based 
Heat Advisory will be issued for most zones from 11 AM until 8 
PM. Although the advisory looks marginal for many areas,
widespread record, early season heat and ongoing Memorial Day 
weekend activities where may folks will be outside support the 
issuance of a cautionary advisory.

Warm mid-level temperatures, a deep dry column, and broad 
subsidence aloft should negate the development of any convection
today. Could see a very brief shower try and form along the sea
breeze across mid-upper Charleston County where low-level 
convergence will be the strongest, but any moist updraft that 
can develop should quickly dissipate as extensive dry air gets 
entrained. Will show a small areas of pops around 5% across 
parts of mid- upper Charleston County as well as eastern 
Berkeley County mid- late afternoon with 0% pops elsewhere. 
Sunny skies this morning will give way to another shallow, high-
based cumulus field this afternoon yielding mostly sunny to 
partly cloudy conditions.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
Tonight: Warm and humid with lows in the lower 70s well inland 
to around 80 at the beaches and Downtown Charleston.

Memorial Day through Wednesday: The mid-levels will consist of 
strong high pressure centered over the FL Panhandle Monday 
morning. The center of the high is forecasted to drift into the 
northeastern Gulf of Mexico late Monday, then remain there 
through Wednesday. Heights over our area will slowly drop 
through Tuesday. But then they may rise a bit Wednesday as the 
periphery of the high tries to build back into the Southeast. 
NAEFS still shows 500 mb heights peaking at about 2 standard 
deviations above normal Monday and above normal temperatures at 
almost all levels of the atmosphere at that time. At the 
surface, areas of high pressure will stretch from the western 
Atlantic into the Southeast states through Wednesday. Each 
afternoon weak thermal troughing will develop either over or 
nearby our inland areas 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 continued the blend of models, thickness 
values, and accounted for the location of the sea breeze. Monday
appears to be the hottest day in the short term because the sea
breeze may be pinned to the coast for most of the day, allowing
most temperatures away from the beaches to reach at least 100 
degrees. Tuesday highs may be a degree or two cooler. What helps
is the sea breeze may make it farther inland earlier in the 
day. This same trend is expected again on Wednesday. Lows each 
night will only cool down into the 70s. Dew points will 
initially mix out each afternoon, then increase along the 
coastal corridor as the sea breeze moves inland. Heat indices 
will be close to 105 degrees on Monday and Tuesday, which is 
Heat Advisory criteria.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
The mid-level ridge will remain in place Wednesday night, then 
finally flatten out Thursday night followed by zonal flow Friday and 
Saturday. Surface high pressure will continue to dominate our 
weather pattern through Thursday. The models still show a cold front 
approaching our area Friday or Saturday. They have trended wetter, 
which seems a little suspicious considering the front will be 
running into our very dry airmass. We opted to only introduce slight 
chance POPs Friday and Saturday. But early indications are rainfall 
amounts won't put much of a dent in our drought. Temperatures will 
trend downwards each day. However, they are still forecasted to 
remain above normal.

&&

.AVIATION /05Z SUNDAY THROUGH THURSDAY/...
VFR.

Extended Aviation Outlook: VFR.

&&

.MARINE...
Through Tonight: South to southwest winds will prevail through
the period. Directions will locally back to the southeast along
parts of the Georgia coast with the formation of the sea breeze.
Speeds will be 10-15 kt today, then rise to about 15 kt to
locally 15-20 kt tonight with a nocturnal surge. Seas will
average 1-3 ft.

Monday through Thursday: Atlantic high pressure will remain the
dominant synoptic feature. Winds will mostly be from the SW, 
backing a bit during the day with the sea breeze and veering a 
bit at night with the the nocturnal low level jet. Away from the
gusty sea breeze, winds will mainly stay at or below 15 kt 
through midweek. Seas will peak at 3-4 ft.

&&

.CLIMATE...
The ongoing heat wave will challenge or break many of these records:

EARLIEST 100 DEGREE TEMPERATURES:
KCHS: June 2, 1985. 
KSAV: May 25, 2019 and 1953.
KCXM: June 1, 1985.

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 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

RECORDS FOR SAT 06/01...

Station     Record High Min   Year(s)
-------     ---------------   -------
KCHS            77            1974 
KSAV            76            1880

&&

.EQUIPMENT...
The Downtown Charleston (KCXM) observation will be unavailable
until further notice. The cause of the outage is unknown.
Technicians will address the outage on Tuesday.

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

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory from 11 AM this morning to 8 PM EDT this evening 
     for GAZ099>101-114>119-137-138-140.
SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening 
     for SCZ042>045-047>052.
MARINE...None.

&&

$$