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Area Forecast Discussion

FXUS62 KCHS 301031

Area Forecast Discussion
National Weather Service Charleston SC
631 AM EDT SAT JUL 30 2016

Atlantic high pressure along with an inland trough will prevail into
early next week. High pressure will then become suppressed further
to the south which could allow a weak cold front to approach from
the north by the middle part of next week.


For Today: The large scale pattern is dictated by a TUTT low
north of Hispaniola that heads toward the southern Bahamas, while
a mid latitude trough extends south from the upper Midwest through
the TN valley. In between the local region lies within a deep
ridge that still refuses to weaken overhead. 500 mb heights are
similar to yesterday around 5910-5920 meters and a 3-4C cap
persists under the associated sinking motion. At the surface a lee
side trough remains anchored in place, as the sub-tropical
Atlantic ridge extends west across FL.

It`ll be another hot and humid day with 850 mb temps ~20C and low
level thickness values similar to what they were yesterday.
However, there is less compressional heating compared to Friday as
the synoptic flow is more SW rather than W, and the sea breeze
gets an earlier start. Plus we actually have our first chance of
convection in about the past 5 days in place for today, albeit
only a low end probability. These conditions should hold max temps
"only" in the mid or upper 90s, with maybe a couple of spots
across interior SE GA hitting 100F. Although there is again a
pronounced inverted-V sounding indicating that dew points will mix
out, the overall dryness of the air is less than recent days and
with the low level trajectories backing to the S and SW, this will
limit dew points from dropping as much as recent days. This will
result in afternoon heat indices peaking at 105-109F across the
vast majority of the CWFA. Moisture will pool in association with
the sea breeze along the US-17 corridor from about 1-4 pm, enough
so that a few spots from the Charleston metro to the Beaufort and
Hilton Head areas, and then toward the Savannah region will
experience some 110-112F heat indices. But the duration and
spatial coverage is low enough where we don`t require a Heat

The potential for showers and t-storms is certainly greater than
the past several days, but still not expecting anything more than
isolated to scattered coverage, since there remains large
condensation pressure deficits, warm mid levels and their
accompanying poor lapse rates. But with the sea breeze boundary
and the nearby proximity to the Piedmont trough and a weak short
wave that skirts by to the N-NW late, we feel that 20-30 PoP is in
order after 1 or 2 pm. Greatest coverage is across the Charleston
quad-county district where the best boundary interaction and
higher Theta-E air is found. DCAPE in excess of 1000-1200 J/kg
equates to a potential for strong or perhaps marginal severe
downbursts if storms in isolated storms.

Tonight: The TUTT low rides up the spine of the Bahamas as a broad
trough is situated over the eastern U.S. We`re in the region
between both of these large scale features, near the southern
extent of the trough. An earlier short wave moves through the area
during the evening, enough to keep at least slight chances of
showers/t-storms going prior to midnight across our N and NW tier.
A warm SW synoptic flow that never fully decouples will again
produce a warm and muggy night with low temps that will struggle
just to dip below 80F. And we might be near record high minimums
for July 30th.


Sunday and Sunday night: Aloft, the upper ridge will continue to
stretch across south Georgia and the Gulf coast through the
overnight, with no significant embedded shortwaves poised to impact
the area. At the surface, the forecast area will remain under the
western periphery of the subtropical high to the east and in between
the inland lee trough. Models indicate the potential for more
coverage of diurnal showers and storms, but a perusal of soundings
doesn`t reveal much significant change from previous days. 500 mb
temperatures are slightly cooler, down to around -7 C at times, with
modestly steeper mid-level lapse rates. This uptick in coverage will
likely have the best chance of occurring further north where the
better instability and moisture will be positioned. The forecast
still features 20-40 percent PoP`s, with the highest situated over
the tri-county region and mainly southeast South Carolina. Lingering
activity should diminish in the evening and the overnight will be
dry for most areas. We could see an isolated shower or storm along
the coast late though. Temperatures are expected to come down a few
degrees, with highs mainly in the mid to upper 90s. Lows will be in
the upper 70s. Please see the Climate section below for more details
regarding the near record warmth through the month of July.

Monday through Tuesday: The upper ridge will break down and become
more centered between the desert southwest and the lower Mississippi
Valley. Moisture will increase across the area, with precipitable
water values around 2.25 inches, and 500 mb temperatures will cool
further to around -8 C. This will all happen as a well defined
shortwave approaches the area from the northwest Monday afternoon
and evening. As such, it appears Monday will likely be the most
active day and the increase in convective coverage will extend
through Tuesday. The near storm environment still isn`t overly
impressive for severe thunderstorms, but there will likely be a few
strong to marginally severe storms where boundary interactions
occur. As the calendar shifts over the August, temperatures will
cool more into the low to mid 90s.


No significant changes were made to the going forecast for the long
term period. A return to more active showers and thunderstorms will
continue at least for Wednesday and Thursday as embedded shortwaves
approach and push through the area from the northwest. The forecast
generally features 30-40 percent chances each afternoon and evening,
and these values will certainly be refined as the time period draws
closer. Temperatures also continue to look cooler, with highs mainly
in the low 90s, which would be right around normal for early August.


While there is a risk for isolated convection near the terminals
from about 18-23z, the probability of any direct impacts is far to
remote to include anything other than VFR conditions with the 06z
TAF set for KCHS and KSAV.

Extended Aviation Outlook: Brief flight restrictions are possible
with afternoon/evening showers/thunderstorms Sunday through
Wednesday. Otherwise, VFR will prevail.


Today: The overall synoptic pattern remains essentially unchanged
from recent days, with an inland trough of low pressure and the
oceanic ridge poking west across FL. The local waters will lie on
the NW periphery of this area of high pressure, and once sea
breeze circulations develop by 16-17Z, W winds of 10-15 kt winds
will back to the S and SW at 12-18 kt. Conditions at and near the
mouth of Charleston Harbor will likely experience the strongest
winds with return flow aloft from inland storms, as gusts peak at
times near 20 kt. Seas will hold at or below 3 ft throughout.

Tonight: High pressure to the south and an inland trough will
dictate the general pattern, and once again another nocturnal low
level jet will traverse the marine community. Geostrophic winds
are as high as 20 or 25 kt, so we won`t require a Small Craft
Advisory, but there is enough mixing to generate S and SW winds as
great as 15-20 kt. Seas will build to as much as 4 ft with the
favorable trajectories and higher winds.

Sunday through Thursday: The persistent pattern of a trough of
low pressure inland and high pressure to the east will continue to
drive south to southwest flow across the local waters. The periods
of strongest winds will likely occur in the afternoon and evening
hours along the land/sea interface with the development of the sea
breeze circulation. Sunday will likely be the day with the
strongest winds, and we could see Small Craft Advisory gusts to 25
knots for a few hours around the Charleston Harbor and the
Charleston County coast. Otherwise, winds will generally top out
around 15 knots. Seas will primarily range 1-3 feet with the
potential for some 4 footers during the time periods with elevated



Record high minimums for 30 July...
KCHS: 80 set in 2011.
KCXM: 82 set in 1999 and previous.
KSAV: 81 set in 1878.

Record high maximums for 30 July...
KCHS: 100 set in 1999.
KCXM: 98 set in 1942 and previous.
KSAV: 101 set in 1896.

***Top 5 Warmest Months on Record by Average Temperature***
Charleston International Airport - KCHS (Records Back to 1938)
1. 86.1 - July 1986
2. 86.0 - July 2016 (2 days left)
3. 85.5 - July 1993
4. 83.9 - July 1992
5. 83.8 - July 1998

Savannah International Airport - KSAV (Records Back to 1874)
1. 86.7 - July 1993
2. 86.0 - July 2016 (2 days left)
3. 85.7 - July 1986
4. 85.7 - July 1875
5. 84.8 - August 2011

Downtown Charleston - KCXM (Records Back to 1893)
1. 86.0 - July 1998
2. 85.5 - June 1998
3. 84.9 - July 1977
4. 84.8 - July 1986
5. 84.8 - July 2016 (2 days left)

***Top 5 Driest Months on Record for July***
Savannah International Airport - KSAV (Records back to 1871)
1. 0.82 - 1888
2. 1.21 - 2016 (2 days left)
3. 1.25 - 1881
4. 1.33 - 1949
5. 1.35 - 1972





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