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Area Forecast Discussion

565
FXUS62 KCHS 280545
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
145 AM EDT TUE JUN 28 2016

.SYNOPSIS...
A cold front will approach from the northwest Tuesday, becoming
nearly stationary and lingering nearby Wednesday and Thursday. The
front will lift back north on Friday as Atlantic high pressure
builds across the region. Another cold front will approach the
area early next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Early this morning: Quiet conditions continue across the forecast
area though not far upstream persistent shower and thunderstorm
activity has impacted much of the Midlands and CSRA. Fortunately,
this activity has been nearly stationary and has dissipated
significantly over the last hour or so. As such, the area should
remain dry through day break. No real concerns for the rest of the
night as dewpoint depressions around 4 degrees for many areas
should preclude the development of much if any fog.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/...
Tuesday: A shortwave ridge will remain over the forecast area in
the morning with fairly deep westerly flow producing broad scale
subsidence. A cold front will be dropping into the SC Midlands by
noon. By afternoon, approaching shortwave energy will weaken the
ridge and help push the cold front into the forecast area. Modest
insolation across southeast GA in the morning and pre-frontal
compression will quickly push temps into the low to mid 90s before
the clouds and convection move in. Heat indices will briefly
approach 105 in a few spots.

The sea breeze will likely remain pinned near the coast during the
morning due to deep westerly flow. The associated subsidence
should minimize convective development prior to the front moving
into the area in the afternoon. We therefore lowered pops a bit
during the morning. Moisture rapidly increases in the afternoon
with Precipitable Water values approaching 2" late in the day.
Fairly good coverage of showers and tstms expected during the
latter half of the afternoon as the front moves in from the
northwest. Weak upper level jet divergence will impact northern
areas late in the day, potentially increasing coverage over the
Tri-County area. Convective parameters are not too impressive
though approximately 20 kt of 0-6 km shear and 1000-1500 J/kg CAPE
values could support some multi-cell storms and isolated severe
storms. Weak steering flow and high PWs will support torrential
rainfall with anything that develops and the potential for
localized flooding issues.

Plenty of moisture, moderate instability, and low-level
convergence will persist into Tuesday evening, likely maintaining
decent coverage of convection until the effects of nighttime
stabilization cause activity to diminish. However, we maintained
20-30 pops through the night due to the persistent stalled front.

Wednesday into Thursday, a broad upper trough will dominate the
eastern United States with several shortwaves rippling through the
area. The surface front will remain stalled across the forecast
area and moisture will remain high, supporting above-normal rain
chances. High temps will mainly be in the upper 80s to around 90
Wednesday and lower to middle 90s on Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
The pattern aloft flattens out with a quasi-zonal flow to develop
over the area Friday through Sunday. This allows a westward
expansion of the sub-tropical Atlantic ridge while a Piedmont
trough develops inland. This equates to a return to a more
typical pattern for summer, featuring mainly diurnal scattered
showers/t-storms. This allows for hotter temperatures and more
uncomfortable heat indices to occur. For early next week another
cold front may approach as the east coast trough begins to develop
yet again.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
The main forecast problem for the next 24 hours revolves around
the potential for direct impacts from thunderstorms this afternoon
and evening. A cold front will approach the area and showers and
thunderstorms are expected to develop to the north. These showers
and storms will then move southward and near the terminals by the
afternoon. Confidence is relatively high that both sites will see
a thunderstorm at some point. The time period for KCHS appears to
be 20z through 00z and the time period at KSAV appears to be 22z
through 02z. Have introduced a TEMPO group for TSRA with just MVFR
conditions for now. At least brief IFR conditions will be possible
as will some low end wind gusts. Once the storms push south and
dissipate overnight, there will be the potential for fog and/or
stratus development. The best chances for fog and/or stratus
appear to be beyond the current TAF window.

Extended Aviation Outlook: Flight restrictions are possible at
least periodically in SHRA/TSRA Wednesday through Thursday. Less
chance of direct impacts on Friday, but still a risk for
SHRA/TSRA.

&&

.MARINE...
Tonight: A weak area of low pressure and associated surface
trough to our east will dissipate. This will result in a weak
surface pressure gradient, allowing winds to ease to 10 kt or
less and to become southerly. Seas will subside to 1-2 feet within
20 nm and 2-3 ft across AMZ374.

A slow-moving cold front drifts into the area late Tuesday and
lingers into Thursday before lifting back north on Friday. Fairly
light wind flow will maintain benign conditions outside of showers
and tstms. A more typical summer-time pattern returns next weekend
as Atlantic high pressure rebuilds.

&&

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

&&

$$

NEAR TERM...BSH
SHORT TERM...JRL
LONG TERM...
AVIATION...BSH
MARINE...JRL/RJB



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