Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 271432

Area Forecast Discussion
National Weather Service Columbia SC
1032 AM EDT Tue Jun 27 2017

A front lingering near the coast will shift farther offshore
tonight. A pressure ridge extending through the Ohio River
Valley today will be in the Mid-Atlantic Region Wednesday and
off the East Coast Thursday. Diminished relative humidity
will be associated with this pattern through Wednesday but
moisture will be on the increase late in the week as the
offshore ridge directs an onshore flow into the forecast area.
This trend will lead to increasing chances of thunderstorms.


Morning analysis revealed a stalled frontal boundary just off
the coast with a strong dewpoint gradient across the
southeastern Midlands with high pressure building into the area
from the northwest. Aloft, water vapor imagery confirms a
digging shortwave trough over the western Ohio Valley and
Mississippi Valley region which will shift eastward through the
afternoon and cross our region this evening. NUCAPS soundings
from around 07z showed precipitable water values over the
Midlands had dropped to near an inch with a gradient in moisture
to the southeast with KCHS 12z observed sounding measuring a 1.43
inch precipitable water value.

As the digging shortwave trough shifts eastward and amplifies a
bit it will pull some of the deeper moisture back towards the
Midlands with forecast soundings raising precipitable water
values up to around 1.4-1.5 inches. Forecast instability is weak
with lifted index values around -3C to -4C with the moisture
generally shallow in the 700-850mb layer. Surface winds will
pick up from the north across the forecast area while a sea
breeze is expected to develop along the coast with the best
moisture convergence and low level forcing along the coastal
plain and far eastern Midlands. Given the overall lack of deep
moisture and weak instability and forcing along with low MOS
guidance pops, will opt to continue slight chance for afternoon
convection mainly eastern Midlands and Pee Dee region. Despite
the widely scattered nature of expected convection, soundings
indicate an inverted-V signature and if a storm is able to
strengthen with any depth it could pose a strong wind gust

Drier and cooler air will filter into the region tonight in the
wake of the passing shortwave with clearing skies expected.
Temperatures this afternoon are expected in the upper 80s to
around 90 degrees with lows tonight expected to be seasonably
cool in the lower to mid 60s with some possible upper 50s in
outlying sheltered areas of the northern Midlands.


The models have been consistent with dry high pressure
dominating Wednesday and Wednesday night. Moisture should be on
the increase Thursday especially in the south part of the
forecast area in an onshore flow associated with the ridge off
the East Coast and a mid-level shortwave trough moving into the
region. Followed the guidance consensus and forecasted chance
pops. Also used the consensus for the temperature forecast.


The GFS and ECWMF display moisture in a southerly flow
associated with offshore high pressure and broad upper
troughing during much of the medium-range period. The pattern
supports scattered mainly diurnal thunderstorms. The GFS and
ECWMF MOS plus GFS ensemble mean indicate chance pops with
temperatures near climatology.


Generally VFR conditions expected through the 24 hr forecast

An upper trough moving through the Ohio/Mississippi Valleys will
cross the region late this afternoon and evening. Weak high
pressure is in place at the surface with a frontal boundary
stalled just offshore. Atmospheric moisture is limited with
precipitable water values less than 1.25 inches. The lack of
sufficient moisture and low level convergence along with weak
instability present will limit convective threat this afternoon.
Some mid level clouds this morning should give way to developing
cumulus with bases around 5-6kft. Cannot rule out isolated
convection across eastern Midlands but coverage expected to be
low enough to not include in OGB TAF but will amend as needed.

Drier air will filter into the region behind the shortwave
tonight with skies generally clearing out late.

EXTENDED AVIATION OUTLOOK...No significant impacts to aviation
expected through Wednesday. A return flow and increasing low-level
moisture may provide a late night/early morning stratus threat
Thu/Fri. Scattered thunderstorms expected Fri/Sat.




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