Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 301409

Area Forecast Discussion
National Weather Service Columbia SC
1009 AM EDT Sun Apr 30 2017

High pressure ridging into the forecast area from the Atlantic
will dominate through today. Strong heating may help support
afternoon thunderstorms but these should be isolated because of
the ridging and shallow moisture. An approaching cold front
tonight will be in the forecast area Monday. Thunderstorms will
be associated with the front. Mainly dry weather is forecast
behind the front Tuesday and Wednesday. Another significant
weather system will impact the region Thursday and Friday.


Low level moisture continues to advect into the area late this
morning within the southerly flow associated with surface high
pressure positioned offshore. Low clouds are already showing
signs of lifting, but cloud streets evident in satellite imagery
are an indication of strong low-level winds which are already
producing gusts to 20 mph in some locations.

The models show the upper ridge shifting slightly eastward
today but with continued shallow moisture in the forecast area.
Model forecast soundings depict mid-level capping. However, most
of the NAM and GFS MOS exhibit small pops and both models
display a subtle surface trough in the west part of the forecast
area. The high-resolution models indicate isolated coverage as
well. The forecast continues to indicate slight chance pops in
west and central sections. Believe there is less chance in the
east closer to the upper ridge.

The chance of severe thunderstorms is low because capping will
likely remain dominate with cloudiness limiting instability but
if thunderstorms can overcome the cap then damaging wind and
hail could possibly occur. The models show moderate instability
with surface-based LI values near -5. Dry air in the mid-levels
may aid downdrafts. Forecast soundings indicate considerable
CAPE in the hail growth region.

The thunderstorm chance should further diminish in the evening
with the loss of heating. However, convergence ahead of the cold
front may increase the chance toward sunrise. We forecasted just
slight chance pops because of main frontal forcing to the west
and nocturnal cooling.

Followed the guidance consensus for the maximum temperature
forecast. Mixing ahead of the front favored the higher minimum
temperature forecast.


A deep closed upper low will lift north into the Great Lakes
region Monday with an associated cold front pushing into the
forecast area Monday afternoon and evening bringing
thunderstorms. The thunderstorms could be severe as the models
indicate moderate instability and shear with surface-based LI
values near -7 and h85 wind about 45 knots. Damaging wind and
hail will be possible. Heavy rain may also become an issue as the
NAM has precipitable water increasing to around 2 inches.
However, a fast storm motion should limit the threat unless cell
training happens to occur. The models indicate general breezy
conditions Monday. The NAM Bufkit momentum transfer tool
suggests gusts 20 to 25 knots. A Lake Wind Advisory may be
needed. The thunderstorm chance should diminish Monday night
behind the front. Followed the guidance consensus for the
temperature forecast.


Stable and dry conditions should return behind the front
Tuesday, and temperatures will be slightly cooler. There is a
slight chance of showers and thunderstorms late Wednesday with a
warm front ahead of the next system. The GFS and ECWMF have
shown consistency with deep moisture associated with a cold
front Thursday. There has been little run-to-run consistency
with the placement and timing of an associated upper low. Have
forecasted pops likely Thursday and chance Friday and Saturday.
Strong instability and shear along with high moisture may be
associated with this system supporting possible severe
thunderstorms and flooding. The threat may be greatest Thursday
and Friday but could linger into Saturday if the cold upper low
associated with this system lingers as some model runs have


Low level moisture is responsible for MVFR ceilings this morning
at the terminals, but expect ceilings to lift to VFR levels by
16-17Z. Isolated showers are possible this afternoon, but the
focus generally appears to remain west of the terminals in
closer proximity to a weak surface trough. Strong low level wind
fields and surface heating will result in wind gusts around 20
kt at times late this morning and this afternoon.

More restrictions may occur early Monday morning mostly from
low CIGS.

EXTENDED AVIATION OUTLOOK...Gusty winds and restrictions in
thunderstorms expected Monday as a cold front moves through the
region. Another round of flight restrictions is possible
Wednesday night into Thursday as another cold front crosses the




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