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Area Forecast Discussion (AFD)

Issued by Columbia, SC (CAE)

FXUS62 KCAE 191806

Area Forecast Discussion
National Weather Service Columbia SC
206 PM EDT Wed Jun 19 2019

The pattern of mainly diurnal thunderstorms will persist through
Thursday with the potential for severe thunderstorms Thursday
afternoon and evening. There will be a break on Friday with 
drier air over the area and a frontal boundary to the south. 
That front will lift northward Saturday bringing back 
thunderstorms to the forecast, potentially severe. The front 
will become diffuse over the weekend under upper ridging through
early next week. This will support a pattern of afternoon 
thunderstorms and above normal temperatures in the long term.


A lee-side surface trough combined with ample moisture and 
diurnal heating, has resulted in scattered showers and 
thunderstorms. A couple of weak shortwaves are expected to pass
through the area during the evening which may enhance any 
convective activity. Precipitable water vales will generally be 
1.7 to 2.0 inches. High resolution models support chance pops 
and diminishing convective activity with loss of heating. Severe
potential appears low given weak shear and moderate instability.
However, isolated strong winds will be possible given DCAPE 
values around 1000 J/kg. Temperatures are on the way to peak in 
the upper 80s and lower 90s. A low level jet will keep some 
boundary layer mixing overnight, so expect lows in the low to 
mid 70s.


The main concern is a threat of severe thunderstorms Thursday 
afternoon and evening.

There will be two features capable of producing thunderstorms on 
Thursday. First, a decaying MCV is projected by most CAMs on 
Thursday morning over the TN/AL/GA area. The outflow from this 
system and associated vorticity maxima will be over the forecast area 
late morning or early afternoon. Thunderstorms may redevelop along 
this feature. Next, the vorticity maxima associated with the main 
shortwave will approach the FA later in the afternoon, better 
aligned with peak heating. Surface convergence along a lee-side 
trough should trigger additional convection as the shortwave passes. 
Although drier west winds and earlier convection may limit 
thunderstorm coverage. 

The greatest chance for severe weather will be in the afternoon and 
into the evening as the main shortwave moves across the FA. 
Instability will likely be moderate with models/SREF probabilities 
suggesting sbCAPE values between 1500 and 2500 J/kg. Whether this is 
realized will depend largely on the extent of convection earlier in 
the day. 0-6 km bulk shear will be strong for this time of year, 
around 30kts, suggesting organized convective lines may develop. Dry 
air aloft, steep mid and low-level lapse rates, and moderate sheer 
suggest the main hazard will be areas of damaging winds. The threat 
of thunderstorms will diminish overnight in the wake of the 
shortwave trough. 

Highs during the day will range from the upper 80s to low 90s. It 
will be breezy during the afternoon with gusts up to 25 mph but 
should remain below Lake Wind Advisory criteria. Lows will be around 
70 degrees.


There will be a brief period of drier weather Friday before another 
chance for severe weather on Saturday.

An upper level trough will lift out of the Northeast on Friday. This 
will push a trailing frontal boundary south of the forecast area 
with drier air behind it. Downslope flow will also contribute to 
dry, warm weather. Forecasted temperatures a little higher than the 
guidance consensus because of downslope flow.

Saturday, the models have been consistent lifting the frontal 
boundary northward into the FA with strong instability south of the 
front. Convergence along the front will likely trigger thunderstorms 
during the afternoon. The strong instability and dry air aloft will 
support the threat of damaging downburst wind and hail.

For much of the remainder of the period, the GFS and ECMWF show 
upper level ridging over area. The ridge will be strongest this 
Sunday, weakening into early next week. Surface ridging will 
also extend from the Atlantic into the Gulf of Mexico. This 
pattern supports warm weather with scattered diurnal convection.
There may be a series of shortwave troughs moving along the 
northern periphery of the ridge which will support convective 
development at times. Guidance suggests above normal 
temperatures with highs mainly in the middle and upper 90s.


Restrictions expected in scattered afternoon/evening convection
and early morning stratus.  

VFR outside of scattered diurnal convection through this
evening. Have included vcsh/vcts at AGS/DNL/OGB given better 
chance for convection affecting the terminals. Winds will be 
southwest 10 to 15 knots with gusts around 20 knots diminishing 
to 5 to 10 knots after sunset. 

Ample low level moisture supports early morning stratus again 
on Thursday. Fog is not expected due to a 30 knot low level jet.
Showers and thunderstorms should develop across the area by
midday Thursday as a decaying MCS moves into the region and
instability increases. West-southwest winds will increase to 
10-15 kts with gusts 20 to 25 knots by late morning. 

EXTENDED AVIATION OUTLOOK...Widespread convection possible into
Thursday night as a cold front crosses the area. Isolated 
diurnal showers and thunderstorms possible Saturday and Sunday.