Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 202118

Area Forecast Discussion
National Weather Service Columbia SC
518 PM EDT Tue Mar 20 2018

An upper level trough will approach the region through this
evening, bringing the chance of thunderstorms mainly to the
eastern Midlands. The upper trough and a cold front will move
through the area overnight and breezy conditions are expected
tonight through Wednesday. Dry high pressure expected Wednesday
and Thursday with cooler temperatures. East coast troughing
will bring more active weather for the weekend.


The atmosphere is recovering from overnight storms with clearing
skies and surface heating, especially across the southeastern
part of the forecast area where LI values are now -4C to -5C
with increasing precipitable water values around 1.2 inches.

SPC has the eastern Midlands in a slight risk for severe
weather this afternoon as an upper trough moving along the Gulf
coast states pushes east toward the Carolinas and becomes
negatively tilted. Instability will remain highest in the
eastern Midlands and increasing wind shear will support some
organized convection with damaging winds and hail as the primary
threats, although much of the ongoing convection has remained
south and east of the forecast area. Mid level lapse rates of
7.0-7.5 C/km and mid level colder air advecting into the area
through the afternoon may support a hail threat. Latest hi-res
model guidance is suggesting the bulk of the convection may
remain just to the east of the forecast area for the most part
but could impact the far eastern Midlands counties 19z-22z time
frame. There is also some convection expected to occur along
the southward sinking front in the northern Midlands this
evening into the overnight hours as strong forced ascent
overspreads the surface boundary but moisture should be more
limited and lower confidence in a severe threat up there
although some hail could not be ruled out.

As the upper low passes overnight and low pressure develops
offshore, wrap-around moisture on the back side of the low will
allow showers to persist into the overnight hours, mainly north
of Columbia. Westerly winds will increase behind the front, and
a Lake Wind Advisory has been issued from midnight through 8pm
Wednesday. Strong winds 15 to 20 mph with gusts to 30 mph will
be possible overnight and through the day Wednesday with deep
mixing tapping into the strong low level wind fields associated
with this system.

Temperatures overnight will steadily fall behind the cold front
with min temperatures expected in the lower 40s.


An upper low over the Appalachian region will shift off the
Mid-Atlantic coast on Wednesday. There will be some wrap around
moisture in the northern portion of the area which may support
rain showers, but most of the southern portion of the area
should remain dry. Continued to trend pops down mainly in the central
and southern portions of the area. At the surface, low pressure
will be off the Mid-Atlantic coast while high pressure builds
into the area from the west which will create a tight pressure
gradient across the area. The main issue on Wednesday will be
the wind speeds. Westerly winds around 20 to 25 mph with gusts
up to 35 mph are expected. A lake wind advisory is in effect
until 8 PM. Wednesday will be a much cooler day than the past
couple of days and below seasonal norms with highs only in the
50s. Wednesday night will be dry with low pressure pushing
further off to the northeast. Skies will be clear Wednesday
night with lows dipping down into the middle 30s. Winds should
stay up Wednesday night which should prevent temperatures from
dropping below freezing in most locations.


The low pressure system off the New England coast will continue
pushing northeastward on Thursday with surface high pressure
building into the forecast area from the northwest. Winds will
be lighter on Thursday with gusts only in the mid to upper
teens. Friday also appears dry with ridging dominating the area.
Moisture will return to the region Friday night and over the
weekend associated with an area of low pressure approaching the
area from the Mississippi Valley region and an associated
frontal boundary near the area. Models also depict shortwave
energy at times in the area. Have continued with chance/slight
chance pops over the weekend. The front appears to drop south of
the area early next week with high pressure wedged into the
area promoting northeasterly low level flow. The models have
trended cooler for this weekend and early next week so have
dropped temperatures down.


In the near term, thunderstorm activity near the coast is
expected to remain south and east of out TAF sites.

Closed upper low will slowly shift east across the
Ohio/Tennessee Valleys tonight and to the Mid Atlantic coast
Wednesday. Associated shower activity to our N and NW appears
will remain north of our TAF sites. Surface boundary near the
NC/SC border, with wedge conditions and lower CIGs north of it.
This boundary may sink a little south tonight into our NE
forecast area (FA) but associated lower CIGs and any shower
activity appears will stay NE of our TAF sites. Spoke of upper
energy to rotate through our region this evening. Surface low to
shift to our NE and intensify tonight and Wed, increasing the
pressure gradient over our FA. Breezy conditions expected
overnight, with breezy to windy conditions Wednesday afternoon.
Peak surface gusts Wednesday afternoon at or above 30 knots
possible. Though some stratocumulus cloudiness possible at times
through the TAF period, cloud bases are expected to remain
above the VFR level.

EXTENDED AVIATION OUTLOOK...Breezy conditions Thursday, otherwise
no significant aviation related issues expected.


GA...Lake Wind Advisory from midnight tonight to 8 PM EDT Wednesday
     for GAZ040-063>065-077.
SC...Lake Wind Advisory from midnight tonight to 8 PM EDT Wednesday
     for SCZ015-016-018-020>022-025>031-035>038-041.


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