Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
627 am EST Monday Dec 9 2013
surface wedge flow will begin to break down today ahead of another
approaching cold front. This cold front will slowly move through
late tonight and into Tuesday...and stall just to our south
Wednesday. Dry high pressure is expected to return the middle to late
week...with another system arriving next weekend.
Near term /today/...
areas of fog and drizzle with visibilities down to around 1 mile
will remain possible through the morning hours as The Wedge front
tries to move through. Latest NAM...local model...and sref
guidance continue to indicate that The Wedge may be slower to
break down during the day. Confidence low on temperature forecast
due to the timing of The Wedge breaking...which makes the
afternoon temperatures very tricky. Although strong south flow in the
boundary layer develops during the morning 30 to 40 kts...model
soundings indicate strong surface based inversion and light winds
near surface. With considerable clouds...cool start and chance
rain...prefer sref temperature mean blended with the NAM/RUC. Expect
large range in temperatures across region...will forecast low 50s
north to around 70 across the southern csra/southeast midlands.
Strongest isentropic lift across Piedmont/north midlands...so
expect higher chance rain in that region...lower chance southeast
Short term /tonight through Tuesday night/...
chances for rain will increase during the overnight period as the
axis of higher precipitable water values and moisture transport
gradually shift eastward ahead of an approaching cold front. Will
continue the gradient in probability of precipitation from likely northwest to low chance
in the southeastern part of the forecast area.
Fast moving shortwave energy will push eastward into the Tennessee
and Ohio valleys late tonight into Tuesday which will push the
cold front across the forecast area late Tuesday morning into
Tuesday afternoon. Pooling of moisture on the front is expected
with precipitable water values rising to around 1.5 inches. A
strong 50 knots low level jet is forecast to precede the front while
shifting across the region and combining with increased low level
convergence and increasing upper forcing as the forecast area
falls within the right entrance region of the upper jet. Therefore
will transition likely probability of precipitation across the forecast area Tuesday from
west to east with a sharp decrease in probability of precipitation late Tuesday afternoon
as the upper flow becomes more zonal which will push the front east
of the area with drier air working in from the west. Temperatures
will rebound to above normal values ahead of the front with strong
mixing of warmer air aloft down to the surface.
Skies will clear from west to east Tuesday afternoon and night as
low level flow becomes northwesterly as surface high pressure
builds over the area ushering in much drier air to the region.
Cold advection Tuesday night will allow low temperatures to fall
into the 30s across the region.
Long term /Wednesday through Sunday/...
medium range models have come into better agreement in keeping the
stalled frontal boundary just to our south on Wednesday and
confining any additional precipitation associated with an inverted
trough off the coast through Wednesday night south and east of the
forecast area. Will keep dry forecast Wednesday through Friday as
precipitable water values remain below 0.5 inches. Temperatures
will be below normal Wednesday through Friday with cool high
pressure settled over the southeast.
Unsettled weather is expected to return by the weekend with GFS
and European model (ecmwf) coming into better agreement. A cut off upper low over
The Four Corners region on Friday will open up and phase with a
digging northern stream trough over the Central Plains and
Mississippi Valley by Friday night. Moisture will increase quickly
ahead of the approaching system Friday night with southerly low
level flow with rain expected to overspread the region by Saturday
as the trough moves eastward into the middle Atlantic region. Will
keep chance probability of precipitation Friday night but have increased probability of precipitation to likely
for Saturday...and hold on to chance probability of precipitation Sunday with low
confidence in the eventual speed of this system. Do not expect any
precipitation type issues despite some initially dry air to overcome.
Temperatures Sat/sun should continue to be near or below normal.
Aviation /12z Monday through Friday/...
strong wedge conditions continue across the area this morning.
All taf sites remain IFR/LIFR due to ceilings and some fog and
drizzle. Model time sections continue to show abundant low level
moisture through the taf period. Models still try to hold on to
The Wedge through midday. Will keep low conditions IFR/LIFR for
much of the period...becoming MVFR by the afternoon. Latest
guidance continues to show conditions dropping once again to
IFR/possible LIFR after 00z Tuesday.
Extended aviation outlook..a cold front will slowly move through
the area Tuesday. There will be a chance of showers and associated
restrictions with the front. The front is forecast to stall just
to our south Wednesday with high pressure building eastward to our
north. A return to VFR conditions possible Wednesday...but
confidence is low. By Thursday...high pressure begins to dominate
the area and VFR conditions are more confident.