Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
1036 PM EST Sat Nov 22 2014
moisture will return to the region tonight through Sunday
night...with plenty of rainfall expected to occur Sunday into
Sunday night. A front will move into the region Monday and is
expected to stall near the coast Tuesday.
Near term /until 6 am Sunday morning/...
dry weather will occur for the first part of the forecast
with rain overspreading the area later tonight and into the
overnight period. High pressure will continue at the
surface...although the center of the high will push further off
the coast overnight. Very weak surface wedge should remain across
the area through much of the night. Aloft...although we start off
dry...clouds and moisture will rapidly be on the increase...especially
across the southwestern County Warning Area as isentropic lift strengthens and
moves over the surface wedge. Regional radar loop shows showers
across northern Florida and southeastern Georgia shifting northeast
into the forecast area. The hrrr model appears to be on track
with current radar trends...so have sped up the timing of the
showers filling in from southwest to northeast across the forecast area.
Temperatures may be somewhat tricky tonight. Clouds will continue
to increase and temperatures should become nearly steady or even
rise slightly for the remainder of the night. Northern counties
should continue to fall until late tonight before becoming steady
towards morning. For now...lows around 50 across the south...and
around 40 across the north still reasonable.
Short term /6 am Sunday morning through Monday night/...
by Sunday...short wave will be across the lower MS River Valley. Low
pressure developing across the Southern Plains. A warm front to
our south will begin to try and push northward through the day on
Sunday/Sunday night. Looking a model Li fields along with some
weak surface riding and surface winds from the NE/east for much of the
day on Sunday. This indicates at least some weak wedge conditions
across much of the County Warning Area...especially across the northern/central
midlands along with the northern csra. With increasing isentropic lift
and moisture flux into the region. Any rainfall should help
sustain wedge conditions. However...by late in the day Sunday and
Sunday night...surface flow will increase from the southeast and S as 50
to 60 knots low level jet approaches. Precipitable water values will rise
dramatically through the period to well above 1.5
inches...approaching nearly 2.0 inches...by Sunday afternoon. This
is much higher than climatology for middle/late November. With such
impressive isentropic lift and moisture flux...the rain will be
heavy at times during the afternoon and evening hours
Sunday/Sunday night. As the warm front tries to move
north/northwest across the area late Sunday into Sunday
night...the airmass across the area will become more unstable.
This is especially true across the eastern portion of the County Warning Area
south of I-20. Storm Prediction Center day two has the southeastern half of the Palmetto state
in a slight risk for severe thunderstorms. This is where the best
shear and instability will develop. Have mentioned isolated to
chance of thunderstorms from late Sunday afternoon into Sunday
across much of the area developing first in the southeastern portion of
the County Warning Area and then north/northwest into the remainder of the County Warning Area.
Rainfall amounts from 1.5 to 2 inches...with locally heavier
amounts...will be possible by Sunday night.
On Monday...the cold front associated with the low in the plains
will try to push eastward across the area...but by
afternoon/evening becomes parallel to the upper flow and will
likely slow/stall along the coastal plain or near the coast. This
is where models begin to disagree on how far the front will push
eastward. At this time...have continue to keep a chance of
rain showers/thunderstorms and rain through Monday with front in the vicinity.
As for temperatures...they will be very tricky on Sunday with
wedge and approaching warm front from the south. Have stayed on
the low side of guidance for Sunday with a tight temperature
gradient from northwest to southeast. The high for Sunday will most likely occur
during the evening hours as the warm front pushes northward.
Temperatures will be dramatically warmer on Monday with breezy
south/southwest winds ahead of the cold front with all of the
guidance in the middle/upper 70s.
Long term /Tuesday through Saturday/...
uncertainties continue in the forecast through the middle of next
week. Latest GFS/previous European model (ecmwf) models begin to shift the main upper
trough axis eastward as energy drops into the base of the trough
across the Southern Plains by Tuesday/Tuesday night. By Tuesday night...both
models begin to develop low pressure in the Gulf of Mexico and
bring a system up along the East Coast. This looks slightly more
westward with precipitation shield as well as cooler than previous
runs. Have lowered highs on Wednesday a couple of degrees from the
previous forecast. By Thursday and Friday...both models have trofiness
across the eastern half of the country...with high pressure
building into the region at the surface. Dry weather Thanksgiving
day through Saturday. Expect temperatures to remain below normal
through the period.
Aviation /04z Sunday through Thursday/...
high confidence VFR conditions through 06z...then MVFR/IFR
ceilings pushing into the region by 12z.
Light easterly winds will allow for some moisture to move in from
the east overnight. The increased moisture and approaching warm
front may allow for widespread pre-frontal fog in the east... with
the largest impact on ogb. At this time confidence in widespread
dense fog is still low however there seems to be agreement between
models that fog will form around 06z and possibly spread into the
Columbia area by 09z.
Strong moisture advection will get lifted isentropically over a weak
surface wedge late tonight. This will bring ceilings down into
MVFR/IFR as the night progresses. Rainfall will aid in deteriorating
the conditions even more towards morning...with LIFR becoming
possible after 12z at all sites. Rainfall may be heavy at times
through the day Sunday...with low ceilings and visibilities expected
to last through the day.
There may be a brief period between 21z and 00z after the warm
frontal passage but before the cold frontal passage where ceilings
may recover and showers become light. However the taf sites will be
in the warm sector and instability will increase possibly allowing
for more showers to form.
Extended aviation outlook...ceiling and visibility restrictions
are likely in rain showers late Sunday through Monday as a low
pressure system affects the region.
SC...Flash Flood Watch through Monday evening for scz030.