Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
154 PM EDT Friday Oct 31 2014
a strong upper level low will move towards the region this
evening...helping to push a cold front through the forecast area
tonight. Behind this front...much colder air will follow along
with breezy conditions. The first widespread frost along with the
first freeze of the season for some areas will likely occur Sunday
Near term /through tonight/...
this afternoon...WV loop already indicating the several short
waves that will deepen the trough across the East Coast as the
ridge continues to build across the west/rockies. The forecast
will remain basically dry through the day. Could see some
scattered showers moving into the western/northern midlands by the
early evening hours. Guidance and local numbers in good agreement
with afternoon high temperatures. Have stayed close to consensus
and forecasted middle/upper 60s northwest/north to lower 70s csra/southern
Tonight...models remain in good agreement with the evolution of
the complex weather pattern across the eastern U.S. The deep upper
level trough will continue across the region...with a strong
shortwave moving around the base of the trough helping to cutoff
the low overnight as it moves through Tennessee and northern Georgia. Given the
strong dynamics of this system...with a strong cold pool aloft
moving towards the region...the models continue the trend of
bringing showers into the western and northern midlands
tonight...with the highest rain chances north. The leading edge
of the front associated with this system should push through
tonight...with winds increasing late tonight and towards morning.
Although there will be a noticeable cooldown behind the leading
edge...the main cold surge will not move in until tomorrow.
Overnight lows right now forecast generally around 40.
Short term /Saturday through Sunday night/...
the closed off upper low will continue to move east into the
upper Savannah River valley by Saturday morning...then rapidly
move towards the coast by early Saturday afternoon.
Have gone with likely probability of precipitation on Saturday across the northern
midlands with a gradual taper in probability of precipitation southward through the
period. The local top-down precipitation tool keeps the County Warning Area in all rain
through the day. Significant cold pool aloft with this
system...and thus with such cold temperatures aloft...would not
be surprised to see a few reports of frozen precipitation mixed in
with the light rain early/midday Saturday. Also can not rule out
shallow convection with the strength of the low...which could also
bring some grauple to the area. No accums...and confidence not
high. Expect rain to be the main precipitation type through the
Temperatures on Saturday will be significantly colder...nearly
15-20 degrees colder than recent days...with highs struggling to
reach 50 degrees in the midlands. Maximum temperatures will range from
the middle to upper 40s across much of the northern midlands...the
possibly the lower 50s in the csra. The other forecast issue to
deal with during this period will be the increasing surface
gradient and the strong 40 to 50 knot low level jet moving across
the region Saturday afternoon and evening. The strongest winds
will develop across the County Warning Area on Saturday and continue Saturday
evening with a gradual decrease toward Sunday morning. With the
lake water temperatures in the upper 60s to around 70 degrees and
strong cold air advection...expect winds to remain rather breezy
across the lakes from Saturday morning to Sunday morning. Will
continue with the Current Lake Wind Advisory which runs from 10 am
EDT Saturday until 10 am EST Sunday. Sustained winds 15 to 25 miles per hour
with gusts as high as 30 to 40 miles per hour expected on Saturday/Saturday
As the upper low moves offshore by Saturday evening...high pressure
associated with a cold dry Canadian airmass will settle over the
area for the remainder of the weekend. A strong pressure gradient
will persist through the overnight hours Saturday night which will
prevent ideal strong radiational cooling from occurring by
keeping much of the boundary layer well mixed. This means that
lows Saturday night and Sunday morning will generally be determined
by the cold advection taking place instead of by radiational
cooling. This puts lows generally in the middle 30s.
Sunday will feature decreasing cloudiness and mostly sunny skies
with slightly warmer but still well below normal temperatures with
highs in the 50s. The best night for widespread frost and the
potential for freezing temperatures appears to be late Sunday
night and Monday morning. Winds should diminish under low-level
inversion...skies will be clear...and airmass will be dry. This
creates ideal radiational cooling conditions. Overnight lows will
fall into the lower to middle 30s...with upper 20s remaining possible
in the typical cold spots. Some of the numbers for Bush Field
still try to take the temperature down into the middle/upper
20s...which is quite impressive and seasonably cold for early
For Sunday night...at a minimum will likely need a frost
advisory...but if guidance continues the downward trend...and it
continues to show ideal radiational conditions...a freeze warning
man be needed instead for portions of the County Warning Area. These would be
issued with later packages if needed.
Long term /Monday through Friday/...
behind this system...cool and dry weather should persist at least
into Wednesday. Monday morning temperatures will start off well
below normal in the lower to middle 30s...with widespread frost
expected along with some areas of freezing/below freezing
temperatures. Full sunshine expected with a dry airmass in place
will yield slightly warmer temperatures compared to Sunday but
still remaining well below normal. The surface ridge will shift
offshore on Tuesday with a return southerly flow expected around
the surface high...which will provide warmer temperatures and
increased low level moisture. Near normal temperatures expected
Tuesday with highs in the upper 60s to lower 70s and much warmer
min temperatures Tuesday night in the upper 40s.
The forecast becomes a bit more challenging and less confident by
middle week...due to timing and strength issues. Will carry slight
chance probability of precipitation Wednesday night/Thursday with approaching front. Temperatures will
warm back to near or slightly above normal values.
Aviation /18z Friday through Wednesday/...
surface low pressure and its associated cold front will cross the
area this evening. Should see increasing clouds ahead of the front
this afternoon. Scattered showers expected to move into the area
later this evening with highest probability of precipitation over the north. Probability of precipitation are too
low at terminals...less than 50 percent to include in the tafs as a
prevailing or tempo group but will put vcsh. Northwest to west winds
will increase behind the cold front early Saturday morning. Wind
gusts to around 30kts are possible from 12z-18z. Have VFR through
around 09z then MVFR to IFR after 09z as ceilings lower due to upper
low crossing the region.
Extended aviation outlook...
some shower activity and MVFR ceilings possible Saturday as very cold
air aloft rotates through the area. Breezy to possibly windy
conditions expected Saturday into Sunday morning.
SC...lake Wind Advisory from 10 am EDT Saturday to 10 am EST Sunday
Georgia...Lake Wind Advisory from 10 am EDT Saturday to 10 am EST Sunday