Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
208 PM EDT Thursday Mar 26 2015
a cold front will slowly shift south through our region tonight
and Friday. Colder air will filter in behind the front. Near or
below freezing temperatures expected late Saturday night and early
Sunday morning...as the center of a cool Canadian high pressure
air mass settles in overhead. A front is expected to move through
Monday providing a slight chance of showers. Some moisture return
expected middle to late next week.
Near term /through tonight/...
amplified upper level trough from the Great Lakes region southwest
across the Southern Plains will continue to move east and drive a
strong cold front toward the region tonight. At the moment...air
mass is relatively dry with shallow low level moisture. Model
k-index values remain low through the early evening. It appears that
chance of showers will remain quite low through the early evening as
moisture limited and middle level cap remains. Moisture flux will
increase during the evening and overnight as upper trough moves
closer to the region. Strong middle level short wave in the northern
Gulf of Mexico will track northeast overnight and enhance upper
level lift and region under favorable entrance region 250mb jet-Max.
Chance of showers increasing after 06z from west to east as front
approaches and moisture/lift increases. Rain may be delayed in the
southeast midlands until pre-dawn hours. Instability appears weak
with surface based cape below 500 j/kg. Strong deep layer shear
however and threat for a few embedded thunderstorms late tonight as
cold front approaches. Low threat severe thunderstorms. MOS
consensus used for overnight minimum temperatures...in the low 50s
north to the low 60s southeast.
Short term /Friday through Saturday night/...
cold front...and associated shower and isolated thunderstorm
activity...is expected to move slowly south through our forecast
area late tonight and Friday. Colder air will filter into the
region behind the front...and most precipitation expected to trend southeast out
of our forecast area during the day Friday...though a period of light shower
activity possible behind the front Friday nt as strong upper trough
moves through. Secondary upper and surface trough to move through
Saturday...but a dry atmosphere is expected to preclude any
precipitation. Cool Canadian high pressure center will build into the
region late Saturday night. Appearance of good radiational cooling
conditions provides concern for near or below freezing
temperatures...and possibly frost...late Sat nt/early sun. Freeze
watches and warnings may be required. Growers and other interests
should closely monitor.
Long term /Sunday through Thursday/...
weakening upper trough to remain along the East Coast Sunday. A
front is prognosticated to come through Monday/Monday nt. Some timing
differences noted between GFS and European model (ecmwf). GFS faster with the front
and indicating less moisture with it. European model (ecmwf) slower to move it
through with appearance of better moisture. Ensemble average probability of precipitation
around 20 percent during that time frame. Will introduce slight
chance probability of precipitation. High pressure behind front to move in by Tuesday. Some
model differences continue next week...with GFS faster with
moisture return Wednesday...with European model (ecmwf) holding off until Thursday. Ensemble
probability of precipitation in the slight chance range Wednesday and chance Thursday.
Aviation /18z Thursday through Tuesday/...
increasing southwesterly flow /mixing and heating ahead of an
approaching cold front will result in mainly VFR conditions this
afternoon and early evening. Rain chance appears low early tonight
as moisture shallow/instability weak and middle level cap present.
Better chance for rain will be after 06z and will continue into
Friday morning. Models show ceiling restrictions returning late
tonight. Think mainly MVFR at this time due to low ceilings/lower
visibility in heavier shower toward daybreak. Thunderstorms widely
scattered/embedded. Surface winds this afternoon will be out of the
southwest at 10 to 15 knots with gusts to around 20 knots
diminishing in the evening. Winds will shift to west-northwest
Friday morning as front moves through the area. Chance rain
continues through the morning and Post frontal precipitation
expected behind front.
Extended aviation outlook...restrictions are possible into Friday
afternoon due to low-level moisture associated with a cold front