Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
248 PM EDT Friday Sep 19 2014
an upper trough and surface boundary will slowly move through the
region today and tonight...and push towards the coast Saturday.
Drier air will enter the region Sunday. A dry front will move
through late Sunday night and early Monday. Dry high pressure will
be in control early next week.
Near term /until 6 am Saturday morning/...
upper trough along the East Coast. Embedded disturbance prognosticated to
continue moving slowly through the region today and tonight and
begin cutting off near the coast late tonight. Surface high over east
Canada to shift east into New England and offshore waters allowing
some ridging to build down the East Coast. Meanwhile surface wave
offshore to develop some in response to upper energy. This will
provide an increasing low level east to NE flow off the Atlantic.
Several surface boundaries appear to be in play. The one that
pushed through our forecast area (fa) this morning appears to be
south and west of our forecast area now. Another boundary/dewpoint gradient
is near the NE forecast area...behind which drier air noted over central/east NC
and NE SC. It appears drier air will enter the NE forecast area today and
preclude shower activity there. Dissipating cloudiness allowing
better diurnal heating to begin...which is expected to result in
shower and possible thunderstorm activity this afternoon and
evening...focused mainly along any boundaries. Latest high res
models focus most activity generally near the southern and western
forecast area. Latest radar indicating activity developing across that area
and near the coast which is drifting northwest. Tonight...a continued and
increasing low level moisture flux off the Atlantic...with an east
flow around 20 to 25 knots prognosticated at 925mb to 850mb...to provide
possibility of shower activity penetrating inland into our
southern forecast area...along with possibility of increasing low level cloud
cover. Most model output focusing most convective activity near
the coastal plain...but latest rap model suggesting activity could
continue to stream into the S midlands and csra. Some uncertainty
but will maintain slight chance to chance probability of precipitation mainly S forecast area/csra
Short term /6 am Saturday morning through Sunday night/...
Saturday...a closed upper level low off the southeast coast will
slowly move northeast. Surface high pressure will continue to wedge
into the western Carolinas from the north. Surface low pressure
off the North Florida coast will move northeast to a position off
the NC coast Saturday night. Moist easterly flow around the
surface low will hold most the the precipitation east of the
midlands. Precipitable water greater than or equal to 1.50 inches is forecast
along and east of a line from Sumter through Columbia to Augusta.
Thus will continue slight chance probability of precipitation for the central midlands and
csra with chance probability of precipitation across the extreme eastern midlands as
showers rotate around the low. Both the surface upper low will
lift northeast away from the forecast area allowing drier air to
filter in from the west Saturday night. Dry forecast Saturday night.
Expect northeasterly winds around 10 knots with gusts around 15
knots Saturday. Highs will be in the lower 80s with lows in the
lower 60s as skies clear.
Sunday...the closed low off the coast will continue to track
northeastward taking the better moisture with it. H850 flow
becomes downslope and precipitable water decreases to below an inch with weak
instability. Have continued to indicate a dry forecast. Sunny
skies and downslope winds should allow temperatures to warm into
the middle 80s to around 90 degrees. Next low pressure system over
the northern Great Lakes region will drag a cold front across the
Ohio and Tennessee valleys on Sunday. This front will move into
the upstate late Sunday night. Went with consensus for lows in the
low to middle 60s.
Long term /Monday through Friday/...
an upper trough over the Great Lakes region will shift east on
Monday pushing a cold front through the forecast area. The GFS is
quicker with the timing of the front than the NAM. The timing of
the front will influence heating and the amount of instability.
Continued to indicate only a slight chance as moisture appears
limited and timing appears too early to be diurnally favorable.
Much drier and cooler air should reach the area late Monday in the
wake of the front...just in time for the fall equinox. Tuesday
morning low temperatures are forecast in the upper 50s north to
lower 60s south. The front will be well offshore by Tuesday with
high pressure building in from the Ohio Valley. The upper trough
will be offshore by Wednesday with an upper ridge building over
the Great Lakes region. High over New England Wednesday through
Friday will create a strong easterly low level flow off the
Atlantic. Have forecast mostly cloudy skies along with a chance of
showers and below normal temperatures for the end of the week.
Highs will be in the 70s with lows in the upper 50s to lower 60s.
Aviation /19z Friday through Wednesday/...
VFR conditions currently. Diurnal heating expected to promote
chance of showers and possible thunderstorms this afternoon and
evening. At this time...will handle with vcsh in the tafs and
upgrade later based on radar trends if/when confidence warrants.
Later tonight...convection may continue to affect mainly southern
and western areas...ogb/ags/dnl...due to location of best low
level moisture flux off the Atlantic. Also...this along with
diurnal cooling expected to result in low cloud development late
tonight into early Saturday morning...with MVFR to IFR ceilings
possible. Expect a return to VFR by late Saturday morning or
midday. Convective activity Saturday expected to favor areas near
the coast and will not include mention in the tafs at this time.
Extended aviation outlook...late night and morning fog/stratus
possible through early Sunday.