Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
756 PM EDT sun Sep 21 2014
a cold front will push through the region late tonight and
Monday bringing a chance of showers and maybe an isolated
thunderstorm...mainly to the eastern midlands and csra. Cooler
and drier air will enter the region behind the front. Moisture
return expected by late week into next weekend.
Near term /until 6 am Monday morning/...
upper low off the coast continues to slowly lift northeastward
away from the area in response to a shortwave trough digging into
the Ohio Valley and Great Lakes region. That trough is driving a
cold front southeastward and the front is currently located from
eastern West Virginia to eastern Kentucky to southwest Tennessee.
Regional radar imagery showing pre-frontal convection pushing
through the mountains at this time but as they move eastward into
the foothills the precipitation is dissipating. Mesoanalysis shows
the precipitable water axis of just under 1.5 inches along the
eastern side of the Appalachians with pooling 925mb moisture
across eastern Tennessee. However...the 850mb flow is westerly and
downsloping east of the mountains which is likely contributing to
the dissipation of precipitation. Think the relatively drier air
over the forecast area and the downsloping flow will limit chances
for measurable precipitation through 12z and will only carry
slight chance probability of precipitation after 09z. Some increase in clouds with the
frontal zone and winds staying up a bit overnight will result in
slightly warmer temperatures overnight.
Short term /6 am Monday morning through Tuesday night/...
models indicate front to be near the northern to central forecast
area (fa) around 12z Monday...slowly slipping south through the
southern half of our forecast area through middle afternoon. Limited moisture
for the front to work with. However...with considerable upper lift
ahead of the short wave along with diurnal heating...slight chance
to chance probability of precipitation cant be ruled out with thunder possible mainly
southern forecast area in the afternoon. Cooler and drier air to filter in
late Monday behind the front. High center will shift from the Ohio
Valley east into New England...while the front appears to stall
offshore. Pressure gradient and wind will impede ideal radiational
cooling conditions...but cold air advection expected to yield lows
in the 50s Monday nt and Tuesday nt.
Long term /Wednesday through Sunday/...
as main east Continental U.S. Upper trough lifts north...models suggest cut off
low will remain behind. European model (ecmwf) has it farther north over the southeast
Continental U.S....while GFS has a weaker one farther south near Florida.
Both models lift the feature to the north eventually...bringing
moisture back into our region. European model (ecmwf) quicker to do so...about 24
hours earlier than GFS...due to differing positions of upper low.
HPC prefers blended solution due to uncertainty. Used blend of
latest HPC and MOS guidance...then made some tweaks from there.
Meanwhile...surface high center will remain anchored over the
NE...ridging down the East Coast into our region through the
period. So...wedge conditions could develop...keeping maximum temperatures
down. A prolonged period of rain chances and below normal high
temperatures will be possible mainly late week through the weekend.
Aviation /00z Monday through Friday/...
VFR conditions expected through the taf period.
Cumulus have dissipated with sunset and some cirrus remain across
the area. Cold front currently moving through eastern Tennessee will move
into the taf sites during the early morning hours. With a dry
atmosphere in place and downsloping ahead of the front showers
will struggle to remain intact overnight and have kept mention out
of tafs. Front will be near the coast Monday afternoon with potential
for convection in the ogb area...as such have included vcsh for
ogb from 19z Onward. Winds will be 5 knots or less through
14z...then become northeasterly around 8 knots through the end of
Extended aviation outlook...restrictions possible by Thursday
associated with increasing low level moisture.