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-- Discussion containing changed information from previous version are highlighted. --
904
FXUS62 KCAE 170745
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
245 AM EST Thu Jan 17 2019

.SYNOPSIS...
A low pressure system will cross the region tonight and Friday,
followed by a more powerful storm system over the weekend with
much colder temperatures early next week. Another storm system
will approach during the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure over the forecast area (FA) currently will lead
to light winds through this morning. Though slightly drier low
level air in place compared to 24 hours ago, along with some
slight increase in high level cloudiness, patchy fog possible in
favored locations. Otherwise, expect increasing mid level
cloudiness later today ahead of a fairly fast moving upper
level disturbance that will move through late today and this
evening, providing a chance of light rain showers.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY/...
The forecast area will be between systems on Friday with the
departing trough off the New England coast and the developing
system over the Plains states. A weak shortwave ridge will
traverse the region through Friday evening with dry weather
expected and then the 500mb flow backs to a more southwesterly
direction later Friday night into Saturday ahead of the
approaching and strengthening storm system over the Mississippi
Valley. Moisture advection will return over the area with Gulf
of Mexico open as southerly 850mb winds increase to 30-40 knots
and precipitable water values increase to just under 1 inch.

Late Friday night and into Saturday there will be increasing
isentropic lift which may result in isolated showers developing
so will have slight chance pops to account for this and gradual
increasing pops during the afternoon Saturday as the storm
system approaches from the west and moisture transport increases
further across the area. Temperatures will be mild and well
above normal with highs in the 60s on Friday and in the 60s to
around 70 in the southeast Midlands on Saturday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The upper trough and associated surface low will move east
across the central Appalachians Saturday night which will push a
cold front across the forecast area. The strongest moisture
transport and deepest moisture with precipitable water values
reaching over 1.25 inches just ahead of the front with 850mb
winds increasing to around 60 knots. Despite very strong wind
shear the instability is not present so there is minimal threat
of severe weather. Expecting generally around a 3-6 hr window
just ahead of the frontal passage when the precipitation is
expected to move across the region sometime between the 00z-09z
time frame. Rainfall may be heavy but the system will be moving
through quickly enough to limit overall rainfall totals with
ensemble QPF guidance still showing generally around 0.5 to 0.75
inches of average rainfall across the area.

The upper trough axis will cross the forecast area on Sunday
but deeper moisture will be shifting out of the area as
precipitable water values rapidly drop to around a quarter inch
by 00z Monday. Strong cold advection behind the cold front will
commence with breezy northwesterly winds. A Canadian polar air
mass will settle over the region Sunday night through Monday
with well below normal temperatures expected.

There is some uncertainty late in the forecast period with
medium range models differing on timing and strength of the next
weather system. The GFS is more progressive showing the next
storm system will be developing over the middle of the country
on Tuesday with yet another digging upper trough resulting in
surface low development over the Plains which will then lift
northeast into the Great Lakes region Tuesday night. This would
bring another cold front across the region Tuesday night into
Wednesday. However, the ECMWF is quite a bit slower with this
next system showing a much deeper upper trough and not bringing
precipitation back to the forecast area until Wednesday night
into Thursday. Given these uncertainties will maintain a
persistence forecast.

Temperatures this period will be above normal on Sunday but
then below normal on Mon/Tue with cold low temperatures on
Sun/Mon nights with the ECMWF much colder. Temperatures will
moderate and return to near normal or slightly above normal
values by Wednesday.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
High pressure over the forecast area (FA) currently will lead
to light winds through this morning. Though slightly drier low
level air in place compared to 24 hours ago, along with some
slight increase in high level cloudiness, patchy fog possible in
favored locations. Will indicate tempo MVFR at CAE/CUB, with
tempo IFR at the fog prone locations AGS and OGB.

Otherwise, expect increasing mid level cloudiness later today
ahead of a fairly fast moving upper level disturbance that will
move through late today and this evening, providing a chance of
light rain showers. Will indicate a tempo group for -SHRA and
MVFR conditions late afternoon and evening.

EXTENDED AVIATION OUTLOOK...CIG restrictions possible late
Friday night and Saturday morning. Showers and associated
restrictions late Saturday through early Sunday. Breezy
conditions may occur Saturday night through Sunday.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.

&&

$$