Scientific Forecaster Discussion
fxus62 kcae 211149
Area forecast discussion
National Weather Service Columbia SC
649 am EST Tue Nov 21 2017
a weak wave of low pressure will shift NE from the Gulf of Mexico to
offshore the Carolinas, proving a slight chance of light rain this
afternoon through early tonight. Another area of low pressure is
expected to shift northeast from the Gulf of Mexico to offshore the
Carolinas, providing a chance of rain Wednesday night and Thursday.
Fair this weekend, with cooler conditions early next week as a dry
cold front pushes through.
Near term /through tonight/...
upper trough axis extending from the Mississippi Valley south into
the western Gulf of Mexico. Surface high axis over the region with
old frontal boundary to our south. Upper energy shifting from the
Gulf of Mexico NE towards Florida and the coastal Carolinas will lead to
isentropic lift and a weak wave of low pressure shifting NE from the
eastern Gulf NE offshore the Carolinas, while the weak surface ridge
axis weakens and shifts north. Best moisture and precipitation is
expected to remain south of our forecast area (fa). Using a blend of
guidance generally yields slight chance pops for most of our forecast area this
afternoon through early tonight, with chance towards the south and
Short term /Wednesday through Thursday night/...
upper troughiness will extend from the Midwest south into the Gulf
of Mexico, with a series of upper impulses shifting through our
region late Wednesday through Thursday night. Our region appears
will be generally in between systems early Wednesday, as first wave
will be departing off to the NE, while a dry frontal boundary will
attempt to shift into our region Wednesday, slowly getting over the
mountains while battling nearly parallel flow aloft. Some model
differences continue on an area of low pressure or two developing in
the eastern Gulf of Mexico and tracking towards Florida and the Carolina
coast, while surface high pressure builds into the mid Atlantic. 00z
GFS stronger and farther north with first low, and therefore much
higher on pop for our forecast area Thursday while also correspondingly lower
on Max temps with a stronger surface wedge. Due to uncertainty, will
take a model blend.
Long term /Friday through Monday/...
both 00z GFS and 00z ec keep the second surface low and most of the
associated moisture offshore Friday/Friday night, with some drier
air working into our forecast area Friday, though depending on how much rain we
get Wed nt and Thu and how good of a low level wedge gets
established, low cloudiness may be slow to erode and push out of the
region. Fair this weekend as system pushes farther offshore and
upper trough digging into the east Continental U.S. Provides a drier northwest flow
aloft, with dry cool Canadian high pressure building into the region
Aviation /12z Tuesday through Saturday/...
VFR conditions expected early in the 24 hr forecast period but
ceiling restrictions expected tonight.
Onshore flow and increasing isentropic lift will continue
through the day with surface high pressure centered off the
Carolina coast. Current satellite imagery shows a plume of lower
clouds expanding across South Carolina. Ceilings are generally
in the 4kft to 5kft range and expect them to remain VFR through
the day with support from latest hrrr and MOS guidance.
Ceilings expected to lower tonight as an upper trough
approaches from the west and isentropic lift strengthens and
saturates the atmospheric column while a weak frontal boundary
pushes into the region. Decided to include vicinity showers
after 21z at ogb where deeper moisture will reside and guidance
indicates isolated to scattered showers may develop. Generally
weak pressure gradient will result in light winds with a
prevailing easterly direction late morning through afternoon.
Light winds and abundant boundary layer moisture tonight could
result in stratus development and possible vsby restrictions
Extended aviation outlook...a front lingering near the coast
may help support MVFR or IFR conditions through Thursday.