Scientific Forecaster Discussion
fxus62 kchs 201739
Area forecast discussion
National Weather Service Charleston SC
1239 PM EST Wed Nov 20 2019
high pressure will prevail across the southeast U.S. Through
Friday. A cold front will move through the area Saturday night,
followed by high pressure for early next week.
Near term /through tonight/...
surface high pressure will continue to expand eastward over the
area today. Meanwhile, heights aloft will build as mid level
ridging shifts towards the East Coast. Deep dry air, as noted by
0.4 inch pwats on the 12z kchs raob, will provide quiet weather
and plenty of sunshine. Highs are forecast to range from the
low 60s across the northern zones to mid/upper 60s near the
Altamaha. Ongoing forecast was in good shape so only minor
tweaks were needed with the early afternoon update.
Tonight: tranquil conditions will prevail as high pressure
settles in just north of the forecast area. Clear skies will
prevail early, before thin cirrus approaches from the west late
in the overnight. Temperatures will be on the cool side, with
lows dipping into the upper 30s to low 40s away from the
beaches. Such values would be roughly 5 degrees below normal for
this point in November.
Short term /Thursday through Saturday/...
Thursday and friday: the mid-levels consist of a weak ridge
moving over the East Coast Thursday, then offshore Thursday
night into Friday as a trough passes to the distant north. This
will lead to semi-zonal flow across the southeast. At the
surface, high pressure in the Lee of the Appalachians Thursday
morning will slowly move over the southeast Thursday night into
Friday. The high is forecasted to move offshore Friday night
while a cold front approaches from the distant west. Plenty of
subsidence and dry air across the region will lead to a dry
forecast Thursday into Friday. Though, clouds will be on the
increase ahead of the front Friday and Friday night. Some of the
models hint at isolated light showers approaching our far
inland counties towards daybreak Saturday. They'll have a hard
time making it here because they'll be battling the drier air
associated with the departing high. So we're only going with
slight chance pops far inland Friday night. The warming trend
continues due to the rising heights, low-level thickness values,
and 850 mb temperatures. High temperatures are expected to be
above normal on Friday as southwest surface winds develop.
Saturday: semi-zonal mid-level flow will be overhead in the
morning. Though, an intensifying/amplifying trough will be
approaching from the west during the day, causing the flow to
turn towards the southwest. At the surface, high pressure
offshore will be moving away while a cold front approaches from
the west. The cold front is not expected to make it to our area
during the daylight hours. However, moisture will increase ahead
of the front. The combination of the moisture and overall
atmospheric lift ahead of the front should generate some showers
during the day. The highest pops are far inland during the
afternoon (chance category), tapering towards the coast. A few
hundredths of quantitative precipitation forecast is possible in our far inland locations,
mainly in the afternoon. Despite mostly cloudy skies, warm air
advection ahead of the front will lead to high temperatures well
into the 70s.
Long term /Saturday night through Wednesday/...
models are in great agreement moving the cold front and its
showers through our area Saturday night. Following the front,
high pressure will build back into the region with drier
conditions and cooler temperatures. Models then develop another
front/system to our west late Tuesday and have it approaching
Aviation /18z Wednesday through Monday/...
VFR will prevail through 18z Thursday.
Extended aviation outlook: VFR through Saturday. A cold front
is expected to bring flight restrictions Saturday night. VFR
returns on Sunday.
today through tonight: high pressure will be the primary
surface feature driving flow across the local waters. North
winds this afternoon will tip more northeasterly as the high
settles in just north of the area tonight. Speeds should
generally average in the 10-15 knot range. Seas will average
2-4 ft, highest in the outer waters.
High pressure will prevail across the southeast U.S. Through
Friday, then move offshore Friday night. A modest pressure
gradient will bring tranquil marine conditions during this time
period. On Saturday, the high continues to move offshore while a
cold front approaches from the west. The front is expected to
move through the coastal waters Saturday night. Small craft
advisories will probably be needed for all of the zones, except
Charleston Harbor, Saturday night due to wind gusts and maybe
seas. The worst conditions are expected across the Charleston
waters and the Georgia waters beyond 20 nm. Sunday morning the front
will be moving offshore while high pressure builds in from the
west. The pressure gradient decreases, allowing winds and seas
to trend downwards.