Scientific Forecaster Discussion
fxus62 kchs 201202
Area forecast discussion
National Weather Service Charleston SC
702 am EST Mon Feb 20 2017
high pressure will linger across the region through the rest of this
week. A cold front will sweep across the region on Saturday. Behind
the front, a Canadian air mass will build east of the Appalachians
on Sunday. Moisture is expected to rapidly stream northward across
the deep south ahead of another large low pressure system on
Near term /through tonight/...
today: after some patchy fog early this morning, mainly near
the Altamaha river, expect a generally sunny day with a few
high clouds. Expect more unseasonably warm temperatures with
highs in the mid to upper 70s away from the cooler coastal
locales where onshore winds will limit heating and keep
temperatures in the 60s.
Tonight: a bit more low-level moisture on tap tonight and with
decent radiational cooling conditions much of the night some fog
will likely develop, especially near the Georgia coast where the
lowest condensation pressure deficits are forecast. Some of the
fog could become dense. Lows should range from the upper 40s
inland to mid/upper 50s at the coast.
Short term /Tuesday through Thursday/...
on Tuesday, longwave ridge axis will shift off the Atlantic coast as
a closed low tracks across the heal of la. At the sfc, large high
pressure centered off the New England coast will continue to ridge
to south across the region. Low pressure remain over the southern
Mississippi River valley. Forecast soundings indicate that cirrus
level moisture will thicken across southeast Georgia and the low country of SC
through the daylight hours. In addition, an inversion is forecast to
persist around h75, likely resulting in moisture to gradually
increase below with llvl on shore flow. The forecast will feature at
least mostly cloudy conditions with low pops. High temperatures
should range from the low 70s across the Santee Basin to the upper
70s south of the Savannah River.
Tuesday night into Wednesday, mid level pattern will become quite
complicated across the southeast Continental U.S.. generally, short range
guidance indicates that the closed low will slip southeast across the Gulf
of Mexico, centered west of Key West by 0z Thursday. Across the cwa,
mid level heights will feature a broad weakness early Wednesday
morning, likely aiding the formation of a weak S/W, rippling over
the Savannah River valley Wed afternoon. Pops will rise to 20-30
percent across the forecast area. Model soundings show shallow cape
developing below a 700 mb inversion. The limited instability and forcing
should yield only showers, with thunder chances greater closer to
the Gulf Stream. Mild llvl thicknesses should keep min
temperatures around 15 degrees above normal, with highs
generally around 10 degrees above normal.
Long term /Thursday night through Sunday/...
progressive pattern will continue across the Continental U.S. Through the
medium range period. Large low pressure will organize over the
central Great Plains late Thursday. A warm front associated with the
low will meld with a old cold front across the mid Appalachians. The
large warm sector should provide the region weak instability and
moderate mid and low level moisture. Pops will remain within schc
range across the County Warning Area on Thursday, mentioning showers with iso
thunderstorms over the offshore waters. On Friday, south winds will
strengthen across the County Warning Area as a cold front pushes east across
MS/al/TN. GFS indicates that 850 mb temps will warm above 13c by late
Fri afternoon. Guidance indicates that high temperatures will reach
the upper 70s near the coast to the low 80s inland. The high
temperatures may challenge record values. Building instability
should yield iso showers/thunderstorms. The cold front is expected
to remain east of the region by daybreak Saturday. Min temps are
forecast to remain very mild, with low 60s common Sat am. GFS shows
the passage of the sfc cold front during the daylight hours on
Saturday. Cape values may range from 1000-1500 j/kg, especially
across the SC zones. Given the timing and instability, it appears
that the environment may yield a band of prefrontal deep convection.
Dry Canadian high pressure is expected to build over the region
Saturday night and Sunday. Cooling thicknesses will yield lower
temperatures, but still remaining around 5 degrees above normal.
Moisture will rapidly stream northward ahead of a dynamic low
pressure centered over the mid west. Strengthening return flow will
likely advect deep moisture and weak instability across the forecast
area on Monday. I will add chance pops for deep convection. Temps
should raise several degrees over Sunday.
Aviation /12z Monday through Friday/...
VFR conditions will generally prevail at both kchs and ksav through
12z Tuesday, although restrictions from low clouds/fog are
possible toward the end of the period at ksav.
Extended aviation outlook: patchy fog is possible each work day
morning. Otherwise, no restrictive conditions are expected
through Friday. A cold front will sweep across the region on
today/tonight: winds/seas will remain well below Small Craft
Advisory levels with high pressure to the northwest shifting
north of the area tonight. Winds will increase a bit tonight as
the pressure gradient tightens a bit across the area.
Tuesday through saturday: east to northeast winds will develop
over the marine zones on Tuesday. Sfc wind will veer southeast
Tuesday night, remain through late in the week. A cold front
will sweep across the region late Saturday. Cold air advection
should occur Saturday night into early Sunday, likely resulting
in gusty conditions. Wave heights are forecast to build over 5
feet beyond 10 nm to 6-7 feet beyond 20 nm on Sunday.
Kchs Fri 2/24 81 set in 2012/1996
kcxm Fri 2/24 81 set in 1930
ksav Fri 2/24 86 set in 2012
Kchs Sat 2/25 80 set in 1949
kcxm Sat 2/25 80 set in 1930
ksav Sat 2/25 82 set in 1985/1930
Record high minimums:
Kchs Fri 2/24 60 set in 1992
kcxm Fri 2/24 61 set in 1901
ksav Fri 2/24 64 set in 1980
Kchs Sat 2/25 62 set in 1992
kcxm Sat 2/25 59 set in 2011
ksav Sat 2/25 63 set in 1992