Scientific Forecaster Discussion
fxus62 kchs 161711
Area forecast discussion
National Weather Service Charleston SC
1211 PM EST Mon Jan 16 2017
high pressure will extend across the area through tonight.
Temperatures will gradually warm into mid week as a cold front
approaches the region. The front is expected to stall over the
coastal plain of South Carolina Wednesday night, then will lift
north as a warm front on Thursday. Mild and moist conditions
will linger across the area this weekend, with greatest chances
of showers and thunderstorms Sunday through Sunday night.
Near term /through tonight/...
today: a light northeast sfc wind will help maintain high pressure
over land before it gradually builds into the mid Atlantic this
afternoon. The main issue for late morning will be the continuation
of dense fog over some locations as weak isentropic lift occurs
over high pressure and the northeast sfc flow. For this reason,
a dense fog advisory will continue for parts of southeast South
Carolina until noon. Forecast soundings indicate fog will gradually
lift into a stratus deck as low-lvl winds increase from the west
early afternoon. There could even be some breaks in cloud cover
over northern areas at some point during peak diurnal heating,
but the general thinking is that some mid-lvl clouds will
persist through much of the day. Given cloud cover, temps should
remain several degrees cooler than yesterday around the tri-County
area. Further south, areas will likely see more sun during peak
diurnal heating. Given the setup, a fair temperature gradient
should be in place with highs ranging around 70 degrees in
northern areas to mid 70s in southern areas. As far as chances
for precip today, a weak coastal trough offshore will gradually
lift north, spawning a few showers that drift onshore late
morning through early evening hours. However, rainfall accumulation
should be quite low with any shower.
Tonight: once again the forecast will favor areas of stratus
and fog development for the entire area. A strong nocturnal
inversion and flux of Atlantic moisture in the boundary layer
will provide a solid foundation for both coastal sea fog
advection potential and a widespread build-down stratus event
inland. The main uncertainty will be clouds and there could be
plenty of high clouds. We think there was enough of a
possibility of dense fog to put it in our hazardous weather
Short term /Tuesday through Thursday/...
on Tuesday, sfc high pressure will remain centered near Bermuda
as a wavy cold front struggles to move over the NC/Tennessee line.
This pattern will support light and steady SW llvl flow across
the forecast area. 850 mb temperatures will rise to around 11.5 c
by 0z Wed. I will forecast pops below schc and sky to feature
partly sunny conditions with cu. After the morning fog dissipates,
the primary forecast challenge will remain with the high
temperatures. Using a blend of the best performing guidance, I
will forecast highs to range from the mid 70s across the inland
counties to low to mid 70s along the coastline, falling short of
records by 3 to 4 degrees.
The front is expected to stall over the southern Appalachians, with
the northern portion sliding south as a backdoor front. Guidance and
overall pattern indicate that the backdoor front will not exit the
forecast area. The boundary may stall across the SC coastal plain on
Wed. Clouds will increase across the forecast area tues night, then
remaining through Wed. Overall, temperatures will not change by more
than one or two degrees from Tuesday, ranging just below records.
Weak sct showers may develop along and ahead of the front, greatest
chances to the north. Rainfall may generally range in just a few
hundredths of an inch.
Long term /Thursday night through Sunday/...
medium range guidance agrees that the axis of long wave 500 mb
ridge will ripple over the region on Thursday. However, the sfc
front is expected to slowly lift north as a weak warm front.
Pops across the forecast area will remain limited to schc, with
values slowly lowering from south to north. High temperatures on
Thursday are forecast to favor values around 70 degrees over
Thursday night into Friday, a negatively tilted 500 mb trough is will
pass over the southern Appalachians, brushing the County Warning Area with weak
Omega by sunrise Fri. The combination of deep moisture, weak
instability, and weak forcing should support sct showers. In the
wake of the front, dry air will spread across the region Sat am.
Saturday night into Sunday, a large low pressure system will
organize over the Great Plains, tracking over the mid west by Sunday
evening. Moist SW flow will gradually increase across the forecast
through the late weekend. In fact, moist and warm llvl flow may
develop a band of sfc based cape as high as 1000 j/kg on Sunday. I
will increase pops to likely, for showers and thunderstorms. The
center of the 500 mb low is expected to pass over the mid Atlantic
region, with wrap around moisture crossing the County Warning Area. Schc showers and
near normal highs expected on Monday.
Aviation /17z Monday through Friday/...
kchs: latest soundings suggest breaking the fog and low clouds
may be slow but we have maintained similar previous trends
which improve conditions through noon. We cannot rule out an
isolated shower this afternoon but chances favor VFR conditions
during this time. Tonight, another round of fog and perhaps
dense fog is possible once again. We introduced some IFR after
06z given the strong model consensus and synoptic pattern.
Ksav: VFR conditions appear likely for most of the day. Tonight,
fog development is possible and we cannot rule out dense fog
Extended aviation outlook: patchy to areas of fog may linger
into mid morning Tuesday. A weak cold front is forecast to
slowly sink move southward across the South Carolina coastal
plain Wednesday night, fog and showers may develop along and
ahead of the front. Restrictive visibility and ceilings may
develop with passing band of showers Thursday into Friday. A
large low pressure system is expected to bring showers and
thunderstorms across the region Sunday through Sunday night.
today and tonight: latest webcam and pilot boat observations
near Charleston, SC indicate dense fog with visibilities reduced
to 1/4 to 1/2 at times. The general consenus in model soundings
indicate that sea fog will gradually improve over the next
couple hours, likely becoming a low stratus deck before continuing
to lift this afternoon. For this reason, a dense fog advisory
will continue in the chs Harbor and nearshore waters off the
Charleston County coast until 1 PM today. Conditions should
remain fog free mid afternoon into early evening, but patchy
dense fog could return and expand somewhat tonight as stratus
lowers along the immediate coast.
Otherwise, stable conditions in the marine layer and light northeast
winds will prevail with the coastal trough out near the Gulf Stream.
Seas through tonight will range between 2 to 3 ft.
Through wednesday: SW winds will remain <10 kt for much of the
period with seas 2-4 ft on average. Sea fog will remain an issue
Tuesday morning, but should diminish Tuesday afternoon and
especially Wednesday as a cold front approaches and low-level
trajectories become less ideal. Marine dense fog advisories could be
needed Tuesday morning.
Thursday and friday: a weak backdoor cold front will push across the
region by Thursday, then expected to stall. Winds will veer from
east to south Thursday night. Another cold front is expected to
slide east offshore on Friday into Friday night, resulting in winds
to shift from the west. Sfc high pressure should build off the SC
and Georgia coast on Saturday. Seas will average between 2-4 feet through
the period. Small Craft Advisory conditions are unlikely.
record highs for Tuesday, 17 january:
kchs: 78/2013 and previous years
Record highs for Wednesday, 18 january:
Marine...dense fog advisory until 1 PM EST this afternoon for amz350.