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Office: CHS

FXUS62 KCHS 120952
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
452 AM EST Tue Dec 12 2017

.SYNOPSIS...
A dry cold front will move through the region today followed by
high pressure through Thursday. Another cold front will push
into the area Friday while low pressure passes offshore. Dry
high pressure will return Saturday and persist into Sunday
before a cold front approaches the area early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Pre-Dawn: Clear skies with enough nocturnal breezes to keep
temps in the 40s this morning. Some inland locations fell into
the upper 30s last evening but have risen overnight, as low
level mixing tended to increase in a region of broad surface
pressure falls ahead of an upstream cold front.

Today: A digging mid level short wave entering Gulf Coast region
this morning, will carve out deeper upper troughing across the
southeast states. Modified continental polar air will surge
southeast across the Ohio and Tennessee Valley areas in the wake
of the surface cold front. This front will race southeast through
our region later this morning and off the coast by mid afternoon.
Increasing afternoon low level cold air advection will occur,
however models suggest morning sunshine and downslope will push
temps into the low to mid 60s along the coastal corridor between
17Z and 18Z. After early afternoon, temps will hold steady and
then dip prior to sunset as advection strengthens. Inland areas
well inland will probably struggle to touch 60 around midday
before tailing off late. Low level wind fields will remain strong
today and breezy conditions are expected once temps approach
daytime highs and then continue into gusty at times into the
evening hours as cold air advection remains steady. Not many
clouds expected today as deep layered moisture is sparse with
downslope trajectories building post-fropa.

Tonight: Clear skies and steadily falling temps will drive another
advection freeze close to the beaches and barrier islands by sunrise
Wed. Overnight breezes likely to keep a fairly uniform low temp range
from the upper 20s northwest zones to the mid 30s along immediate
coastal GA.

Lake Winds: Increasing low level mixing should allow gusty winds
to develop along western and southern shores during the early
afternoon then winds will ramp up later in the day and especially
early to mid evening when a periods 20-25 knots over open waters
a possibility. We have issued a Lake Wind Advisory for Lake Moultrie
in Berkeley County SC this afternoon through tonight.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday and Thursday: Dry sfc high pressure will prevail over the
Southeast along the base of a large and broad mid/upper trough of
low pressure extending from the Central United States to the
Northeast United States. The pattern favors quiet weather, but
slowly modifying temps each day. Cold air advection will be slow to
weaken on Wednesday, limiting afternoon highs to the mid/upper 40s
over Southeast South Carolina and lower 50s over Southeast Georgia.
Clear skies will once again lead to chilly temps Wednesday night
with lows that dip into the lower 30s away from the coast.
Conditions will then be noticeably warmer on Thursday as low
pressure passes to the north and helps produce a west/southwest flow
over the Southeast. In general, highs should approach the lower 60s
Thursday afternoon under mostly sunny skies. A light west/southwest
flow will continue through Thursday night, favoring a warmer trend
compared to the previous night. In general, Thursday night lows
should range in the upper 30s inland to mid 40s near the coast.

Friday: Latest guidance has come in a bit slower and drier in
regards to a cold front that pushes into the region early this
weekend. However, strong divergence associated with the right-rear
quadrant of an upper lvl-jet should help promote some clouds and
rain/shower activity, especially closer to the coast as the front
shifts offshore. At this time, a slight chance to chance of
rain/showers will remain in the forecast Friday afternoon and
evening. Afternoon temps should peak in the upper 50s to lower 60s,
highest near the coast where fropa occurs last.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
Dry and slightly cooler high pressure will build over the Southeast
Friday night into Saturday, leading to temps in the low/mid 30s
Friday night under clear skies and highs in the mid/upper 50s
Saturday afternoon. High pressure will then become centered over the
area Saturday night, leading to strong radiational cooling and temps
that dip into upper 30s to lower 40s. Conditions will be noticeably
warmer on Sunday as a light southerly wind develops on the west side
of high pressure shifting offshore. Temps should approach the
low/mid 60s Sunday afternoon. The next chance of showers should
begin Sunday night and increase into Monday as a plume of moisture
characterized by PWATs near 1.5-1.75 inches advects over the
Southeast along/ahead of a cold front that shifts through the area
Monday evening. Temps should be fairly warm ahead of the front,
peaking in the upper 60s to near 70 Monday afternoon.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
VFR conditions will prevail at KSAV and KCHS through 06Z
Wednesday. Deep mixing and a tight gradient associated with the
passage of a cold front on Tuesday will lead to gusty westerly
winds in the afternoon, with highest speeds of at least 20-25
kt.

Extended Aviation Outlook: VFR conditions will prevail at both CHS
and SAV terminals Tuesday through Thursday. Low chances of MVFR
conditions are possible at either terminal as low pressure passes
offshore. VFR conditions should prevail Saturday.

&&

.MARINE...
We have Small Craft Advisories either already in effect or
coming up later this morning all waters including the Charleston
Harbor. Until a cold front passes early this afternoon, the
strongest flow should reside seaward from the pilot buoys, then
ramp closer to shore later this afternoon and evening. The cold
air advection with favorable mixing and jetting conditions
spell solid SCA conditions prior to midnight and then only a
slow decreasing trend nearing dawn. Seas will be predominately
wind wave, 2-3 ft near shore early increasing to 3-5 ft tonight
with highest seas near 20 NM offshore. Seas may reach 8 ft well
off the coast, closer to the well wall of the Gulf Steam.

Wednesday through Saturday: High pressure will build across the
waters behind a cold front shifting over the western Atlantic.
Winds/seas are expected to improve to below Small Craft Advisory
levels by late morning, but a temporary surge of winds is possible
Wednesday night. High pressure will persist into Thursday with
conditions that remain below Small Craft Advisory levels. On Friday,
winds/seas will deteriorate as the pressure gradient tightens
along/near a cold front that pushes over coastal waters by Friday
night. Small Craft Advisories will be possible for most of the
coastal waters near and behind the front Friday evening and night.
High pressure should then build over the waters Saturday with
conditions that remain below Small Craft Advisory levels.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Lake Wind Advisory from 1 PM this afternoon to 5 AM EST
     Wednesday for SCZ045.
MARINE...Small Craft Advisory from 11 AM this morning to 10 AM EST
     Wednesday for AMZ352-354.
     Small Craft Advisory until 10 AM EST Wednesday for AMZ350-374.
     Small Craft Advisory from 1 PM this afternoon to 10 PM EST
     this evening for AMZ330.

&&

$$
NEAR TERM...
SHORT TERM...DPB
LONG TERM...DPB
AVIATION...DPB
MARINE...DPB



Office: CAE FXUS62 KCAE 120919 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 419 AM EST Tue Dec 12 2017 .SYNOPSIS... Dry cold front will cross the forecast area late this morning with high pressure and reinforcing cold air moving into the region this afternoon and tonight. High pressure will control the region for Wednesday through Thursday with unsettled weather for Friday through early next week. && .NEAR TERM /THROUGH TONIGHT/... Dry cold front currently moving into the Upstate will cross the forecast area late this morning into early this afternoon then offshore by late afternoon. High pressure along with drier air and cold air advection will begin building back into the forecast area this afternoon along with strong and gusty winds. Temperatures will warm through the early afternoon hours then begin cooling by mid afternoon as the cold air advection becomes dominant and temperatures dropping rapidly with sunset. Winds on area lakes will be around 15 mph with gusts to 25 mph from this afternoon through the early morning hours Wednesday resulting in issuance of a lake wind advisory. High temperatures this afternoon will range from the mid 50s over the western Midlands to the upper 50s to low 60s in the eastern Midlands. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... High pressure will be over the region for Wednesday through Thursday with the next system moving into the region Thursday night. Expect some increasing clouds Thursday night as some Gulf moisture begins returning northward while low pressure digs into the mid MS Valley. Models continue to depict the moisture return as a split stream with much of the Gulf moisture remaining south of the area Thursday night with the northern stream only reaching the TN Valley and remaining north of the area. With the split stream and dry air to overcome have remained without mention of rain Thursday night. High temperatures Wednesday afternoon will only reach the mid to upper 40s and moderating to the mid and upper 50s on Thursday afternoon. Overnight lows will be in the low 30s Wednesday night and the mid to upper 30s Thursday night. && .LONG TERM /FRIDAY THROUGH MONDAY/... Weather for Friday through Monday remains unsettled with models continuing to make run to run changes and differences in timing and intensity of features between models. Models do agree upper level trough swinging through the forecast area Friday night with much of the moisture associated with the system maintaining a split flow around the area. Have remained with slight chance pops for Friday due to low confidence and pops quickly exiting the area Friday night as the system ejects from the region. High pressure will quickly build back into the region Saturday and with the upper level pattern becoming less amplified systems will begin quickly crossing the area. On Sunday the high pressure will move away from the region as the next low pressure system develops over the southern Plains region and ushers Gulf moisture northward. Models differ with timing and intensity of this system however agree on rain returning to the forecast area Sunday afternoon through Monday. Temperatures through the long term will be below normal Friday and Saturday with near normal for Sunday and Monday. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... High confidence in VFR conditions through the 24-hour TAF period. However, low-level wind shear will occur. An approaching cold front will move through the area Tuesday morning. Ridging along the Gulf Coast will limit moisture recovery ahead of the front. Expect just a little high cloudiness associated with the front. A little mixing associated with a low-level jet ahead of the front should help prevent fog. Based on the NAN we have included low-level wind shear late tonight until around 14z when mixing and gusty winds along and behind the front will explicitly indicate shear. The NAM Bufkit momentum transfer tool and GFS LAMP support gusts near 25 knots. EXTENDED AVIATION OUTLOOK...No significant impacts expected. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...Lake Wind Advisory from 1 PM this afternoon to 4 AM EST Wednesday for GAZ040-063>065-077. SC...Lake Wind Advisory from 1 PM this afternoon to 4 AM EST Wednesday for SCZ015-016-018-020>022-025>031-035>038-041. && $$
Office: GSP FXUS62 KGSP 120823 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 323 AM EST Tue Dec 12 2017 .SYNOPSIS... Dry high pressure will build across our region through mid week as a deep trof crosses the area. Temperatures will be several degrees below normal on Wednesday then recover to near normal Thursday. Expect another series of fronts to cross our region going into next week. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM EST Tuesday: A vigorous shortwave will cross the southern Appalachians this morning, helping further dig a deep longwave trough over the eastern CONUS. Meanwhile, an associated clipper low will deepen over the Great Lakes and force a strong cold front thru the CWFA by late morning. The front was analyzed just entering the Great Tennessee Valley a couple hours ago. The front has no low-level RH to speak of along the boundary; however, an area of stratocu can be seen on IR and in the METARS behind the front covering a bit chunk of the Ohio Valley and Mid-MS Valley. The estimated time of arrival of this moisture to the TN/NC border looks to be around 10-11z (5 or 6 AM). From there, winds will shift out of the NW and increase to around 40-50 kts across the NC mountains, and scattered to numerous snow showers should develop with the upslope flow. Strong 850 mb CAA will ramp up across the entire area and winds will approach advisory criteria not too long after daybreak. Temps will likely peak late morning or midday in the mountains and early afternoon in the Piedmont, then fall fairly quickly thru the rest of the day, resulting in a cold, breezy evening. Highs will be mainly in the 30s in the mountains and upper 40s to lower 50s east. Snow amounts seem to be barely 1-2" in the winter weather advisory, with locally higher amounts possible. Snow showers should taper to flurries by early evening. The NAM is the one operational model that seems to hold onto some snow shower activity well into tonight. But looking at the NAM sounding at TNB reveals very shallow moisture depth. So I still like the diminishing PoPs this evening. As temps continue to plummet and winds remain quite gusty, wind chill values will dip to 5 below zero or colder across much of the areas above 3500 ft near the TN border. With all that said, the current advisories look well placed and no changes will be made with this forecast package. Lows tonight will be quite cold, in the teens to single digits in the mountains and 20s in the piedmont. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 245 AM EDT Tuesday: The rest of the middle part of the week should be relatively quiet. A short-wave ridge moves overhead on Wednesday with surface high pressure located to our south. The 850 mb thermal trof will already be past by midday Wednesday with some warm advection returning in the afternoon. Temps are still expected to be below normal, but the fcst reflects a warming trend. On Wednesday night, a clipper-type low is forecast to zip from the Midwest to the Mid-Atlantic region, dragging another cold front down from the NW toward daybreak on Thursday. The combination of some weak dpva and NW flow moisture could generate some snow shower activity mainly over the nrn mountains near the TN border beginning before daybreak but only continuing through early afternoon Thursday when the moisture pulls out. Think a 20/30 pct chance will suffice for the time being, with minimal accumulation expected. In spite of the passage of this next front, temps return to near normal for Thursday as cold advection is weak and short-lived, being overwhelmed by downslope warming E of the mtns in the afternoon. The next system will not arrive before the end of the Thursday night period. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 135 AM Tuesday: the extended fcst picks up at 12z Friday with an approaching 500mb trof which has an axis roughly from the Great Lakes to Memphis at 12Z. Models show height falls through the day on Friday. The GFS has a slug of moisture arriving late Friday for the NC and TN border areas with max impact in NW Flow early Friday night. The old ECMWF has a quick shot of NW Flow Friday morning and gone by early PM. The 500mb flow nearly levels out over the weekend from west to east with dry surface high pressure. By late Sunday, however, there are significant differences between the GFS and EC. The GFS starts good Gulf influx of moisture along an approaching cold front bringing rain to the mountains late Sunday and to the rest of our forecast area Sunday night and Monday. The EC has a strong low crossing the Great Lakes with low POP chances for us Sunday night with the frontal passage. We hope for better agreement as we get closer in time. The current forecast ends Monday and Monday night with a dry period beginning. The new EC just came out with even drier period Friday. However, the new EC has trended much more in agreement with the GFS and even wetter than the new GFS. I will incorporate this trend into this forecast, but not go completely into that trend as it is nearly a week away. Things can change. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... At KCLT and Elsewhere: The leading edge of a clipper system can be seen about to enter the NC mountains early this morning, bringing a band of mainly high clouds and a wind shift from SW to NW. The associated cold front should rapidly cross the region by mid-morning, shifting all sites to NW winds by about 15z. Other than a period snow showers and low clouds along the TN border, conditions should be VFR. A brief period of snow shower activity may reach KAVL, most likely in the 14-17z time frame. I have a tempo for some MVFR cigs and a mention of -SHSN. Winds will get quite gusty, especially at KAVL, as low-level CAA ramps up. Winds should subside gradually outside the mountains, but will remain very gusty in the mountains tonight. Outlook: Restrictions may be possible Thursday night into Friday, especially at KAVL, with a system approaching from the west. Otherwise expect dry and cool, VFR conditions. Confidence Table... 15-21Z 21-03Z 03-09Z 09-12Z KCLT High 81% High 82% Med 68% Low 56% KGSP Med 70% Med 75% High 83% Med 64% KAVL High 94% High 85% Med 70% High 87% KHKY High 100% High 83% Med 66% High 100% KGMU Med 76% High 86% High 85% Med 63% KAND Med 76% Med 65% High 90% Med 61% The percentage reflects the number of guidance members agreeing with the scheduled TAF issuance flight rule category. Complete hourly experimental aviation forecast consistency tables and ensemble forecasts are available at the following link: www.weather.gov/gsp/aviation && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...Winter Weather Advisory until 7 AM EST Wednesday for NCZ033- 048>052. Wind Advisory until 7 AM EST Wednesday for NCZ033-048>052-058- 059-062>064. Wind Chill Advisory from 10 PM this evening to 7 AM EST Wednesday for NCZ033-048>052-059. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...ARK SHORT TERM...PM LONG TERM...DEO AVIATION...ARK