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Office: CHS

FXUS62 KCHS 211005
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
605 AM EDT Tue Aug 21 2018

.SYNOPSIS...
The area will remain between an inland trough and Atlantic high
pressure today. A cold front will approach from the northwest
tonight, then cross through late Wednesday as high pressure
passes to the north. The front is expected to stall offshore
through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
NOTE: The NWS College Park data center is experiencing network
and communications issues. This impacts products from some NCEP
Centers as well as surface observations and some model data.
See the Senior Duty Meteorologist NWS Administrative Message
(AWIPS ID: ADMNFD, WMO Header: NOUS42 KWNO) for the most up to
date information.

Increased sky cover and lowered ceilings across far interior
Southeast Georgia where some stratus as advected in from the
west and southwest. This may make it as far east as Metter to
Allendale before it begins to mix out with the onset of
insolation after sunrise. High resolution guidance continues to
show a weakening area of showers/tstms moving into the region
late this afternoon and pushing west-east through the area this
evening. The current low pop forecast looks on track for the
sunrise update.

Subtropical high pressure will quickly breakdown today as the
mature cyclone over the upper Mississippi Valley opens up and
kicks out to the northeast across the Great Lakes into Ontario.
The trailing shortwave will quickly traverse the Ohio and
Tennessee Valleys into the Deep South this afternoon and push
offshore of the eastern CONUS by daybreak Wednesday. The
associated cold front will approach from the west today, but
will gradually slow down as it propagates across the Deep South.
All available data suggest the front will remain to the west
through sunrise keeping the entire forecast area in the pre-
frontal warm sector. Despite lowering heights aloft, forecast
soundings and omega profiles suggest there will be enough
subsidence from the decaying subtropical high to keep the
region rain-free for much of the day with a broken line of
scattered showers/tstms likely approaching the far interior
Southeast Georgia by late afternoon. While a brief shower/tstm
could still pop along the resultant sea breeze this afternoon,
suspect any such activity will be brief and fairly transient.
Will highlight non-mentionable pops (<15%) for all but the
Reidsville-Millen corridor where pops will be capped at 20%.
Highs will once again warm into the lower 90s away from the
coast with heat indices peaking 100-103 degs.

A broken line of showers/tstms are forecast to move into the
western zones by early evening as aforementioned shortwave
energy approaches. The various CAMs are showing a number of
possible solutions with this line of convection, ranging from
one member depicting a solid line pushing west-east across the
forecast area to the line quickly dissipating as it moves into
the local area (most members with various flavors). Despite
favorable positioning of the right entrance region (RRQ) of the
upper jet, modest instability and PWATs over 2 inches, model
cross-sections suggest any vertical velocities induced by the
RRQ and DCVA field ahead of the shortwave itself will remain
quite weak and displaced from the most favorable deep layered
RH. This likely explains why the bulk of the CAMs members,
including the RAP and H3R, quickly weaken the approaching line
of showers/tstms as it moves west-east across the forecast area
between sunset and midnight. Plan to limit pops to 20-30% for
evening hours with any lingering convection expected to exit off
the coast by midnight. Skies will remain mostly cloudy for a
good portion of the night, possibly thinning out a few hours
before sunrise. Lows will range from the lower 70s well inland
to the upper 70s/near 80 at the beaches.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday: In the morning the mid-levels will consist of a trough
stretching from the Great Lakes Region down into the Southeast. This
trough is expected to remain in place into the night and amplify. At
the surface, a cold front will be just west of our area in the
morning. It will slowly move eastward during the day, pushed by
strong high pressure initially centered in the Plains States. As the
high becomes located over the Middle MS Valley late at night it will
cause the front to become located over the immediate coast or just
offshore late at night. PWATs are forecasted to drop below 2" during
the day, possibly dropping below 1.5" far inland late at night.
Models keep the highest risk of precipitation offshore. Hence, the
coastal counties generally have slight chance POPs while inland
counties appear to remain dry, mainly due to the drier air and
subsidence associated with the building high. Any remnant
precipitation shifts offshore late in the evening and overnight.
High temperatures should be 2-3 degrees above normal.

Thursday: In the morning the mid-levels will consist of a trough
stretching from the Northeast U.S. down into the Southeast.
Meanwhile, broad high pressure will be located over the Southern
Plains. As the day progresses the trough will lift to the northeast
and deamplify, followed quickly by a weak ridge. Meanwhile, high
pressure over the Southern Plains will try to build towards the
Southeast. At the surface, a stationary front will be located just
offshore in the morning while strong high pressure is centered over
the Middle MS Valley. As the day progresses, the high will move
eastward, which will help nudge the front further to the southeast.
The high will also push more dry air into our area, keeping PWATS
below 1.75". Some models hint at them dropping close to 1" across
portions of our area, which is well below normal for this time of
year. In simpler terms, dewpoints could fall into the upper 60s
inland and the lower 70s near the coast, making it feel comfortable
for August. Despite this dry air models still indicate the potential
for precipitation. This might be overdone, but to maintain a
consistent forecast with our neighbors, the highest probabilities
are along the coast and across our GA counties, generally where
PWATs won't be as low. Meager instability will make it hard for
thunderstorms to develop. But we're keeping them in the forecast
because climatology says they should be in there. The precipitation
threat shifts to the immediate coast and offshore during the
overnight hours. Temperatures will be near normal during the day.
Though, the drier air could allow them to fall into the mid to upper
60s far inland overnight.

Friday: The mid-levels will consist of broad high pressure over the
Southern Plains gradually building into the Southeast. At the
surface, high pressure will be located over the Mid-Atlantic States
in the morning while a stationary front is just offshore of our
area. As the day progresses, the high will shift to the northeast
and offshore while the stationary front tries to inch its way closer
to use. POPs are generally in the chance category, highest across
GA, closer to influences of the front. Instability starts to creep
up and so does the potential for storms with gusty or maybe damaging
winds. But this potential will get refined with upcoming forecasts.
Lower 850 mb temperatures and northeast winds will lead to the
"coolest" high temperatures the area has seen in a while. Expect
highs generally in the mid 80s across our SC counties and the mid to
upper 80s across our GA counties.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
Broad high pressure initially over the Southern Plains Friday night
will strengthen and expand across the Southeast into Monday.
Meanwhile, a stationary front will remain offshore during this time
period, possibly dissipating on Monday. The exact location of the
front will determine the precipitation potential. There is
uncertainty, so we went with a model blend for the forecast.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
VFR for both KCHS and KSAV. A broken line of showers/tstms will
approach the terminals this evening, but the guidance suggest
much of this will dissipate before reaching the terminals. Will
not include any mention of SHRA or TSRA for either terminal for
the 12z TAF cycle.

Extended Aviation Outlook: Convection associated with a stationary
front offshore could bring brief flight restrictions, especially
each afternoon/evening.

&&

.MARINE...
Through Tonight: No concerns with a southerly flow regime hold
firm. South to southwest winds 10-15 kt will prevail today with
another noctural surge likely pushing winds into the 15-20 kt
for most legs tonight. Seas will average 1-3 ft today and build
to 2-4 ft tonight.

Wednesday through Saturday: A cold front will approach the area
from the west on Wednesday, then stall just to the east of the
coastal waters through the weekend. The resulting winds will be
from the southwest Wednesday, then veering to the northeast
Thursday where they are expected to prevail into the weekend.
Though, if the front shifts, then more changes may be needed
with the wind forecast. The highest winds are expected Wednesday
afternoon due to the proximity of the front. Wind gusts at this
time should peak around 20 kt. Though, a few gusts could
briefly approach 25 kt across the northeastern portion of the
Charleston waters. No marine headlines are expected. Seas will
generally be in the 2-4 ft range this week. The exception will
be Wednesday when some 5 footers are expected in the
northeastern portion of the Charleston waters.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$



Office: CAE FXUS62 KCAE 211013 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 613 AM EDT Tue Aug 21 2018 .SYNOPSIS... There will be a moist southwest flow between high pressure in the Atlantic and a cold front approaching the forecast area from the northwest through tonight. The front will move into the area Wednesday and be near the coast Thursday. Drier air will be in the area behind the front Thursday and Friday. && .NEAR TERM /THROUGH TONIGHT/... Moisture will remain high in the southwest flow between high pressure to the east and the approaching cold front to the northwest. Deepest moisture will be today and this evening ahead of upper troughing. The moisture combined with diurnal heating and convergence into a pre-frontal trough supports thunderstorms. The high-resolution models have not been consistent with the timing of greatest thunderstorm coverage. Deepest moisture is depicted shifting east of the area before maximum heating. The greatest moisture also is shifted east of the area before the main mid-level shortwave trough moves through the area late this afternoon and evening. The models indicate h5 warm advection and a dampening trough which should help limit thunderstorm coverage. We have forecasted chance pops because of the inconsistencies with the greatest chance late this afternoon and evening because of diurnal heating and shortwave trough timing. There will be some threat of severe thunderstorms this afternoon and evening. There will be increased shear ahead of the front with h85 wind 25 to 30 knots. Instability is forecast to be moderate. The NAM and GFS depict surface- based LI values -5 to -6. The models also indicate mid-level drying in the area and associated evaporative cooling may help enhance downdrafts. The thunderstorm chance will diminish overnight because of more shallow moisture behind the mid-level shortwave trough and nocturnal cooling. The NAM and GFS Bufkit momentum transfer tool plus GFS LAMP indicate wind gusts around 20 mph this afternoon. We leaned toward the higher temperature guidance ahead of the cold front today. Followed the consensus for the temperature forecast tonight. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... Despite more shallow moisture, convergence along the cold front supports a continued thunderstorm chance Wednesday into Wednesday evening. The NAM indicated greater moisture compared to the GFS and ECMWF Wednesday evening. We forecasted pops of just 20 percent because of shallow moisture Wednesday and Wednesday evening which was a little above the guidance consensus. It should be less humid with lower temperatures behind the front for Thursday. However, a lingering surface trough and slightly more moisture closer to the stalled front near the coast supports keeping slight chance pops in the extreme east section. The guidance consensus supports highs in the lower 90s Wednesday, and middle and upper 80s Thursday. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... High pressure in the mid-Atlantic region Thursday night into Friday will be shifting into the Atlantic over the weekend. The result will be an onshore flow with increased low-level moisture in the forecast area. However, upper ridging should limit thunderstorm coverage. The GFS and ECMWF MOS have pops 20 to 40 percent with the GFS pops highest. We used an average of the guidance. The MOS supports near normal temperatures through the medium-range period. && .AVIATION /10Z TUESDAY THROUGH SATURDAY/... VFR conditions are expected for a majority of the 24-hr TAF period outside of possible early morning stratus and scattered showers and thunderstorms. IFR/LIFR stratus has developed at AGS/DNL early this morning, and satellite trends indicate that it is spreading northward toward the CAE/CUB terminals. Expect IFR stratus to reach CAE/CUB by 09Z. Stratus may also reach OGB later this morning. Low-level winds should remain strong enough to help limit fog, so stratus remains the primary concern. Stratus is expected to improve by mid morning. An upper level trough will approach the region today and cross the area tonight. This feature coupled with deep moisture in place should promote scattered shower and thunderstorm development mainly during the afternoon and evening hours. Some storms may contain strong winds. Convection should taper off with loss of heating this evening although a few showers and storms could continue into tonight. Fog is not expected to develop early Wednesday morning given a 25 knot low level jet. EXTENDED AVIATION OUTLOOK...Areas of late night and early morning stratus and fog are possible during the outlook period. There will also be a chance of mainly afternoon and evening thunderstorms. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$ SYNOPSIS...99 NEAR TERM...99 SHORT TERM...99 LONG TERM...99 AVIATION...99 FXUS62 KCAE 211041 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 641 AM EDT Tue Aug 21 2018 .SYNOPSIS... There will be a moist southwest flow between high pressure in the Atlantic and a cold front approaching the forecast area from the northwest through tonight. The front will move into the area Wednesday and be near the coast Thursday. Drier air will be in the area behind the front Thursday and Friday. && .NEAR TERM /THROUGH TONIGHT/... Moisture will remain high in the southwest flow between high pressure to the east and the approaching cold front to the northwest. Deepest moisture will be today and this evening ahead of upper troughing. The moisture combined with diurnal heating and convergence into a pre-frontal trough supports thunderstorms. The high-resolution models have not been consistent with the timing of greatest thunderstorm coverage. Deepest moisture is depicted shifting east of the area before maximum heating. The greatest moisture also is shifted east of the area before the main mid-level shortwave trough moves through the area late this afternoon and evening. The models indicate h5 warm advection and a dampening trough which should help limit thunderstorm coverage. We have forecasted chance pops because of the inconsistencies with the greatest chance late this afternoon and evening because of diurnal heating and shortwave trough timing. There will be some threat of severe thunderstorms this afternoon and evening. There will be increased shear ahead of the front with h85 wind 25 to 30 knots. Instability is forecast to be moderate. The NAM and GFS depict surface- based LI values -5 to -6. The models also indicate mid-level drying in the area and associated evaporative cooling may help enhance downdrafts. The thunderstorm chance will diminish overnight because of more shallow moisture behind the mid-level shortwave trough and nocturnal cooling. The NAM and GFS Bufkit momentum transfer tool plus GFS LAMP indicate wind gusts around 20 mph this afternoon. We leaned toward the higher temperature guidance ahead of the cold front today. Followed the consensus for the temperature forecast tonight. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... Despite more shallow moisture, convergence along the cold front supports a continued thunderstorm chance Wednesday into Wednesday evening. The NAM indicated greater moisture compared to the GFS and ECMWF Wednesday evening. We forecasted pops of just 20 percent because of shallow moisture Wednesday and Wednesday evening which was a little above the guidance consensus. It should be less humid with lower temperatures behind the front for Thursday. However, a lingering surface trough and slightly more moisture closer to the stalled front near the coast supports keeping slight chance pops in the extreme east section. The guidance consensus supports highs in the lower 90s Wednesday, and middle and upper 80s Thursday. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... High pressure in the mid-Atlantic region Thursday night into Friday will be shifting into the Atlantic over the weekend. The result will be an onshore flow with increased low-level moisture in the forecast area. However, upper ridging should limit thunderstorm coverage. The GFS and ECMWF MOS have pops 20 to 40 percent with the GFS pops highest. We used an average of the guidance. The MOS supports near normal temperatures through the medium-range period. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... VFR conditions are expected for a majority of the 24-hr TAF period outside of possible early morning stratus and scattered showers and thunderstorms. Stratus has developed at AGS/DNL/CAE/CUB this morning, and satellite trends indicate that it will reach OGB very soon. Stratus has fluctuated between categories quite a bit, so used a TEMPO group to account for this. Stratus is expected to improve by mid morning. An upper level trough will approach the region today and cross the area tonight. This feature coupled with deep moisture in place should promote scattered shower and thunderstorm development mainly during the afternoon and evening hours. Some storms may contain strong winds. Convection should taper off with loss of heating this evening although a few showers and storms could continue into tonight. Fog is not expected to develop early Wednesday morning given a 25 knot low level jet and drier air moving into the area. EXTENDED AVIATION OUTLOOK...Areas of late night and early morning stratus and fog are possible during the outlook period. There will also be a chance of mainly afternoon and evening thunderstorms. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$
Office: GSP FXUS62 KGSP 211055 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 655 AM EDT Tue Aug 21 2018 .SYNOPSIS... A cold front will approach from the west today and is forecast to move across the region this evening. In the front's wake, dry high pressure will spread over the area for the latter half of the week, making it feel more like mid-September. The warm and humid air will return for the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 635 AM EDT Tuesday: Cloud cover has been gradually increasing over the past few hours, with multiple sites reporting stratus decks in the 500 to 1000ft range. Overall coverage is expected to gradually increase later this morning as broader scale ascent increases with the approaching upper trof. We've been seeing areas of fog over the far western mtn valleys and more recently, patchy fog has developed over parts of the NC Foothills. Otherwise, the upper low currently over the central CONUS will open back up as it approaches the Appalachians later today. The associated sfc cold front will reach the Foothills by roughly 00Z Wed. Ahead of the front is ample moisture with precip water amounts just over 2''. The front will be accompanied by some upper support, and widespread showers and thunderstorms are likely this afternoon and evening with activity progressing from the mountains to the southeast. Wind profiles will strengthen today due to the influence of the frontal system, with bulk shear peaking in the 25 to 30 knot range this afternoon. This will increase the chance for severe weather; primarily severe wind gusts from storm outflows. This is represented by a Marginal Risk area from SPC. Instability amounts will be similar to the past few days, with lapse rates and sfc dewpts similar to yesterday. More rapid storm motion will limit excessive rain potential, though some flooding potential exists if training or repeated rounds of precip occur over locations. Rain and clouds will limit highs today to the low to mid 80s. Winds will remain persistently SWLY ahead of the front with some speed increases and gusts later this afternoon as the front approaches. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... As of 235 AM EDT Tuesday: The models are still on board with giving us a brief respite from summer during the latter half of the week. A cold front should be well to our east by daybreak on Wednesday, with a relatively strong WNW flow aloft for this time of year as an upper trof axis lingers overhead. Lingering low level moisture will fuel the development of upslope showers near the TN border through the day, so a chance of precip was kept in that location. Although the flow will be generally inhospitable east of the Blue Ridge, some bands of showers are possible in axes of low level convergence downwind of some of the higher terrain, such as the Balsams. A trailing short wave is expected to dive down into the upper trof during the afternoon, which should enhance the precip chances late in the day. Thus, have generally accepted the slight chance seen in the NAM across Upstate SC and the wrn Piedmont of NC. The loss of heating will take care of this activity Wednesday evening, while the upslope moisture will taper off near the TN border. The downslope east of the mtns should keep temps a bit closer to normal than otherwise expected on Wednesday, but that will not be the case for the rest of the week. The rest of the fcst is dry with temps about five degrees below normal courtesy of sfc high pressure moving past to the north on Thursday and lingering off the New England coast on Friday. Might even get cool enough to open the windows Thursday night and Friday night. The difference in humidity should be notable, with dewpts down in the mid/upper 50s east of the mtns. && .LONG TERM /SATURDAY THROUGH MONDAY/... As of 320 AM EDT Tuesday: Alas, summer will return over the weekend, not quite with a vengeance, but the models suggest the upper pattern will evolve toward one that usually spells above normal heat for August during the early to middle part of next week. In the mean time, a progressive upper trof moving past to the north on Saturday will push a dying front toward the region. An easterly low level flow ahead of the trof will fuel a return to diurnally-driven showers and storms on Saturday with temperatures still about five degrees below normal. That changes on Sunday as an upper anticyclone over the srn Plains plods eastward thru Monday. This feature will bring a warming trend, with temps going up a category for Sunday and another one again on Monday. Precip chances favor diurnal showers over the higher terrain. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... Cloud cover has been gradually increasing over the past few hours, with multiple sites reporting stratus decks in the 500 to 1000ft range. As broader scale ascent increases with the approaching upper trof, additional coverage of mid-lvl clouds is expected. So far this morning we've only seen visby restrictions over the far western NC mtns, however additional development is possible thru daybreak. Otherwise, a fairly robust cold front will approach the region later today from the NW, with the front reaching KAVL by roughly 00Z Wed. Winds will remain SWLY ahead of the front in the 5 to 15kt range with some gusts likely this afternoon/evening. They will veer more NLY after 00Z once the front passes. The front will help to focus showers and thunderstorms today, with significant activity expected along and ahead of the front. Timing of VCTS and PROB30s for TSRA reflect the expected progress of the front, with storms once again beginning over the mountains and spreading south and east. Outlook: Expect good coverage of diurnal showers and thunderstorms into early Wednesday. After which, drier high pressure is expected to build in behind the front with restrictions less likely for the end of the work week. Confidence Table... 11-17Z 17-23Z 23-05Z 05-06Z KCLT High 83% High 87% High 100% High 100% KGSP High 83% High 94% High 100% High 100% KAVL Med 66% High 100% High 100% Med 75% KHKY High 83% High 87% High 100% High 100% KGMU High 83% High 94% High 100% High 100% KAND Med 75% High 87% High 100% High 100% 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...None. SC...None. && $$ SYNOPSIS...PM NEAR TERM...JPT SHORT TERM...PM LONG TERM...PM AVIATION...JPT