Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 271129
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
629 AM EST Mon Feb 27 2017
Cool high pressure will move off the Carolina coast tonight, with
warmer air returning during the first half of the upcoming week. A
warm front will lift north through the area Tuesday then a cold
front crosses from the northwest Wednesday night. Cool high pressure
brings temperatures a little below normal at the end of the week.
.NEAR TERM /THROUGH TONIGHT/...
Mid and high level clouds will continue to increase across the
forecast area today, in advance of a short wave trough ejecting from
the southern Great Plains. This trough is currently associated with
an area of showers and embedded thunderstorms extending from the
Arklatex into the TN Valley. However, the short wave is expected to
dampen as it encounters increasingly confluent flow across the
eastern Conus. Thus forcing for UVV will diminish as this area of
precipitation approaches the southern Appalachians later today. In
fact, the general consensus among model guidance is that showers
will struggle to make it as far east as western NC and northeast GA
in any organized form. We will therefore continue to only feature
pops ranging from 20-40 percent across the western third of the
forecast area by the end of the day.
Farther southwest, despite the weakening deep layer forcing,
guidance indicates isentropic lift will interact with sufficient
moisture/buoyancy and shear to maintain convection across the Deep
South throughout the day. Several mesoscale models bring this
activity into South Carolina by the end of the evening, although the
consensus is to take the bulk of it south of our forecast area with
the richer moisture and surface-based instability. On the other
hand, guidance does indicate increasing elevated instability across
the forecast area by daybreak, so would not completely rule out some
showers or even a storm or two to sneak into the Piedmont overnight.
Nevertheless, data suggest only a 20-30 pop is warranted tonight.
Max temps will be a solid 5 degrees or more above climo today, and
as much as 20 degrees above normal tonight, as impressive moisture
advection occurs in association with a warm front. In addition to
increasing low clouds, areas of fog and perhaps patchy drizzle may
be seen by daybreak Tuesday.
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 230 AM EST Monday: The short range fcst period kicks off on
Tuesday morning amidst weak H5 ridging across the southeast states,
while a shortwave rides along the mean flow into the TN/OH Valleys,
all ahead of a deep trough out west. At the surface, southerly
return flow will be setting up across the deep south as warm front
surges northward ahead of a rigorous cold front marching through the
plains into the MS Valley. Pattern evolution through the period
will be highlighted by increasing moisture into the Southern
Appalachian region on Tuesday warranting increased pops across
the region thanks to said warm frontal intrusion and weak upper
support by way of the passing shortwave. Lapse rates on Tuesday do
improve with time, however still aren`t all that impressive. Thus
think light, primarily upglide forced rain will dominate early on
before transitioning to showers across the the western two thirds
of the fcst area where upper support will be maximized thanks to
the passing shortwave impulse. Pops will taper southeast to slight
chances where the warm front will be surging, however likely to
be too late in the day to yield any significant precip concerns.
The primary feature of the short term will be the approach of the
upper trough, and the passage of the associated surface cold front
on Wednesday evening. Persistent southerly waa will have further
increased surface td`s leading to a marginally unstable airmass
Wednesday out ahead of the front, however midlevel lapse rates still
leave a bit to be desired as fcst soundings actually indicate the
potential for modest warm nosing. That said, enough instability
combined with falling heights associated with the approaching upper
trough will likely be enough to support a few showers/tstorms,
especially along the southern facing slopes of the escarpment
where improving H85 flow will upslope. Moving to the fropa itself,
due to the nature of the upper trough, upper jet placement, and an
increasing llj, shear is ample with nearly 60-65kts expected in the
deep layer. Timing will likely play a significant role into the
equation by way of overall convective available energy ahead of and
along the front. Guidance has some issues with phasing/timing,
however all models generally favor only ~500j/kg sbcape tops
thanks to the poor midlevel lapse rates mentioned above. Thus,
the chances for severe weather are marginal at this point, with
the primary threats being damaging winds thanks to veered llv flow.
All said, we are still 3 days out and much could change regarding
the details. As for the fcst, pops will ramp up significantly
through Wednesday afternoon/evening, tapering into the overnight
hours as the front pushes east of I77 by around 12z Thursday.
Temperatures through the short term will moderate to mild levels
with highs on Tuesday warming into the lower 70s across the
Piedmont, with mid 60s favored in the mtn valleys, and upper 50s
at the peaks/ridgetops. Further warming in expected on Wednesday,
generally at levels 5-7 degrees warmer than on Tuesday.
.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 300 AM EST Monday: The medium range fcst period kicks off
on Thursday morning amidst broad troughing aloft, while at the
surface a cold front moves over the western Atlantic and cool/dry
high pressure slides east into the Southern Appalachians. Pattern
evolution through the period will feature passage of a shortwave
to the north across the Great Lakes, with no precipitation related
affects to be felt this far south. Reinforcing high pressure will
dive southeast out of northwest into the Plains states overnight
into Friday amidst flattening H5 flow. This ridge will transition
rather quickly through the OH/TN Valleys Friday evening, setting up
over the Carolinas by Saturday morning, before eventually sliding
over the western Atlantic to round out the weekend amidst building
shortwave ridging aloft. Sensible weather in response to these
pattern fluctuations will favor dry conditions, and generally
near normal temperatures favored through Friday, a bit cooler on
Saturday, before warming on Sunday given veered southerly flow
thanks to the migrating surface high.
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: VFR will persist through at least the next 15
hours or so, with gradually increasing high and mid level clouds
expected through the daylight hours. Low level moisture will begin
increasing by late Monday evening, resulting in development of low
VFR cigs at most terminals by 06Z. Cigs are expected to lower
further during the pre-dawn hours, although guidance varies widely
regarding how low cigs will become prior to 12Z (VFR, LIFR, and
everything in between). Based upon signals in raw model output, will
advertise MVFR cigs developing at most terminals by the end of the
period, with the lowest (~015) occurring at KCLT. Certainly cannot
rule out IFR developing before the end of the period, but
uncertainty is much too high to include that in the forecast attm.
With the increasing moisture, there will also be very small chances
for showers tonight. Otherwise, winds will become light SE by late
morning, and continue through much of the period, with perhaps light
NE winds developing tonight.
Outlook: Chances for restrictions, along with gradually improving
shower chances continue into Tue before diminishing somewhat Tue
night into early Wed. Late Wednesday a cold front approaches from
the west and brings additional chances of showers as well as some
thunderstorms. Drier conditions end the week following the fropa.
11-17Z 17-23Z 23-05Z 05-06Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL High 100% High 100% High 100% High 100%
KHKY High 100% High 100% High 100% High 100%
KGMU High 100% High 100% High 100% High 100%
KAND High 100% High 100% 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: