Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 280235
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1035 PM EDT Mon Mar 27 2017
Moist southerly flow will linger over the southeast through Tuesday,
with several rounds of showers and thunderstorms possible. Drier air
will briefly return by the middle of the week as a cold front
settles south of the area. Rain chances return to end the week as a
low pressure system approaches from the west and interacts with the
.NEAR TERM /THROUGH TUESDAY/...
As of 1020 PM, convective band continues to weaken across north GA
and far western NC. However, a couple of stronger cells have popped
up along the leading edge of the band across the southern NC mtns.
The main threats going forward will most likely be heavy rain, small
hail and gusty winds. Would not completely rule out a brief isolated
severe storm or two tonight, but it appears that the threat of
organized severe weather is waning. Another QLCS that has developed
behind the initial band is approaching Chattanooga at the present
time. Based upon the latest SPC mesoanalysis, this feature may be
elevated in nature, and indeed is not producing much of a response
in wind observations as it passes regional METAR sites. On its
current trajectory, it would reach our northeast GA zones circa 06Z.
Again, it doesn`t appear this is going to pose much of a severe
weather threat, as the initial convective band continues to
stabilize the surface layer. Lows Tue morning will be around 15
degrees above normal.
The upper trough swings across the area Tuesday but the surface cold
front moves more slowly. Convective coverage overall will be greater
in the morning as that`s when the deepest moisture and forcing will
be over the area. Coverage will be better along and east of the I-77
corridor during the afternoon. The best overlap of instability and
shear will be to our north and east Tuesday. However, there could be
enough overlap during the afternoon along and east of the I-77
corridor for an isolated severe storm. The air mass behind the front
is not very different, and with the slow movement, highs will be 10
to 15 degrees above normal.
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 215 PM EDT Monday: In the Short Term, an upper ridge will
cross the Eastern CONUS, while a deep upper low ejects out of the
Four Corners region into the Southern Plains. At the surface, a weak
cold front will slide east, as high pressure builds into the the
Great Lakes. Low-level CAA will be weak behind the front, so well
above normal temps are expected Tuesday night and Wednesday.
Conditions should be dry under partly cloudy skies.
Wednesday night and Thursday, as a vigorous low pressure system
tracks across the Plains, low-level flow will turn out of the south
atop the CWFA, with WAA and upglide supporting the development of
clouds and spotty light showers. With an ~1032 mb surface high
centered over central Quebec, hybrid cold air damming should set up
by daybreak Thursday. This will make for a tricky temp forecast, as
precip will be forced mainly by isentropic lift and weak southerly
upslope flow. So mainly drizzle and sprinkles with a few light
showers are expected. PoPs still ramp up to likely in the southwest
corner of the CWFA by the end of the day on Thursday. If the models
prove to be overdone on precip, temps may end up being a couple
categories warmer than the going forecast. Both the NAM and GFS show
elevated CAPE above the wedge in the upper Savannah Valley. So will
keep a chance of thunder mention thursday afternoon there. But
severe threat should remain well to the west closer to the
approaching cold front.
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 230 PM EDT Monday: The medium range fcst period kicks off
on Thursday evening amidst a highly amplified upper pattern that
is highlighted by a ridge axis along the east coast, as well as
a closed and robust H5 cyclone embedded in a longwave trof atop
the Plains and MS Valley regions. At the surface, the pattern
is just as complex thanks to an entrenched hybrid CAD centered
off the Jersey shore, while cyclogenesis dominates the field
across Dixie Alley, eastward into the Southern Appalachians by
way of an approaching zone of baroclinicity. With that, the
cold front associated with said surface cyclone will be well to
west by fcst initialization, likely yet to cross the MS river,
however a warm front will have laid out across the I75 corridor
region in GA. Moisture advection tied to this pattern still looks
as if it will lift isentropically atop the wedge airmass leading
to increasing chances for stratiform precipitation into the early
overnight hours. At that point the fcst becomes quite interesting
given the approaching upper wave to provide synoptic scale lift,
as well as cooling the mid levels and thus increasing lapse rates.
Meanwhile, the CAD will begin to retreat to the east leading to
intrusion of the warm front, and thus providing focus for llv srh
enhancement given remnant backed surface flow. Eventually the
flow will veer leading to straightening of hodographs, at least in
the 0-1km layer, however improved mid level lapse rates will yield
increasing instability while the primary shortwave passes overhead.
Given the fcst range these details are still a bit uncertain,
yet it still looks as if the pattern could be rather convectively
active Friday morning/afternoon before the cold front sweeps in
Moving on, remnant northwest flow showers are progged behind the
fropa on Saturday while the remainder of the fcst area tends to dry
out as deep layer ridging builds in for Sunday. This deep ridging
looks dominant through Monday as well, however with sly flow to be
reestablished as the surface ridge shifts over the western Atlantic.
Meanwhile another deep upper system will be building across the
Plains, before sharply ejecting northeast into the OH/TN valleys
toward periods end, which will lead to another round of wet weather
across northeast GA and the western Carolinas into midweek.
As for the fcst itself, pops will ramp up sharply on Thursday night,
holding at widespread high chance to likely levels through much of
the day Friday. Said pops will taper into the overnight of Saturday
morning given the fropa, thus no mentionable pops are featured by
12z regionwide with the exception of the TN line upslope regions.
By midday Saturday, those pops are removed leading to dry conditions
through Sunday and into Monday when pops increase slowly from
the west as the next system ejects from the southern Plains.
Temperatures through the period will be a bit variable, however
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere, the main concern for this forecast cycle will
be the fate of the band of showers and embedded thunderstorms
currently moving across the TN Valley and approaching the southern
Appalachians. Sufficient instability and lift should support this
activity into at least the western TAF sites, and tempos for TSRA
have been included at all sites except KCLT from late evening into
the early part of the overnight. As far as KCLT, anticipate a tempo
being needed at some point, but there`s still too much uncertainty
surrounding timing, but also regarding in what state the convection
will be in by the time it arrives in the Piedmont. (The intensity of
the convection is already trending down, and we have several hours
of cooling before it would arrive in the Piedmont). Therefore, have
opted to only mention a VCSH at KCLT for now. Otherwise, statistical
guidance is in general very pessimistic regarding visby and esp cigs
toward daybreak. We are highly skeptical of this, as the statistical
guidance is often much too pessimistic with nocturnal cigs in warm
sector regimes. (Although areas that receive heavy rainfall from any
convection would be susceptible to seeing fog and/or low stratus
developing toward daybreak.) All things considered, opted to back
away from the IFR mention and maintain MVFR conditions during the
Convection chances are expected to dwindle by daybreak. Cigs should
improve during the afternoon, although additional convection could
develop as a cold front pushes slowly across the area. Most
terminals should see W/SW winds develop by the end of the period
(except NW at KAVL).
Outlook: Drier conditions should briefly return during mid-week
before another storm system begins affecting the region Thursday and
02-08Z 08-14Z 14-20Z 20-00Z
KCLT High 100% High 94% Med 77% High 100%
KGSP High 100% Med 73% High 95% High 100%
KAVL Med 79% High 95% High 91% High 100%
KHKY High 100% High 82% High 93% High 100%
KGMU High 100% Med 75% Med 77% High 100%
KAND High 100% Med 78% High 87% 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: