NWS Greenville-Spartanburg, SC wrote its last area forecast discussion before the first event at Jun 14, 4:58 PM EST, 1 hour 21 minutes earlier.
Area forecast discussion, Jun 14, 4:58 PM EST, 1 hour 21 minutes before
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
558 PM EDT TUE JUN 14 2016
.SYNOPSIS...
Warm and humid conditions are expected through the end of the work
week. A cold front will push across the region on Friday, with dry
and cooler high pressure arriving this weekend.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
As of 550 PM: I will issue another quick update to increase PoPs
across NE GA...NC mtns...and the upstate through early this evening.
Widespread CAPE and moderate DCAPE will favor the development of
long lasting outflow boundaries to drift across the region...with
cells triggering along the boundaries. This process will continue
across the CWA, until the instability is cut off from the expanding
outflows. I will update temperatures with the latest observations.
KAVL saw its fourth day in a row with highs 91 or more. Today the
high of 92 broke the old record of 90 set in 1981.
As of 240 PM: A weak frontal boundary remains essentially stationary
across the CWFA, dividing hot and very humid subtropical air
from notably drier continental air. This boundary can be seen on
satellite as the northern edge of a Cu field. Southerly flow is
expected to push the boundary north again overnight. Meanwhile, an
upper ridge is seen over the mid-eastern CONUS. A weak shortwave
trough is moving through the ridge, across the Gulf states,
and will move over the Carolinas Wednesday morning. Storms along
and south of the boundary will pose a threat of damaging wind,
mainly on account of SBCAPEs near 2000 J/kg and high DCAPEs well
over 1000 J/kg. Shear is relatively weak but may allow storms to
grow into clusters. SPC has expanded the Marginal Risk in their
Day 1 outlook to cover most of the Upstate.
Confidence in the overnight forecast is somewhat limited given
varying degrees of convection featured during the afternoon. It
appears some of the short range guidance, e.g. 4km NAM, depict
"worked-over" profiles by late evening that would not support
additional precip. However, many SREF members show a modest
amount of elevated instability persisting throughout the night,
and something like that would account for the lingering PoPs
suggested by a guidance consensus. That of course assumes some
source of lift. The incoming trough does not have the dynamics to
expect much intiation from it alone, but weak warm upglide could
also have an effect. I'm handling the situation by reflecting
a very slowly decaying PoP trend tonight. Robust thunderstorms
are not expected to last past the loss of the sfc instability,
however. Moist conditions and convective debris will keep temps
several degrees above normal.
The shortwave axis will be entering the CWFA from the west a little
after daybreak. Models generally key on this and rapidly develop
convection in the morning. The wave is trailed by a broad cold
frontal zone, most notable for enhancing low level convergence as it
moves thru the area during the day. CAPE values peaking below those
Tuesday given slightly cooler conditions. Prog soundings are not as
dry, and shear will remain rather weak, so heavy rain may end up
being our most significant threat given PWAT values remaining 1.9
to 2.0 inches over much of the area per NAM. Max temps will not be
as hot, but still 2-3 degrees above normal. Despite sfc dewpoints
expected to exceed those Tuesday, heat indices will be lower.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 145 PM EDT Tuesday...the second half of the week looks
problematic in terms of coverage and strength of deep convection.
The period begins Wednesday evening with lingering showers/storms,
especially over the Piedmont zones. Most of the convection will do
the usual diurnal weakening and be gone by late evening. However,
the models continue to indicate the approach of a wave/vort lobe
from the lower OH valley region after 06Z Thursday. The question is
whether or not this feature will support/drive any thunderstorm
activity south/east of the Ohio River after dark. The model guidance
shows an unstable boundary layer overnight with substantial CAPE,
probably 1000 J/kg or so, across the area to the west of the NC
mountains, which would support keeping convection alive that would
be able to reach the NC mountains in the pre-dawn hours. For that
reason, a chance of precip was retained on the TN border overnight.
Thursday is more of a question, especially in light of the Day 3
slight risk across most of the forecast area. What is interesting
with this part of the forecast is that the operational NAM and GFS
fail to respond with much of any convection on Thursday. In that
regard, the Slight Risk appears to be based on the ingredients seen
in the model guidance, that being a surface boundary dropping down
across the OH valley and toward the Srn Appalachians Thursday
evening, substantial surface-based CAPE ahead of the boundary
(perhaps greater than 2000 J/kg), and what would also be substantial
deep layer shear brought on by a mid-level jetlet. If the
operational models are wrong with their failure to develop storms,
then we could have some kind of severe wind-producing MCS coming at
us from the Cumberland Plateau in the evening hours. An idea worth
letting simmer away on a back burner for now. Precip chances will be
kept modest for the time being for Thursday and Thursday night, and
temps will be seasonally warm. Friday looks a bit less busy and
naturally a bit more uncertain. An upper low dropping down across
the central Appalachians and Mid-Atlantic will help to bring a
surface boundary down across the region during the day. This will
probably take the form as more of a back-door cold front as it wraps
around the mountains. How far the front gets will determine the
extent of precip coverage and the high temps. For now, a chance of
precip is shown across mainly the NC part of the fcst area. The
temp will be more tricky, perhaps limited to the mid 80s across the
NW Piedmont but still in the mid 90s in northeast GA ahead of the
southward moving front.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
At 230 PM Tuesday: On Friday evening an upper trough will be along
the eastern seaboard, with an upper low moving reaching the NC
coast. The GFS closes off this low near the SC coast by Sunday
evening, while the ECMWF closes off a deeper low off the northeast
NC coast. The GFS low moves to western FL by Sunday evening, while
while the ECMWF low remains in the vicinity of the NC Outer Banks.
By Monday evening the weakening GFS low reaches the AL coast, while
hte stronger ECMWF low moves up the Gulf Stream east of NJ. By mid
week, the models solutions diverge, with the GFS showing a
reamplfied and retrogresses low over the eastern USA, and the ECMWF
showing zonal flow over the same area.
At the surface: On Friday evening high pressure will set up along
the east slopes of the southern Appalachians in the wake of a cold
front, and will linger into Sunday. By Monday a northward return
of the front will allow precipitation to spread inland towards the
mountains, and this pattern persists into Tuesday. Temperatures will
run slightly below normal until Tuesday, when the rise above normal.
&&
.AVIATION /22Z TUESDAY THROUGH SUNDAY/...
At KCLT: Midday visible satellite imagery shows a line of enhanced
Cu stretching acrs the immediate vcnty of KCLT, highlighting
the position of a stationary front. This front is expected to
gradually shift northward this aftn, bringing warmer and more moist
air over the field. Regardless of whether a shower develops along
the front itself, a round of convection will be most likely in the
late afternoon with heating and destabilization. A TEMPO has been
retained to cover these possibilities, but some SHRA or even TSRA
could recur later in the evening. The longer initiation is delayed,
the later into the evening the activity could last, as the energy
could be realized by an advancing (but weak) shortwave. With the
front expected to move north, a southerly wind shift is expected,
and low stratus are not likely to develop with only very weak
warm upglide occurring. A chance of diurnally driven convection
does exist tomorrow, and overall will be higher than today, so a
PROB30 has already been included late in the period.
Elsewhere: Trends mostly as at KCLT. Anywhere south of the frontal
boundary will have at least a small chance of seeing TSRA this
afternoon and evening. Chances warrant a TEMPO at all terminals
except KHKY, which is expected to remain on the cool/north side
until tonight. Smaller chances of mainly just light precipitation
do persist overnight, though if widespread convection develops and
diminishes diurnally (early evening) the advancing trough may not
be able to produce much further activity. Though very moist sfc
conditions will be in place south of the front tonight, low level
profiles are not supportive of dense fog or low stratus, so VFR is
expected. That said, some ground fog could develop particularly
in areas where rain falls this aftn. Unstable conditions and SCT
SHRA/TSRA are expected to ramp up again late Wed mrng.
Outlook...Mostly VFR conditions are expected, except for possible
valley fog in the NC MTNS each morning. Coverage is expected to be
more isolated for Thursday and Friday in the wake of a departing
trough.
Confidence Table...
22-04Z 04-10Z 10-16Z 16-18Z
KCLT High 100% High 100% High 82% High 93%
KGSP High 100% High 100% High 90% High 100%
KAVL High 100% High 97% High 86% High 100%
KHKY High 100% High 100% High 90% High 100%
KGMU High 100% High 100% High 90% High 100%
KAND High 100% High 100% High 90% High 100%
The percentage reflects the number of guidance members agreeing
with the schedule 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...JAT
NEAR TERM...NED/Wimberley
SHORT TERM...PM
LONG TERM...JAT
AVIATION...Wimberley