Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1055 am EDT Sat Jul 26 2014
high pressure will remain dominate across the area through Sunday.
A cold front will reach the area early on Monday morning and push
through by the late afternoon hours. High pressure will regain
control on Tuesday...lasting through middle-week with below normal
temperatures likely. Temperatures will moderate somewhat near the
end of the week as warm/moist easterly flow returns leading to
increased precipitation chances on Thursday and Friday.
Near term /through tonight/...
as of 1035 am...low stratus is rapidly dissipating across our
eastern Piedmont areas...and in the mountain valleys...giving way to
sunny skies until cumulus begins to pop early this afternoon. Based upon
the latest available guidance and observational trends...the dry
forecast for the afternoon still appears on track. Temperatures aloft will
warm as the upper ridge axis extending from strong Southern Plains
subtropical high attempts to nose into the area. Additionally...
there/S a fairly strong signal that dewpoints will mix out into the
Lower/Middle 60s across the area...as increasing southwest flow removes
some of the juicier low level moisture lingering across the area.
Instability is therefore expected to be too weak this afternoon to
support deep convection. It will be quite warm this afternoon under
rising heights/low level thicknesses...with maxes expected to range
from the upper 80s across the mountain valleys...to lower 90s in most
areas southeast of the Blue Ridge.
As of 650 am...low clouds and fog across portions of the area will
dissipate an hour or two after daybreak leaving mostly sunny skies
with developing high based cumulus for the afternoon. Otherwise...going
forecast looks on track with updates mainly for current conditions.
As of 210 am...clouds moving SW across the area have thinned
allowing areas of fog to develop. An area of low stratus over the
sandhills and midlands has also developed and is advecting into the
southeastern County warning forecast area. These clouds could spread into the eastern upstate and I-77
corridor of NC with the southerly low level flow. For now...do not expect
more than patchy dense fog...but will have to keep an eye on this as
the fog could become more widespread before daybreak. Either way...
expect the fog and/or low clouds to dissipate relatively quickly
after daybreak. Should end up being a mostly sunny day across the County warning forecast area
with southwesterly winds as weak high pressure settles across the area.
Although there is some elevated instability...a low level cap
remains in place through the day keeping any convection at Bay. With
rising thicknesses...highs end up back to near or slightly above
High pressure begins to weaken tonight as a Lee trough develops ahead
of an approaching cold front. Middle and high clouds will increase
across the area overnight...and should keep any fog patchy. A dry forecast
is still expected as any precipitation associated with the front will be
well to our northwest. Lows will be a few degrees above normal.
Short term /Sunday through Monday night/...
as of 245 am EDT Saturday...the short term period remains
highlighted by a rather potent July frontal passage Sunday night through
Monday afternoon. Forecast period initializes Sunday morning
amongst strong southerly flow and an approaching upper trough axis.
This trough will likely be located along the middle Mississippi River
valley Sunday morning with heights beginning to fall upstream across
the central/southern Apps. Diurnal destabilization supported by
temperatures in the lower to middle 90s at peak heating will likely be
sufficient for convective development across the high terrain by
middle/late afternoon. Westward steering flow aloft is expected to
propagate some of this activity into the foothills/Piedmont regions
late in the day before deteriorating after sunset. The environment
will be moderately unstable with cape values approaching
1500j/kg...with increasing sheer aloft. Although limited due to
lack of strong upper forcing...would not be surprised to see a few
strong to severe storms in the warm sector Sunday
afternoon/evening. As for the forecast...probability of precipitation will gradually rise
through the day and into the overnight hours with solid chance level
probability of precipitation across the high terrain...and slight chance probability of precipitation elsewhere.
Prefrontal shower and thunderstorm activity is expected to
develop/persist into the early morning hours on Monday across the
high terrain. The atmosphere will likely remain somewhat unstable
as dry air slowly advects in aloft allowing middle level lapse rates to
steepen. Sheer will be improving throughout the day on Sunday with
nocturnal 50kt low level jet developing after midnight as frontal convection
arrives. Despite the thermodynamic environment not being optimal
due to overnight frontal passage timing...shear and upper divergence beneath
right entrance region of upper jet maximum will be sufficient for deep
updrafts and severe thunderstorms with damaging winds and hail as
primary threats. Expecting a lull in strong/severe activity around
daybreak as the front slowly pushes through the mountains and better
upper divergent region slides northeast. That said...not expecting
this to last long as convection will ramp up in coverage and
intensity as heating steepens lapse rates and dry air continues to
advect through the region. Uncertainty remains regarding the
placement of said convective re-initiation as models keep the
majority of quantitative precipitation forecast response south of Interstate 85 along the eastern
fringes of the forecast area. Regardless...wherever this occurs am
expecting rapid intensification to severe levels with large hail and
damaging winds being of most concern. Will continue with possible
severe wording in the severe weather potential statement for the mountains Sunday evening into
Monday morning...spreading east into the Piedmont by early
afternoon. As convection will likely be scattered in nature...only
chance level probability of precipitation are forecast for Monday across the entire
Long term /Tuesday through Friday/...
as of 315 am EDT Saturday...the extended range period initializes
Tuesday morning with surface cold front lying well to the southeast
along the Carolina coast. Deep upper trough will still be in place
across the eastern Continental U.S. With strong northwest flow prevailing. A
series of upper impulses will surge through the mean upper flow
leading to potential rounds of showers across the high terrain on
Tuesday...perhaps spreading into the foothills by the afternoon
evening hours. Meanwhile...surface high pressure will finally spill
into the Midwest and slowly slide east leading to northerly flow at
the surface into Thursday. Models continue to indicate weak warm
advection returning to the region by weeks end as low level flow
veers easterly leading to increasing precipitation chances.
Thus...the forecast will feature slight chance pop across the
mountains on Tuesday and Wednesday with probability of precipitation increasing across the
higher terrain to solid chance levels on Thursday and Friday.
Outside of the mountains...the forecast will initialize and remain
dry through Thursday where only low end slight chance probability of precipitation are
highlighted due to increasing moisture and persistent upper trough
pattern. Temperatures through the extended range period will
actually be the most notable portion of the forecast. Expecting
cold advection behind the departing front to allow temperatures to
fall to nearly 10 degrees below normal on Tuesday and Wednesday
before gradually moderating by weeks end.
Aviation /15z Saturday through Wednesday/...
at kclt...low clouds have remained away from the airfield...but
cannot rule out a brief ceiling the next hour or two. The MVFR fog should
dissipate by 13z or so with VFR expected through the rest of the
period. Expect some high based cumulus this afternoon which will
dissipate this evening when middle and high clouds increase overnight.
Light southwesterly wind this morning increases in speed through the day then
GOES light again overnight.
Elsewhere...SC sites will remain VFR through the period. NC sites will
see IFR dissipate by 14z leaving VFR Thursday much of the period. High
based cumulus develops this afternoon then dissipates this evening when
middle and high clouds increase overnight. These clouds will keep fog
formation to a minimum...with kavl having the best chance of MVFR fog
toward daybreak. Light SW wind increases in speed through the day
then GOES light again overnight. Kavl will see northerly wind this morning
becoming SW this afternoon then northerly again overnight.
Outlook...scattered thunderstorms may return to the forecast area Sunday
afternoon through Monday as another cold front approaches and then
moves through the area by Monday night. VFR conditions will then linger
through middle week.
15-21z 21-03z 03-09z 09-15z
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: (must be lower case)