Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
152 PM EDT Monday Aug 3 2015
dry high pressure will remain in place across the area today. Low
level moisture will gradually return through the work week as a cold
front approaches from the area from the northwest.
Near term /through Tuesday/...
as of 145 PM EDT...the latest run of the hrrr is still advertising
isolated convection forming in the mountains near the NC/SC line
this afternoon...but it has not initialized especially well through
17z. There also remains a lot of dry air in the profiles...so will
curb probability of precipitation toward the conservative side and confine to locations near
the Escarpment through late day.
Otherwise...the forecast area will remain in the base of a broad
trough extending from eastern Canada through the southeast United States
tonight through Tuesday. The low level circulation moving NE along
the southeast coastline early in the period should confine all associated
moisture to the coastal plain overnight. Another seabreeze front may
work in from the southeast to further elevate dewpoints and keep mins on
the warm side of climatology.
A cold front will approach the northern tier on Tuesday and possibly
trigger isolated to scattered convection along the northern Blue Ridge
during the afternoon hours. Westerly steering flow would then drive
any convection eastward over the NC Piedmont through late day.
Profiles are still on the dry side...but 850 to 500 mb lapse rates
should steepen to 6.5 degree c or better and the approaching boundary
will aid triggering. A MOS blend of low end probability of precipitation for the northern half
seems reasonable. Maximum temperatures may gain another degree over Monday
values ahead of the boundary in most areas tomorrow afternoon.
Short term /Tuesday night through Wednesday night/...
at 230 am EDT Monday...on Tuesday morning zonal upper level flow
will exist across the southern tier of states...to the south of an
upper low over James Bay and a ridge over the northern rockies. This
pattern persists into Wednesday night.
At the surface...a weakening stationary front will be near the
Carolina and Georgia coasts on Tuesday morning...while a cold front moves
south of the Ohio River valley. The cold front reaches the NC
mountains Tuesday evening....moving into the upstate SC on
Wednesday. The boundary then returns north as a warm front on
Wednesday night and reaches Virginia by Thursday morning.
Precipitation chances will increase as moisture spreads east along
the front through Wednesday night. Instability will actually be
greater on Tuesday before the front arrives and moisture increases.
Temperatures will run above normal as cold advection never really
sets up with front retreating.
Long term /Thursday through Sunday/...
at 145 PM EDT Monday...starting at 00z Friday...with nearly zonal
west to east upper flow and shortwaves moving through the middle level
flow topping the SW ridge going east. Two significant shortwaves
will be crossing the southern Appalachians Thursday night and
Friday. Some amplification of the pattern will occur Friday and
Saturday with the axis of the upper East Coast trough roughly across
the Carolinas. Upper ridge at that time will be centered over West
Texas. For Sunday and Monday...upper ridge builds a bit more east as
upper trough holds along the eastern Seaboard. Another significant
shortwave passing through in middle week will dig threshold 500mb trough over
Carolinas and suppress ridge to the west.
At the surface...the slow moving weak cold front will drop south
over our region with the passage of the shortwave. This front will
gradually move just south of our area over the weekend with the
front becoming stationary Sunday and Monday over south Georgia and
the southern tip of SC.
Raised probability of precipitation a bit for Thursday night and Friday with the shortwaves
and frontal passage. Instability will be weak to moderate south of
the front and best chances of any rain will be suppressed south of
the frontal boundary. Temperatures will be around or slightly below
normal over the weekend.
Aviation /18z Monday through Saturday/...
at kclt...isolated showers may formed over the NC foothills this
afternoon...but the convection allowing models focus the best isolated
to scattered coverage back west toward the mountains through late day. Will
thus keep the kclt taf dry. Expect mainly high based cumulus during
the daytime parts of the taf...with mostly thin high clouds at
night. None of the guidance has low stratus making a run toward the
airfield early Tuesday morning...but this will need to be monitored
as another seabreeze and reinforcing boundary layer moisture returns
this evening. MVFR fog seems the best consensus for daybreak
visibility. Will keep the taf dry through 18z Tuesday...but convection
chances look better to the northwest through Tuesday afternoon with a front
approaching. Winds will remain light S to southeast the first half of the
period...likely toggle west-northwest to northwest Tuesday morning...but still light.
Elsewhere...showers/tsra near the Escarpment should stay away from
the terminal locations through the late afternoon hours. Expect
little more than scattered high based cumulus most areas as dewpoints
continue to mix out. Winds will remain light...generally srly across
the foothills and northwest at kavl. Morning MVFR fog is
likely...especially at kavl where some few stratus will also be
hinted at. Precipitation chances look better across western NC on Tuesday...but
probably after 18z. Winds will veer throughout as a boundary
approaches from the north.
Outlook...gradually increasing precipitation/restriction chances are
expected through the week as moisture returns along a stalling front
through middle week...and ahead of a low pressure system late week.
18-24z 00-06z 06-12z 12-18z
kclt high 100% high 100% high 97% high 100%
kgsp high 100% high 100% high 94% 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 97% high 94%
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)