Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
634 am EST Sat Dec 27 2014
high pressure will move off the Carolina coast today as a cold front
approaches from the west. Expect temperatures to be a few degrees
above normal this weekend. The front will cross Monday with a
secondary front passing in middle week dropping temperatures to below
normal. The next cold front will arrive at the end of next week.
Near term /through tonight/...
as of 630 am...light returns on regional 88ds are beginning to lift
NE of the area. There was actually a little light sleet reported
underneath some of this activity across the mountains earlier...which is
surprising considering the very dry subcloud layer (with clouds
bases at around 10 kft). With radar ehcoes diminishing...will
continue to feature a precipitation-less forecast this morning.
Temperatures should warm to around 50 across the Piedmont/fhills and mountain
valleys by late morning.
A low amplitude ridge will persist along the East Coast today...
before moving off the coast by the end of the period...as an
upstream trough begins to eject from Texas/the Southern Plains.
Today will see a varying degree of middle/high level cloud cover across
the western Carolinas and northeast Georgia...resulting in partly
cloudy skies across much of the area. Maximum temperatures will average around
10 degrees above climatology.
Rain chances increase tonight...as a weak frontal zone and
associated weak low pressure move across the tenn valley. Resultant
isentropic lift/low level convergence and weak middle-level short wave
trough should support rain moving into the western zones by midnight
or so. Rain chances diminish toward the southeast...as the best
forcing is expected to lift northeast across the County Warning Area between 06 and
12z. Probability of precipitation will range from categorical across the mountains/NC
foothills/northwest upstate...to the low end of likely across the
southeast zones. Rainfall amounts through 12z should range from a
quarter to half inch across the mountains and adjacent foothills...
to less than a quarter inch across much of the Piedmont. Min temperatures
will be well above normal.
Short term /Sunday through Monday night/...
as of 300 am Sat...on Sunday the fairly broad frontal zone will
extend from Quebec southwestward to the western Gulf Coast...bisecting the tenn
valley just to our west. At least one weak wave is prognosticated to ride up
the front during the day as a result of cyclonic upper flow over the
boundary containing embedded weak vortices. Though such a wave would
likely provide local enhancement to low level warm/moist advection ahead
of the front...the existence of one is in question given the poor
agreement and consistency from guidance on how this occurs. Overall
the forcing Sunday is just not all that impressive. Little to no
instability is prognosticated over the County warning forecast area and though a good slug of
moisture transport is present on NAM/GFS forecasts the low level lift is
limited. At any rate...through Sunday the front remains nearly
stationary across the southeast...the parent low continuing to progress
eastward with the active northern stream while the broad southern stream trough is
held off by the Bermuda high. It appears the front will not actually
enter the area until Monday morning...with a distinct 500mb shortwave
accompanying it as well as upper divergence associated with rr quadrant of a
Two Peaks of precipitation activity are suggested when the total forcing is
maximized...Sunday morning and then early Monday morning. However it is
difficult to pick out a point between where a lull should be
between...with the overall pattern remaining favorable for at least
light precipitation. Will continue to advertise likely probability of precipitation most of the area
throughout Sunday...but concentrating more quantitative precipitation forecast close to the
aforementioned peaks. Despite clouds and rain...in the warm airmass
temperatures should top out 5-9 degrees above normal Sun afternoon...with mins
Monday morning being even more above normal...upper 40s and lower 50s. Maximum
temperatures Monday will be slightly warmer than Sunday over the Piedmont
with the front not yet having an impact.
Progression of the upper pattern is still pretty slow through Monday
night...with the County warning forecast area near the inflection point between the plains
trough and the Atlantic ridge. Probability of precipitation decline only gradually through the
end of the period with most of the guidance indicating some quantitative precipitation forecast
continuing on the back side of another frontal wave developing near
the Georgia/SC coast. Colder air will begin to return to all areas on the
ensuing northerly flow Monday night...though min temperatures will still be around 10
degrees above climatology.
Long term /Tuesday through Friday/...
as of 200 am Sat...quasi-zonal upper flow continues over the sun belt
Tuesday even as a polar trough moves into the Continental U.S. And shears into
two shortwaves to our north and west. One wave moves over the Great
Lakes and contributes to gentle height falls over the southeast
mid-week...while the other cuts off over the southwest and leads to
the development of a surface low over the Southern Plains or arklatex by the
end of the week. Confluence downstream of the SW trough will produce
a sprawling surface high which will spread across the Ohio Valley and southern
states Tuesday night through Friday. This will bring seasonably cool conditions
for our area with temperatures a shade below climatology. Most of the period looks
dry before probability of precipitation start ramping up Thursday night ahead of the developing
Aviation /12z Saturday through Wednesday/...
at kclt and elsewhere...high/mid level clouds of varying degrees of
thickness and coverage will pass over the region throughout the
day...with cloud heights expected to be around 10 kft or higher.
Ceilings will develop/lower this evening...as a cold front and
associated weak low pressure approach from the west. This is
expected to bring -ra and MVFR ceilings to most of the taf sites by the
end of the period. Winds will be light through the period...
generally favoring a SW direction this afternoon/evening.
Outlook...periods of rain and flight restrictions are expected
throughout Sunday...Monday...and Monday night before gradual
improvement occurs throughout Tuesday. Dry high pressure should
return by mid-week.
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% medium 60%
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)