Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
224 PM EST Friday Nov 27 2015
dry and warm high pressure will persist through Saturday before a
cold front pushes in from the northwest on Sunday. A cool and moist
air mass will settle across the area Monday and Tuesday...with
another cold front arriving by the middle of next week.
Near term /through Saturday/...
as of 145 PM EST...1032 mb surface high pressure remains stretched
across the forecast area. The surface high will slowly weaken
tonight through Saturday as the 500 mb ridge aloft gets suppressed
toward the southeast coast by falling heights from the west. This will
permit increasing high clouds through the period...with middle level
cloudiness increasing mainly across the northern tier through Sat
afternoon. 850 mb flow will take on a light westerly downslope...
which should keep any lower clouds at Bay overnight. Morning patchy
fog will be the primary concern as boundary layer moisture slowly
rebounds and winds remain light. Otherwise...dry conditions will
persist with maxes/mins running 10 degrees or more above climatology.
Short term /Saturday night through Monday/...
as of 215 PM Friday...on Sunday...a backdoor cold front will slowly
slide south across the western Carolinas under zonal middle level flow.
12z runs of the short range models indicate greater potential for a
weak middle level vorticity maximum to track across Tennessee...reaching the NC mountains
during the afternoon. In addition...a field of jet divergence will
develop across the forecast area during the afternoon. Short range
guidance indicates that measurable rainfall will generally occur
across the southern Appalachians...I will highlight with high chance
probability of precipitation. Temperatures will remain mild...with low 60s within the mountain
valleys to middle to upper 60s east.
On Monday...surface low pressure will organize over the Great Plains as
high pressure settles over New England. Circulation around the low
will lift the old back door cold front as a warm front across the
Ohio River valley. However...east of the Appalachians...surface high
pressure will ridge southwest across the foothills and Piedmont.
Light NE wind...southeast h925-850 mb winds...and widespread cloud
cover should result in cad. Using a blend of preferred MOS...I will
forecast highs in the middle to upper 50s across the region. Probability of precipitation
should range from likely across the mountains to 30-40 probability of precipitation east.
Long term /Monday night through Thursday/...
as of 215 PM Friday...models in decent agreement on tracking a
closed upper low slowly across the Great Lakes Tuesday and
Wednesday...dragging a trailing vorticity lobe and cold front across the
southern Appalachians Wednesday night. An associated surface cyclone
will track from Iowa to the northern Michigan. The County warning forecast area looks to be in a
hybrid cad wedge to start out the medium range...but is likely to
erode Tuesday...as parent high drifts off the coast and a weak low
develops off the middle Atlantic. However...there may be a lingering
cold pool...as southwesterly upglide flow will persist/strengthen through the
day ahead of the system to the west...keeping low clouds and spotty
precipitation around. Probability of precipitation will continue to be in the high chance to likely range
through the day...and into Tuesday night. Highs will be slightly below
normal under the clouds/precip. Quantitative precipitation forecast amounts Don/T look
impressive...as forcing remains modest at best and precipitable waters hover
around 1 inch.
On Wednesday...guidance still slightly diverges on timing of a cold
front from the west. The GFS has the usual earlier arrival...blowing
the front through by middle afternoon. The European model (ecmwf) has another round of moderate
quantitative precipitation forecast with a slower-moving front during the day...drying this out in
the evening. I have gone with the superblend which keeps a solid chance
pop. Temperatures should be at or slightly above normal...as wedge should be
long gone and colder thicknesses still back to the west.
Thursday through Friday night...the 12z GFS and European model (ecmwf) really
diverge...as another piece of energy carves out a southern stream
trough behind the the closed low. This trough may be split from the the
northern stream...or it may remain somewhat phased. This has a big
impact on the forecast...as the GFS (like previous ecmwf)...as a Miller-a
type low develop in vicinity of Florida...then track up the Carolina coast. This
would bring a round of precipitation with potential for high-elev snow. The
12 European model (ecmwf) drags the trough through the area faster and doesn/T develop a
surface low until well offshore. So this period may be dry and sunny or
cool and wet with p-type concerns. Too early to favor one solution over
the other. I have probability of precipitation ramping up to chance with some light snow above
3500 feet Thursday night into Friday. This forecast will likely change
significantly over the next few days.
Aviation /20z Friday through Wednesday/...
at kclt and elsewhere...the period will be marked by slowly
increasing and lowering high clouds through midday Saturday. Light
NE winds will continue under the surface high east of the mountains...with
light southeast winds at kavl...becoming nearly calm throughout overnight.
Light west to SW flow will develop on Saturday. The MOS remains bullish
on MVFR to IFR restrictions in fog developing after 09z tonight...
but it has been overdone on restrictions the past couple of
mornings. With the boundary layer continuing to slowly moisten...and
winds going calm...some fog is possible. However...this should be
offset by increasing high clouds aloft. Will thus feature no worse
than a brief window of MVFR fog around daybreak at all taf sites.
Outlook...moisture will increase late in the weekend through Monday
as a back door front settles southward into the region. The best
chances of precipitation and associated restrictions will be on
Tuesday...with a cold frontal passage expected on Wednesday.
19-01z 01-07z 07-13z 13-18z
kclt high 100% high 100% high 100% high 96%
kgsp high 100% high 100% high 96% high 96%
kavl high 100% high 100% high 96% high 96%
khky high 100% high 100% high 96% high 96%
kgmu high 100% high 100% high 100% high 96%
kand high 100% high 100% high 100% high 93%
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)