Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
247 PM EST Thursday Nov 26 2015
dry high pressure will prevail through the first half of the weekend
before a cold front approaches from the north and west Saturday
night into Sunday. Cool and wet high pressure will prevail on Monday
before another front arrives from the west on Tuesday.
Near term /through Friday/...
as of 200 PM EST...1040 mb high pressure over Virginia will remain nosed
SW through the western Carolinas and NE Georgia through Friday. The only real
moisture to be found in profiles around the area will be in the
surface to 850 mb layer...and southeast flow in this layer should permit
the low level moisture to pool mainly along the eastern slopes of the
southern Appalachians tonight. The potential for any light quantitative precipitation forecast will be
greatest in the upslope zones during the late evening and early
morning hours...but with nothing more than isolated pop for light rain
along a narrow sliver near the Escarpment. Mins should run several
categories warmer Friday morning than Thursday morning given the expected
clouds and recovering boundary layer temperatures.
A 500 mb ridge axis will remain stretched from the Gulf Coast to the
forecast area through the near term...but with minor height falls
and a shortwave arriving from the west late Friday. This feature
will have little to no moisture to work with so expect little more
than lingering scattered cirrus. At lower levels...veering of the
850 mb flow will reduce the upslope moisture through the day on
Friday. The resulting decent insolation should permit maxes to reach
the middle to upper 60s most locations east of the mountains...with
plenty of 60s in the mountain valleys.
Short term /Friday night through Sunday/...
as of 220 PM Thursday...the axis of a 500 mb ridge is forecast to slide
east of the western Carolinas by Saturday afternoon. The GFS and
European model (ecmwf) indicates that a slow moving cold front will sink southward
across the central Appalachians and Ohio River valley. Middle and high
clouds will likely increase across the region through the day.
However...mild thicknesses and weak downslope flow should result in
high temperatures 5 to 10 degrees above normal. I will forecast middle
60s within the mountain valleys to near 70 east.
On Sunday...the middle level pattern will feature a shallow ridge
across the Gulf of Mexico...a deep closed low across The
Rockies...and a l/west trough across New England. The County Warning Area will remain
under zonal flow...slight ridging over TN/KY. The surface front will
continue to move slow south through the day...bringing thick cloud
cover across the region. However...based on weak synoptic scale
forcing and weak low level flow...I will decrease probability of precipitation to schcs across
the County Warning Area. In fact...the 12z NAM keeps the region completely dry on
Sunday. Temperatures under the cloud cover will range within a
degree or two of normal.
Long term /Sunday night through Thursday/...
as of 230 PM Thursday...the medium range begins Sunday evening with
a backdoor front clearing the area to the south and bringing the
onset of hybrid cold air damming atop the County warning forecast area. In the upper
levels...a large closed low will slowly drift east from the
intermountain west to the Great Lakes. This will keep our area under
increasing southwesterly flow aloft...with embedded disturbances
rippling through the flow. In the llvls...an 850 mb front will activate
over The Wedge...increasing warm air advection and upglide atop the County warning forecast area. Probability of precipitation should
ramp up to chance across the Piedmont and likely across the high terrain.
The cad should keep min temperatures well above normal...but maximum temperatures
slightly below normal. Quantitative precipitation forecast looks rather light...as precipitable waters only hover
around 1 to 1... forcing remains weak.
The 12z GFS and European model (ecmwf) are in better agreement on pushing a cold
front through the area on Wednesday...as the upper low gets absorbed
into the northern stream westerlies and crosses the Great Lakes. A
brief period of northwest flow showers may be possible behind the front
along the Tennessee border into Wednesday evening...but otherwise...things
should dry out for Thursday. Temperatures will be tricky on Wednesday...as
cad breaks and skies clear out before the stronger cold air advection ramps
up...which may result in warmer temperatures east of the mountains than the
current consensus. On Thursday...temperatures will be back below normal as
Canadian high pressure builds in.
Aviation /20z Thursday through Tuesday/...
at kclt and elsewhere...surface high pressure will remain draped
over the area through the period...with persistent east to southeast flow in
the surface to 850 mb layer bringing some Atlantic moisture into the
picture. The MOS/models have been way too aggressive with low clouds
in most areas recently...but boundary layer relative humidity recovery will permit
a better chance of restrictions early Friday morning. Will feature a
window of MVFR ceilings and visibility most areas despite the more dire MOS
forecasts of IFR to LIFR conditions. Expect NE surface winds less than
10 knots through the period...except light southeast at kavl.
Outlook...generally dry high pressure will persist into the early
weekend...but with moisture and associated restrictions possibly
returning with a back door cold front Sunday into Monday. The
moisture and rain chances will increase into Tuesday.
19-01z 01-07z 07-13z 13-18z
kclt high 100% high 100% high 83% high 86%
kgsp high 100% high 82% high 82% high 88%
kavl medium 73% medium 77% high 85% high 81%
khky high 83% high 83% high 89% high 88%
kgmu high 100% high 86% medium 76% high 85%
kand high 100% high 84% medium 79% medium 78%
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)