Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
103 am EST sun Nov 29 2015
high pressure will weaken and move east before a frontal boundary
sinks southward into the area late Sunday. A cool and wet air mass
will settle in behind this front for Monday and Tuesday...with
another cold front clearing things out in the middle of the week.
Near term /through today/...
as of 12:43am Sunday...temperatures have been running warm this
evening due to extensive and increasingly dense cloud cover ahead of
frontal system...so warmed overnight lows a couple degrees. Rest of
forecast has only minor adjustments for latest model guidance which
still shows rain moving into the area from the northwest beginning
Sunday afternoon. Total precipitation from Sunday afternoon through
Wednesday morning is expected to be around 1 to 2+ inches...with the
heaviest amounts in the higher terrain areas of western North
0230 UTC update...winds were updated with a blend of the latest NAM
and adjmav. Sky cover was updated from infrared satellite imagery.
Overnight probability of precipitation and quantitative precipitation forecast were adjusted up slightly along the Tennessee border
based for a better fit with neighboring offices. Temperatures were
adjusted slightly based on the latest model data.
2315 UTC update...sky cover has been adjusted per the latest
infrared satellite imagery. Winds were updated with the latest NAM
As of 200 PM EST...water vapor imagery shows a broad plume of
moisture in the westerlies stretching from the Southern Plains to
the Appalachians this afternoon. Most of this moisture is at middle and
high levels in and near our region. At the surface...a front remains
draped along the Ohio Valley this afternoon. This boundary is forecast
to approach from the north as a back door front through Sunday as
1034 mb high pressure gets established over eastern Canada.
Meanwhile...the western portion of the frontal boundary will advance
toward the southern Appalachians as weak low pressure slides up the
frontal zone into central Tennessee. Moisture in the model profiles
steadily thickens and lowers through the period...but with any
deeper moisture through Sunday affecting mainly far northern and
western sections. Light rain chances will improve into the likely
range across most of the mountains toward evening...with
considerably less chance farther east. Minimum temperatures
overnight should be 15 degrees or more above climatology given the
increasing middle clouds. Maxes should be at least a couple of
categories above climatology Sunday...but likely a bit cooler than today
given all the cloudiness.
Short term /tonight through Tuesday/...
as of 230 PM Saturday...the short-term period begins Sunday evening
with a backdoor cold front approaching the forecast area. This is as
a weak area of low pressure rides northeast along a slow-moving cold
front draped from the lower Mississippi Valley to the middle
Tennessee Valley. The Tennessee Valley low is quickly absorbed by
another low crossing Arkansas early Monday morning. Meanwhile...the
backdoor front slides into the area as the cad parent high settles
into the northeast U.S. In fact...high temperatures will likely
occur in the morning for much of western North Carolina and parts of
upstate South Carolina as temperatures stay steady or fall slightly
during the daylight hours on Monday.
There is good agreement between the NAM...GFS..and to a lesser
extent the European model (ecmwf) that a strong lobe of upper divergence associated
with the shortwave and aforementioned surface low will cross over
the forecast area Monday morning. This feature will increase probability of precipitation
from chance to likely overnight and induce a widespread round of
0.50-1.00 inch 12-hour rainfall accumulations ending middle-morning
With the cad ridge axis oriented along the western
Piedmont...easterly to southeasterly upglide flow will develop
Monday afternoon and evening allowing light rainfall to persist
through the day especially in the favored upslope regions of the
Blue Ridge Escarpment and mountains. Another 0.25-0.50 inches of
widespread rainfall is expected through Monday evening with locally
higher amounts in the favored upslope areas.
Meanwhile...a vigorous upper-level closed low ejects out of the
intermountain west into the Central Plains as the attendant occulded
surface low lifts NE towards the western Great Lakes. The
associated cold front will March into the lower Mississippi and
Tennessee valleys Monday evening as the parent cad high slides into
the Atlantic...eroding the cad wedge as the cad front lifts back
north as a warm front Tuesday morning. This will taper upglide-
induced precipitation and as the warm sector returns...probability of precipitation return to
chance outside of the mountains and rainfall should be light for
most areas through the late afternoon hours on Tuesday. With the
retreating cad front...high temperatures are expected to rebound to
near normal on Tuesday.
Overall...total rainfall accumulations Sunday evening through
Tuesday evening...48-hrs...will likely range from 1-2 inches for
most of the area.
Long term /Tuesday night through Saturday/...
as of 215 PM Saturday...models are converging on pushing a cold
front through the area during the day on Wednesday. Given the upper
level vorticity lobe being very positively-tilted and becoming sheared
out across the southeast states...the slightly slower timing makes
sense. So will continue with the high-end chance to likely probability of precipitation Tuesday
night through midday Wednesday...then ramp probability of precipitation down Wednesday afternoon.
Quantitative precipitation forecast looks modest with the front...and no SBCAPE is prognosticated on the
GFS or European model (ecmwf). The front should push through to the east by Wednesday
evening...with deep layer drying commencing atop the County warning forecast area. Cold air advection will
drop 850 mb temperatures to around 0c along the Tennessee border overnight...but
moisture looks shallow and flow rather weak for any northwest flow snow
showers. I have probability of precipitation dropping below slight chance before temperatures allow for
snow in the grids. Highs will be above normal on Wednesday ahead of
the front...the near normal Wednesday night.
For Thursday on to next weekend...the 12z GFS and European model (ecmwf) are trending
toward drier weather...as secondary shortwave trough in the southern stream
doesn/T induce a new wave until the frontal zone is well offshore.
Meanwhile...a large area of high pressure will build in across the Great
Lakes and Ohio Valley. So expect generally clear to mostly clear
skies and slightly below normal temperatures for the rest of the medium
Aviation /06z Sunday through Thursday/...
at kclt and elsewhere...with frontal system approaching from the
west...rain and reduced ceiling and visible will be reaching all taf sites
by Sunday evening. Rain will begin over the mountains of western
North Carolina by Sunday afternoon and spread southeastward across
the area. Cloud cover currently around fl120 will continue to
deepen with ceilings lowering to around fl070 Sunday afternoon and down
to MVFR or lower Sunday evening. As rainfall increases Sunday
night...visibility will also decline to MVFR or lower. Front and
surface pressure trough are poorly defined east of the
mountains...and surface winds will be light...veering from
southwesterly through Sunday afternoon to northerly Sunday night.
Outlook...moisture will increase across the area Sunday night into
Monday as a backdoor cold front settles southward into the region.
Unsettled conditions will continue Tuesday before a drying cold
front crosses the area on Wednesday.
06-12z 12-18z 18-24z 00-06z
kclt high 100% high 98% high 100% low 16%
kgsp high 100% high 100% high 100% low 16%
kavl high 100% high 93% high 81% low 6%
khky high 100% high 100% high 100% low 13%
kgmu high 100% high 100% high 100% low 16%
kand high 94% high 94% high 100% low 13%
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)