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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC
1040 PM EDT Monday Mar 30 2015

Synopsis...
high pressure will rebuild over the region today and linger through
most of Tuesday. Another weak cold front will move over the area
tomorrow night with high pressure quickly building again for
Wednesday and Thursday. Yet another cold front is expected to
approach the Carolinas by late Friday.

&&

Near term /through Tuesday/...
as of 1030 PM...decent mixing persists across much of the Piedmont
and foothills...as well as the high elevations and French Broad
valley in western NC. Meanwhile...decoupling is occurring across the
southwest valleys of NC...with the Franklin AWOS already sitting at
45. Strong radiational cooling conditions will persist through the
overnight...as winds continue to diminish and skies remain cloud-
free. I suspect that sheltered/typically cold spots southwest of the
French Broad valley will likely see a light freeze tonight...but
confidence is too low in widespread-freezing temperatures to warrant an
upgrade to a warning...so the frost advisory will be allowed to
stand. Meanwhile...the middle and lower French Broad valleys should
see a light up-valley wind persist until about daybreak...likely
precluding any freeze concerns. Outside the mountains...temperatures were bumped
up a smidge in the upper Savannah River valley. Those areas should
too eventually decouple...but temperatures there are still in the lower 60s
at this hour.

As of 735 PM...other than some patchy cirrus pushing southeast of
our area at this time...clear skies cover much of the southeast early this
evening. The main concern for the very near term is overnight
temperatures...especially over the mountains...as a strong radiational cooling event is
beginning to take shape...especially within the sheltered valleys. While it
appears a light up-valley flow will predominate across the middle and
lower French Broad valley...likely preventing temperatures from cratering
too much overnight...this looks like a case in which strong
radiational cooling and cool air drainage will do its business
across the little tenn valley and surrounding drainages. Min temperatures
were therefore lowered to right around freezing. It doesn/T appear
that freezing temperatures will be widespread enough to warrant a freeze
warning...but the frost advisory will be expanded to include the
little tenn...as well as the Pigeon River drainages.

As of 245 PM...a cold front will completely sweep east across the
region by early this evening. In the wake of the front...a few
diurnal cumulus will linger across the County Warning Area...primarily along the Tennessee
border. The cumulus will dissipate quickly as the sun sets...leaving the
region under mostly clear conditions overnight. At the surface...near
term models indicate that the center of high pressure will build
across the southern appalachian region...resulting in calm to light
and variable conditions. Forecast soundings indicate that a bl
inversion will develop across the region tonight. As the inversion
lowers tonight...very dry air will become exposed to the mountain
ridges...lowering late night high elevation dewpoints to around
zero. Mountain Valley values are forecast to range around 30 degrees. Low
temperatures should range from the middle 30s to the upper 30s across
the I-40 corridor of the foothills and Piedmont...areas from the
upper Savannah River valley to the clt metropolitan area range around 40.
The combination of close dewpoint depressions...calm winds...and middle
30s will likely yield widespread frost within the French Broad
valley tonight. We will highlight with a frost advisory for the
French Broad valley. Patchy frost is possible across the I-40
corridor.

On Tuesday...high pressure will shift over the western Atlantic as a
cold front approaches from the west. Return flow should support high
temperatures reaching into the u60s across the mountain valleys and low
70s east. Dewpoints should remain mainly steady in the middle to upper
30s. Afternoon relative humidity values are forecast to range in the middle to upper
20s with gust winds. After coordination with ncfs we will highlight
the NC zones from the French Broad valley east across the Piedmont
with a Fire Danger Statement.

&&

Short term /Tuesday night through Thursday/...
of 230 PM EDT Monday...an upper trough and associated surface low
will move off the East Coast Tuesday night. A trailing cold front from
the East Coast low will move across the area Tuesday night. Some
convection associated with the front will make a run at the NC
mountains Tuesday evening. The 12z NAM is most aggressive in bringing
showers/storms into the mountains. The GFS is much more muted with
convective available potential energy quickly dwindling Tuesday evening and the ec essentially has a dry
frontal passage. Hence...will not go overboard with probability of precipitation...and will
keep things dry east of the mountains with deep layer west/northwest flow
through the column. Will maintain the low end chance to slight
chance probability of precipitation over the NC mountains Tuesday evening. Behind the
front...high pressure is forecast to settle over the region from the
north producing clearing by Wednesday morning and temperatures a notch above
climatology on Wednesday. Quiet conditions are expected to continue through Wednesday
night as the high moves off the East Coast.

As southerly flow kicks in on Thursday...moisture will increase
across the area. A west to east moving short wave will act with the
increased moisture to produce scattered showers and perhaps a few
thunderstorms Thursday afternoon. Temperatures on Thursday will be near climatology
with increased cloud cover and scattered precipitation.

&&

Long term /Thursday night through Monday/...
at 230 PM EDT Monday...on Friday evening nearly zonal flow will be
over the southern tier of states as weak upper ridging will be off
the East Coast...and low amplitude troughing will extend from the
upper Midwest to the SW USA. The upper trough moves to the Great
Lakes and central MS River Valley by Saturday...but upper flow
remains almost zonal over the southeast. The trough amplifies
slightly as it crosses the southern Appalachians...then deamplifies
as it moves off the East Coast on Sunday. By late Sunday the models
go out of phase off each coast...resulting in differences in flow
over the southeast.

At the surface...a cold front will approach from the northwest on Thursday
night and Friday...preceded by robust Gulf inflow into the southern
Appalachians. The front crosses our area early Saturday...followed
by dry high pressure on Sunday. By Monday the surface high moves off
the East Coast...but high pressure remains lodged along the eastern
Seaboard...while Gulf inflow spreads moisture up the MS...Tennessee and Ohio
River valleys. This moisture and associated rainfall spreads east
across our area during the day. Temperatures will run above normal
ahead of the first front...slightly below normal behind it...then
return to above normal ahead of the second front.

&&

Aviation /03z Tuesday through Saturday/...
at kclt and elsewhere...VFR through the period. In fact...the next
24 hours will be largely free of clouds of any type...while dry air
will preclude any visby issues. Thus...mainly a wind forecast for
this set. Winds are expected to continue or turn toward the northwest this
evening and weaken to around 5 kts...likely going light/variable or calm
by daybreak. S/SW winds will then develop after sunrise...reaching
the 10-15 knots range at most terminals during the afternoon. Some
gusts to around 20 kts will also be possible during that time.

Outlook...VFR through Wednesday. An approaching warm front and
resultant moisture return will bring better chances for
precipitation/restrictions across the area later in the week...perhaps
starting Thursday morning. A cold front will affect the area Friday
into early Saturday...bringing another round of rain/possible
thunderstorms and restrictions.

Confidence table...

02-08z 08-14z 14-20z 20-00z
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% 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 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)

Www.Weather.Gov/gsp/aviation_tables

&&

Gsp watches/warnings/advisories...
Georgia...none.
NC...frost advisory until 9 am EDT Tuesday for ncz048-051>053-058-
059-062-065.
Fire Danger Statement Tuesday afternoon for ncz033-035>037-
048>050-053-056-057-065-068>072-082-501>510.
SC...none.

&&

$$
Synopsis...jpt
near term...jdl/Ned
short term...lg
long term...jat
aviation...jdl

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