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fxus62 kgsp 241849 

Area forecast discussion
National Weather Service Greenville-Spartanburg SC
249 PM EDT Fri Mar 24 2017

high pressure will continue to move off the East Coast tonight. A
low pressure system emerging from the Great Plains over the weekend
will bring moisture to the southeast Saturday and Sunday. Unsettled
weather will continue through Tuesday as another low pressure system
moves from the plains to the Ohio Valley, allowing Gulf of Mexico
moisture and some storms to persist over the southeastern states.


Near term /through Saturday/...
as of 230 PM EDT...a mixture of low, mid, and high clouds continue
to stream across the County warning forecast area from the S and SW this afternoon. With
daytime heating, overall cloud cover has diminished some over the
past few hours with the best coverage remaining over the southern
and southwestern mts. Things should remain dry thru the overnight,
with no substantial increase in pops until late tomorrow.

Otherwise, Stout upper lvl ridging remains in place well into
Saturday allowing temps to climb higher. By the end of the period
00z Sunday, a large upper low will be approaching the region from
the west, but is not expected to have much impact on the fcst area
over the near-term period. At the sfc, high pressure will continue
to slide further offshore tonight and tomorrow while a large low
moves east across the Southern Plains and then begins to lift NE and
towards the Great Lakes late Saturday/early Sunday. No significant
pattern changes are anticipated over the period with southerly low-lvl
flow persisting over the region and temps expected to remain above
normal. The region of deep moisture associated with the approaching
sfc low is looking like it will take a bit longer to reach the fcst
area. Most of the model guidance currently suggests that it won't
reach our western zones until just after 00z Sunday. This should
keep precip chances at Bay until late Saturday.


Short term /Saturday night through Monday/...
as of 230 PM EDT friday: the Gulf of Mexico will open up and say
aaahhh this weekend...with southerly flow transporting moisture over
the western Carolinas and northeast Georgia right on through the
period and into early next week. That should make for a relatively
unsettled weather regime. Upper forcing, in the form of a short
wave acquiring a negative tilt, will be on our doorstep Saturday
evening. This wave should translate northeast across the region and
act upon the plume of deep moisture to bring numerous to widespread
shower coverage... eventually. The trend in the guidance has been
to slow down the eastward progress, thus the I-77 corridor stays
drier a bit longer into Sunday. Precip chances ramp up from the
Blue Ridge Escarpment outward through the night and into Sunday
morning, with the best probability near the Blue Ridge owing to
the contribution of mechanical lift with the southerly flow at low
levels. After the first wave passes, chances may go down during
Sunday afternoon, but the timing is questionable. The GFS is a
bit slower and would suggest keeping a higher chance over the east
for longer. The main focus or problem for the short range is the
severe weather chances on Sunday. The model guidance provides an
environment with surface-based cape on the order of 500-1000 j/kg,
shear on the order of 30 kt, and sunrise helicity in the 150-200 m2/s2
range. At face value, this would make one go hmmm...but looking
at fcst soundings, the lapse rate is nothing to get excited about
and is thought right now to be a limiting factor. A trigger is also
in doubt in the wake of the main upper wave. Still, the hodographs
are impressive, so it would be most wise to not turn one's back on
the possibility. The day 3 convective outlook features a marginal
risk, and I agree that it does in fact appear marginal, so we will
not mention this in the severe weather potential statement just yet. From late Sunday Onward,
we maintain the southerly moist flow, so a shower could develop
at just about any time. Will keep a precip chance across most of
the region, favoring the mountains and foothills, through Sunday
night and Monday. Temps will remain above normal through the period.


Long term /Monday night through Friday/...
as of 220 PM friday: not much of a pattern change is anticipated
during the medium range, as a fairly amplified/split flow regime,
with a very active northern stream and somewhat less active southern
stream should persist through the period. The result will be a
continued tendency for upper lows to form across the south central
part of the conus, only to get kicked out a day or two later by the
next strong wave bombarding the West Coast.

The period will begin Monday night with a dampening, but
nevertheless negatively tilted short wave trough approaching our
forecast area from the Tennessee Valley. Although a decent amount of
buoyancy is expected to develop ahead of this feature Monday
afternoon, it appears that the diurnal cooling cycle may be
underway by the time the deeper forcing arrives Monday evening.
Based upon the latest guidance, shear parameters are not expected to
be especially impressive. Thus while the severe weather potential is
non-zero, it leaves much to be desired.

Cold front sweeps across the area Tue night and early Wed, resulting
in gradual drying. Otherwise, the Mon night through Thursday period
will be marked by well above normal temperatures.

By the end of the period, the global models depict surface high
pressure spilling east of the Appalachians, in the wake of a
substantial short wave trough pushing away from the New England
coast. This signals the potential for some cooler and drier air to
spill into at least part of the forecast area from the northeast.
Meanwhile, the global models are in good agreement that the next
Southern Plains upper low will be kicked out across the Ohio Valley
by the end of the period, bringing another potential round of
showers and thunderstorms to our area. However, based upon the
expected surface pattern, there will be the potential for cold air
damming to impact part of the forecast area during this time.
Temperatures will therefore be forecast a little closer to (although
still above) climo by the end of the period.


Aviation /19z Friday through Wednesday/...
at kclt and elsewhere: VFR conditions expected thru tonight and
the overnight with cigs lowering after about 09z. Both kclt and
kavl carry MVFR cigs from 10z Onward with kavl improving to VFR
by about 15z.Cigs at kgsp, gmu, and and lower to IFR by roughly
11z with a 2-hr tempo for LIFR cigs at those sites. They will
likely improve to VFR again by the end of the taf period. Otherwise,
winds will weaken tonight and remain predominately southerly with some
sites seeing light and vrb winds during the overnight and early
morning. Kavl and khky have been getting some decent gusts in the
18 to 22kt range over the past few hours, but these should subside
by the early evening.

Outlook: increased precip chances return late Saturday thru Sunday
which will likely create flight restrictions across the area. An
unsettled and moist pattern will persist next week and maintain the
chances for low ceilings and visibility.

Confidence table...

18-24z 00-06z 06-12z 12-18z
kclt high 100% high 100% high 94% high 84%
kgsp high 100% high 100% high 91% high 93%
kavl high 100% high 100% high 84% high 92%
khky high 100% high 100% high 81% high 89%
kgmu high 100% high 100% high 90% high 89%
kand high 100% high 100% Med 79% high 85%

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:



Gsp watches/warnings/advisories...



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