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fxus62 kgsp 171430 

Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1030 am EDT Sat Mar 17 2018

increasing moisture will return from the west early this morning, as
a low pressure system moves east out of the plains. This low will
move southeast across the southern Appalachians through tonight,
keeping conditions unsettled. High pressure will briefly return on
Sunday before stronger low pressure arrives from the west early next


Near term /through tonight/...
as of 1025 am: first batch of weak convection was moving east and
out of the fcst area as of 14z. Meanwhile, upstream, next batch of
weak convection was on a downhill trend, with the best-looking area
making move of a southeastward push toward Metro Atlanta. The latest
guidance from the rap really harps on a dry day across most of the
region for the better part of the day, and with convective debris
and without much forcing to work with, I am forced to agree. So,
I have followed the trend and pulled back on the precip chances
through the afternoon. That being said, the latest day 1 convective
outlook has upped the ante across the nrn zones for later in the
day, with an upgrade to a slight risk along our nrn border. So,
we will stick with the scenario of afternoon destabilization,
especially over ern Kentucky/SW Virginia/NE TN, and will keep an eye out for
signs of thunderstorm development. The Storm Prediction Center discussion hits all
the important points and is Worth reading, so I will direct you
there. As for high temps, too early to give up just yet, and we will
assume that our clouds will thin out enough early enough to make it.

Otherwise, a closed low is expected to open up over Illinois
this afternoon and then dive southeast over the Ohio Valley and
across the southern Appalachians tonight. The best combination
of forcing, instability, and wind shear will likely be across the
I-40 corridor late this evening. 850 to 500 lapse rates building to
7 to 7.5 degree c/km with the approaching shortwave will provide
for plenty of elevated instability, and the strong DPVA with the
passing wave should force northern tier parcels to the level of free convection despite
the persistent low-level inhibition. With 35+ kt of westerly 850
mb flow, and sfc to 6 km bulk shear values likely rising above
65 kt, a marginal risk of severe thunderstorms for the northern
tier seems appropriate for this evening. This will be highlighted
in the severe weather potential statement. Precipitation should end abruptly most areas after
midnight behind the passing shortwave, but lingering northwest upslope
moisture could continue scattered showers near the Tennessee border in
the western mountains.


Short term /Sunday through Monday night/...
as of 200 am EDT saturday: the short term forecast period begins
Sunday morning as the gradually weakening system which is expected
to bring unsettled weather to the area today (saturday), will be in
the process of pushing offshore with Canadian high pressure quickly
infiltrating in behind it. With dry conditions in place and breaks
in the clouds, expect temperatures on Sunday to climb into the upper
60s/lower 70s across the upstate, down into the lower 60s across the
northwest Piedmont, and cooler across the mountains. While the warmer/drier
pattern in store for the end of the weekend will be pleasant, it
will also be short lived as sfc high pressure moves offshore and
increasing cloud cover begins to expand across the forecast area into Sunday
night with the return of SW flow ahead of the next approaching

Insitu wedge from sfc high offshore will allow for cooler high
temperatures (up to 10 degrees cooler in some locations from sunday)
to spread across the forecast area on Monday, while back to the west, attention
remains focused on an approaching potent storm system. Latest
guidance continues to be in fairly good agreement with the placement
of a sfc low across the Central Plains Monday morning as it's
eastward extending sfc boundary remains south of the forecast area. With
dewpoints in the 60s and much better forcing/instability/shear south
of the fa, expect Alabama to (southern) Georgia is where the potential for
severe weather will remain as already noted by a slight risk in the
Storm Prediction Center convective outlook for Monday. As for US across northeast Georgia and
the western Carolinas, it'll be the progged isentropic lift and
upslope flow that supports our increasing rainfall chances during
the day and well through the overnight hours into early Tuesday
morning. With weak instability/shear noted by guidance, would not
entirely rule out a few embedded thunderstorms across the forecast area on
Monday as the warm front slowly propagates northward. Overnight lows
Sunday night and Monday night will almost identical, with upper
40s/around 50 degrees across the upstate and northwest Piedmont, into the
low to mid 40s across the northern foothills and back across the NC


Long term /Tuesday through Friday/...
as of 245 am EDT saturday: the unsettled weather pattern from the
end of short term period will carry over into the first half of the
medium range period which begins Tuesday morning. Expect rain to be
falling across the forecast area in the morning hours as guidance depicts the
sfc low from the Central Plains will have moved through the
overnight hours east-northeast across the southern portions of the Ohio Valley
into the Carolinas, allowing for it's associated cold front to push
through and a brief disruption in the influx of moisture from the
gom. As this low moves offshore, guidance highlights a secondary
cold front setting up just to our west. Do expect showers to
continue during the day with a gradual decrease in pops across the
upstate and portions of the northwest Piedmont into the evening hours as
the secondary front pushes through. With colder temperatures along
The Spine of the Appalachians, anticipate a rain/snow mix along the
Tennessee border beginning Tuesday night.

Guidance continues to overall key in on a developing upper longwave
trough across the southeast with a handful of embedded shortwaves
throughout the day on Wednesday, though the specific
temporal/spatial details are not the same across the board with the
models. But nonetheless, increasing available moisture and
supportive dynamics will likely lead to another round of showers
across the forecast area on Wednesday (rain/snow along the Tennessee border). With a
Miller-b setup taking shape, another sfc low is progged to develop
across the Carolinas and move offshore into Wednesday night, slowly
moving northeastward up the eastern Seaboard. With pops decreasing
from south to north across the forecast area Wednesday afternoon, most of the
guidance holds onto precip (rain changing over to all snow) into
Wednesday night along the Tennessee border, possibly even longer into
Thursday morning - winter is not over yet! Some models suggest that
snow showers Wednesday night into Thursday morning could spill over
into the northern foothills. Confidence on this as well as snow
amounts are low given how far away we are from this event, but will
be something to keep a close eye on.

After quite the busy weather week, Canadian high pressure will build
in on Thursday allowing for dry and quiet conditions to persist for
the remainder of the work week, ahead of the next approaching system
from the west just beyond the forecast period. Temperatures
throughout the forecast period will remain below normal.


Aviation /15z Saturday through Wednesday/...
at kclt and elsewhere: winds will remain fairly light across the
region this morning with a stalled surface frontal boundary draped
west to east through the area. Showers developing to the west and
over the southern tier should clear out or dissipate through late
morning. After the showers push through, a region of MVFR to lower
VFR cigs will likely develop, with the best chance of prevailing
MVFR at kand. Expect winds to toggle south to southwest east of the
mountains and become gusty with the arrival of the showers from the
west. Kavl will be the main exception, with light winds becoming

A digging shortwave will cross western North Carolina this evening
and provide the best triggering for stronger showers/thunderstorms.
Will feature prob30 for convection mainly from khky to kclt after

Outlook: drier conditions return briefly on Sunday before moisture
returns again from the west with a complex low pressure system on
Monday and Tuesday. Colder air may wrap south into the region behind
the system on Wednesday and some mixed precipitation cannot be ruled
out. Restrictions will be likely in the Mon-Wed period.

Confidence table...

14-20z 20-02z 02-08z 08-12z
kclt high 100% high 100% high 96% high 100%
kgsp Med 72% high 100% high 100% high 100%
kavl high 100% high 100% high 100% high 85%
khky high 100% high 100% high 100% high 100%
kgmu Med 70% high 100% high 97% high 100%
kand high 93% high 87% high 80% 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:



Gsp watches/warnings/advisories...



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