Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
709 am EDT Monday Mar 17 2014
waves of low pressure will move northeast from Florida to along the
Carolina coast through Tuesday. Cold high pressure near New York
state will bring a cool northeast breeze east of the mountains which
will result in wintry precipitation for some of our area Monday
night and early Tuesday. Expect a weak cold front to cross our
region late Wednesday. High pressure will be in control Thursday
and Friday. Expect another cold front to cross on Saturday.
Near term /through tonight/...
as of 645 am EDT...observation and laps analysis have freezing temperatures from
the northern Blue Ridge to Taylorsville to Mocksville...with spotty
freezing temperatures as far south as Salisbury to Old Fort. Updated the
forecast to add slightly more icing along the eastern slopes of the Blue
Ridge this morning as better showers are working NE along the higher
terrain into the subfreezing temperatures from Jonas Ridge to near Blowing
Rock. An Special Weather Statement has been issued for Rowan County...but the advisory
might need to be expanded if better light rain gets into the
Salisbury area this morning. Otherwise...the forecast is on track
with a trough axis moving through the lower MS River Valley...a
closed circulation developing farther SW over the Texas Gulf
Coast...and deeper moisture streaming toward the forecast area. At
the surface...the cad boundary wraps neatly around the southern periphery of
the forecast area...with freezing temperatures now solidly in place north
of Interstate 40 and along the northern Blue Ridge. Some weak convective
elements continue to ride up the mountains in SW flow aloft...sending
better precipitation rates into the northern tier where icing potential will
continue through the morning hours.
The northern portion of the upstream trough will move eastward to the base of
the southern Appalachians through the day...while the more amplified southern
wave sweeps east along the Gulf Coast. Surface low pressure over western Georgia
early this morning will slide east along The Wedge front today and move
off the Carolina coast. A pocket of better middle level lapse rates
will lift northward across the mountains and the cad layer today...but any
elevated convection should remain fairly shallow. Between lingering
upper jet divergence...weak isentropic lift...and scattered showers
in the better moisture feed...will mainly likely probability of precipitation at times...and
embedded drizzle between the showers. This will keep temperatures
locked in in the 30s and lower 40s this afternoon for most of the
area...except for some lower 50s in the far SW mountains
The best dynamics with the deamplifying southern wave will likely pass
mainly southeast of the region tonight. Expect middle levels of the atmosphere
to dry out from the west tonight behind the wave...with isentropic
lift tapering off. Also...a NE Gulf of Mexico surface low associated
with the southern wave will transition to a deepening offshore waters low
overnight...sending cooler air spilling southward into the Carolinas.
However...the NAM once again appears overdone with the degree of
cooling so will lean toward a GFS/European model (ecmwf) blend on surface temperatures. In
addition...minimal precipitation and limited ice nucleation in
soundings will severely limit the potential for ice accretion in the
coldest northern tier areas tonight. It thus appears that freezing
drizzle across parts of western NC tonight will be the primary threat.
Will hold off on any additional advisories at this point given the
uncertainty over the southward pentration of subfreezing temperatures and the quantitative precipitation forecast.
Short term /Tuesday through Wednesday night/...
as of 300 am Monday...the southern stream shortwave trough will finally get
ejected out into the Carolina coastal waters by early
Tuesday...taking the deeper moisture and lift east of the area. The
NAM and GFS in good agreement on very shallow moist layer lingering
on back side of the system...as cold air damming/wedge holds on
ahead of the deeper northern stream trough entering the upper Midwest. All
the op models seem to agree on little if any additional quantitative precipitation forecast response
after 12z Tuesday. So I have probability of precipitation tapering off with must a mention
of some slight chance -ra and dz for Tuesday morning. The low level flow will
back out of the southeast...with the approach of the next system. The forecast
soundings show a persistent inversion with moist upslope flow
developing. The moist layer deepens to a few thousand feet by
Tuesday evening. So I have probability of precipitation ramp up to slight chance to low-end
chance...favoring the Blue Ridge/se-facing slopes. Quantitative precipitation forecast should be spotty
and very light. With plenty of stratus likely to remain through the
day...temperatures will be held in the 40s along and east of the Blue
Ridge...and into the 50s where clouds can clear out in the high
terrain and SW NC mountain valleys. Again the NAM is a cold
outlier...bringing subfreezing temperatures to northern Blue Ridge...as the southeasterly
upslope increases. Since the NAM has been way too cold so far with
this current cad event...I did not go that cold with temperatures. So not
expecting any freezing rain/drizzle Tuesday night.
Wednesday and Wednesday night...the northern stream trough will quickly
track through the Great Lakes...with a surface low underneath. The low will
drag a cold front across the Ohio Valley. The front looks quite dry in
pretty much all the guidance. In fact...the model quantitative precipitation forecast fields show
more response with the upslope/upglide ahead of the front. I will
keep a slight chance in for Wednesday...but even that may be overdone.
The front will be strong enough to scour out the cad/stratus...and
allow temperatures to warm back into the upper 50s to middle 60s (near normal).
Skies continue to clear Wednesday night...and low level northwesterly cold air advection flow
will bring temperatures down into the 30s mountains and upper 30s to lower 40s
Piedmont by Thursday morning.
Long term /Thursday through Sunday/...
as of 200 am EDT Monday...the medium range period starts at 12z
Thursday with high pressure building in from the west and transiting
to off the Carolina coast late Friday. The Canadian model is the one
in disagreement as it brings a shortwave west to east across our
region late Thursday with a third of an inch or less quantitative precipitation forecast. This is
not on the GFS and European model (ecmwf) and prefer to keep it out of the current
forecast. The next cold front crosses from the northwest on Saturday
bringing a quarter of an inch of rain or less then moves it southeast with
a 1030 high pressure centered near northern Illinois at 12z Sunday. All
precipitation with the frontal passage will be liquid form as temperatures should
be way too warm for anything else. This high is forecast to move
toward the middle Atlantic by 12z Monday continuing dry weather for
much of the eastern states. Both the GFS and European model (ecmwf) show a broad
upper trough over the eastern two thirds of the nation next Sunday
with upper ridging over California. Our temperatures will be a little above
normal Thursday through Sat and then drop behind the front to a little
Aviation /11z Monday through Friday/...
at kclt...persistent NE flow in the existing cad layer will continue
to bring cooler temperatures in from the NE...but favor rap/GFS
profiles over NAM in not producing any freezing rain or fzdz this morning.
Expect mainly light rain and drizzle today along with IFR to LIFR
ceilings. Temperatures will cool further tonight...and fzdz could make a run at
the terminal in the 08z to 12z time frame. A prob30 group for fzdz
will be added to the taf.
At khky...NE flow and LIFR to IFR ceilings will persist at khky along
with mainly rain and drizzle today. A narrow window of light freezing rain is
in place through about 15z. Better cooling of temperatures on the NE flow
tonight will increase fzdz chances after 04z.
Elsewhere...expect mainly LIFR to IFR ceilings through the period with
rain or drizzle at times. NE flow will continue at the upstate taf
sites in the cold air damming layer...while flow will be more srly
initially at kavl...becoming northwest later in the period. Will keep any
freezing rain or fzdz mention for tonight out of the forecast at
present...but it could get close to a kavl to kgsp line toward the
end of period if any precipitation lingers.
Outlook...cold air damming and associated low restrictions will
linger through Tuesday before slowly scouring ahead of the next
approaching front Tuesday night into Wednesday. Drying high pressure will return
Thursday into Friday.
11-17z 17-23z 23-05z 05-11z
kclt medium 72% medium 73% high 82% high 90%
kgsp medium 64% high 80% medium 77% medium 71%
kavl medium 74% medium 76% high 82% high 81%
khky medium 65% medium 73% high 82% high 82%
kgmu medium 69% high 80% medium 69% medium 71%
kand medium 71% high 80% medium 74% medium 75%
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)
NC...Winter Weather Advisory until noon EDT today for ncz033-