Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
749 PM EDT Monday Mar 10 2014
dry and warm high pressure will persist through Tuesday. A low
pressure system will approach the region from the west by
Wednesday...with temperatures becoming colder following the
associated cold frontal passage. Drier high pressure will return for
the end of the work week.
Near term /through Tuesday/...
as of 745 PM...forecast is on track. There is some increasing orographic
cirrus across the I-40 corridor. Guidance not picking up on it all
that well...but the general idea is with upper ridge building...the
moisture and jet will lift north of the area this evening. So I bumped
up sky cover to start out the update...but should clear out for the
most part within the next 3-4 hours. No changes made to min temperatures.
As of 225 PM...mostly clear skies and warm temperatures will prevail over
the forecast the rest of this afternoon and into this evening. I bumped
up maximum temperatures a degree or 2 from the last update to better account
for the warmer thickness values. Min temperatures were not changed
appreciably and should remain above climatology overnight even with
the clear skies. Maximum temperatures tomorrow are still on track to be even
warmer with values over the lower elevations in the upper 70s and
highs over the mts in the low 70s. Although this will be
unseasonably warm for middle March...it looks like no record highs will
be reached/broken. Dewpoints were also lowered a few degrees over most
areas which will keep relative humidity values down through the period. Other than
that...the forecast is dry through Tuesday night with some gusty winds
returning late tomorrow morning/afternoon over the central and
northern NC mts.
Short term /Tuesday night through Thursday/...
as of 245 PM Monday...the main concern through the short range will
be the passage of a strong short wave Wednesday night that will
drive a fairly strong cold front across the region late in the day
on Wednesday. The models are consistent in showing moisture
returning from the SW Tuesday night...but not before about 03z...so
we continue to impose a delay to the onset of showers until well
after dark. Out ahead of the approaching system...warm advection and
cloud cover should keep min temperatures mild...as low as the middle 40s over
the mountain peaks...so precipitation type will not be an issue at
onset. Showers will develop out ahead of the front early Wednesday
morning so pop ramps up to likely over the western half of the forecast
area by sunrise...and continues going up from there through midday.
Moisture looks deep and forcing looks adequate to warrant a very
high pop...into the categorical range across most of the forecast area.
The first issue will be the possibility of severe weather ahead of
the cold front. Shear looks decent enough...courtesy of a 40kt west-southwest
low level jet at 850mb in the afternoon. Buoyancy will be the key.
The GFS only manages about 100 j/kg of surface-based cape...although
the NAM as usual has considerably more. If the NAM depiction is
correct...then the see text area in the day 3 outlook from Storm Prediction Center looks
well placed...and we will have to be concerned with high shear Low
Cape type storms. For now...the forecast will limit the thunder to the
chance range...but this will likely go higher. After the front moves
through...cold air moves in rapidly in the late afternoon over the
mountains high temperatures will probably occur by midday over the higher
terrain. The precipitation over the mountains will change over to snow during
the evening hours from high to low elevation. The models are in good
agreement that a northwest flow snow event will continue through most of
Wednesday night...tapering off around daybreak Thursday. Snow amts
appear to be sub-advisory for the time being...but it is possible
this could go higher. It should be quiet on Thursday as upper
ridging and high pressure will move in from the west.
Long term /Thursday night through Monday/...
as of 230 PM EDT Monday...heights will rise Thursday night through Friday as
a departing East Coast trough pulls farther east and broad ridging settles
over the area. Surface high pressure slipping off the southeast coast will allow
low level flow to adjust to southwesterly and permit thicknesses to
start rebounding. A northern stream wave crossing the Great Lakes Friday
night will drag a shallow trough axis across the forecast through
Sat. Models differ on the degree of any moisture...but with no
apparent Gulf fetch...expect mainly some increased clouds before
upper flow returns to zonal late Sat.
Major model differences then develop in the split flow regime across
the Continental U.S. Through Sunday. A preferred ecm/CMC/ensemble blend sends
energy diving southeast from The Rockies Sat night and carving out a southern
tier cutoff low over OK/Texas on Sunday. Deep layer SW flow may then
set up over the southeast U.S. In response...with a warm front steadily
activating eastward toward the forecast area through Sunday. Some degree
of surface reflection forming from the Gulf Coast to the southeast coast then
looks likely through Monday...but with high uncertainty given the
tremendous model spread. Will opt for a slow steady increase in probability of precipitation
Sunday through Monday with all liquid ptypes for light rain at this
Aviation /00z Tuesday through Saturday/...
at kclt and elsewhere...expect VFR conditions through 00z taf
period. Skies should be primarily clear...with varying amounts of
cirrus from time to time. Clouds will increase/thicken more
noticeably Tuesday afternoon...as an upper disturbance approaches from the
west. Winds will favor SW through the period (except northwest at kavl until
Tuesday aftn). Generally light...with less gust potential Tuesday
than what occurred today.
Outlook...rain and associated restrictions are expected to spread
back into the area Tuesday night and into Wednesday...as a
fast-moving low pressure system crosses the area. Dry high pressure
returns for late week.
23-05z 05-11z 11-17z 17-23z
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)