Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
336 PM EST Wednesday Mar 4 2015
a slow moving cold front will cross the region from the northwest
through Thursday. Cool and dry high pressure returns for
Friday...then a significant warm up over the weekend. Expect a
couple of low pressures to come out of the Gulf next week.
Near term /through Thursday/...
as of 335 PM...a quick update to account for clearing skies and
warmer temperatures. Have also slowed precipitation onset per regional radar.
As of 200 PM EST Wednesday...stratus associated with remnant cool
pool is finally lifting and mixing out across the Piedmont. Maximum
temperatures should still be able to reach the upper 60s to around 70 even
where clouds persisted. Regional radars indicate the remainder of
the afternoon should remain dry as precipitation associated with the cold
front is still back over east central Tennessee.
For the overnight...the cold front will begin making progress
southeastward as a short wave moves southeast into the Great Lakes by early
Thursday and then to New England by Thursday evening. The front is a classic
anafront in that the associated precipitation is located mostly behind the
front. Hence...will ramp up probability of precipitation with the expected frontal passage
and then hold on to them for a rather long duration. The front will
push through most of western NC by 12z Thursday and then through NE Georgia
and upstate SC during the morning. With most of the precipitation falling
behind the front in the cold air...some precipitation type problems emerge.
The shallow cold airmass will lower surface temperatures to freezing or
below over most of the mountains and perhaps the northern foothills.
Hence...a period of freezing rain is likely...gradually
transitioning to a period of sleet...and then even to snow in some
areas where the column has a chance to cool through the warm nose.
Used a top down approach for weather grids which brings freezing rain
into a large portion of the mountains...with most of the sleet/snow
occurring over the Tennessee border counties. Will issue a Winter Weather
Advisory on Thursday for all of the Tennessee border counties extending
into the central mountains and into the northern NC foothills.
Elsewhere...just a cold rain is anticipated.
Temperatures will be mild overnight...especially in NE Georgia...upstate SC and
the southern NC Piedmont where the cold front will not arrive. On
the flip side...min temperatures will fall to near freezing in the Tennessee
border counties by 12z Thursday.
On Thursday...a non-diurnal temperature trace will occur with temperatures
falling. The Piedmont areas will see maximum temperatures occur in the morning
(upper 50s to lower 60s) and then fall into the upper 30s to lower
40s by the end of the day.
Short term /Thursday night through Saturday/...
as of 130 PM EST Wednesday...the short term forecast period initializes
Thursday evening amongst an upper trough digging across the middle
Mississippi River valley leading to falling heights over the
southern/central Apps. At the surface...slow moving anafront will
be spreading through the region with some wintry precipitation of concern
early on in the period. Probability of precipitation will initialize at slight chance
levels across much of the SC/NC/GA high terrain with low end chance
probability of precipitation favored further east along and south of Interstate 85 in closer
proximity to the primary moisture axis. At that time...cold air advection regime
in full effect across the central/northern NC mountains will lead to a
wintry mix of precipitation...mainly along and north of the
Interstate 40 corridor. Critical thickness values along with latest
forecast soudnings indicate mostly sleet/snow favored...with perhaps
some very brief periods of freezing rain on the southern most fringe
of the advecting cold airmass. Either way...not expecting this to
amount to much into the evening as probability of precipitation fall off sharply with a dry
forecast prevailing regionwide by midnight.
Beyond that...high pressure will slide across the Ohio Valley before
setting up a brief cad wedge regime for Friday. In
response...cloudy skies will prevail early on before scattered out through
the afternoon hours. This combined with light NE flow at the
surface will likely yield high temperatures on Friday nearly 1-2 cats below
normal. Conditions will recover somewhat on Saturday as mostly
sunny skies dominate amongst gradually southerly veering flow. Weak
warm air advection regime will allow for moderating temperatures with highs surging to
just below normal on Saturday.
Long term /Saturday night through Wednesday/...
as of 210 PM EST Wednesday...the medium range forecast picks up at 00z
on Sunday with very broad upper troffing over the eastern Continental U.S. And
multiple embedded upper shortwaves passing over the Great Lakes
region. Over the next couple of days...the pattern gradually
deamplifies and weak upper ridging begins to build over the southeast
region by next Wednesday. The latest 12z GFS is a bit more bullish
with the upper ridge compared to the European model (ecmwf)...yet both solutions
trend in the same direction.
At the surface...dry high pressure will still be in control of the
pattern at the start of the period. As we move into Monday
afternoon...the GFS tries to briefly restrengthen the high as it
slides eastward and puts the Carolinas under a weak cad pattern. The
European model (ecmwf) and the Canadian solutions do not strengthen the high as much
and allow a broad area of deep layer moisture...that originates to our
SW...to move into the County warning forecast area by early Tuesday. By 12z...the GFS also has
the same plume of deep moisture overspreading the County warning forecast area yet it
maintains a more persistent northeasterly surface wind. Beyond this point...the
GFS keeps the deep moisture over the forecast area through the remainder of
the medium range while the European model (ecmwf) dries things out by early Wednesday and
keeps the deeper moisture just to our south. As for the sensible
forecast...I am confident that sun will be dry and most of Monday will
likely be dry as well with only some slight chance probability of precipitation in the forecast.
The rest of the period is pretty uncertain with slight to solid
chance probability of precipitation for the County warning forecast area. I think the GFS is too optimistic with its
precipitation forecast...especially on Tuesday...and the European model (ecmwf) is too dry on Wednesday.
Temperatures should persist right around climatology with lows a bit warmer
than normal for early/middle March.
Aviation /21z Wednesday through Monday/...
at kclt and SC airfields...cool pool finally mixing out allowing
ceilings to rapidly improve. Expect VFR conditions by 20z with generally
VFR ceilings around 040. Winds will be gusty SW. Airfields will stay in
the warm sector overnight ahead of advancing cold front so VFR ceilings
should predominate. Can't rule out perhaps a tempo MVFR ceiling but did
not put that in already lengthly tafs. The cold front will cross the
airfields in the 12z-15z timeframe with lowering ceilings/visibility to at
least low MVFR and possibly IFR. Winds shift to the northwest by 15z.
At kavl...VFR conditions until about 02z when MVFR ceilings ahead of
approaching cold front should arrive. Expect cold frontal passage in
the 07z-08z timeframe with ceilings/visibility lowering to IFR with rain.
Temperatures drop rapidly and can't rule out some freezing rain toward the
end of the taf period.
Outlook...the cold front will push out of the area Thursday evening
allowing for improving conditions at the airfields to VFR. VFR
conditions are expected to persist then through the weekend.
13-19z 19-01z 01-07z 07-12z
kclt high 95% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl medium 74% high 100% high 100% high 100%
khky medium 77% 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)
NC...Winter Weather Advisory from 6 am to 6 PM EST Thursday for