Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1013 PM EST Monday Mar 2 2015
cool Canadian high pressure will build into the region through
Tuesday...but moist and milder air should be back on Wednesday out
ahead an approaching cold front. This front is forecast to pass
through the area on Thursday...drying US out by Thursday night.
Near term /through Tuesday/...
evening update...surface wedge developing farther SW across the County warning forecast area is
allowing for better isent lift -shra coverage across the western zones.
Moisture flux will continue from the gom/atl overnight and most
areas will see -ra by 08z or so. The latest soundings indicate a
pronounced warm nose and surface mins will drop off just enough across the
northern Blue Ridge for pockets of -fzra/frdz just before and after
sunrise...so no adjacent were made to the fz.Y.
As of 630 PM...made upward adjacent/S to hour/ly temperature trends which are
still affected by the warm afternoon heating. Will likely bump up
tonight/S min temperatures a little and run new diurnal curve...even
with wedge boundary beginning to push in.
As of 430 PM...updated the grids to account for peak temperatures across
the area running warmer than the forecast grids. Observed winds are a
Cat or so stronger across the NC Piedmont associated with the
backdoor front and have been updated. Still expect isolate/scattered -ra to
reach the SW/rn zones by 00z.
As of 230 PM...the tardy back door cold front continues to wreak
havoc upon the temperature forecast this afternoon...with temperatures once
again running about two categories warmer than forecast as of 19z. Will
significantly bump temperatures up once more...and adjust to the trend that
was taken from a super-blend of guidance starting early this
evening. Not seeing much in the way of precipitation development yet...so
pop trend was also knocked down.
What we have over the next 24 hours is another nuisance-type
situation developing early Tuesday morning...mainly over the northern
foothills and northern mountains of NC. In the bigger picture...a broad upper
ridge will build in from the west tonight...with the upper ridge
axis moving overhead midday on Tuesday. A weak upper wave will top
the ridge and move through on Tuesday morning. The main problem
arises when the upper ridge carries a cold dry surface high past to
the north this evening and then into a position over the middle Atlantic on
Tuesday morning to support a hybrid cold air damming event. Low
level moisture return and isentropic upglide commence on the back
side of the high and over the top of the old back door cold front
late tonight. Precipitation may develop as early as this evening across the
Savannah River basin/upstate/srn NC mountains as the upglide begins. Will
start with a chance pop there and gradually expand/increase the
pop...favoring the Blue Ridge. As in the previous forecast...there will
be a sliver or area of temperatures that drop down to something sub-
freezing mainly near the Blue Ridge north of I-40 after midnight. Precipitation
amts will be less than one tenth of an inch and probability is
likely at best...but the precipitation type would be freezing rain/drizzle.
Think it best to raise a Freezing Rain Advisory for that region for
late tonight/Tuesday morning. Temperatures will rise above freezing by late
morning. The rest of area should remain above freezing. Will hold
onto a likely pop for the balance of Tuesday mainly over the west...
with a chance over the eastern fringe. Temperatures on Tuesday will seem like
a cruel joke...nearly 20 degrees colder than today...with a NE wind.
Short term /Tuesday night through Thursday/...
at 300 PM EST Monday...the short term forecast period initializes
Tuesday evening amongst weak upper ridging aloft over the
east...while a trough slides through the northern plains. At the
surface...a potent cold front will be sliding through the Ohio
Valley while a modest warm sector establishes itself over the
southeast aided by southerly flow around western Atlantic surface
ridge. The forecast initializes with likely probability of precipitation across the mountains due to
southerly upsloping while Lower Middle range chance probability of precipitation are featured
further east. Probability of precipitation will decrease through the overnight across the
eastern tier of the forecast area while solid likely probability of precipitation remain over
the high terrain into Wednesday.
Models continue to indicate some destabilization in the warm sector
across the mountains on Wednesday ahead of the front...thus added mention
of thunder where needed although no deep organized convection is
forecast. Outside of the mountains only showers were mentioned. Probability of precipitation will
gradually increase across the entire region Wednesday night into
Thursday as the frontal passage occurs leading to solid likely probability of precipitation by early
morning Thursday. At that point...the primary focus of the period
becomes wintry weather concerns along the NC mountain zones near the Tennessee
line. Models indicate a period when thermal profiles yield a
subfreezing layer near the surface...ahead of the deeper cold
advection aloft. The NAM being the most aggressive with such would
yield a prolonged period of freezing rain across The Spine of the
Apps...before a change over to all snow. The GFS leaned towards a
faster cold advection pattern...thus a shorter period of freezing rain.
Opted for the GFS solution...which happened to be much aligned with
the new European model (ecmwf). Therefore...forecast features a period of freezing rain along the
Tennessee line on Thursday morning...before a phase change occurs to
sleet...then all snow. Total snow and ice accumulations remain
below advisory criteria at this point therefore will not mention in
severe weather potential statement. Further east along the front...profiles will remain supportive
of all rain processes with probability of precipitation decreasing into the late afternoon
hours. Temperatures on Wednesday will be above normal amongst warm air advection
regime...while below normal temperatures return Post frontal passage on
Long term /Thursday night through Monday/...
as of 200 PM Monday...surface front will depart the area to the east Thursday
night as sprawling Canadian high pressure fills in from the northwest. Low level
profiles along the tenn border indicate a low chance of lingering
snow showers in northwest flow...but this diminishes quickly. Global models
now in strong consensus that the high will continue to push the
frontal boundary to the fla Panhandle. Dry conditions will prevail
Friday-Sat as a result. Maximum temperatures 10 to 15 degrees below climatology Friday
before airmass modifies and top out around 5 below climatology Saturday.
However cool temperatures are reinforced by a second cold front Saturday
night. While the frontal passage itself appears generally dry except possibly
along the tenn border...the 02/00z ec and a handful of naefs
ensemble members suggest a wave could develop along the old
stationary front over the central Gulf states and lift into the area
sun or Sun night. Probability of precipitation were allowed to ramp back up from the SW
beginning Sunday. Temperatures Sun night will be cool enough that a
rain/snow mix could result over parts of the area. Further
moderation in temperatures is in store for Monday as skies begin to clear.
Aviation /03z Tuesday through Saturday/...
at kclt...flight conds will deteriorate after midnight with surface boundary
stalling and atl moisture flux increasing. With wedge moistening by
08z...ceilings will fall pretty quickly into at least the MVFR range
through the morning. Incoming -shra/dz will reduce ceilings to IFR by
early afternoon...persisting through the period. A 40 knots SW/ly jet
will be developing at 3 kft after 20z...a little too elevated for a
sigfnt windshear concern...but close enough to keep an eye on with
high directional shear.
Elsewhere...flight conds will degrade through the overnight at all
taf sites. A moist wedge will develop overnight and quickly bring
ceilings down into the MVFR range. With light rain and drizzle
developing by middle morning...ceilings will drop again into the IFR range
and remain through the period. Kavl and khky will see a 40 knots SW/ly
jet develop after 20z around 3 kft. A little high for a definite
windshear issue...but good directional shear nonetheless.
Outlook...a cold front will move slowly through the region Wednesday
through Thursday...bringing chances for heavier rainfall and low
ceilings/visibilities to the area. Friday and Saturday look VFR.
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...Freezing Rain Advisory until noon EST Tuesday for ncz033-049-