Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
648 am EST Monday Nov 30 2015
a cool and wet air mass will settle in today in the wake of a back
door cold front...and persist through Tuesday. Another cold front
is likely to bring additional rain Wednesday...before dry high
pressure arrives Wednesday night.
Near term /through tonight/...
630 am update...widespread light to moderate rain does continue
along the southern tier of NC...seemingly becoming oriented more
distinctly within the baroclinic zone atop The Wedge due to the
expected weakening of upper divergence. Highest accums in the
past hour are 0.3 to 0.4 inch. Short range guidance for the most
part shows the rain remaining somewhat spotty the rest of the
morning...and beginning to shift northward this afternoon. Certainly can/T
rule out some pockets of 0.25 to 0.5 inch per hour rates but it does
not look like Hydro threat will increase significantly this morning.
This morning...high pressure centered over the St Lawrence Valley
continues to ridge down the East Coast...in a cold air damming
configuration. A broad baroclinic zone extends along the southern fringe
of the high...with warm advection atop the cad wedge aided by a
weak surface low over Tennessee. Upper divergence is also present over
the area at this time...this associated with right rear quadrant of jet streak which
will move off the middle-Atlantic coast this morning. The divergence
accordingly is shown to diminish through the day. The high will shift
off the New England coast today...as deep closed upper low moves
through the Central Plains. As these features move the baroclinic zone
begins to focus north of our area...though low level upglide remains
more or less constant until winds veer tonight in response to the
low lifting toward the western Great Lakes...leaving only shallow lift.
The most significant concern for the near term /and really through
midweek/ is the degree of Hydro issues that will result. Most
guidance peaks rainfall rates in the first half of the day today
while the deepest upglide/moisture is still enhanced by middle to upper
level dynamic lift. Rates appear to remain similar to those being
seen in the heavier pockets early this morning...0.2 to 0.3 inches
per hour. While several hours of such rates will likely produce
notable responses on rivers...and perhaps even some minor issues in
low lying areas...currently the setup does not appear primed for
widespread or flash flooding. We will maintain heavy rain wording
in the severe weather potential statement but do not meet criteria for a Flood Watch. Furthermore
rates are expected to taper off this afternoon...allowing a lull
tonight before forcing increases again prior to the eventual frontal passage.
Wedge will still be in the building phase today...with temperatures
remaining steady or falling slightly as the day GOES on over most
of NC...values being mainly in the lower to middle 50s. Portions of
the upstate and NE Georgia will remain outside the boundary and will
see temperatures warm into the 60s. Temperatures will remain nearly steady
tonight...though mins will be on the order of 15 degrees above
Short term /Tuesday through Wednesday night/...
as of 320 am Monday...the main problem through the short range looks
like it will be associated with the passage of the cold front on
Wednesday. A deep upper low moving steadily from the northern
plains...across the upper MS river basin...to the Great Lakes on
Tuesday and Wednesday will help to build a downstream ridge that
keeps a SW flow aloft. The front will have some difficulty making
eastward progress as a result. Expect precipitation production to lift northward
Tuesday morning as a remnant boundary drifts back northward...so the
precipitation chance has been cut back over the upstate and southern Piedmont.
This will be short lived as the cold front inches closer from the
west. By Tuesday night...the better upper forcing and deeper
moisture will drift across the NC mountains have raised the precipitation
chances into the categorical range over the mountains to account for
this. The models suggest the best forcing will lift NE and out of
the region on Wednesday as the front finally slides across the mountains
and then east of the forecast area by evening. As it stands right now...
there does not appear to be enough of a threat of heavy rain over a
short enough time period to support issuing a Flood Watch for
Tuesday night and Wednesday. The front makes its way to the east on
Wednesday evening...so precipitation chances taper off quickly to the east.
As for temperatures...the most important change was to the high on
Tuesday...as it appears that cold air damming will break down early
enough to allow temperatures to climb higher over the southern part of the
Long term /Thursday through Sunday/...
as of 315 am Monday...the latest model runs show surface high
pressure building into the region on Thursday as a cold front moves
off the southeast coast. A blocking pattern develops late in the
week with an upper low closing off over the southern/central
Appalachians. However...any surface reflection of low pressure
develops along the front well off the coast on Friday...such that no
precipitation is seen inland. This appears to be a drier trend in the new
model runs. Have opted to remove the slight chances of precipitation that
creep in around the southern/eastern edge of the forecast area for the weekend
based on the model trend. Temperatures still look they will be below normal
for the period.
Aviation /12z Monday through Friday/...
at kclt...tricky forecast for this morning as cold air damming takes
its time becoming established across the area. IFR ceilings are very
nearby apparently due to saturated low levels resulting from
persistent rain. The actual wedge boundary appears to be hung up
north of I-40...but is expected to push southward later today and bring
a steady IFR ceiling lasting through Tuesday morning. Periods of rain mainly will
occur today...causing minor visibility concerns...and though some chance
does exist through tonight rates at that time are not expected
to be enough to cause restrictions on their own. Guidance is
nearly unanimous on low IFR ceilings and IFR visibility from fog developing
tonight. Expect prevailing northeasterly winds...near due east at times today.
Elsewhere...warm upglide in developing cad regime is the story
at all taf sites...enforcing restrictions around the region. The
Wedge boundary is expected to push southward this afternoon...and
some improvement may briefly come in the late morning prior to its
entrenchment. However ceilings will likely stay IFR to low MVFR even
if that occurs. A lull in forcing should allow slowing rain
rates going into the aftn/evening...but ceilings and visibility will crash
tonight. Mainly NE winds over the Piedmont and southeast at kavl.
Outlook...unsettled conditions and associated restrictions will
continue Tuesday into Wednesday before a cold front crosses the
area midweek to bring drying.
11-17z 17-23z 23-05z 05-06z
kclt medium 69% high 83% low 55% high 83%
kgsp medium 75% high 83% medium 78% high 83%
kavl high 100% high 100% high 89% high 91%
khky high 94% high 83% medium 72% low 58%
kgmu medium 75% high 83% high 83% high 83%
kand high 81% high 94% medium 61% medium 66%
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)