Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Greenville-Spartanburg SC
248 PM EST Friday Feb 5 2016

Synopsis...
an upper level ridge and dry surface high pressure will slowly cross
the forecast area throughout the weekend. A cold front will push
through the region on Monday...ushering in below normal temperatures
and an increase of moisture into the middle of next week.

&&

Near term /through Saturday/...
as of 230 PM...wind has diminished across the western Carolinas and
northeast Georgia...as high pressure builds in from the west and the
pressure gradient relaxes. Otherwise...a sunny afternoon with temperatures
seasonally cool.

The next 24 hours looks relatively quiet across the western
Carolinas and northeast Georgia...in spite of the approach of a
vigorous looking upper system tonight and its arrival by late
afternoon Saturday. High pressure should move overhead tonight but
weaken. Min temperatures will be on the order of five degrees below
normal...even with decent radiational cooling conditions...owing to
the source region of the air mass. On Saturday...the next system
will encroach from the west in the morning and reach at least the
western half of the forecast area by the end of the day. Although
middle/upper forcing look more than sufficient for precipitation...our
sources of moisture are completely cutoff and unavailable. Thus...
expect it to remain dry this far inland. High temperatures will be cool
again as increasing/thickening high/middle clouds keep temperatures below
normal again.

&&

Short term /Saturday night through Monday/...
as of 235 PM Friday...very interesting weather expected off the
Carolina coast on Sunday. Short range models indicate that a closed
500 mb low will track across the deep south Sunday morning. At 300 mb...the
core of a 135 kts jet will lift along the Atlantic coast of the
Carolinas Sunday morning. Short range models indicate that surface low
pressure will rapidly organize and deepen off the SC coast between
0z to 12z Sunday. By 0z Monday...the 12z GFS indicates 700 mb Omega
increasing to over 150 ubar/S on the west side of the surface low
center. Simply put, this enviroment is expected to result in
explosive or bomb cyclogenesis on Sunday. The 12z NAM is the most
reactive with central pressure falling from 1017 mb at 0z sun to 984
mb at 21z sun. However...the 12z GFS and European model (ecmwf) indicate a very
similar rate of pressure falls. This would meet or exceed the
pressure fall rate to qualify as a bomb cyclone. Fortunately...short
range guidance keeps the deep moisture and precipitation associated with
the system east of the forecast area. However...by middle Sunday
afternoon the pressure gradient may range to 5 mbs...supporting
gusty northwest winds across the region. The gradient will decrease
quickly Sunday evening as the coastal low races off to the
northeast. High temperatures are forecast to range from the 40s
across the mountains to low to middle 50s east.

Monday...a cold front associated with another low over the Great
Lakes will sweep over the southern Appalachians by sunrise. Precipitation
should begin as snow across the mountains...given low temperatures in the low
30s. However...after sunrise...temperatures will slowly warm...changing
precipitation to rain. By the afternoon...temperatures are forecast to range from
the low 40s within the valley floor to near 50 east. Precipitation will
generally fall as liquid rain. However...elevation above 3500 feet
may remain as snow through the afternoon hours. By the end of
daylight Monday...several High Mountain peaks near the Tennessee line may see a
couple of inches of snowfall. We will continue to highlight in the
severe weather potential statement.

&&

Long term /Monday night through Thursday/...
as of 215 PM Friday...the medium range will start out Monday evening
with a large upper level vortex/trough over the southern Great Lakes
and Ohio Valley...with spokes of vorticity pivoting around the
circulation. One of those spokes/vorticity lobes will cross the County warning forecast area on
Tuesday...producing another round of modest middle to upper level qg
forcing. However...it does not look as impressive...and middle level
lapse rates will not be as steep as on Monday. Still...moisture and
lift along with increasingly better northwest upslope flow should keep
scattered to numerous snow showers along the Tennessee border. As for
precipitation from the Blue Ridge and east...models have backed off on
precipitation /breaking containment/...so I will only forecast a slight
chance of rain and snow showers across the NC foothills and northwest
Piedmont. Temperatures will be about 10-15 degrees below normal under the
trough.

Tuesday night and beyond...the axis of the upper trough will swing
east of the area...but a large Miller-b like low will be ongoing
across the Great Lakes and the northeast. So a prolonged moist northwest
flow will continue along the Tennessee/NC border...before tapering off
Wednesday night. The 850 mb temperatures will bottom out Wednesday into
Wednesday night...resulting in temperatures 15-20 degrees below normal and
potentially Wind Chill Advisory conditions in the high terrain.
Temperatures start to rebound Thursday and Friday...as the eastern trough
starts to flatten out. Another reinforcing trough or weak clipper
system will dive into the Great Lakes and Ohio Valley early Friday.
This may bring a brief shot of moisture and northwest flow snow shower
activity.

&&

Aviation /20z Friday through Wednesday/...
at kclt and elsewhere...VFR through the period with clear sky
through daybreak Saturday. Will continue to have occasional gusts
through middle afternoon...but that should abate by late afternoon.
Direction will be mostly north or north-northwest. On Saturday...wind should come up
from the NE or east-northeast by mid-morning...and high clouds should invade
from the SW ahead of the next system.

Outlook...weak high pressure will remain across the region through
the weekend. A strong upper air disturbance could bring enough
moisture to wring out a few rain or snow showers on Monday.

Confidence table...

19-01z 01-07z 07-13z 13-18z
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 schedule taf issuance flight rule category. Complet hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:

Www.Weather.Gov/gsp/aviation

&&

Gsp watches/warnings/advisories...
Georgia...none.
NC...none.
SC...none.

&&

$$
Synopsis...sbk
near term...PM
short term...Ned
long term...Arkansas
aviation...PM

National Weather Service Glossary of Abbreviations