Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 251759
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1259 PM EST Sat Feb 25 2017
Cooler high pressure will build into the region from the west
through Sunday. Warmer air should return during the first half of
next week. A warm front lifts north through the area around midweek
as a cold front approaches from the west bringing showers and storms.
.NEAR TERM /THROUGH TONIGHT/...
As of 1245 PM: Low pressure now over Ontario/Quebec continues to
drive a cold front onto the Eastern Seaboard. Winds have shifted
to NW across the mountains and foothills, with gusts as high as
30-35 kt in isolated locations. Expect frequent gusts of 20-25 kt
in all areas until late afternoon.
Sfc based convection is present over the NC Piedmont just ahead of
the front. SPC Mesoanalysis shows 500-1000 J/kg of SBCAPE present
in this area, though most of the associated cumulus looks stunted
on satellite. Until the front departs in the 20-21z timeframe,
there is a chance of an isolated shower or even t-storm in the I-77
corridor. So far one cell has managed to produce pea size hail;
small hail cannot be ruled out with any subsequent cells. There is
a threat of marginally severe winds as well. Strong mid to upper
level winds are producing effective shear of 50+ kt in that area.
Once the wind gusts diminish, clear and much cooler weather will
return to the area tonight. Dewpoints have already plummeted
20-25 degrees F in the wake of the front, and will trend gradually
downward over the next few hours. Fire Danger Statement remains
in effect for Upstate SC and most of NE GA to highlight the gusty
winds, RH below 25 percent, and dry fuels.
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 305 AM Saturday, A low-amplitude/quasi-zonal upper air pattern
will persist through the short term period, with gradually building
heights anticipated across the East. The end of the weekend will be
marked by dry and seasonably cool conditions, with high clouds
expected to increase late Sunday into Sunday night, as a shearing
vorticity max moves rapidly from the southern Great Plains to the
Mid-Atlantic Sunday night through Monday. In response, moist
isentropic lift will develop across the western Carolinas and
northeast GA throughout Monday, with increasing clouds and
precipitation chances expected, peaking by Monday evening.
Some guidance sources are more bullish than others regarding the
overall extent of the precip Monday into Monday night. Some models
(e.g. the ECMWF) indicate a bit more in the way of surface wave
development along the Carolina coast, which tends to disrupt the low
flow across and shut off the upglide more quickly across our area.
The upshot of this would be significant QPF confined to our western
areas, with little to nothing across the eastern zones. With that in
mind, pops range from 60-70 across western areas, to 40-50 along
the I-77 corridor. Monday`s temps will be a bit tricky, depending
upon how quickly precip arrives. As sufficient low level dry air
should be in place to force establishment of in-situ cold air
damming where precip falls. Nevertheless, with current data
indicating that precip is likely to hold off until afternoon, will
advertise maxes near to slightly above climo across the west, and
about 5 degrees above normal across the NC Piedmont.
Pops taper off gradually Monday evening. However, isentropic lift is
expected to increase across the region once again by daybreak
Tuesday, as large scale height falls overspread much of the western
half of the Conus. Another round of precip is therefore possible by
the very end of the period. Temps Monday night will be well above
.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 155 AM EST Saturday: Low level SW flow at the 925mb level will
persist Tuesday and Wednesday ahead of the approaching cold front.
GFS 925mb wind speeds maximize on Wednesday with 30 to 45kts in the
vicinity of I-85 from GA to NC. Moisture will be abundant with GFS
Precipitable water around 1.4 along I-85 Wed afternoon. Instability
is generally restricted to along and south of I-85 Tuesday PM,
especially on the GFS where very low if any CAPE is north of the
corridor. On Wed PM, CAPE of 400 to 600 from NE GA to CLT area along
with the wind shear will give strong to severe storm concern. Of
course, timing of frontal passage coincident with max daytime
heating would make for the max circumstance with dynamics coming
together. The 500mb trough crosses the western states early Tuesday
with axis over the Plains States 12Z to 18Z Wed with low pressure
forming in the eastern trough inflection point and moving NE across
the Appalachians Wed evening. At least the models are in closer
agreement as compared to 24HRs ago. GFS still the fastest model in
taking the front across our area around midnight Wed while the EC
has it passing a few hours later.
After the front passes, there will be lingering moisture along the
TN border with NW Flow combined with shortwave energy crossing just
north of NC on Thursday and early Friday. Thickness values will be
falling Wed night into Thursday and will be low enough for snow in
the NC Mtns by late Thursday morning. The second shortwave could
bring a brief NW Flow snow shower period around daybreak Friday for
the central and northern NC Mtns.
Temperatures are forecast to be 10 to 15 degrees above normal
Tuesday and Wednesday then fall to near or slightly below normal
behind the cold front for the second half of the week.
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
At KCLT: Cold fropa expected within the first couple hours of
the TAF period. Isolated to scattered SHRA will accompany the
front thru the Piedmont, but the chance of restrictions or direct
impacts is small enough to only mention as VCSH. If a shower does
pass overhead some pea size hail may also occur at the field. WSHFT
to NW expected by 21z with gusts picking up and persisting until
sunset. SKC tonight with winds gradually tapering off.
Elsewhere: The cold front has pushed through all sites leaving
only brisk NW gusts as the impact weather for the aftn/evening;
the influx of much drier air will result in VFR lasting thru Sunday,
with the few clouds that persist being associated with upslope over
the NC mountains. Winds will take their time to really diminish
but should be of little consequence by daybreak.
Outlook: A dry continental airmass will maintain VFR thru Sunday. A
shortwave exits the lower Mississippi Valley on Monday, once again
increasing chances for precipitation/restrictions which may last
into Tuesday. Somewhat unsettled weather will last until the passage
of a cold front associated with another Midwest low late Wednesday.
18-24Z 00-06Z 06-12Z 12-18Z
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 scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
Gusty W/NW winds and much drier air will overspread the area in
the wake of a cold front Today. Minimum RH of 25 to 30 percent is
expected across much of the SC Upstate and Northeast GA, and may dip
below 25 percent in some areas. Sustained winds will increase and
veer nwly behind a departing cold front into the 15-20mph range with
gusts nearing 30-35mph. These critical conditions could overlap
for an hour or two this afternoon. Thus a fire danger statement has
been issued for the all of northeast GA minus Rabun County, as well
as all of Upstate SC starting at noon today, running through 6PM.
GA...Fire Danger Statement until 6 PM EST this evening for GAZ017-
SC...Fire Danger Statement until 6 PM EST this evening for