Area forecast discussion
National Weather Service Greenville-Spartanburg SC
133 PM EDT Friday may 24 2013
Synopsis...
an upper level trough will move off the Atlantic coast tonight and
Saturday while surface high pressure continues the cooler than
normal temperatures this weekend. Expect afternoon showers and
thunderstorms next week...mainly over the mountains. A rather strong
upper ridge will bring very warm temperatures for the second half
of the week.
&&
Near term /through tonight/...
as of early afternoon...the forecast is on track with temperatures and with
gusty northwest wind remaining below advisory levels. No changes.
Remainder of previous discussion...
Today...dry high pressure will begin to continue build into the area
from the northwest. Most of the guidance...the NAM in particular...indicate
breezy to windy conditions across the County warning forecast area. In fact...the high terrain
and some of the valleys where a gap wind will set up may approach
wind advection criteria...mainly during the morning hours. Confidence not
high enough to go with a wind advection in the mountains elsewhere...breezy
conditions warrants caution on area lakes. Temperatures will be below
normal under sunny to mostly sunny skies.
Tonight...the surface high will still be centered to our northwest...so mixing
is expected to continue through the night. Clear skies and cold air advection will
allow temperatures to drop into the 30s in the mountains and 40s across most of
the Piedmont. Patchy frost is possible in the sheltered
valleys...but widespread frost is not expected due to the mixing
across the high terrain.
&&
Short term /Saturday through Sunday night/...
as of 200 PM Friday...northwest flow aloft will continue through Sunday as
an intense upper low moves up the East Coast. The flow will
Delaware-amplify on Monday with building heights as the low moves out the
picture. At the surface...high pressure will will ridge south from
the southern Great Lakes with a weak backdoor front moving through
the area on Sunday. This front will move north as a warm front on
Monday. A more dominate high is forecast to develop off the southeast coast
on Monday.
A series of impulses embedded in the northwest flow are forecast to move
across the area Sunday and Monday. The airmass over the region will
be quite dry in the lower levels initially with dewpoints in the 30s
and 40s on Sunday. Hence...the lack of significant quantitative precipitation forecast response in
the model forecasts for Sunday is not surprising. Would expect that
any precipitation that falls Sunday and Sunday night will be mainly virga
or perhaps some sprinkles in the mountains. Monday is a different
story as low level moisture improves with dewpoings rising intot eh
50s as the warm front lifts NE. Therefore...would expect some
scattered showers developing int he mountains in the morning...with
scattered showers and perhaps even some thunderstorms in the
afternoon....mainly over the mountains and the NC
foothills/Piedmont.
Temperatures will be well below average through Sat night and
Sunday...with moderating temperatures on Monday approaching seasonal
levels.
&&
Long term /Monday through Thursday/...
as of 240 am Friday...the extended forecast looks good and no major
changes have been made to the grids. The 00 UTC GFS and ydays 12 UTC
European model (ecmwf) are in good agreement in gradually building a long wave ridge
across the lower MS River Valley and deep south states through the
period. We will start out the period under northwest flow on the back side
of a large long wave ridge centered over the western Atlantic. The
models have quite a bit of middle and upper level moisture on the back
side of the trough...the result of low and middle level isentropic
upglide. Still...the surface dewpoints are low and precipitation chances Monday
should mainly be confined to sprinkles or light high-based showers
over the mountains Tuesday through Thursday boundary layer moisture increases as the
surface ridge axis moves off the coast. The GFS has the best instability
by far over the mountains Tuesday and Wednesday...with a little more drying on
Friday. At this point low chance probability of precipitation over the mountains and slight chance
probability of precipitation elsewhere all three days still looks good. I did nudge temperatures up
a little Tuesday. I think Wednesday and Thursday are probably a little too
cool...but I/ll leave that for the day shift to decide.
&&
Aviation /18z Friday through Wednesday/...
at kclt and elsewhere...VFR through the period. A few stratocu with
bases at 050 to 060 through sunset...then clear after 01z. Wind will
remain gusty from the northwest through sunset but will quickly diminish
after that as the center of the high builds in. Most places will go
light and variable early Saturday morning and stay that way through
the rest of the taf period...the exception being kavl where a northwest
upvalley wind will be maintained. Could be some fog or frost in the
little Tennessee River valley around daybreak Saturday...but not around
kavl.
Outlook...with dry high pressure dominating the weather across the region
through the weekend...no significant aviation concerns are expected. A
return to diurnal thunderstorms is expected for Monday through
Wednesday with associated restrictions in the vicinity of storms.
Confidence table...
17-23z 23-05z 05-11z 11-17z
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: (must be lower case)
Www.Weather.Gov/gsp/aviation_tables
&&
Fire weather...
it will be windy over the mountains and breezy over much of the rest
of the forecast area today. Afternoon minimum relative humidity
values will fall to between 25 and 30 percent. With recent
widespread rainfall...fuel moisture values are generally still
high...and we do not anticipate needing any fire danger products
today. If any land management officials think that a Fire Danger
Statement is warranted please contact our office.
&&
Gsp watches/warnings/advisories...
Georgia...none.
NC...none.
SC...none.
&&
$$
Synopsis...level
near term...Ark/PM
short term...McAvoy
long term...McAvoy
aviation...PM
fire weather...
