Area forecast discussion
National Weather Service Greenville-Spartanburg SC
831 am EDT Sat may 18 2013
Synopsis...
a middle level disturbance will drift across the region this weekend. A
warm and moist airmass will remain over the area next week. A cold
front will approach the western Carolinas from the north next
weekend.
&&
Near term /through tonight/...
as of 710 am...line of rain showers and isolated thunderstorms and rain will move across the
area this morning with rain showers filling in behind. Have tried to time
this with more thunderstorms and rain developing for the afternoon.
Open upper low slides into the central Appalachians today as the
attendant trough moves into the southern Appalachians. Southerly flow ahead of
this system is spreading moisture and rain showers into NE Georgia ND the western
Carolinas. As this flow and moisture move eastward today...the
precipitation will as well. Looks like instability will remain weak as
clouds retard heating...but low level moisture will be high.
Therefore...expect thunderstorms and rain to develop given the forcing even with weak
instability. That said...as the upper trough moves into the area...
isolated strong to possibly severe storms could develop. Cannot rule
out isolated heavy rain over the mountains as well. However...does not
appear to be widespread enough for a Flood Watch at this time. Highs will be
around 5 degrees below the readings from Friday.
The low and trough slide into the Piedmont tonight. The southerly flow
slides eastward as well. This will take the focus of the convection
east as well. Best precipitation chance will be over the Piedmont during the
night and diminish elsewhere. Expect the best quantitative precipitation forecast to slide east through
the night as well. Wpc quantitative precipitation forecast forecast is 1 inch or less total through the end
of the night. Therefore...while isolated heavy rainfall is
possible...widespread heavy rainfall is not. Especially as it looks
like the mountains will see the highest rainfall during the day and the
Piedmont during the night. Lows will be 5 to 10 degrees above normal.
&&
Short term /Sunday through Monday night/...
at 300 am EST Saturday...on Sunday morning...the remains of an upper
low will be somewhere over the central Appalachians. A weak trough
associated with this system will cross the western Carolinas and NE
Georgia Sunday and Sunday night. Upper level ridging moves slowly east
over the southern and central Appalachians on Monday and Monday
night in the wake of the upper trough.
Moisture associated with the trough will support widespread
precipitation on Sunday. Instability will be limited by cloud
cover...but should still be sufficient for convection. Model
soundings show a very moist profile...with little dry air aloft and
limited dry air beneath the cloud layer for evaporative cooling or
downdraft production. Steering flow will be enough to keep cells
moving slowly to the NE. A light southerly surface flow will provide
upslope flow enhancement of precipitation...mainly along the south
facing Blue Ridge Escarpment. Some instability will persist through
Sunday night as the upper trough passes...with steering flow
gradually veering to the east.
On Monday some dry is introduced at middle levels as the upper trough
departs. Clouds heights rise...with more dry air at the surface.
Instability increases...supporting more of a convective Mode to
precipitation...though with decreasing coverage. Moisture will be
slow to depart to the east on Monday night...but the best moisture
will be near the coast.
Maximum temperatures will be near normal...with minimum temperatures
a couple of categories above normal. Precipitation totals could
exceed one inch along the south facing Blue Ridge Escarpment of
SW NC...with most of that falling on Sunday and Sunday night.
&&
Long term /Tuesday through Friday/...
at 300 am EST Saturday...an upper ridge will move slowly across the
Carolinas and Georgia on Tuesday and Wednesday...while an upper trough
associated with another closed low in the plains moves to the MS
River Valley. The trough deamplifies as it crosses the Ohio and Tennessee
valleys on Thursday...and reaches the central and southern
Appalachians on Friday.
A warm and moist air mass remains over the southeast from Tuesday
through Friday. Diurnally modulated convection is expected on
Tuesday and Wednesday. On Wednesday night both the GFS and European model (ecmwf)
show a convergence of Atlantic moisture with moisture left over from
a dying cold front that arrives from the west...just about over the
southern Appalachians. This moisture linger over our area into
Thursday...before starting to move off to the east on Friday. If
this scenario hold...precipitation would be more likely to persist
overnight...with greater coverage and accumulation. On Saturday a
cold crosses the area from the north.
Temperatures will briefly warm above normal as the upper ridge axis
arrives...falling to around normal as heights fall with the advance
of the upper trough.
&&
Aviation /13z Saturday through Wednesday/...
at kclt/khky...line of rain showers...with isolated thunderstorms and rain will move toward
the airfields this morning. Visby has been consistently lowering to
IFR across far western NC and upstate SC as this precipitation passes
over...so tempo for IFR conditions has been introduced this morning.
Meanwhile...ts have been very isolated and short-lived so far...so
we feel comfortable with omitting a ts mention for this morning.
The precipitation shield should move east of the terminals during early
afternoon...but showers should develop/linger through the
afternoon...with scattered ts expected to develop as well.
Conditions deteriorate after midnight as ceilings fall through MVFR to IFR
in lingering rain showers. Southerly wind continue through the period.
Elsewhere...precipitation shield producing widespread/persistent IFR visby
will shift east of the terminals between 14z and 15z...with
improvement to VFR expected for the afternoon. However...showers
should develop/linger through the afternoon...with scattered ts
expected to develop as well. Conditions deteriorate after midnight
as ceilings fall through MVFR to IFR in lingering rain showers. Southerly wind continue
through the period.
Outlook...showers and thunderstorms...and associated restrictions...
will persist through Monday. Fair weather may return by Tuesday.
Confidence table...
12-18z 18-24z 00-06z 06-12z
kclt high 100% high 100% high 100% high 85%
kgsp high 100% high 100% high 94% high 91%
kavl medium 69% medium 74% medium 69% high 91%
khky high 100% high 100% high 89% high 93%
kgmu high 89% high 100% high 92% high 93%
kand high 96% high 100% high 100% medium 77%
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
&&
Gsp watches/warnings/advisories...
Georgia...none.
NC...none.
SC...none.
&&
$$
Synopsis...jat
near term...rwh
short term...jat
long term...jat
aviation...jdl/rwh
