Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Greenville-Spartanburg SC
1000 PM EDT Tuesday may 26 2015

a Bermuda high pattern will persist across the southeast states
through the end of the week. This will produce a moist southerly
flow with increased chances for widespread showers and thunderstorms
each day.


Near term /through Wednesday/...
945 PM update...convective line has become somewhat effectively being discrete cells lined up along
the leading edge of a cold pool. If nothing else it looks like the
structure will hold up enough to bring isolated downpours to most of
the yet untouched part of the County warning forecast area over the next couple of
hours...including the Charlotte metropolitan. Gusts have become weaker and
less widespread. 00z radiosonde observation from Atlanta was taken in the wake of the
line and reflected a stable airmass. Latest rap forecasts suggest little
to no rebound will be seen overnight despite moist advection in the
continuing southerly flow. So new probability of precipitation reflect the departure of the
present round of convection later in the evening and just chance
probability of precipitation for the area after midnight. We will still see the upper
dynamic features move across potentially kicking off shower
activity...but high impact storms will likely be history.

As of 230 PM EDT...deep southwest flow has set up over the forecast
area between offshore high pressure and a low pressure system
lifting NE from the plains. Precipitable water values continue to
increase and will maximize at nearly 1.75 inches over The Heart of
the area tonight. Meanwhile...several consecutive runs of the hrrr
have been quite accurate in handling the widespread convection
developing over western Georgia this afternoon as an outflow boundary from earlier
deep south convection works east. The hrrr shows this activity
moving toward the upper Savannah River region around 22z and then
across the upstate and western NC through the evening hours and early
overnight. This is consistent with the expected arrival of upper
divergence over the southern Appalachians this evening...along with
a weak 500 mb voriticity lobe. Instability will be marginal in most
areas...but a lobe of briefly enhanced low level bulk shear...and
any outflow push with the arrival of the convection...could produce
marginally severe winds into far SW sections this evening with any
strong thunderstorms and rain. The activity should wane overnight with just lingering
scattered showers expected. Anticipate another night of very warm
min temperatures as a blanket of low clouds forms in the moist boundary

Although the 500 mb pattern will flatten out somewhat through
Wednesday...additional weak shortwaves will move over the area in the
broad SW flow aloft...with deep moisture persisting. Heating will
get off to a slow start again on Wednesday with the abundant morning
clouds...but SBCAPE values should rise to 1500 j/kg or better by Wednesday
afternoon with any breaks given the elevated dewpoints. Anticipate high
scattered to low likely rain showers/thunderstorms and rain coverage in the moist airmass on
Wednesday afternoon...but low level convergence will lead to the best coverage
over the NC mountains temperatures will struggle through the 70s again to maximum
out near 80 east of the mountains...lower 80s in the Piedmont.


Short term /Wednesday night through Friday/...
at 200 PM EDT Tuesday...on Wednesday evening high pressure will be
centered off the East Coast...while weak upper troughing will be
over the western USA...and a shortwave moves across the Great Lakes
and Ohio River valley. The shortwave moves off the New England coast
on Thursday...followed by rising heights aloft into Friday.

At the surface...Atlantic high pressure maintains a foothold over
the Carolinas and Georgia from Wednesday evening into Friday...while low
level moisture remains banked up against the southern Appalachians.
Instability is expected to be somewhat limited under the upper
ridge. With a lack of isentropic upglide...and only modest low level
upslope flow...precipitation should be rather modest...and greatest
near the Blue Ridge. Temperatures will exhibit a reduced diurnal
trend due to cloud cover and moisture.


Long term /Friday night through Tuesday/...
at 200 PM EDT Tuesday...on Saturday morning...high pressure will be
centered southeast of New England and Atlantic Canada...while upper
troughing will extend from Hudson Bay to the southern US plains. The
upper high will very slowly breaks down....while the upper trough
slowly progresses...such that by Tuesday the upper trough crosses
the MS River Valley.

At the surface...on Saturday high pressure will extend from the
western Atlantic tot he southern Appalachians....while modest Gulf
inflow exists over the Gulf states...and a cold front crosses the
Great Lakes...middle MS River Valley...and Southern Plains. High
pressure starts to weaken over the Carolinas and Georgia on Sunday...
while the approaching front stretches from New England to the Ohio
River valley. The eastern portion of the front stalls to our north on
Monday...while the southern portion moves into the lower MS River
Valley. Moist inflow from the Atlantic improves ahead of this front.
On Tuesday the front stalls to our north and west.

With heights falling aloft...and instability and moisture
increasing...convective chances should improve with time. Moist
inflow never really gets precipitation is not expected
to be excessive on a grand scale. Temperatures will run within a few
degrees of normal.


Aviation /02z Wednesday through Sunday/...
at kclt...thunderstorms and rain moving through northwest SC and SW NC at 00z are expected to
hold together in some form and affect the field late in the evening.
It is not out of the question earlier thunderstorms and rain will affect the will need to closely monitor conditions. The storms are
entering a less unstable airmass so they are not expected to be as
strong when they arrive. Additional development is possible after
midnight as upper shortwaves or mesoscale convective vortex/S drift overhead. Though lamp
ceilings have not verified well lately...tonight rainfall will have
introduced low level moisture which was not there previously. So its
IFR forecast has been favored for the morning. Precipitation chances are low in
the morning...enough so they have been omitted. Diurnal convection
is expected to return Wednesday afternoon...though coverage is expected to
remain scattered at best.

Elsewhere...intense linear convection will cross the upstate sites
and kavl not long after the start of the period. Brief IFR to LIFR
visibility and strong southwesterly wind gusts expected with the arrival of the
line. Expect light rain with occasional rumbles of thunder through the
remainder of the evening. Later tonight precipitation chances become low
enough to omit...though remain nonzero. IFR ceilings are expected to
develop at all sites an hour or two before daybreak. This deck will
slowly lift through the morning back to VFR by midday. Destabilization may
be delayed by the low clouds...but late in the day prob30 chances
return around the region.

Outlook...moist SW flow will continue to affect the terminal
forecast area right through the upcoming a cold front
lays over to the north of the area. Expect morning stratus to result
each day...with continued better than climatological chances of
afternoon/evening rain showers/thunderstorms and rain each day.

Confidence table...

02-08z 08-14z 14-20z 20-00z
kclt high 95% high 84% medium 77% high 100%
kgsp high 90% medium 60% medium 77% high 100%
kavl high 81% medium 69% medium 74% medium 70%
khky high 98% low 58% medium 76% high 100%
kgmu high 90% medium 75% medium 77% high 100%
kand medium 76% low 45% high 83% 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)



Gsp watches/warnings/advisories...


near term...hg/Wimberley
short term...jat
long term...jat

National Weather Service Glossary of Abbreviations