Scientific Forecaster Discussion
fxus62 kgsp 210716
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
316 am EDT Thu Sep 21 2017
a weak trough will settle over the southeast coastline today. Moist
easterly flow will develop through Friday. Drier and stronger high
pressure will settle across the region over the weekend and likely
persist through early next week, as tropical systems Jose and Maria
remain off the East Coast.
Near term /through tonight/...
as of 310 am EDT thursday: patchy fog continues to highlight the
early morning hours across the region with the mtn valleys being the
most dense. Given the moist bl, think some additional development
outside of the valleys across the Piedmont is possible, yet should
remain isolated and well above any dfa criteria. Otherwise, sharp
upper ridging will regain control of the pattern aloft today as the
weak upper shortwave that moved overhead yesterday ejects eastward.
At the surface, northeasterly flow amidst high pressure will
dominate amidst mostly sunny skies. Profiles once again exhibit
modest lapse rates, with MUCAPE values likely pushing into the
1500j/kg range with little shear and weak nly steering flow.
Given said steering flow and improving nva, think convection is
most likely to occur over the high terrain where any inhibition
will be weakest, which correlates well with the cams. Outside of
the mtns, the aforementioned profiles could support convection
if any forcing mechanisms are in place, which doesn't look to
be the case. That said, will include a low end slight chance
pop over the fthills/Piedmont regions of NC/SC and northeast GA,
while featuring mid/high chances over the mtns/ridgetops. As for
thunderstorm intensity, said mtn profiles would support deep
convection, therefore wouldn't be shocked if a few cells became
strong with gusty winds and lightning being the primary threats.
Temperatures today will once again top out nearly a category or
two above normal levels, generally 70s to lower 80s in the mtns,
mid/upper 80s elsewhere.
Short term /Friday through Saturday night/...
as of 250 am EDT thursday: a dominant 590 dm mid-level ridge axis
will stretch from the Great Lakes to the Southern Plains on Friday,
with a trough axis lingering over the southeast coastline.
Meanwhile, low-level easterly flow will provide some upslope
triggering along the high terrain on Friday, with peak shower
coverage during the diurnally favored afternoon period. Cape values
in model profiles appears a bit less on Friday compared to Thursday
across the northern tier, but with some fairly decent 1000 to 1500
j/kg values in the southern tier where thunder will be more
Maria will continue a slow but steady March northward well east of
the southeast coastline through the weekend. Drier air should wrap
southward along the appalachian mountain chain from high pressure
building over to the north, with associated lower precipitation
chances Saturday given the diminished moisture and instability.
Temperatures will remain about 5 to 10 degrees above climatology for
min temps through the period, with maxes 3 to 7 degrees above climo.
Long term /Sunday through Wednesday/...
as of 255 am EDT thursday: still anticipate a complicated
interaction of Jose and Maria over the coastal/offshore waters of
the western Atlantic Sunday through Wednesday, but with subsidence
and ridging persisting over the southern Appalachians and
surrounding areas through the period. Temperatures will remain at
least a couple of categories above climo. A full latitude central
Continental U.S. Trough will then likely begin sweeping east of the plains on
Wednesday. Southwesterly flow will increase ahead of this feature
and possibly push maxes to around 10 degrees above climo by
Wednesday afternoon, with some lower Piedmont highs around 90 not
out of the question.
Aviation /07z Thursday through Monday/...
at kclt and elsewhere: VFR conditions expected at all sites tonight
aside for at kavl where mtn valleys fog is expected once again,
and thus MVFR/IFR restrictions are included. Otherwise, light/calm
nly flow under a few low/mid cu and high cirrus will dominate.
Winds will increase slightly through the morning hours on Thursday
at all sites with nly flow expected in the 4-6kts range regionwide
amidst developing llv cu and high cirrus. Aside for a prob30 at
kavl and vcts at khky accounting for mtn convection, all remaining
sites are wx free through the period.
Outlook: chances for diurnally favored showers and thunderstorms
remain in the fcst thru Friday. Restrictions from early morning
fog across the northern NC Piedmont and foothills, as well as in
the mtn valleys will also be a concern. Drier weather is expected
to return for the weekend.
07-13z 13-19z 19-01z 01-06z
kclt high 96% high 96% high 100% high 100%
kgsp high 96% high 96% high 100% high 100%
kavl low 48% high 96% high 100% high 96%
khky high 86% high 96% high 100% high 96%
kgmu high 100% high 100% high 100% high 100%
kand high 96% high 96% 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: