Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 200857

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
457 AM EDT WED JUL 20 2016

A typical Bermuda high pressure pattern will set up across the
region through the end of the week, resulting in typical midsummer
conditions. High pressure will strengthen this weekend, then a cold
front will approach from the northwest early next week.


As of 315 AM EDT Wednesday: 3AM and all`s well across the western
Carolinas and NE GA, though my precip forecast yesterday certainly
left something to be desired, as that lee trough set up a little
farther SE than anticipated. Today, however, should be a bit easier
with the upper high over the Plains un-ridging (I know that`s
probably not a word, but easiest way to describe it) over our area as
the flow aloft transitions to more NNW rather than NW, with
continued weak diffluence. Should still see a bit of lee troughing
across eastern zones, but with mesohigh in place as usual across the
mountains. Should see a fairly diurnal, maybe slightly less than
diurnal trend to convection today with highest chances over the
mountains, and not much over the Piedmont, with most precipitation
dissipating after 00z. SPC just has general thunder over the area
and profiles seem to line up with this thinking, especially as
afternoon mixing mixes out some of the instability. As usual, can`t
rule out an isolated strong storm or two, but without an upper
impulse moving through to provide some lift, should be more just
terrain-induced. PW values remain high and so will have to watch
heavy rainfall potential. High temperatures will be pretty close to
those yesterday.

For tonight, a little more uncertain when it comes to precip
potential. All of the models have the remnants of yesterday
evening`s convective complex working its way southeast around the
northern periphery of the upper high and toward the TN Valley late
this evening. The GFS and NAM are a little more aggressive with
taking a piece of this energy and redeveloping it across the Upstate
(in the GFS) or Midlands (NAM) of SC toward the very end of the
period. ECMWF remains dry. WPC used a blend of the NAM/GFS/CMC and
does have some precip advertised across our southern zones after
midnight tonight. For now, will continue to advertise a dry forecast
per the ECMWF, but the day shift will have to take a close look at
this and adjust if necessary. For overnight lows, very little change
from what we`ll be seeing this morning.


As of 245 AM Wednesday...The gargantuan upper level anticyclone will
continue to dominate the central CONUS Thursday, then begin to break
down slightly and retrograde more toward the west on Friday. The
models continue to be all over the place with individual impulses
riding around the periphery of the high. Nothing substantial appears
to cross our area during the short term. So the expected forecast is
for typical midsummer weather with diurnally driven pulse
convection, starting in the Mountains and then favoring the Piedmont
in the evening. It is interesting how all the operational models
agree on convection converging on the Upstate Thursday evening. For
now will go with chc PoPs for that. PoPs on Friday will be around
climo, if not more isolated. Temps will be about a category above
normal Thursday and another category or two warmer on Friday, as the
subtropical ridge strengthens over the Southeast.


As of 315 AM Wednesday...The broad upper ridge will continue to
expand into the Southeast states Saturday and Sunday, then a trough
within the northern stream will try to make some inroads across the
Great Lakes and Ohio Valley Monday and Tuesday. The 00z GFS and
ECMWF have perhaps backed off the high temps slightly for the
weekend. But still expect upper 90s to around 100 both days. Heat
indices will flirt with 105 across the Piedmont both days, with
Sunday looking to have have the highest values. A cold front will
approach form the NW on Monday, and may keep dewpts even more
elevated while temps remain in the mid 90s. So Monday`s forecast
heat indices have been trending up. Will continue to mention
excessive heat possible in the HWO. As for PoPs, they should be on
an increasing trend, especially Monday and Tuesday, as the front
approaches and the upper ridge weakens. The model Superblend has
likely PoPs in the mountains both days, but I will cap it at
high-end CHC for now.


At KCLT elsewhere except KAVL: Well, convection to the E of KCLT
has spat out an area of MVFR cigs moving W across KCLT for the 09z
update. Have added TEMPO BKN015 through 10z, based on the movement
of the back edge. May have to extend the TEMPO or go prevailing if
the area of MVFR expands. Otherwise, VFR through the period, with
the exception of some possible predawn MVFR fog at KHKY. Winds will
favor N/NNE this morning (though KCLT is seeing Ely winds at TAF
time due to outflows from previous convection, so have started the
TAF with a TEMPO for that), veering around to ENE and finally SE by
late in the period. For the most part just some SCT mid-level
clouds, and convection chances too low for PROB30 TSRA at this time.

At KAVL: For now, just expect some predawn MVFR fog, though kept
previous TEMPO IFR. Will watch winds closely as they could fog in
quite a bit more than expected if winds stay calm. Already dewpoint
depression is lower now than it was all last night so confidence is
particularly low. Convection expected this afternoon across the
mountains warrants continued PROB30 TSRA after 18z.

Outlook: Expect fairly typical midsummer weather with afternoon
showers and thunderstorms during the middle and latter part of the
week. Morning fog and low stratus will be possible each day in the
mountain valleys and also in locations that received heavy rainfall
in the preceding afternoon/evening.

Confidence Table...

            09-15Z        15-21Z        21-03Z        03-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High  94%     High 100%     High 100%     High 100%
KAVL       High  98%     High 100%     High 100%     High 100%
KHKY       High  88%     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:




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