Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 241740

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
140 PM EDT Mon Jul 24 2017

A surface front will become stationary from west to east across our
region and dissipate into mid week.  High pressure moving by to the
north is expected to provide cooler temperatures on Wednesday.
Another front will move in from the northwest late in the week.


As of 135 PM EDT Monday: Forecast generally on track. Radar shows
convection developing just south of the CWFA with some across the
Upper Savannah River Valley. Latest CAM guidance shows best chance
of convection over NE GA and the western Upstate. Have updated PoP
trends to show this. Temps not warming as fast as expected due to
the mid clouds over the area. These clouds scatter out and move east
during the afternoon, and temps will quickly jump with sunshine. looks much quieter overall convection-wise, as the
axis of a mid-level trough will cross the area and overall drier air
filters in from the west. The surface front is still analyzed up
over the Ohio Valley and central Appalachians, but the air mass
across the region will likely not recover completely from all the
overturning from yesterday`s convection. So temps will be a notch
cooler and dewpts mixing into the upper 60s across much of the area
this afternoon. The latest CAMs agree with showing most of the deep
convection today south and east of the CWFA. So PoPs were trimmed
back, but still slight CHC in the north and CHC in the south. If I
went strictly with the CAMs, it looks like a dry day, except for a
few isolated cells across the Upstate. In any case, the severe
threat today look low.

Tonight, the cold front is progged to push into NC from the north,
ushering in more dry air. Overall, looks like a quiet night with
perhaps some mountain valley fog. Temps will be one to two
categories above normal.


As of 245 AM Monday: The middle of the week still looks like a
welcome break from our recent hot weather. Tuesday might still be
very similar to today with temps a few degrees above normal with
an old boundary strung out west-to-east across the fcst area. That
boundary should provide the focus for more mainly diurnal showers
and storms. The guidance suggests a north/south gradient in precip
chance and most of the response is actually across northeast GA and
the Upstate, however the uncertainty with the actual placement of
the boundary keeps the chance across the entire fcst area. Think the
severe storm threat will be relatively low if mid-level temps remain
relatively warm as seen in NAM fcst soundings. Subtle changes are
expected to take place Tuesday night as a positively tilted upper
ridge moves in from the west, pushes the old front to the south, and
brings some drier air in from the NW. More importantly, the ridge
will push a surface high past to the north and across New England
on Wednesday. The upshot is a period that almost resembles a weak
wedge, if the NAM is correct, with a light NE flow and high temps
that remain a category BELOW normal. The low level flow will favor
the development of precip near the Blue Ridge, but there should
be enough moisture and instability to account for a chance across
the entire fcst area. However, it might not end with sunset as the
weak upglide continues near the escarpment through the night. No
indication of excessive rain in any of the guidance.


As of 330 AM Monday: The latest guidance out in the medium range
continues to show unsettled weather across the region. The upper
ridge axis at the start of the period on Thursday morning gets
suppressed to the south as the next upper wave drops down across
the Gt Lakes/Midwest, and eventually the upper anticyclone over the
Plains retreats to the west by the end of the week. This results
in a sort of pattern change for the weekend with upper troffing
taking up residence over the east which would keep temps at or
below normal for a few days. Friday would have the best chance for
precip as a cold front is driven across the region. After that,
it depends on where the front stalls. Some of the guidance keeps
this boundary close enough to suggest keeping a chance across the
region through the end of the period, but if it stalls farther
south we could end up with a situation where precip chances are
closer to climo, with chances only over the mtns.


At KCLT and elsewhere: Mid clouds will slowly move east of the area
with developing Cu. Latest guidance keeps best chance of afternoon
convection across the SC sites. Have limited any TS mention to those
locations, but did keep a VCSH at KCLT. Cu diminishes this evening
with cirrus the main clouds overnight. That said, mountain valley
fog/stratus is likely and possible at KHKY/KAND. After any
restrictions burn off Tuesday morning, expect developing Cu once
again. Any convection would be later in the day and more likely for
the SC sites. W to SW wind today becomes light N overnight and NE
Tuesday. KAVL remains NW throughout.

Outlook: Scattered diurnal convection can be expected each day this
week across the region. Chances for morning fog and stratus will
also be possible each day in the mountain valleys.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  83%     Low   35%
KHKY       High 100%     High 100%     High 100%     Med   66%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     Med   66%

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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