Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 241049

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
649 AM EDT Mon Jul 24 2017

A surface front will drop down from the north today and is
expected to become stationary from west to east across our region on
Tuesday before dissipating. 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 645 AM EDT Monday: The last few echos from overnight
convection is dissipating on radar across the eastern escarpment.
This activity definitely worked over the air mass across the region
from the TN Valley to the Carolina Piedmont, as the latest SPC
mesoanalysis page shows a minimum of MUCAPE and plenty of CIN across
the region.

So today 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: patchy stratus developing across the Piedmont
at time of TAF issuance. Bases range from 200 to 1500 ft AGL. The
clouds are thin and patchy on satellite, so I expect the cigs to
scatter out within the first hour or so of the 12z TAFs. From there,
VFR-level cumulus field is expected to develop, with most extensive
cloud cover across the Upstate and southern NC Piedmont, where the
best moisture will be today. These areas have at least a slight
chance of TSRA this afternoon, so will continue VCTS and PROB30 at
the Upstate and KCLT sites. With less precip expected across the
area, it looks like restrictions will be limited to mainly the
mountain valleys tonight. So will add some fog mention at KAVL.
Winds will be out of the SW thru late tonight, then switching out of
the NW as a cold front pushes in from the north before daybreak
Tuesday. The exception will be at KAVL, where winds will stay NW
thru the period.

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...

            10-16Z        16-22Z        22-04Z        04-06Z
KCLT       Med   77%     High 100%     High 100%     High 100%
KGSP       High  94%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High  80%     High 100%     High 100%     High 100%
KAND       High  97%     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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