Scientific Forecaster Discussion
fxus62 kgsp 241427
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1027 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.
Near term /through tonight/...
as of 1025 am EDT monday: morning soundings show the atmosphere
across the northern County warning forecast area is much less unstable than the southern
portions. The latest cam guidance reflects this with better
convective coverage across NE Georgia and the upstate and little across
NC. The current forecast is in line with these trends. Severe
chances are less today as well. However, there is decent dcape seen
on the kffc sounding, so an isolated damaging downburst cannot be
ruled out. Hot and humid again today, but not nearly as bad as the
past few days.
Otherwise...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 County warning forecast area. So pops were trimmed
back, but still slight chance in the north and chance 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.
Short term /Tuesday through Wednesday night/...
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 Georgia 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 northwest. 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.
Long term /Thursday through Sunday/...
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.
Aviation /15z Monday through Friday/...
at kclt and elsewhere: any lingering patchy stratus will burn off
before noon. VFR-level cumulus field is expected to develop
relatively quickly, 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 thunderstorms and rain this
afternoon, so will continue thunderstorms in the vicinity at the upstate sites but remove
prob30 from kclt due to time rules and less chance than areas to the
south. 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 northwest as a cold front
pushes in from the north before daybreak Tuesday. The exception will
be at kavl, where winds will stay northwest 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.
14-20z 20-02z 02-08z 08-12z
kclt high 94% high 100% high 100% high 100%
kgsp high 97% high 100% high 100% high 100%
kavl high 100% high 100% high 100% Med 79%
khky high 98% high 100% high 100% high 87%
kgmu high 100% high 100% high 100% high 100%
kand high 100% high 100% high 100% high 95%
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: