Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 231746

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
146 PM EDT Fri Mar 23 2018

High pressure remains over the area today. The next low-pressure
system arrives over the weekend with precipitation and well-below
normal temperatures. The cold weather will persist through Monday as
strong high pressure builds down the Appalachians. Temperatures
rebound back above normal by Wednesday as moisture increases ahead
of a cold front.


As of 130 PM: Developing low pressure in the lee of the Rockies will
begin to move through the Plains late this aftn and evening. A warm
front will activate ahead of it, initially over the mid-Mississippi
Valley. The axis of a midlevel ridge will shift overhead tonight as
the warm front edges its way eastward, setting up from eastern KY to
the NC Piedmont by Saturday morning. However, weak upglide will
develop over our mountains well before dawn, and that is when precip
chances are expected to quickly increase. Unfortunately it`s not
looking like the event will unfold in a straightforward manner from
that point. It looks likely that temperature profiles will feature
non-freezing values only in the sfc layer, but the arrival of the
warm front will gradually change that, introducing a warm nose.
While warm advection generally should continue through the day,
850mb plots from the NAM/GFS seem to reflect wet-bulb cooling for a
time after the onset of precip. Even the development of the warm
nose thus looks difficult to time. Furthermore, as CAD begins to
develop over the course of the day, sfc temps will remain cool
across the northern mtns and NW NC Piedmont, which will maintain the
possibility of wintry wx. This will be a tough p-type fcst for the
mountains and I-40 corridor.

Additional details to come after the aftn fcst pkg is finalized in
collaboration with neighboring offices.


As of 420 AM Friday: Very complicated and tricky forecast for the
short range. Miller B type clipper system moves in from the NW with
differing temps and thermal profiles depending on the model. Have
issued a Winter Storm Watch for the northern NC mountains due to the
potential for a significant mixed precip event. Amounts and p-types
are much more uncertain across the rest of the NC mountains and the
northern foothills and NW piedmont. Therefore, have kept those areas
out of any winter products for now, but an advisory may be needed as
the event nears. Just rain is expected across the rest of the area.

Precip chances increase Saturday with the highest chances during the
afternoon and evening. With strong cold air damming developing,
temps fall to create the winter weather potential. A strong warm
nose develops with cold air below it. The profiles suggest snow
across the northern mountains Saturday morning then becoming rain
mixed with sleet for the afternoon as the warm nose develops. Precip
becomes freezing rain Saturday night over the northern mountains
with the warm nose remaining in place and cold low level air moving
in from the north. Sleet or snow will mix in across the I-40
corridor depending on the how the thermal profiles develop. Precip
returns to mainly rain Sunday with warming then ends as a mixed bag
across the mountains Sunday night. The highest QPF and any accums
would be mainly Saturday afternoon through Sunday morning. Temps
will be well below normal for all but the southern portions of the
CWFA Saturday.

Precip tapers off Monday. Highs will again be well below normal.


As of 345 AM Friday: Looks like dry high pressure briefly builds in
Tuesday before moisture returns ahead of a cold front Wednesday and
Thursday. That said, there could be enough lingering moisture
Tuesday for some light showers across the mountains. For now, have a
dry forecast Tuesday with increasing PoP Wednesday and Thursday.
Temps start our below normal Tuesday then rise above normal for
Wednesday and Thursday.


At KCLT and elsewhere: Conditions will be VFR until tomorrow
morning, when warm frontal activation over the area will permit
precip to develop overnight, and ceilings to subsequently
lower. None of the TAF sites are expected to see wintry wx, but
areas of the mtns and NC Piedmont (particularly north of KAVL/KHKY)
are not out of the woods. Cigs are progged to continue lowering
as precip continues into Saturday. Development of CAD Sat aftn
looks to lock in LIFR over KHKY and other northern Piedmont sites,
though the chance of this occurring before the end of the TAF
period precludes its inclusion in this set. Right now it appears
the IFR/LIFR will remain north of KCLT until after 00z Sun.

Outlook: Elevated precipitation chances and periodic flight
restrictions will occur this weekend with another approaching low
pressure system. Cool and dry high pressure will try to build in
from the north early next week.

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 100%     Med   78%
KHKY       High 100%     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:


NC...Winter Storm Watch from Saturday morning through Sunday
     morning for NCZ033-049-050.


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