National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
997
FXUS62 KGSP 180006
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
706 PM EST Sun Feb 17 2019

.SYNOPSIS...
A moist warm front will continue to move north from Georgia
tonight as low pressure crosses Tennessee.  Expect Canadian high
pressure ridge down into our area from North Dakota by late Monday
giving us a short dry period.  Rain returns on Tuesday as a series
of low pressure systems will track from southwest to northeast
across the region, resulting in a persistent moist pattern through
most of the week.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 650 PM EST Sunday: Precipitation coverage has ramped up very
quickly this evening, and deeper forcing and moisture will move in
from the west through the late evening hours. Have thus hastened the
west to east increase in PoP trends this evening, maximized the
coverage early overnight, and boosted QPF values a bit in the
southwest NC mountains for this update. Also lowered minimum
temperatures a touch, but these are of no real consequence as mins
are occurring right now and temperatures should rise slightly
overnight throughout.

Otherwise, the cold air damming wedge will remain locked in across
the region into the overnight hours now that a chunk of the parent
high has broken off over the Mid-Atlantic region. Low-level
isentropic lift will improve through late evening in the 295-300K
layer, which should drive the development of a large area of
moderate to occasionally heavy rain that is expected to move across
the fcst area through at least 06Z. The improving SW flow should
focus the heavier precip over the SW-facing mtns, meaning the
biggest threat for excessive rainfall will be in the Little TN River
valley. There is some concern about precip amounts and how that
might relate to flood potential. As it stands right now, our QPF is
only on the order of half the 1hr FFG, so think we should be able to
tolerate what falls. That being said, it will only serve to further
increase our potential for flooding later this week. The precip
should end steadily from the west with the passage of a sfc wave and
the ending of the isentropic lift. Will hold onto some higher
chances on the TN border a bit past daybreak, but that should also
end quickly. Downslope quickly ensues by midday Monday, so we should
clear out and warm up nicely for Monday afternoon. Might be the only
decent weather we get all week.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 255 PM EST Sunday: The fcst will start off dry across the area
as a broad Canadian high builds south across the Glakes region
and begins to ridge down the east coast. Temps will drop to arnd
freezing across the NC mtns while a developing warm front begins to
approach the area arnd daybreak. There is some uncertainty with the
level of moisture with this front as the NAM continues to have very
little qpf response by 12z Tue. Likely a null chance of any wintry
precip Tue morning as any light precip shud not arrive until temps
warm abv freezing. Temps wont rise much during the day...probably
remaining 40s all locales as sfc-based CAA continues and cloud cover
increases.

The fcst becomes quite tricky Tue night as a parent 1040 mb high
sets up across the ern Glakes. The high config looks to be classical
in nature and bad for wintry precip across the colder NC mtn areas
as a stg llvl sw/ly jet brings in a sigfnt warm nose aloft. Model
temp guidance has trended down overall so mixed in lower values with
the previous fcst numbers. This gave more areas for accum fzra over
the NC mtns and even a -ra/fzra mix across the nrn fthills and nrn
NC piedmont. Temps look to hover just north of freezing generally
outside the nrn mtns...but a degree or two difference in sfc Tw/s
could create wintry/icy precip.

The amt of precip is not totally certain as there could be robbing
convec south and the overall depth of saturation will likely be
limited to arnd h7. Therefore...ice nuclei may not be activated esp
as the morning progresses...per the latest GFS/NAM soundings.
Thus...will anticipate an onset of freezing precip arnd 02z with
likely a switch to -fzdz...before a changeover to all rain occurs
arnd 14z. Expect a light glaze of ice at most across the
non/mtns...and the best ice accum potential of a couple tenths over
the nrn NC mtns and high elev nrn fthills...and perhaps even further
south across the Black Mtns. Right now...this event is certainty adv
level and as the fcst changes warning level conds could develop. A
light cold rain will continue thru period with temps only reaching
the L40s north and L50s over the far sw/rn zones as the wedge is
slow to lift out of the area.

Another issue Tue night into Wed will be the potential for stream
flooding across the sw/rn NC mtns. WPC has the area in a Day 3
slight risk of flooding the favored upslope sw-facing regions will
likely recieve arnd 2 inches to near 3 inches by then in continued
high saturated soils.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 200 PM Sun: An active pattern is still depicted across the CWFA
throughout the medium range, still with a strong ridge centered over
the eastern Caribbean and deep troughing over the southern Rockies
and vicinity. As low pressure traverses the Great Lakes region early
Thursday, a cold front will move thru the lower Mississippi Valley,
then pivot across the Appalachians as the sfc low moves thru New
England. That will promote erosion of the midweek CAD affecting our
area, though with the boundary lingering, unsettled weather will
persist. Furthermore, global models depict yet another seasonably
strong sfc high moving eastward north of the boundary, suggesting CAD
will return by Friday. Temperatures within the weekend CAD event
currently do not look cold enough for wintry precip, so the main
impact initially may just be to prolong the already cloudy/damp
conditions.

Model consensus shows pattern change finally occurring next weekend
as a shortwave ejects from the Rockies, cyclogenesis occurs somewhere
to our northwest, and a cold front swings thru the Southeast. This
front is most likely to reach our area on Sunday. The European and
Canadian solutions depict a stronger low and better defined cold
front than does the GFS, though all of them show at least modest
instability in the warm sector preceding the front, while CAD
persists for some of our area.  These trends are worth watching as
they imply some severe weather threat may result for those parts of
our area along/south of the wedge boundary.

All in all it is difficult to identify any meaningful break in precip
chances between Wednesday evening and Saturday morning, so we will
advertise at least likely PoPs for nearly the whole area during that
timeframe. A limited diurnal range is expected due to cloud cover
and/or wedging, but overall temps will remain near climo. Chances
were allowed to drop a bit by Saturday afternoon as warm front shifts
northward ahead of the developing low.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: With the steadier rainfall now spilling
east across the terminal forecast area, cigs are already locked into
IFR and falling into or near the LIFR range at issuance time. Expect
mainly steady LIFR cigs and IFR vsby as the heavier rain passes
through 06Z or 08Z east. Conditions will begin to improve from the
west before daybreak as flow turns westerly and a light downslope
flow develops east of the mountains. It may take some time, perhaps
through mid morning, to scatter the shallow wedge and lingering
boundary layer moisture, but once it starts happening it should
scatter quickly through noon. Anticipate some low end gusts
developing in the westerly flow with mixing near the end of the
period, with perhaps more robust gusts well into the 20s at KAVL in
the French Broad Valley flow.

Outlook: After brief improvement through Monday evening, a series of
low pressure systems will move through or near the region through
much of the rest of the week. This will produce precipitation and
associated restrictions for long periods of time during each wave of
precipitation.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High  83%     Med   72%     Med   73%     High 100%
KGSP       High  84%     Med   62%     High  88%     High 100%
KAVL       Med   66%     Med   70%     High  96%     High 100%
KHKY       Med   69%     Med   70%     High  91%     High 100%
KGMU       Med   74%     Med   62%     High  87%     High 100%
KAND       Med   75%     Med   69%     High  99%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...DEO
NEAR TERM...HG/PM
SHORT TERM...SBK
LONG TERM...Wimberley
AVIATION...HG/PM