Area Forecast Discussion

FXUS62 KGSP 212344
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
644 PM EST Thu Feb 21 2019
The moist pattern will continue into the weekend until a 
robust cold front finally moves through the region on Sunday. 
After a brief dry period early next week, another system will
approach by mid-week.
630 PM Update...Light precip is becoming more widespread across the 
FA as a frontal zone remains stationary across the srn zones. Not 
expecting new issues with hydro over the next few hrs as streams 
have fallen a bit from previous rainfall and runoff is on the low 
end. The atmos is rather stable currently...but there is a couple 
hundred joules of elevated instability deeper cells may 
develop across the sw/rn zones and produce a few general tstms by 10 
As of 245 PM: With an overall lull in precipitation and breaks in 
the once earlier expansive cloud cover, the wedge in place continues 
to weaken and retreat to the NE this afternoon, as latest obs 
highlight SW winds across northeast GA, the Upstate, and even into 
portions of the NW Piedmont. As a result, temperatures this 
afternoon (which were projected to be quite the challenging forecast 
given the uncertainty of the eroding wedge) have climbed into the 
lower 60s across the Upstate and northeast GA, while still in the low 
to mid 50s within the wedge. Anticipate temperatures to climb 
another degree or two before capping off for the day.
As sfc high remains well offshore with upper ridging over the SE, 
and another sfc high off to the NW progged to shift towards the OH 
Valley, CAD returns tonight with a stalled boundary remaining south 
of the FA through the near term forecast period. Thus, the expansive 
cloud cover will return tonight and continue into Friday, with rain 
chances returning as well with plenty of moisture overrunning the 
upper ridge in place and the progged setup of upglide/isentropic 
lift/return of the wedge, per latest guidance. Given recent 
rainfall, already saturated grounds, and ongoing flooding concerns, 
the Flood Watch for portions of the FA will remain in effect through 
Friday evening attm. With current water levels and additional 
rainfall amounts of 1"+ possible, especially across western NC, it 
won't take much for rapid rises on area rivers and streams. Low 
temperatures tonight will remain well above normal, as high 
temperatures on Friday remain much cooler than today, and below 
normal, with the return of CAD.
As of 228 PM EST Thursday: We remain in the throes of cold air
damming Friday night and Saturday, and confidence is high that
the fcst will not change much, with such a strong signal seen
in the model guidance. Precip chances will remain fairly high,
but for fairly low precip amts. The deeper forcing remains off to
the north and west Friday night, which should support the higher
swath of precip outside our fcst area. Thinking that our threat
for additional heavy rain looks relatively low, so the Flood Watch
will not be extended in time (yet). Instead, we will keep the low
level forcing and isentropic lift that will maintain light rain
and drizzle through the period. Precip chances slowly go down
through Saturday as the forcing slowly weakens. There is some
controversy for Saturday night as to the possible destruction of
the wedge before the advancing cold front arrives. The guidance
suggests maintaining the southeasterly warm advection at 850 mb
and low level upglide thru 06Z Sunday, altho we lose support from
the parent high. We may scour out around the edges, but think it
a bad bet that we will uncover the NC foothills and NW Piedmont
before the cold front arrives just after daybreak Sunday. The
fcst temps will reflect this thinking, as will our low chances
of thunder (for the time being), as there is little sfc-based
instability. The cold front will sweep through early in the day,
so naturally our high temps east of the mtns will be 15-25 degrees
warmer on Sunday afternoon than Saturday. Ah, the confusing wonder
of downslope flow and wedge destruction. The early frontal passage
should allow us to salvage Sunday afternoon, with ample sunshine
allowing us to dry out a bit.
As of 243 PM EST Thursday: Still looks fair and tranquil for the
early part of next week, with a flat upper pattern that will support
high pressure approaching Sunday night, moving overhead Monday,
and then off the Carolina coast Tuesday. Moisture returns with a
weak srn stream system over the lower MS River basin Tuesday night,
so some light precip may move back in from the W/SW by Wednesday
morning. However, confidence in the timing of features in this
pattern is fairly low, but at least we look to be cut off from any
cold air that would cause p-type issues. The fcst generally follows
the GFS with low precip chances for the middle part of the week,
but the new ECMWF casts doubt on our already meager chances. Temps
should be at or slightly above normal.
At KCLT and elsewhere: A good amt of llvl moisture will remain 
across the area as sfc bndry remains draped across the srn Upstate 
and moist sw/ly flow persists underneath a mlvl inversion. Light 
precip will become more widespread and all sites will see prevailing 
-shra by daybreak. Expect lowering CIGs to IFR/LIFR all sites 
overnight with VSBYs generally remaining in the MFVR/IFR range as 
showers will occasionally scour out BL moisture. Conditions 
wont improve too much during the day Fri as a wedge of high pressure 
builds in from the north and quickly becomes saturated. This will 
pattern will likely hold CIGS in the MVFR and possibly IFR range thru 
the period.     
Outlook: A highly moist atmosphere will persist into Saturday and 
make for a good chance of precipitation with associated low flight 
restrictions. A cold front is expected to dry out the region on 
Confidence Table...
            23-05Z        05-11Z        11-17Z        17-18Z 
KCLT       Med   75%     Med   61%     Low   27%     Med   75%     
KGSP       Med   69%     High  94%     High  94%     High  81%     
KAVL       Med   69%     High 100%     High  83%     High  87%     
KHKY       Med   69%     Med   72%     Low   55%     High  81%     
KGMU       High  81%     High  89%     High  89%     High  81%     
KAND       High  94%     High  89%     Med   72%     High  81%     
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:
GA...Flood Watch through Friday evening for GAZ010-017-018-026-028.
NC...Flood Watch through Friday evening for NCZ048-051>053-058-059-
SC...Flood Watch through Friday evening for SCZ001>007-010.