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FXUS62 KGSP 230600

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
100 AM EST Thu Feb 23 2017

Brief drying develops today into early Friday before a significant 
cold front brings chances for rain and thunderstorms Friday night 
and Saturday. Overall, daytime temperatures will remain well above 
normal through Saturday, with a return to normal for Sunday. Above 
normal temperatures and chances for rain return for early next week.


100 AM EST Update...Keeping an eye on the dense fg potential 
overnight. The suspect areas look to be the NC mtn valleys...fthills 
and piedmont per sfc layered cdp/s and recent obs. Tdd/s are running 
a little high across the Upstate...however this is the area that 
received better precip yesterday.  

0230 UTC Update: Minor changes were made to overnight temperatures 
based on the latest model guidance.

As of 230 PM EST...An upper low will continue to drift SEWD over FL 
tonight thru thursday, while an upper ridge builds back in across 
the Southeast states. At 850 mb, the circulation around the upper 
low will keep a persistent SELY Atlantic fetch into the CWFA. This 
will keep plenty of low clouds and fog for the overnight thru 
Thursday morning. Forcing remains weak, so only spotty light showers 
and patchy sprinkles/drizzle is expected, and mainly favoring the 
SELY upslope areas of the Blue Ridge. That's where PoPs will be 
highest (in the chance range, slight chance or less elsewhere). 
Temps will only cool slightly under the clouds, into the upper 40s 
to mid-50s.

During the day on Thursday, expect the low clouds and fog to 
eventually lift and scatter out, revealing some sunshine, especially 
in the southern Piedmont. Lingering surface high pressure will nose 
in from the east, but temps should be able to warm into the 70s 
across the entire Piedmont with nothing to lock in any remaining 
cold pool.


As of 240 PM EST Wednesday: Short wave ridging builds over the area 
Friday before an upper low developing over the Northern Plains moves 
east across the Great Lakes on Saturday dragging a trailing trough 
across our area. Southerly low level flow remains over our area 
Friday as high pressure moves east and a strengthening cold front 
moves into the MS valley. There will be enough low level moisture to 
combine with the flow for some isolated showers along the Blue Ridge 
Thursday night/Friday morning and scattered showers and isolated 
thunderstorms on Friday afternoon. Lows will be 15 to 20 degrees 
above normal with highs around 20 degrees above normal but still a 
couple of degrees below record levels.

Winds pick up and moisture increases Friday night as the cold front 
to our west moves into the mountains toward daybreak. However, deep 
moisture is shunted off to the north. The best forcing is also to 
our north where the best short wave energy moves through the trough. 
Despite the guidance showing some elevated instability ahead of the 
front, the NAM and GFS forecast soundings show quite a cap in place 
for all but maybe the NC Mountains and I-40 corridor. The best 
SBCAPE develops during the afternoon east of our area as the front 
quickly moves across the area. There will be quite a bit of bulk 
shear and helicity ahead of the front. However, the best instability 
and shear do not overlap over our CWFA. Therefore, the chance of any 
severe storms is very low, but we will need to keep an eye on this 
system as it approaches. There will be some NW flow snow showers 
along the TN border in the lingering moisture and developing NW flow 
behind the departing front. However, any accums look to be below 
advisory level for now. Finally, winds will increase and become 
quite gusty across the high elevations ahead of the front Friday 
night then all areas on Saturday behind the front. Winds linger 
across the high elevations Saturday night. Lows Friday night around 
20 degrees above normal fall to near normal Saturday night. Highs 
Saturday will be around 10 degrees above normal across the 
mountains, and could be earlier in the day than normal, and 15 to 20 
degrees above normal elsewhere.


As of 2 PM EST Wednesday...starting to wonder if winter is really 
over. The upper pattern looks like it should remain progressive 
through the medium range with all the colder air kept well to our 
north. In the wake of the Saturday system, expect Sunday will be the 
only seasonal day in the first half of next week. We should be under 
a flat ridge that supports high pressure at the surface, which 
should keep temps merely five degrees above normal. After the 
surface high moves off the coast Sunday night, our weather should 
get more active through the rest of the period. A short wave moving 
over the Srn Plains Sunday night will organize surface low pressure 
that moves up the OH valley on Monday. Model guidance is not in very 
good agreement as to how organized or deep the low will be, but 
there is some agreement that a surface front will lay down across 
the area Monday and Monday night. Precip prob slowly ramps up into 
the chance range over the mtns and a slight chance east of the mtns. 
The models suggest a lull in the action Tuesday morning, so will try 
to indicate a break in the low-end precip chance at that time. There 
is also some agreement that the old boundary will reactivate Tuesday 
night as another low organizes over the Plains. Altho this low will 
track over the Midwest/Gt Lakes, it should push a cold front toward 
the region on Wednesday. That should bring a chance of precip across 
the whole fcst area. Will hold back with including any likely precip 
prob due to lack of confidence out on day 7. Temps will gradually 
rise through mid-week, getting back up into the well above normal 
range for Wednesday.


At KCLT...Expect lowering of cigs overnight as back end of cloud 
shield works east. Vsby will also lower as hires cpd/s show max 
saturation in the sfc layer around daybreak. A drop to IFR conds by 
10z and possible LiFR vsby by 12z. A lifting and scattering out will 
occur quickly aft 15z with drier air mixing in underneath a building 
mlvl ridge allowing for good sfc heating.  

Elsewhere: KHKY will be the trouble spot wrt to IFR/LIFR conds thru 
daybreak. Previous rainfall and calm conds under a sfc ridge will 
enable a highly moist sfc layer to persist thru mid morning. KAVL 
will also be under the gun for IFR vsby/cigs a few hrs before 
daybreak. Across the Upstate...VFR dropping to MFVR conds with 
perhaps IFR vsby...esp at KGSP/KGMU where tdd/s are running lower 
and cpd/s drop the most. A quick return to VFR conds will occur arnd 
14z with relatively drier air mixing in and sfc heating commencing. 

Outlook: Moist southerly to easterly low-level flow will persist 
across the area until a cold front pushes thru on Saturday. This 
will keep high chances of morning stratus and possibly fog each day 
thru Saturday morning. Drier conditions set up on Sunday.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z 
KCLT       High  90%     Med   76%     High 100%     High 100%     
KGSP       High  80%     High  92%     High 100%     High 100%     
KAVL       Med   66%     Med   79%     High 100%     High  97%     
KHKY       Med   66%     Med   77%     High  99%     High  97%     
KGMU       Med   79%     Med   77%     High 100%     High 100%     
KAND       Med   79%     Med   77%     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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