Area Forecast Discussion

FXUS62 KGSP 220220
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1020 PM EDT Tue May 21 2019
Strong high pressure will set up and persist over the southeast the 
rest of the week. This will greatly limit the potential for daily 
showers and thunderstorms and keep temperatures well above normal. 
The ridge of high pressure will strengthen further over the weekend 
into early next week, leading to near-record high temperatures over 
the Memorial Day holiday weekend.
As of 1020 PM: Winds have begun their adjustment back to the NE 
outside of the mountains. A few clouds are floating around with 
mostly clear skies expected until clouds move in near daybreak.
An upper ridge will gradually build/amplify across our region
with the axis tilting from negative to positive and moving to the
east coast through Wednesday. The movement of the northern extent
of the ridge should push surface high pressure from the Great
Lakes today to the Mid-Atlantic/New England coast by Wednesday
afternoon. As that happens, the high will ridge down stronger in
wedge-like fashion late tonight and Wednesday. The model guidance
shows the return of low level moisture in a low level easterly
flow starting around daybreak, but right now the moisture appears
too shallow to result in anything more than a low cloud deck in
the morning mainly over the wrn Piedmont/foothills of NC. If the
cloud deck forms, it would have an affect on how quickly temps
warm in that area. The plan for now is that clouds would break up
in the afternoon enough to bring our temps up to around normal,
but on the order of five degrees cooler than today. If there is
any shower/tstm activity, it should be down across Upstate SC and
maybe the Savannah R basin, where deeper moisture may pool along
a de facto wedge boundary. For now, a small chance will suffice.
As of 220 PM EDT Tuesday: the short-term fcst picks up at 00z on 
Thursday with the upper ridge amplifying across the Eastern CONUS
as deep upper trofing remains over the west. The upper ridge will 
remain in place well into the extended period. At the sfc, broad 
high pressure will be gradually moving off the Atlantic Coast as 
the period begins, putting the fcst area back under SLY low-lvl 
flow. During the day on Thurs, a low will move across the Great 
Lakes and lay a weak cold front along our northern periphery 
late Thurs into early Fri. By the end of the period late Fri, 
the above low will be moving off the New England Coast as the 
front washes out to our east. This will allow low-lvl winds to
veer around to a more WLY direction on Fri. As for the sensible 
wx, no significant changes were needed to the fcst. Thurs will
see near-climo chances for convection, with the best chances for
more sct to widespread coverage across the higher terrain. The
above-mentioned upper shortwave energy should provide some limited
upper support once convection gets going, however the severe 
potential still looks more isolated. The profiles on Friday do
have some decent sfc-based instability, however the lack of any 
upper-lvl support coupled with the downsloping wind component 
will likely make it difficult to initiate convection. Otherwise, 
temps will remain well-above normal through the period, with Fri 
being the hottest of the two days.
As of 225 PM EDT Tuesday: the extended forecast picks up at 00z 
on Saturday with the persistent upper ridge firmly in place across 
the region. Over the next 24 to 48 hrs, the ridge flattens a bit
as broad upper trofing moves across SE Canada. As we move into 
Monday, the ridge axis shifts to the west and heights fall across
the southeast. In addition, numerous weak upper shortwave pulses
stream across the our area from the NW on Monday. By the end of
the period on Tues, the long-range guidance has the ridge axis 
shifting back to the east with heights rising again over the fcst
area. At the sfc, we will remain under the overall influence of
the very broad-scale, sub-tropical high centered to our east. We 
do have a few weak boundaries that pass to our north over the 
weekend, however they are far enough to the north that they will
have little, if any, impact on our sensible wx. On Monday, the
long-range guidance appears to move a more robust front just to
our north and in its wake, a more substantial lee trof develops 
over the Carolinas. This will likely moisten profiles and increase
the chances for more widespread convection, especially across the
higher terrain. Otherwise, with the persistent upper ridge remaining 
in place, temperatures will approach record values over the weekend
and early next week. Anyone working outside will need to stay well
hydrated and take necessary precautions to avoid heat-related 
At KCLT and elsewhere: VFR through the end of operations this 
evening. Wind still tricky as the directions have gone anywhere from 
SE to SW, with winds returning to NE or ENE during the evening or 
early overnight. KAVL will keep a S wind. Still expect the 
development/arrival of low level moisture and cloudiness, mainly 
over the Piedmont and Foothills of NC, around daybreak. Guidance is 
now favoring low MVFR with IFR possible. Have gone low MVFR for now 
with SCT IFR to show the potential. Guidance suggesting VFR for the 
rest of the TAF sites. Low clouds will be slow to lift with MVFR 
lingering into the afternoon at KCLT but improving earlier at KHKY. 
Expect low VFR cigs to develop elsewhere by afternoon. Some 
shower/tstm activity could develop in the afternoon, but the chances 
are relatively low. Did add VCSH at KCLT for the evening as chances 
increase during the night with low clouds returning.
Outlook: The potential for morning valley fog will continue through 
the weekend. After Thursday, convective chances will remain limited 
due to developing upper level high pressure.
Confidence Table...
            02-08Z        08-14Z        14-20Z        20-00Z 
KCLT       High 100%     High  86%     High  93%     High 100%     
KGSP       High 100%     High 100%     High  92%     High  95%     
KAVL       High 100%     High 100%     High 100%     High 100%     
KHKY       High 100%     High  96%     High  82%     High 100%     
KGMU       High 100%     High 100%     High 100%     High  97%     
KAND       High 100%     High 100%     High 100%     High  97%     
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:
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      90 1939     57 1923     65 1953     36 1931    
   KCLT      95 1939     57 1923     71 1953     43 1931    
                1903                    1903                
   KGSP      94 1962     60 1923     73 1953     41 1917    
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      89 1896     57 1979     68 1953     39 1925    
   KCLT      95 1953     59 1923     73 1953     41 2013    
   KGSP      96 1962     63 1963     72 1953     46 2005    
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      88 1989     59 1956     65 1982     34 1925    
                1916                    1953                
   KCLT      96 1926     64 1992     73 1998     45 1979    
   KGSP      96 1953     60 1963     70 1989     45 1979    
                1926                    1953                
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      93 1890     55 1961     68 1991     36 1961    
   KCLT      96 1916     60 1901     77 1916     41 1961    
   KGSP      98 1916     65 1963     72 1991     43 1961