Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Greenville-Spartanburg SC
636 am EDT Thursday Jul 24 2014

a cold front will approach from the northwest this morning and
should move across the Carolinas and north Georgia this afternoon
and evening. High pressure will build in behind the front for Friday
and the weekend. Another front is expected to pass on Monday.


Near term /through tonight/...
as of 520 am...latest water vapor images indicated that the middle
level trough was located generally over the Tennessee/NC line...with a short wave
over the Piedmont. Kgsp and tclt radar indicated showers and
thunderstorms associated with each feature. I will update the
forecast to increase probability of precipitation along and east of the observed convection.
Otherwise...the current forecast appears in great shape.

As of 330 am...recent regional radar indicated that the convection
across eastern Tennessee has decreased to isolated showers...with a secondary
patch of showers across the southern I-77 corridor. West/v showed the
middle level trough axis was located across eastern KY/TN...sweeping
east. At 330 am...W/v and rap indicated that several short wave existed east
of the trough axis...with stronger short wave across the western Ohio River
valley. I anticipate that widely scattered to scattered rain showers will drift or
develop across NC mountains early this morning. By middle day...the middle
level trough is expected to ripple over the southern appalachian
region. By 17z...forecast soundings indicate that convective available potential energy will range
between 1000-1500 j/kg across the region. As weak middle level forcing
reaches the mountains and foothills early this afternoon...convection
should develop across the east facing slopes and foothills. Forecast
soundings indicate that the steering flow will push cells northwest to southeast
across the western Carolinas and NE Georgia. Shear may remain weak
through this afternoon...but possibly enough to organize convection
into a band. Once developed...the band should slide
quickly east...reaching the clt area by late afternoon. These storms
may result in strong to severe thunderstorms and rain wind gusts across portions of
the of the forecast area. In addition...dcape across the eastern
Piedmont may range from 500-1000 j/kg. We will highlight in the severe weather potential statement
the potential for damaging wind gusts associated with the forecast
thunderstorm band. High temperatures may range from 80 within the
mountain valleys near 90 east of I-85.

This evening...convection will propagate east...exiting the County Warning Area
early this evening. Overnight...conditions will dry with cloud cover
decreasing from west to east. Low temperatures may range 2-3 degrees
cooler than this morning.


Short term /Friday through Saturday night/...
as of 300 am Thursday...the short range is shaping up to be
relatively quiet. The front should be driven far enough S to not
affect the region on Friday. The upper trough over the east should
pull out or fill a bit on Friday into Saturday with weak surface
high pressure moving over the region. The models continue to
alternately depict isolated/widely scattered shower development
during heating on Friday and Saturday...but the situation does not
appear to have a whole lot going for it as moisture should be much
less than the last week. A few short waves will move across the
region but the models do not respond to any great degree. At this
point...would prefer to remain optimistic for the first part of the
weekend and have kept the forecast dry. Any brief drop in temperatures on
Friday will be wiped out for Saturday as the air mass modifies back
to normal. Toward the end of the period...there is some potential
for an mesoscale convective system or remnants to approach from the west or a small pop
was introduced on the Tennessee border.


Long term /Sunday through Wednesday/...
as of 330 am Thursday...the medium range has perhaps a bit more
uncertainty thrown in for Sunday and Monday. The return moisture
does not appear to be as great on Sunday and any upper support for
convection should move past to the the point where the
GFS/European model (ecmwf) both fail to develop much in the way of precipitation. At the
same time...the models continue to suggest some sort of mesoscale convective system
activity...but keep it moving across the Ohio Valley/central
Appalachians. There is the potential for a boundary to move down
from that activity which could trigger some storms. Will not make
any changes to the precipitation probs for Sunday...but keep in mind the
trend is for less activity on that day. The models continue to
deepen the upper trough over the east again on Monday with stronger
waves driving another surface cold front southeast across the region...most
likely on Monday. In spite of this boundary being more significant
in terms of air mass change...the model response is underwhelming in
terms of precipitation. Again...will not make any changes...but a downward
trend might be started later today. Still looks below normal for the
middle of next week as a surface high of Continental origin drops
down from Canada/northern plains. Have nudged temperatures/dewpoints down a bit
more for Tuesday night into Wednesday.


Aviation /12z Thursday through Monday/...
at kclt...the primary forecast challenge will be the timing of
afternoon thunderstorms and rain. The 4km WRF and 6z nam12 indicates that convection
will develop across the NC foothills between 18z-19z...forming a
band. Steering flow and cold pool generation should result in the
band to move briskly east during the afternoon...likely passing
across the clt metropolitan area between 20z to 22z. I will highlight the
thunderstorms and rain potential with a tempo group from 21z to 24z. Although frontal passage
should occur between 18z-0z...light north winds are not forecast to
develop until this evening. The combination of light north
winds...lingering middle level cloud cover...and 2-3 degree dewpoint
depressions should favor VFR conditions tonight.

Elsewhere...all terminals will likely see convection either over the
terminal or vicinity through 0z. I will highlight the convective
period with thunderstorms in the vicinity or tempo groups...generally between 19z-22z. Ahead
of the cold front flow will remain from the southwest between
5-10kts. Winds will veer from the north this evening. Kavl could see
north-northwest winds develop this morning...remaining through the rest of the
12z package. NAM condensation pressure deficits and MOS indicates
that kavl could see IFR ceilings during the pre dawn hours Friday.

Outlook...Friday and Sat should be quiet and VFR...except for the mountain
valleys where early morning fog may occur. Thunderstorms will return
to the forecast for Sunday afternoon through Monday as another cold
front approaches and then moves through the area on Monday.

Confidence table...

10-16z 16-22z 22-04z 04-10z
kclt high 98% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl medium 65% high 100% high 92% medium 66%
khky high 97% 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: (must be lower case)



Gsp watches/warnings/advisories...


near term...Ned
short term...PM
long term...PM

National Weather Service Glossary of Abbreviations