Scientific Forecaster Discussion
fxus62 kgsp 192121
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
521 PM EDT Mon Aug 19 2019
an area of low pressure and elevated moisture will persist across
the western Carolinas and northeast Georgia through Wednesday. A
moist cold front will approach the region Thursday and become
stationary on Friday. The front will gradually settle south of the
area through the weekend as high pressure builds in from the north
and maintains cooler than normal temperatures.
Near term /through Tuesday/...
as of 510 pm: situated in between a ridge of high pressure both to
the west and east, as a few upper shortwaves swing through overhead,
an unsettled weather pattern persists across the western Carolinas
and northeast Georgia this evening. A weak deformation zone is
present aloft, with a small 500mb low over south Georgia. Convection
has focused along an axis from NE Alabama, across our I-85 corridor
and into central NC. Storm motions are erratic, reflecting weak
shear, but the consensus of meso models gradually propagates
activity southward thru the evening--possibly as outflows enter
the more unstable lower Piedmont zones. Updated pops trend this way.
A few light showers overnight could not be entirely ruled out
with moist low levels and a slight southerly upslope flow. With
the expectation of mid to high level clouds overhead through the
overnight hours as weak sfc low meanders north into the area, expect
min temperatures to remain above normal. Some of the guidance/fcst
soundings continued to suggest fog development towards daybreak
on Tuesday, but confidence is fairly low attm given anticipated
A similar pattern is expected on Tuesday, though the potential for
strong to severe storms will be slightly less. Temperatures will
remain just above normal, with heat indices in the low to mid 90s.
Short term /Tuesday night through Thursday/...
as of 1:35 PM EDT monday: the short-term forecast picks up at 00z on
Wednesday with our region stuck between upper ridging to the west and
weaker upper ridging over the western Atlantic. On Wed, broad upper
trofing begins to dig down across the Great Lakes as the ridges amplify
on either side of US. On thurs, the upper trof persists over the Great
Lakes as heights fall over our area and upper-lvl flow strengthens
from the west. At the sfc, the Bermuda high will continue to be the
main driver of our synoptic pattern thru most of the period, keeping
a moist, tropical airmass over the County warning forecast area. On thurs, a moist cold front
will make its way southeastward from the Ohio River valley and approach
the fcst area early thurs. The front is expected to move through the
County warning forecast area late thurs and into early Fri. No major changes were needed for
the sensible fcst with above climatology pops each day, with thurs
carrying likely pops across roughly the northern half of the County warning forecast area.
Instability will be decent each day/evening, with little in the way
of shear on Wed and a bit more on Thursday as the front approaches.
Instability will probably be limited to some extent on Thursday as
cloud cover is expected to increase thru the day. Temperatures will
remain just above normal.
Long term /Thursday night through Monday/...
as of 115 PM EDT monday: an slow moving cold front will continue
pushing over the forecast area to begin the ext range. With the upper flow
becoming more diffuse the front will become broad and stall while
slowly drifting south thru Fri. Good agreement is seen in the latest
guidance in developing a 1024 mb Canadian high over the Midwest
early Fri and traversing it east thru the period and this shud setup
a wedge scenario across the forecast area thru the weekend.
In the meantime...good instability will be had along and ahead of
the sfc bndry which will instigate deep tstms. Deep layered
shear remains quite low however...so the Mode will likely remain
pusley with multicellular lines probable into the evening. The latest
GFS is the quickest with bringing in NE/ly flow within the sfc-h8
layer Fri afternoon at khky and then arnd 00z at kgsp. The other op
models are much slower with The Wedge idea development arnd 12z Sat.
So...some uncertainty is had with the onset time of more stable air
and a general decrease in thunder activity Fri evening.
The Wedge does look to become mature by Sat afternoon tho and expect
atl and gom moisture adv to reinforce the pattern...which could
linger into Mon per the GFS. Max temps on Fri will be right arnd
normal...then below normal temps by a couple cats or so over the
weekend. Pops will remain abv normal outside the mtns in isentropic
lift...with The Wedge bndry likely become convectively active across
the extreme ern to SW/rn zones each afternoon Sat and sun.
Aviation /22z Monday through Saturday/...
at kclt and elsewhere: VFR prevails at all taf sites this afternoon,
with convection already blossoming across the entire forecast area.
Thus, all taf sites have prevailing vcsh/thunderstorms in the vicinity for the afternoon
hours, with tempo groups to account for possible short-lived flight
restrictions due to any rain showers/thunderstorms and rain that moves over a taf site. Expect
convection to wane into tonight, with lingering mid to high level
clouds and light winds. Latest fcst soundings continue to suggest
the potential for stratus, while some are hinting at fog
development. Confidence is low in regards to fog given the
anticipated cloud cover, but attm, could not entirely rule it out
Outlook: the potential for afternoon/evening showers and
thunderstorms is expected to increase throughout the week, as a cold
front approaches from the northwest into Thursday. Morning fog and low
stratus will be possible each day across the mountain valleys.
Otherwise, expect VFR.
21-03z 03-09z 09-15z 15-18z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 98% high 97% high 96%
kavl high 100% high 100% high 81% high 100%
khky high 100% high 100% high 100% high 100%
kgmu high 100% high 100% high 97% high 96%
kand high 100% high 100% high 85% high 90%
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: