Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
753 PM EDT sun Mar 16 2014
low pressure will pump abundant moisture across the Gulf Coast
states as it moves towards the Carolina coast through Monday. Cold
high pressure will settle in over the northeastern states late
Monday into Tuesday bringing colder temperatures into the Carolinas
along with a chance of some wintry mix mainly in the northern
mountains and Piedmont areas of North Carolina. A weak cold front is
expected to cross the area Wednesday night followed by a dry high
building back in Thursday through Friday.
Near term /through Monday/...
530 PM EDT update...dry slot should continue to make slow progress
across the Piedmont into this evening...eventually tapering more
robust returns...if you can call them that...down to lighter
upglide driven stratiform precipitation. Overall...sensible weather will change
little through midnight...lingering low overcast...periodic upglide
driven light rain and/or drizzle with temperatures slowly falling.
As of 230 PM EDT...surface low now sitting over the lower tenn valley
with sharp positively tilted shortwave to its west over the Ozarks.
Cad is somewhat weak across the forecast area with the 1033mb parent high still
over the Great Lakes. The Wedge however will strengthen tonight as
the parent high shifts east...as does the shortwave...initiating
A dry slot ahead of the low is evident across the southeast...and
extending into the western County warning forecast area...from radar/satellite trends. While a
lull in precipitation is expected for much of the area this afternoon...plentiful
low level moisture and modest upglide will remain over The Wedge tonight.
Some upper divergence ahead of the upper trough will be at play also.
Probability of precipitation thus remain high overnight though gradually diminish as the
moisture becomes more shallow. For the same reason quantitative precipitation forecast should become
very light. Latest round of guidance generally trended slightly
warmer for lows tonight. Following bourgouin technique and
expectation of strong warm nose over The Wedge...ptype issues should
be rain vs. Freezing rain. Ice accumulate still mainly across the foothills/Piedmont
north of I-40...though with the rain/freezing rain line now not quite as far
south. Winter Weather Advisory will stand as-is...but will update wording.
Further precipitation should only reinforce The Wedge...with temperatures
struggling to rise out of the 30s in most areas tomorrow. Probability of precipitation are
modest with midlevel moisture and upglide really waning as the surface
low departs...though the shortwave will be in position to provide
some weak upper forcing mainly over the Piedmont. Temperatures should be
able to warm enough to allow all rain for most of the day...but a
changeover could occur again over the Piedmont by sunset as cold
advection increases as the coastal surface low spins up...and low level
Short term /Monday night through Wednesday/...
as of 230 PM EDT Sunday...confidences is above average as latest
models have come into better agreement through the short term period.
A southern stream upper closed low over the central Gulf Coast on
Monday night will become an open wave as it translates eastward into
the southeast coast by 12z Tuesday. Models agree that a cyclogenesis will occur
well off the southeast cost by 12z Tuesday in response to the upper wave. This
will lead to the best qg forcing and deep layered moisture moving
south of the area. The 12z NAM...which used to be a wet outlier
during this period...became a dry outlier as the surface low will
form well offshore and the region will be under the best upper
convergence regime. In fact...the 12z NAM has little to no quantitative precipitation forecast
response...mainly east of the mountains...while the sref/GFS/ECMWF have
very light quantitative precipitation forecast response in light of better moist upglide on top of a
surface cold arm damming wedge. With that said...have lowered probability of precipitation
from likely to the chance range across much of the region Monday night
and Tuesday. In addition...quantitative precipitation forecast was lowered accordingly. As for the
p-type...model thermal profile is still supportive of freezing rain
across the Blue Ridge and the NC Piedmont Monday night into early Tuesday.
However...due to very light quantitative precipitation forecast...ice accums appear to be minor at
As the parent high moves off the New England coast and a cold front
approaches from the Mississippi Valley...the cad will gradually
erode across the region Tuesday night into Wednesday morning and ongoing light
moist upglide precipitation will taper off as well. Hence...Wednesday looks
mostly dry...with probability of precipitation ramping up to the slight chance range along
the Tennessee line by Wednesday afternoon as the weak cold front reaches the
southern Appalachians. Temperatures on Tuesday will be around 20-25
degrees below normal east of the mountains with 10-15 degrees below over
the western zones of mountains for Wednesday...temperatures will warm up by 15-20
degrees but it will still be around 3-5 degrees below normal.
Long term /Wednesday night through Sunday/...
as of 200 PM EDT Sunday...the extended range period initializes
Wednesday evening in the wake of a passing cold frontal boundary.
Probability of precipitation will remain elevated at slight chance levels across the
mountains to start...then decrease into the middle morning hours. High
pressure will build in behind the frontal passage for Thursday and Friday
leading to moderating temperatures amidst mostly sunny skies.
Expecting daytime highs by weeks end to reach back to well above
normal levels regionwide. Long range guidance remains consistent
with the next low amplitude upper wave crossing the Great Lakes
region Friday night and into Saturday morning. A cold front will
push through the southern Appalachians during the day on Saturday
leading to increases to chance level probability of precipitation. Temperatures behind the
frontal passage for Sunday and Monday will suffer slightly as cooler Canadian
high pressure builds across the area leading to the return of
slightly below normal temperatures.
Aviation /00z Monday through Friday/...
at kclt and elsewhere...little change was made to the going thinking
for terminal locations across the forecast area. Cold air damming regime will
linger through the period allowing IFR conditions...especially
ceilings...to continue. Areas of rain and/or drizzle...driven primarily
by the low level warm air advection flow will continue to result in IFR/MVFR visibility.
With the latest lamp guidance still doing reasonably well with the
conditions this evening...will plan on following the flight
restrictions trends closely through the period.
Outlook...cold air damming will persist through Monday night. Widespread
restrictions are expected to linger into Tuesday...with wintry weather
possible over the northern foothills/Piedmont Monday and Monday night.
Widespread VFR conditions may return Tuesday night or Wednesday.
00-06z 06-12z 12-18z 18-24z
kclt medium 79% medium 76% medium 66% high 80%
kgsp medium 73% medium 75% low 59% high 83%
kavl high 93% high 85% low 57% high 87%
khky high 82% medium 75% low 56% medium 77%
kgmu medium 77% medium 75% medium 61% medium 79%
kand high 84% medium 71% low 56% medium 78%
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)
NC...Winter Weather Advisory from midnight tonight to noon EDT
Monday for ncz033-035>037-049-050-056-501>506.