Scientific Forecaster Discussion
fxus62 krah 181204
Area forecast discussion
National Weather Service Raleigh NC
805 am EDT sun Aug 18 2019
a weak surface trough will remain across the area today, while an
area of low pressure lifts northward along the NC coast. Otherwise,
an area of high pressure positioned offshore will maintain a warm
and humid air mass over central NC through mid week.
Near term /through tonight/...
as of 340 am Sunday...
Early this morning, an abundantly moist air mass in the lowest 10k
ft of the atmosphere and a near calm wind regime will permit the
development of widespread low clouds and fog this morning over most
of central NC. Currently appears the threat for thick/dense fog will
be in vicinity and east of Highway 1. Confidence not high enough at
this time to issue a dense fog advisory; though, will continue to
monitor. Otherwise , local radar and satellite imagery depict a
compact area of low pressure drifting newd between Wilmington and
Morehead City early this morning. Circulation/convergence around
this low may spread enough lift and moisture to warrant a slight
chance pop this morning along our eastern periphery, with a higher
pop warranted east of our region.
Once the fog/low clouds burn off later this morning, expect partly
cloudy/mostly sunny skies and hot temperatures. Relative humidity cross sections
depict a relatively dry atmosphere in the mid/upper levels with the
better moisture confined to the lowest 10k feet. In addition, weak
subsidence on the backside of the retreating low along the NC coast
will inhibit vertical lift, especially east of Highway 1. Thus,
expect pop chances this afternoon-early evening to be no worse than
slight or small, and mainly confined to the western Piedmont and
Expect afternoon temperatures to be notably hotter than Saturday,
with highs in the 90-95 degree range. These temperatures will
translate to heat indices this afternoon around 100 degrees over all
but the northwest Piedmont.
Tonight, expect mostly clear to partly cloudy skies. It will remain
abundantly moist in the lower layers though a light sly wind should
occur most of the night. This stirring may be enough to inhibit fog
formation though stratus may still occur. Continued warm/humid with
overnight temperatures generally in the low-mid 70s.
Short term /Monday and Monday night/...
as of 405 am Sunday...
An area of low pressure will form later today over the northeast
Gulf of Mexico and drift inland over the Florida Panhandle Monday. A weak
mid level emanating from this low will extend into central NC. This
feature will aid funnel a narrow plume of moisture into central NC.
Afternoon heating coupled with a passage of a weak upper disturbance
to our north should trigger scattered afternoon-early evening
convection, primarily across the southern and western Piedmont. Due
to a relatively weak steering flow, convection may occur repeatedly
over the same location, potentially leading to minor flooding in a
few spots. Cannot rule out the potential for a wet microburst,
though the threat for organized convection is minuscule as the bulk
shear is 10kts or less.
Prior to convection initiation/development, temperatures will climb
back into the low-mid 90s.
Anticipate convection to slowly diminish with loss of heating, with
mostly clear/partly cloudy skies in its wake. Overnight temperatures
in the low-mid 70s.
Long term /Tuesday through Saturday/...
as of 300 am Sunday...
The long term will be characterized by weak steering flow with
central North Carolina sandwiched between two mid-level ridges.
The First Ridge will be located across the Central Plains while
the Second Ridge will be centered near Bermuda. Tuesday morning,
leftover vorticity will be meandering across Georgia and slowly
nudge northeast over North Carolina and eventually get picked
up in a long wave trough axis over Canada. Pwats at this time
will be around 1.70", or between the 75th and 90th percentile
for this time of year. Overall, the best instability and
moisture appear to be on Tuesday, while Wednesday the primary
band of instability and moisture will be more towards the
sandhills and coastal plain. Due to this have continued slightly
higher pops for Tuesday compared to Wednesday. The lack of
strong forcing mentioned above means pops were kept towards a
persistence- leaning pattern of isolated pops in the night
through morning hours, followed by scattered to numerous showers
and thunderstorms from late morning through mid evening.
Temperature wise, both days appear to again be warm with highs
and lows above normal. 850 mb temperatures Tuesday into
Wednesday remain near 19 degrees c with 1000/850 mb thicknesses
around 1430 M. This will easily support highs in the lower 90s
A mid-level low will deepen near the Hudson Bay Thursday with a
cold front surging south through the Ohio Valley. The front
will then stall across southern Virginia Friday. Thursday night into
Friday pwats will continue to surge and likely reach 2.00". The
surface convergence working in tandem with the anomalously high
pwats will help increase pops Thursday through Friday with
coverage becoming widespread. The latest run of the GFS tries
to bring the lower precipitable water air into central NC, but given the time
of year this currently appears unlikely. For now will keep pops
elevated into Saturday.
Aviation /12z Sunday through Thursday/...
as of 805 am Sunday...
Areas of IFR/LIFR ceiling and visibility across central NC this
morning will lift dissipate prior to 14z. After 14z, expect mainly
VFR conditions with a scattered-broken cu field expected and bases
4000-6000ft. Convection should not be as prominent as the past few
days with coverage no worse than 20 percent this afternoon through
sunset, mainly near and south of The Triad.
Tonight, VFR parameters will give way to patchy areas of IFR/LIFR
due to low clouds and fog. Scattered convection expected Monday
afternoon-Monday evening with MVFR/IFR parameters probable in
vicinity of the heavier showers. Expect more of the same through the
remainder of the work week as the atmosphere over central NC will
remain moist and slightly unstable, supportive of early morning
fog/stratus, and late afternoon-early evening convection.
gso upper air flights have been scheduled through 12z Tuesday,
including 00z flights this evening and Monday evening.