Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
1005 am EST Friday Dec 26 2014
Synopsis...high pressure will remain over the Carolinas through
Saturday...then shift offshore Saturday night. A cold front will
approach from the northwest on Sunday and gradually move southward
through the region on Monday.
Near term /today and tonight/...
as of 1000 am Friday...
Latest surface and upper air analyses shows high pressure dominating
central NC. Therefore another day of clear skies and relatively mild
weather is in store. Highs should be a few degrees warmer than
yesterday as the low level thickness values increase some...with
upper 50s to lower 60s expected. The surface high will start to
shift offshore tonight and with the resultant light return flow...
overnight lows should not be as cool. Therefore...mostly lower 30s
are expected (with maybe a few upper 20s in the normally cooler
Short term /Saturday and Saturday night/...
as of 1230 am Friday...
Southwest flow aloft will become established over the region on
Saturday as an upper level low currently over the Desert Southwest
progresses toward the lower Midwest and the upper level ridge
currently over the southeast coast shifts offshore. Moistening will
occur throughout the day in associated/west the onset of a southerly return
flow in the lower levels and the advection of middle/upper level
moisture downstream of precipitation expected to develop across the
deep south and lower MS River Valley as a weak cold front attendant
a progressive northern stream trough tracks into the Ohio/Tennessee Valley.
Expect dry conditions to persist during the day...with increasing
middle/upper level cloud cover during the aft/eve. Confidence in the
forecast decreases Sat night...especially with regard to precipitation chances.
Strengthening low-level warm advection and moistening aloft may lead
to elevated destabilization Sat night...in the presence of an
increasing potential for small amplitude waves or convective
vorticity maxima tracking into the region via SW flow aloft. Model
guidance varies with respect to precipitation coverage and amounts
between 06-12z sun...apparently as a result of differences in the
evolution of disturbances in SW flow aloft and low-level height/wind
fields over the Carolinas. Will make little change to the previous
forecast...showing overcast skies and increasing probabilities for
rain after midnight...highest in the western Piedmont. Lows will be
warmer due to cloud cover...in the 40s. -Vincent
Long term /Sunday through Thursday/...
as of 222 am Friday...
A cold front will move from the Tennessee Valley at 12z sun to the NC
foothills/western Piedmont by 00z Monday. A short wave trough...
prognosticated to move across our region in advance of the front...coupled
with a surge of moisture moving up from the S...appears to support a
decent chance for showers early Sunday. Then after a break in the
rain chances during the afternoon and evening...the remaining precipitation
associated with the front should hold off until after sunset. The front
is prognosticated to slip south across our area overnight into early Monday
morning. A few light showers may linger across our area behind the
front during the daytime Monday as cooler air moves in behind the
front...but quantitative precipitation forecast values are prognosticated at less than a tenth of an inch.
For the rest of the long term period...recent models runs have
trended drier...with the synoptic pattern now featuring flow that's
more westerly over our area...and drier...thanks to the confluence
of the northern and southern streams in vicinity of the central appalachian
and middle-Atlantic regions.
Regarding temperatures during this time...forecast low level thicknesses
are prognosticated to drop nearly 90m from their peak around 1375m just
before frontal passage Sunday evening...to around 1285m by early Thursday...a
somewhat gradual process as a 1055mb high over the northern rockies
early Monday moves south and east across the plains and eastward
during the middle-week period. Will see high temperatures gradually lower each
day...from highs on Sunday in the upper 50s to lower 60s...to highs
in the middle 40s to near 50 by mid-week. Low temperatures will follow a
similar trend...upper 40s to lower 50s Sunday night...falling back
closer to normal (lower 30s) by mid-week.
Aviation /12z Friday through Monday/...
as of 620 am Friday...
24 hour taf period: VFR conditions and light/variable winds will
prevail through the taf period in associated/west high pressure over the
Looking ahead: VFR conditions will persist through Saturday. Expect
an increasing potential for MVFR/IFR ceilings and rain late Saturday
night through Sunday night as a slow moving front progresses across
the region. -Vincent