Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
1240 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 1215 am Friday...
Clear skies and dry conditions will prevail through tonight as an
upper level ridge amplifies over the southeastern Continental U.S.. attendant
surface high pressure over the Carolinas will begin to shift offshore
tonight. Expect afternoon temperatures similar albeit slightly warmer than
yesterday...in the middle/upper 50s to near 60f. Lows tonight will be
similar to this morning...in the lower 30s except upper 20s in
rural and low-lying areas...especially along/east of Highway 1. -Vincent
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 252 PM Thursday...
Sunday through Monday night: left behind southern stream shortwave
over The Four Corners region late Saturday will shear out as it
ejects eastward across the Southern Plains-lower MS valley on
Sunday...nearly sheared apart by the time it moves through the area
between 12-18z Monday. Models are in above average agreement with
the timing of the attendant wavy frontal zone through the
area...prognosticated to slip south through the area Sunday night and into
Monday...and trending more progressive as it drives the front well
south of the area on Tuesday.
Surge of strong warm air advection with precipitable waters increasing to 1.3-1.6" coupled with
DPVA from short wave disturbances embedded in the southwesterly flow aloft will
support widespread showers across the area on Sunday. There could be
a possible lull late Sunday afternoon/evening as the deeper moisture
moves east and north of the area...with renewed lift/forcing
arriving as the cold front sinks slowly south into the area
overnight and into the Monday. Rain chances should decrease
drastically after 18z with the passage of the trough and subsequent
middle-level drying...as front slips south of the area. Rain and clouds
will cool temperatures slightly on Sunday...with more pronounced north-
south temperature gradient on Monday as cold air begins to advect
into the area from the north.
Tuesday-thursday: upper flow will become zonal downstream of the
developing closed low over the SW US. An expansive 1050mb Arctic
high will bring a shot of cold air down the nations middle-
section...with central NC on the eastern periphery of this cold
airmass that will support slightly below normal temperatures through
Aviation /06z Friday through Monday/...
as of 1230 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