Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
301 PM EDT Friday Aug 29 2014
Synopsis...a nearly stationary backdoor cold front will remain
across central North Carolina through tonight...before gradually
dissipating over the weekend as a light southerly return flow
develops across the region.
Near term /through tonight/...
as of 250 PM Friday...
As of 18z...latest observations/analysis indicates the backdoor
front has made it through at least 2/3rds the forecast area and
should become mostly stationary through tonight. Extensive cloud
cover is noted within the northeasterly flow along and north of the
front...with mostly clear skies across the extreme south. There
could be some brief breaks (or lifting) of the clouds over the next
several hours...but overall mostly cloudy skies should persist.
Instability has stayed down today given the cloud cover...although
across the south where there are little to no clouds...temperatures have
been able to warm into the low 90s and some marginal instability has
developed (per Storm Prediction Center mesoscale analysis). Therefore...there could be a
shower or two that develops through the evening hours...although
chances are rather small. Given the light winds tonight and the
moist air mass...patchy fog and/or low clouds will be likely towards
Saturday morning. Overnight lows will generally range from the upper
60s across the north to the lower 70s further south.
Short term /Saturday and Saturday night/...
as of 250 PM Friday...
Central NC will remain under the influence of an upper level ridge
on Saturday. The lingering backdoor front is expected to wash out
during the day as the surface high shifts offshore and a light
southerly return flow develops across the region. All of this will
result in a typical summertime pattern...with highs rising into the
lower 90s. With marginal instability expected to develop (highest
across the southeast)...isolated diurnal convection will be
possible...although many area likely remaining dry. Overnight lows
are expected to be in the upper 60s to lower 70s.
Long term /Sunday through Friday/...
as of 250 PM Friday...
Shortwave energy originating from the western Gulf of Mexico and
associated tropical moisture plume will track northward into the Tennessee
and Ohio Valley on Sunday and then northeastward into the Middle-
Atlantic States on Monday. Subtropical ridge centered over the
southeast coast should initially deflect the better rain chances
west of the area through sunday(via ring of fire moisture return
convection pattern across the NC mountains and foothills). However by
Monday...upper ridge axis begins to deamplify in response to the
aforementioned shortwave moving through the middle-Atlantic region with
middle/upper level shear axis and Lee side thermal trough providing
sufficient forcing to support isolated to scattered convection
Monday afternoon and evening.
Expect a typical summertime pattern through middle to late week as
subtropical ridge axis shifts westward into the middle south-lower MS
valley...allowing for isolated to widely scattered storms to fire
along Lee side thermal trough each afternoon. Highs in the upper 80s
to lower 90s with lows in the upper 60s t0 lower 70s.
Models continue to delay the arrival of a back-door cold front into
the area...with latest timing now suggesting Thursday night and into
Aviation /18z Friday through Wednesday/...
as of 130 PM Friday...
A cold front has shifted south through the area throughout the day
today...with fairly extensive cloud cover along and north of the
boundary...with mostly clear skies south of the front (i.E. Extreme
southern portions of the forecast area...kfay). These MVFR ceilings have
persisted all day and will likely persist for at least the next
couple of hours. Some breaks this afternoon are still possible...
with a brief return to VFR conditions into the evening hours.
However...the moist air mass and light and variable winds overnight
should result in fog/low stratus development...with IFR/LIFR
conditions expected (especially towards the northeastern portions of
the forecast area...krwi...krdu). Conditions are expected to improve
to VFR by middle Saturday morning as the front gradually washes out
over the area. An isolated shower or storm will be possible later
this afternoon/evening and again Saturday afternoon...although
coverage will rather sparse.
Outlook...a summertime pattern will persist through early/middle next
week...with isolated to scattered afternoon/evening convection and a
potential for early morning fog/stratus.