Area forecast discussion
National Weather Service Raleigh NC
325 am EDT Wednesday Jun 19 2013
Synopsis...
cooler high pressure will build into the region from the northeast
through the end of the week.
&&
Near term /through tonight/...
as of 255 am Wednesday...
Today: surface observational data at 06z reveal a 1008 mb surface
wave just east of Chesapeake lighthouse Virginia (chlv2)...with a cold
front trailing west southwestward and evident as a krax radar fine
line from Greenville (kpgv) to Sanford NC (ktta)...then
southwestward to near Anderson SC (kand). Nwp guidance suggests this
boundary will drift to a position over southeastern NC...including
across the southern NC coastal plain. This boundary/convergence axis
and northern bound of surface dewpoints at or above 70 degrees will mark the
northern edge of precipitation chances over central NC (sampson
Colorado.)..and mostly cloudy conditions through midday-early
afternoon...with decreasing clouds to partly sunny elsewhere.
However...a chance of showers will be renewed during the middle-late
afternoon hours mainly over the northern/northeast Piedmont and
northern coastal plain (roughly from Raleigh and points north and
eastward)...as a secondary northern stream cold front analyzed over
northern Virginia this morning...and augmented this afternoon by
northeasterly maritime flow and associated sea/Bay breezes...
settles south southwestward into those areas coincident with peak
diurnal heating. While convergence with this feature will be limited
owing to overwhelming northeasterly low level flow behind the lead
front over southeast NC...this area will also be under the influence of
deeper layer forcing for ascent accompanying an approaching
positively-tilted middle level trough axis and pair of embedded
shortwave disturbances from the Ohio and middle MS valleys this morning.
The coupling of this low and deep (albeit relatively weak)
lift...and with forecast k-indices between 25 and 30 c and weak
instability of generally 500 j/kg or less fueled by afternoon
temperatures and dewpoints in the low to middle 80s and 60s
respectively...a small chance of showers is justified in those
areas...with precipitation elsewhere and otherwise less than 15
percent.
Tonight: height rises in northwest to northerly flow aloft...
suggests skies will clear or becoming mostly so...though with few
patches of stratus or fog in NE low level flow toward morning.
Cooler...with lows mostly in the lower to middle 60s.
&&
Short term /Thursday and Thursday night/...
as of 315 am Wednesday...
Modified Continental polar high pressure and associated lack of deep
moisture characterized by precipitable water values over central NC
falling from around 1 to 1.25 inches Thursday morning to a half an inch
or so by Friday morning...will extend southwestward into central
NC through the short term...and beyond. The presence of the high
will yield stable/dry and mostly clear conditions...aside from any
lingering morning low clouds/light fog...then mainly just a few fair
weather cumulus over the western Piedmont Thursday afternoon giving way to
thin cirrus in advance of a moisture-starved middle-upper wave forecast
to cross the central Appalachians Thursday night. Cooler with lower
humidity...characterized by dewpoints falling into the 50s in
northeasterly flow around the surface ridge...with highs in the
lower to middle 80s. Upper 50s to Lower-Middle 60s Thursday night...
coolest NE and in the typically cooler sheltered/rural areas.
&&
Long term /Friday through Wednesday/...
as of 325 am Wednesday...
Friday and Saturday...cool high pressure off the middle Atlantic coast
will extend southwest into the area...providing US with a couple of
mostly sunny days with slightly below normal temperatures in the
ensuing easterly flow. Highs will be in the low and middle 80s with
morning mins generally from 60 to 65.
The surface high will shift further offshore and flow will veer more
southerly as the weekend progresses...increasing humidity and weak
warm air advection. Meanwhile...a broad upper ridge over the Midwest
will gradually build eastward...further promoting a slow warmup back
to seasonal highs in the upper 80s Sunday to the upper 80s to lower
90s Monday and Tuesday. Conceptually...instability will be at least
modest Sunday through Tuesday...but the upper ridge will both
block/divert approaching impulses and convectively cap our
airmass...so in the absence of readily identifiable forcing
mechanisms...will maintain probability of precipitation in the slight chance category at
best.
&&
Aviation /06z Wednesday through Sunday/...
as of 145 am Wednesday...
A line of showers lingers along the southern tier of the area
ahead of the surface cold front...which has moved south of all but
the Fay terminal. Ensuing drying in northerly flow has effectively
cleared out IFR/LIFR ceilings over the bulk of the area...and tafs
will show an improving trend through the remainder of the
night...although patchy MVFR...or even IFR ceilings and visibility
are possible at times through an hour or so after sunrise.
VFR conditions will be prevalent beyond 12z...although a trailing
upper short wave will be sinking south into the area in the late
afternoon. This short wave will be accompanied by broken stratocu or
altocu...and possibly scattered showers across the northern tier
after 21z. Conditions are not likely to fall below VFR anywhere
except possibly rdu and rwi towards 00z...and will not include this
possibility due to the low probabilities at this time.
Looking ahead: high pressure will build into and linger over central
NC Wednesday night through the weekend. This weather system will
bring dry and stable conditions leading to VFR parameters. The
exception will be a brief period of MVFR visibility due to
fog...mainly in the coastal plain.
&&
Rah watches/warnings/advisories...
none.
&&
$$
Synopsis...Badgett
near term...mws
short term...mws
long term...mlm
aviation...mlm
