Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
730 am EDT Wednesday Jul 30 2014
dry and cool weather will continue through into late week as
Canadian high pressure settles across the area. A coastal front
will lift back north across the area Friday and into the
weekend...bringing good rain chances into early next week.
Near term /through tonight/...
as of 610 am Wednesday...the unusual amplified upper longwave trough
to remain in place this period...basically affecting the U.S. East
of the Mississippi River. The north-S oriented upper trough axis is
prognosticated to remain just west of the forecast area. Overall...the ilm County Warning Area will
continue to experience below normal temperatures and comfortable rhs. For
this time of the year to have comfortable rhs is difficult to come
by...but to have potentially up to 3 to 4 days in a row...is a
gift. Will basically use persistence for the near term forecast.
Channeled weak vorticity traveling within the upper trough...as seen
with 7h and 500 mb forecasts...will push across the forecast area. This forcing and
enough moisture existing below the subsidence level will result in
cumulus/ac/SC clouds at almost any time across the forecast area. Majority of it
will be scattered in coverage. The forcing from the resultant wind
boundary will be enough for additional clouds to develop...
producing intervals of partly and mostly cloudy skies. Will remain
on the fence as far as placing isolated showers in the forecast.
The forcing from the resultant wind boundary and limited juice ie.
Cape...will be available. For now...probability of precipitation will be advertised just
under 15 percent. Temperatures have been a headache the past several days
..mainly the maximum temperatures. However...will go along with persistence
..and thus staying closer to the GFS MOS guidance...Which has
been performing well of late.
Short term /Thursday through Friday night/...
as of 300 am Wednesday...cool weather will continue for the short
term thanks to a closed low pressure near the Hudson Bay maintaining
an anomalously strong middle-level trough across the east. This feature
will very gradually weaken and lift to the northeast by the
weekend...and thus subtle thickness increases will occur...but at the
same time this will allow winds to back more to the S/SW off the
surface...increasing column moisture. Precipitable waters Thursday around 1.75
inches are right around seasonable values for the beginning of
August...and scattered showers/thunderstorms will be possible Thursday.
Friday is expected to be the wetter day however...as coastal
trough/warm front begin to lift back towards the coast...likely
moving onshore late Friday. Precipitable waters rise to around 2 inches...which
will combine with surface convergence along the boundary...and
continued upper diffluence within the jet-streak embedded downwind
of the large scale trough...to create a good chance for showers and
storms. There will be some diurnal enhancement/nocturnal decrease of
the convection Friday...but do expect showers to continue throughout
Temperatures will remain below normal for the date...with middle 80s expected
Thursday...although a few spots in the Pee Dee region of SC may
approach 90. Although thicknesses rise Friday...clouds and precipitation
will limit warming...and thus highs will be a degree or two cooler
than Thursday. Mins both nights will fall into the upper 60s
inland...around 70 at the coast.
Long term /Saturday through Tuesday/...
as of 300 am Wednesday...a wet period expected the first half of the
long term...making the first weekend of August cool and unsettled.
Large upper trough which has been plaguing the eastern Continental U.S. For
some time will finally...slowly...begin to erode thanks to the
weakening of the parent vortex...and the amplification of the ridge
across the Atlantic Ocean. While this ridge will eventually overcome
the persistent trough across the east...it will likely take until
Tuesday for any noticeable warming/drying to occur locally...and
temperatures will remain below normal through the period.
The reason for this is because as the trough begins recede to the
west...a coastal trough/warm front will stall near the area during
the weekend. This provides strong low-level moist advection...while
middle-level moist advection occurs on increasing S/SW flow downwind of
the trough axis. This produces precipitable waters over two inches...which combine
with surface convergence and upper diffluence within the jet streak
around the base of the trough to create scattered to widespread
showers and thunderstorms Saturday...Sunday...and even into Monday.
Finally by Tuesday the surface trough washes out...ridging takes
hold aloft...and more seasonable weather develops for the middle of
Aviation /12z Wednesday through Sunday/...
as of 12z...expect VFR to prevail through this taf period. Surface high
pressure over the eastern half of the country will dominate our
weather today. Northeast winds around 5 knots this morning will become
east-southeast at or below 10 knots this afternoon as high pressure moves eastward.
Kflo/klbt may see periods of light/vrb winds today as the gradient
is fairly weak. Some 4-6kft cumulus will develop after midday...but forecast
soundings are very dry above 700 mb. Therefore will not mention any
precipitation in the tafs at this time. Middle/high cloud cover will increase tonight
and winds will diminish to east at or below 5 knots. NAM guidance hints at some
MVFR visibilities overnight at kflo/klbt...but will hold off on reduced
visibilities given the expected increase in cloud cover.
Extended outlook...increasing chances for rain showers/thunderstorms and rain and periods of
MVFR conditions Friday through Sunday as a front stalls over the
near term /through tonight/...
as of 615 am Wednesday...synoptically the area waters will lie in
between a broad surface low well offshore along the stationary
front...and the center of weak high pressure across the Carolinas.
The resulting surface pressure pattern and relaxed gradient across the
ilm waters will produce NE-east winds around 10 knots. The exception
will be the near shore waters for this afternoon and evening...with the
development and inland progression of the resultant wind
boundary...winds will become southeast at 10-15 knots. Significant seas will
continue to be the combined efforts of the locally produced 1-2
foot wind driven waves at 4 second periods...and the east-southeast 1-2 foot
ground swell at 8-9 second periods. In essence...significant seas
will be around 3 feet thruout the forecast period.
Short term /Thursday through Friday night/...
as of 300 am Wednesday...stalled cold front/coastal trough well
offshore will be pushed back towards the coast Thursday before
moving onshore during Friday. The gradient will remain weak near
this feature...with winds around 10 kts through the period...but a
veering from the east Thursday...to southeast on Friday...will occur behind
this boundary. Several wave groups will exist within the
spectrum...but a low amplitude southeast ground swell and east and
southeast wind waves will combine to produce 2-3 feet seas through the
Long term /Saturday through Sunday/...
as of 300 am Wednesday...coastal trough/warm front will lift northwest of
the waters by early Saturday...and remain inland during the weekend.
Winds behind this feature will veer slowly from southeast to SW...at speeds
of 10-15 kts. Wave heights will be predominantly 2-3 feet through the
extended...but some 4 feet seas are possible Sunday thanks to the
longer spatial fetch from the S/se.