Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
143 am EDT Thursday Jul 24 2014
Bermuda high pressure will give way to a a cold front approaching
from the northwest today. This front will become stationary
over the region this weekend. A second cold front will approach
the region Monday night into Tuesday and it too will stall along
the coast late Tuesday and Wednesday.
Near term /until 6 am Thursday morning/...
as of 1030 PM Wednesday...diurnally driven popcorn type showers
and thunderstorms have finally dissipated across the ilm County Warning Area.
This in response to the loss of daytime heating. Colliding outflow
boundaries that kept convection going several hours after sunset
are no longer available to sustain convection. As a result...have
dropped all probability of precipitation for the remainder of the night. Will mainly have
to deal with thinning convective debris cloudiness overnite. With
skies becoming mostly clear...fog may become an issue especially
away from the coast. Prognosticated low level south-southwest-SW jet overnight may
keep the low levels mixed enough to prevent fog development along
the coast. Current min temperature forecast of generally middle 70s remains
aok...with isolated lower 70s well inland...and possibly upper
70s to around 80 along the immediate coast.
Short term /6 am Thursday morning through Friday night/...
as of 320 PM Wednesday...Thursday is setting up to be a hot and
stormy afternoon and evening. The the synoptic scale a 500 mb
trough axis will shift toward the coastal Carolinas and forecast
area will be on the east side of the trough through the period. At
the surface a cold front is expected to shift to the coast Friday
evening. Ahead of this front with a west southwesterly winds
temperatures are expected to reach middle 90s especially in inland
northeast South Carolina. These temperatures combined with the
dew point in the lower 70s will produce heat indices values in the
100 to 103 degree range especially inland areas.
For storms with the frontal boundary coming across a a weak middle
level jet can not rule out strong winds with the storms but the
high precipitable waters of over 2 inches will ME heavy downpours
are possible and isolated flooding is possible.
For Friday...with the front in the region and cloud cover expect a
chance of thunderstorms but high temperatures will be in the upper
80s to near 90.
Long term /Saturday through Wednesday/...
as of 320 PM Wednesday...a weak upper impulse crosses the region on
Saturday while Piedmont trough/frontal remains sit to our west.
Tough to completely rule out isolated convection in such a setup but middle
levels remain too dry for any more coverage than that. Much the
same will apply on Sunday...and both days will likely offer up
fairly seasonable temperatures. Sunday night into Monday may start
getting active as middle level cyclonic flow and surface cold front
approach from the northwest...both in response to unseasonably strong
troughiness developing in the Great Lakes. This front pushes through
Monday night into Tuesday morning. Some cooler and drier air will
then filter in behind it for the midweek period. Exception may be
along the coast where sufficient moisture may linger for small rain
Aviation /06z Thursday through Monday/...
as of 06z...currently VFR at the terminals. Winds will stay elevated
early this morning from the SW. This should work against any
significant fog formation...but could still see tempo MVFR visibilities/scattered
stratus at kflo/klbt in the pre-dawn hours. Coastal terminals should
SW winds increase by middle morning to 10-20kt at the coastal terminals
and to around 10kt at kflo/klbt. Expect a decent chance of tempo
thunderstorms and rain/MVFR by 18z. Best lift plays out after 21-22z as the airmass
stabilizes...but showers could persist into the evening hours.
Extended outlook...showers/tstms/tempo MVFR possible through
Friday...as well as Sunday and Monday.
near term /through tonight/...
as of 1045 PM Wednesday...pressure pattern and tightening
gradient overnight will yield SW winds increasing to 10 to 15
knots...or possibly a solid 15 knots. This in response to the surface pg
tightening-some between Bermuda high pressure centered well
offshore and the Piedmont trough across the Carolinas which will
eventually get consumed by the approaching cold front from the northwest
Significant seas will be the combination of 2 entities. 1. An
east-southeast to southeast 1-3 foot ground swell exhibiting 7 to 9 second periods.
2. Locally produced 1-3 foot SW wind driven waves exhibiting 3 to
5 second periods. Either 1 of these entities could dominate the
significant seas at any 1 time.
Short term /Thursday through Friday night/...
as of 320 PM Wednesday...winds will be from the southwest through
the period with an increase in winds as a surface cold front
approaches the waters but stalls just on shore. When the front
stall the winds will weaken just a bit. A sea heights are expected
to increase to 3 to 4 feet on Thursday and then settle back to 2
to 3 feet range on Friday.
Long term /Saturday through Monday/...
as of 320 PM Wednesday...Saturday will bring fairly typical
conditions for the time of year...a southwesterly flow resulting
from west Atlantic high pressure and a weak Piedmont
trough/frontal boundary inland. A sharpening of the latter on
Sunday will tighten the flow and seas could build to advisory
levels. The approach of an unseasonably strong cold front on
Monday will further tighten the gradient and an advisory appears
even more likely. Both days are a tougher call over southern zones
where 6 feet seas may have a harder time getting close enough to
shore to be in the 20nm forecast zones.