Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
1000 am EDT Wednesday Jul 23 2014
Bermuda high pressure will build into the area today. A cold front
will approach from the northwest Thursday...stalling near the coast
for the weekend. Another cold front will approach from the northwest
Monday or Tuesday.
Near term /through tonight/...
as of 1000 am Wednesday...inland fog has become a low stratocumulus
deck since sunrise and should lift further into a cumulus deck over
the next hour. This moisture will be the seed for scattered
thunderstorms this afternoon with coverage averaging about 30
percent of the forecast area. Synoptically the old stationary front
near the coast is nearly gone with Bermuda high pressure offshore
expected to turn surface winds southwesterly later today. A
landbreeze pushed offshore before sunrise with light west to
northwest winds observed at the beaches. The daytime seabreeze will
turn these wind directions south to southwesterly by early afternoon.
The airmass remains quite moist with precipitable water values near
2.0 inches and surface dewpoints 72-75 degrees. Light steering flow
and modest lapse rates aloft will limit the coverage and development
of storms today...but virtually all model guidance shows there
should be some convective activity out there this afternoon. A
limiting factor that will still be in play is the presence of
widespread convection over the Gulf Stream off the Georgia-SC-NC coast.
Sustained rising motion within this convection will lead to a
corresponding ring of subsidence around the edge...including over
the coastal Carolinas. For this reason my forecast probability of precipitation remain below
the GFS/NAM MOS consensus today.
I have bumped forecast highs up a bit with lower 90s forecast inland
and upper 80s at the coast. With dewpoints probably remaining in the
lower 70s even during peak heating we could see heat indices reach
100 degrees in spots this afternoon.
Short term /Thursday through Friday night/...
as of 330 am Wednesday...some drier air streaming in initially
on Thursday with southwest flow and pcp water values down around 1.5
inches but as the day progresses a cold front will move into and
slowly through the Carolinas. As the front approaches from the
northwest the gradient will tighten with gusty SW winds and
increasing low level winds up to 30 kts. Moisture pools ahead of
the front with increased convective activity by late Thursday as pcp
water values reach up over 2 inches. Expect most widespread
shower/thunderstorm activity by late Thursday afternoon as pre frontal trough nears
the area and greatest shortwave energy rides around the base of
the 500 mb trough through the Carolinas. The best upper level support
will lay just west of local forecast area on Thursday afternoon but
heading into Thursday night...steering flow will veer to become more
SW to west and should see a fair amount of convection into our area.
The front will get hung up over the coastal Carolinas and should
see Friday more active along the coast while drier air will make
its way in across inland areas. The middle to upper trough shifts off
the coast through Friday night before it lifts off to the northeast
leaving a deeper drier flow and increased subsidence heading into
Decent westerly downslope component to the winds with low level
thicknesses peaking Thursday. Expect high temperatures to reach into the 90s
and with dewpoint temperatures into the 70s...temperatures will feel as if they
are over 100 degrees in places especially across northeast South
Carolina. As trough digs down and heights lower for
Friday...expect temperatures to be a few degrees lower but still up
around 90. Clouds and increased shower activity will affect the
temperatures especially late Thursday through early Friday. Low temperatures both
nights will be in the middle 70s.
Long term /Saturday through Tuesday/...
as of 330 am Wednesday...lingering cold front may remain near
the coast as it weakens leaving weak high pressure over the area
for the weekend. Although the surface boundary remains close
by...enough dry air will make its way into the area in westerly
flow aloft with column moisture appreciably lower above 850 mb. Pcp
water values will be down near 1.5 inches through Saturday and
even lower inland. The gradient will relax as the front shifts
south and east and weakens through Saturday. Middle to upper trough
lifts far enough out of area and although a broad trough remains
over the Great Lakes...heights will rise over the Carolinas as
ridge tries to nose into the southeast through the weekend.
Overall expect a good deal of sunshine through the weekend with
lower probability of precipitation in more localized shower activity and warm temperatures.
By late Sunday into Monday the middle to upper trough begins to dig
south again pushing another cold front east into the Carolinas.
Therefore should see another round of increased convective
activity across the area ahead and along the cold front as it
moves through the coastal Carolinas Monday into early Tuesday. Looks
like the main 500 mb trough axis will shift off the coast Tuesday pushing
front far enough east to allow for deeper drier air to move into
the area as high pressure builds in for middle week. The main trough
will continue to plague the East Coast with lower heights and
temperatures pushed to the cooler side of climatology for middle week next week.
Temperatures will start out above normal in a warm and humid air mass
with readings in the 90s for highs through much of the weekend but
by Tuesday maximum temperatures will be in the 80s most places with dewpoint
temperatures dropping into the 60s.
Aviation /12z Wednesday through Sunday/...
as of 12z...areas of IFR this morning due to low ceilings and areas of
fog...improving to VFR later this morning and continuing through
tonight with isolated to scattered rain showers/thunderstorms and rain possible today.
Overnight possible MVFR/IFR due to patchy fog.
While the coastal sites are currently VFR...IFR prevails at the
inland sites due to fog and low ceilings...which will improve to VFR
over the next few hours. Latest radar imagery depicts all rain showers/thunderstorms and rain
activity offshore this morning...but expect throughout the day for
chances to increase for isolated to scattered rain showers/thunderstorms and rain across the
area...tapering off later this evening. As for winds...southwesterly
winds are expected with sustained winds at or below 10 kts. Overnight into
Thursday morning...expect VFR to prevail with the exception of the
inland sites which may experience MVFR/IFR due to fog before
Extended outlook...chance of showers/thunderstorms will persist through the
extended period. Expect predominantly VFR conditions with tempo
periods of MVFR/IFR ceilings/visibilities in storms.
near term /through tonight/...
as of 1000 am Wednesday...more typical middle-Summer weather will
develop today as the old stationary front of the past two days
dissipates and Bermuda high pressure well offshore takes hold. A
weak landbreeze pushed offshore before sunrise producing west to
northwest winds across the coastal waters. These wind directions
should turn back onshore this afternoon with the seabreeze...with
wind speeds increasing to near 15 knots by early evening. The
overall pressure gradient should tighten overnight with 12-16 knot
winds expected through much of the night.
Seas currently consist almost exclusively of a 7-8 second southeast
swell around 3 feet...perhaps closer to 2 feet along the South
Carolina coast where we have no buoy data. A little more wind chop
should develop on top by this evening...with combined seas averaging
3-4 feet away from shore.
Short term /Thursday through Friday night/...
as of 330 am Wednesday...cold front will move slowly through the
Carolinas late Thursday into Friday before stalling out near the
coast on Friday. Overall should see a tightened gradient flow out of
the southwest up to 15 to 20 kts late Thursday into early Friday. Seas
around 2 to 4 feet early Thursday will build up to 3 to 5 feet by Thursday
evening and possibly reaching close to Small Craft Advisory thresholds Thursday evening. Winds
and seas will diminish through Friday as front weakens along the
Carolina coast. May see a period of more west winds on Friday depending
on how close the front makes it before coming back around to the
S-SW through the weekend.
Long term /Saturday through Sunday/...
as of 330 am Wednesday...will maintain a SW flow around Bermuda
high around 10 to 15 kts through Saturday. The winds will increase
Sat night through Sunday as gradient tightens as Piedmont trough
becomes more pronounced and next cold front approaches the western
Carolinas by early Monday. Seas will diminish through Sat morning
and then will begin a rise through Sat night and Sunday possibly
reaching above Small Craft Advisory thresholds by Sun night. Seas 3 feet or less Sat
morning will reach up to 3 to 5 feet by sun evening and near 6 feet by
early Monday morning.