Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
300 PM EST Tuesday Jan 27 2015
strong low pressure affecting New England will continue to move
north as high pressure builds into the Carolinas tonight through
Thursday. A cold front will move across the eastern Carolinas
Thursday night. Moisture will return to the region on Sunday ahead
of a strong cold front that will cross the area late Sunday night.
Canadian high pressure will build over the southeast early next
Near term /until 6 am Wednesday morning/...
as of 3 PM Tuesday...stubborn low clouds will continue for a couple
more hours across southeastern North Carolina before dry air finally
swoops in and wins the battle. There's quite a difference in
temperature across the area from around 50 in Kingstree (south of
florence) to 40 on the beaches east of Wilmington. Northwesterly
winds will continue this evening in the flow between strong low
pressure off the New England coast and high pressure over Wisconsin.
A deep and very cold trough remains across the East Coast of the
United States. A vorticity maximum currently moving south across Ohio will
sweep southeastward into the base of the trough tonight...bringing
one final reinforcing shot of cold air into the eastern Carolinas.
At 850 mb the renewed surge of cold advection begins shortly after
06z/1 am Wednesday with 850 mb temperatures falling to -5c to -7c by
daybreak. Once any lingering clouds move offshore early this
evening...skies should remain clear overnight with only low chances
for some some thin stratocumulus at the base of the subsidence
inversion late tonight.
With a good amount of wind overnight my forecast lows are on the
high end of the MOS guidance range...26 along the I-95 corridor to
27-30 along the coast. Wind chill values could fall into the upper
teens by daybreak.
Short term /6 am Wednesday morning through Thursday night/...
as of 3 PM Tuesday...surface high builds in from the north Wednesday as 500 mb
trough pushes farther off the East Coast. Deep northwest flow and
subsidence keeps precipitable water values under 0.20 inch. Sunny
skies will prevail Wednesday but despite this highs will struggle to reach
middle 40s across much of the area in the face of strong cold
advection. Surface ridge axis moves overhead Wednesday evening...bringing
an end to cold advection and setting the stage for strong
radiational cooling. Calm winds and deep dry air should help
maximize cooling Wednesday night. One potential issue showing up in
forecast soundings is an increase in moisture around 500 mb. This
layer will not result in any cloud but could limit effectiveness of
the cooling closer to daybreak. Either way lows will be well below
climatology...low to middle 20s.
Surface high shifts off the coast Thursday under weak 500 mb shortwave ridge.
Brief period of warm advection ahead of the front will push temperatures
into the 50s but most areas will ultimately end up short of climatology.
Skies start off clear but increasing moisture aloft ahead of next
shortwave creates a cirrus deck late in the day. Duration of south
to southwest flow Thursday afternoon limits moisture return ahead of the
front. Think some showers cold develop along the boundary but there
are limiting factors. Moisture with the front is not very deep and
the lowest levels remain dry. So even if precipitation were to develop have
a hard time believing measurable precipitation will occur. Cold air does
not arrive until the very end of the period...keeping lows near
climatology Friday morning.
Long term /Friday through Tuesday/...
as of 3 PM Tuesday...a dynamic and changeable pattern for the
extended period...where initially an upper trough axis along
the Appalachian Mountains early Friday slips offshore Friday
night and becomes replaced by a short-wave upper ridge Saturday
night. Another vigorous trough approaches Sunday bringing a very
good chance of rain Sunday night into early Monday.
At the surface this translates to exiting isolated showers at the
coast early Friday...and dry high pressure over the area Saturday
through early Sunday. Comparison of the GFS/European model (ecmwf) surface fields
show good agreement that a moderately strong cold front with a
healthy Gulf moisture tap will approach Sunday...bringing soaking
rains Sunday night into daybreak Monday.
Wpc guidance and other numerical depictions suggest 0.75-1.25
inches of rainfall storm total Sunday night through early Monday
as the Gulf moisture if lifted ahead of energetic trough and the
attendant cold front.
Aviation /20z Tuesday through Sunday/...
strong low pressure of the coast of New England will slowly pull
away to the northeast this afternoon. North northwest winds will be
observed over the region this afternoon...along with scattered
mainly middle cloud. Ilm and lbt could see a lingering MVFR ceiling for
the first hour or so. Winds diminish for diurnal reasons this
evening...however with falling dewpoints and weak cold air
advection...do not expect any fog formation. Wednesday...sunny skies
with with a moderate northerly wind.
Extended aviation outlook...VFR conditions are expected at all
terminals through the weekend...but a few showers are possible
Thursday night with a passing cold front.
near term /through tonight/...
as of 3 PM Tuesday...strong low pressure off the New England
coastline and high pressure over Wisconsin are driving northwest
winds across the Carolinas. This will continue overnight...with a
reinforcing surge expected to move south across the area after
midnight. This will maintain wind speeds near 20 knots through the
night...especially away from shore. Seas currently 2-3 feet
nearshore and 4-5 feet near 20 miles offshore should change little
through the night. A "small craft should exercise caution" headline
will remain on the forecast through the night.
Short term /Wednesday through Thursday night/...
as of 3 PM Tuesday...northwest flow around 20 knots to start the period
will decrease Wednesday as gradient relaxes and cold advection shuts off.
Surface ridge axis moves to the coast Wednesday night with winds veering
to northeast and continuing to weaken. Ridge axis moves offshore
with light and variable winds Thursday. Surface high is quick to depart
east with return flow setting up late in the day Thursday then increasing
to a solid 20 knots Thursday night as cold front approaches from the west.
Front moves east of the waters as period ends and offshore flow
develops Friday morning. Cold air trails the front with wind speeds
ahead of and behind the front similar...20 knots or so. Seas 2 to 4 feet
for a majority of the period build to 3 to 5 feet late in the period
ahead of the advancing cold front.
Long term /Friday through Sunday/...
as of 3 PM Tuesday...Friday may need a caution statement for 20
knots north-northwest winds and 5 foot seas outer waters. Conditions will vastly
improve into Saturday as high pressure settles nearly overhead.
Manageable marine conditions will also prevail into Sunday. Winds
and seas will begin to increase Sunday night ahead of a moderately
strong cold front and an advisory may be needed late Sunday night
into Monday for blustery S winds and agitated seas.