Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
330 am EST Tuesday Feb 9 2016
Synopsis... a couple of upper level disturbances will move over the
region through this evening... otherwise cold high pressure will be
in place through mid-week. This will be followed by an even colder
Arctic high pressure for the weekend.
Near term /through tonight/...
as of 255 am Tuesday...
An area of cloudiness and associated light rain or sprinkles will
affect the region this morning per the latest radar and satellite
trends. The water vapor satellite imagery depicted the middle level
disturbance approaching the region from the west early this morning.
Satellite and surface observations indicated considerable cloudiness
developing over west central NC in response to the lift associated
with this feature. Radar indicated patchy very light returns (rain)
extending from Albemarle to Carthage... moving east-northeast toward
the northern sandhills and eastern Piedmont. With the cold air
lagging behind the cold front... surface dew points... surface
temperatures... and corresponding wet bulb temperatures were in the
middle to upper 30s along this line and extending eastward into the
areas that are in line to get some very light precipitation this
morning. Therefore... we are not anticipating or forecasting any
travel issues or associated impacts of the light rain. Areas to the
northwest over The Triad are colder... but any precipitation that
falls there should be only a brief flurry with no accumulation. The
cold front will advance east through the region this morning with
cold air advection this afternoon in westerly winds at 10-20 miles per hour.
Another disturbance aloft is forecast to track over southern Virginia and
northeastern NC this afternoon. As the surface temperatures warm
into the lower to middle 40s... this will combine with the cooling
aloft to produce steepening lapse rates again this afternoon.
Isolated to widely scattered showers may develop in the cumulus
field this afternoon where it becomes enhanced at times...
especially north and east of the Triangle.
As for p-type (again no impact)... temperatures near the surface
will be well above freezing... the cold air aloft and web bulb
profiles indicate that there would likely be a mixture of
rain/snow/sleet showers. Still... no impact is expected. Any of the
widely scattered or isolated showers would be brief with only trace
amounts... and temperatures in the 40s.
Short term /tonight through Wednesday night/...
as of 255 am Tuesday...
Cold advection will continue tonight and Wednesday with the high
pressure building in from the northwest. The first middle/upper cold
trough will maximize over the region Wednesday before beginning to
lift out. However... the northwest flow aloft with yet another
disturbance passing through should lead to variably cloudy skies in
the afternoon again Wednesday. A passing flurry is possible. Lows
tonight 20-25. Highs Wednesday only in the upper 30s to middle 40s
north to south. The skies will become mostly clear again Wednesday
night with diminishing breezes. Lows 15-20 north to 20-25 south.
Long term /Thursday through Monday/...
as of 330 am Tuesday...
..a secondary colder intrusion of Arctic air will descend south
into the region this weekend...
The cold thermal trough axis associated with anomalous eastern US
trough will be centered over the region Thursday morning which will
support another chilly day with daytime temperatures generally in
the 30s. Heights aloft will rise briefly late Thursday/early Friday
before reloading of the eastern upper trough gets underway courtesy
of a strong Arctic vortex dropping south into the northeast/southern
New England late Friday into Saturday. Models are in good agreement
that this secondary intrusion of Arctic air will be even colder than
the initial early/middle week installment. Anchored by a strong ~1040mb
Arctic high...temperatures this weekend will average 20 to 25
degrees below normal...with a good chance that temperatures
Valentines day will remain at or below freezing with nighttime lows
in the single digits to low teens.
Models are trending drier with a clipper like wave and accompanying
weak surface wave reflection through the area on Friday.
Temperatures will be could enough aloft to support a light rain/snow
mix. However...given limited moisture with northwest flow events along with
boundary layer temperatures in the lower 40s...impacts should
Arctic high will begin to retreat off the middle-Atlantic coast on
Monday. A progressive shortwave tracking eastward from the Central
Plains moves will result in strengthening warm moist advection into
the region from the west Monday-Monday night. With antecedent polar
airmass in place...cold air damming could present mixed p-type
concerns across the Carolina Piedmont.
Aviation /06z Friday through Saturday/...
as of 1230 am Tuesday...
Areas of fog with LIFR to IFR ceilings/visibilities around krdu and krwi
through 09z should get scoured out by the increasing mixed layer
aloft before 12z. Surface winds should increase to 5-10kt by 12z.
Otherwise... the westerly winds and deep mixing will increase to 10-
15kt with gusts to 20 to 25kts on Tuesday... with possibly some ceilings
at around 4 to 5 kft along with maybe a few sprinkles or flurries.
Outlook...Wednesday and Thursday will feature VFR conditions with
gusty northwest winds of 20-25 kts. The next chance of sub-VFR
conditions will come Friday as a weak low pressure system crosses