Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
940 PM EST Friday Feb 12 2016
Synopsis...Arctic high pressure will build over the region over the
weekend. A developing storm system will approach from the west
Sunday night and then move eastward through the area Monday through
Near term /through tonight/...
as of 940 PM Friday...
Starting to finally see better west to east clearing of moisture
around 6000-7000 feet as a jet on the back side of the upper trough
approaches and northwest flow strengthens. Low-level moisture is
still more prevalent on the coastal plain where some sub-1000 feet
stratus is lingering. A period of patchy fog may develop in the
southern coastal plain as the higher level clouds clearing (hinted at
by sref probs and kfay/kgsb rap soundings)...but it would likely be
brief...prior to 06z...with a northwest wind and cold advection
forecast to slowly strengthen after midnight. Otherwise...while we
may see a some patches of stratocu drift across the area given all
the moisture banked upstream of the mountains...clearing skies and
cold advection will push lows into the lower 20s north and west to
upper 20s south and east.
Short term /Saturday and Saturday night/...
as of 300 PM Friday...
As East Coast trough tries to pull off the coast...very strong cold
air advection will ensue behind the exiting coastal system. With
very strong pressure gradient across the area...cold temperatures
and strong winds will be the forecast problem of the day. Expect
winds to remain sustained out of the north or northwest at 10-15 kts
with gusts of 25-30 kts for much of the daylight hours. After sunset
gusts will subside. High temperatures only in the low to middle 30s and
with wind chill values in the upper 10s to low 20s for much of the
day. As an aside...with the cold but also dry airmass in place...min
relative humidity values will dip down into the low 20s. Combine these values with
the higher winds and there will be a small increase in fire danger
Saturday in our southern counties that may squeak into the lower
Saturday night will see the gusts slack off but sustained winds to
remain up in the 5 to 10 knots range keep things mixed a little.
Combine this with very cold expected low temperatures in the low to
middle teens...wind chill values Saturday night will reside in the 5-10
degree range. Preparations should be made now to protect anything
susceptible to the cold wind chills...especially pets. Some clouds
will begin to approach the area late Saturday night into Sunday
morning from the west in advance of the next storm system.
Long term /Sunday through Friday/...
as of 315 PM Friday...
..storm system likely to bring wintry weather threat Sun night/Monday
followed by heavy rain threat and a few storms Monday night/Tue...
Sunday: continued chilly with the Arctic high pressure extending
from the eastern Great Lakes down through NC. Will have increasing
clouds ahead of the approaching storm... as our middle level flow
shifts from fast northwesterly to west-southwest... a function of
Pacific northwest energy diving into an initially flat/broad central
Continental U.S. Trough causing its amplification. Statistical guidance still
supports highs from 29 NE to 35 SW. -Gih
Sun night through Tue:
Overview: confidence is beginning to increase regarding the
timing... most probable precipitation type pattern... and primary weather
threats for the incoming system. Latest guidance shows a bit quicker
onset... with precipitation arriving in the northern/western County Warning Area Sun night... as
well as a slightly earlier departure on Tuesday. Longwave troughing will
continue to amplify along the miss valley as northern stream energy drops
into its base over the Gulf states... culminating in a narrow deep
shortwave trough taking on a positive tilt as it swings east-northeast into the
Carolinas. At the surface... the polar high situated over the
northeast and midatlantic states Sun night continues to push
steadily northeast and offshore through Monday... while a coastal front
forms along the Carolina coast extending back to developing low
pressure over the central Gulf states. This low then tracks east
then NE through western NC Monday night/Tuesday morning before moving quickly
into the northeast states... with a trailing front sweeping through
central/eastern NC by early Tuesday afternoon.
Precipitation chances: the initial processes to force ascent Sunday
night into early Monday including DPVA and moist isentropic upglide
are rather weak and focused primarily on western and northern portions of
central NC. Will trend probability of precipitation up to likely northwest and retain high chances
across the south and east Sun night into Monday morning... with quantitative precipitation forecast
fairly light... under a quarter inch mainly in the northwest. But this
changes quickly with the addition of strong upper divergence (due to
ideally juxtaposed polar and subtropical jets) and vigorous low
level moisture transport east of the low. Will ramp up probability of precipitation further
to categorical west/likely east late Monday... then to categorical
everywhere Monday night through Tuesday morning... ending SW to NE Tuesday
Ptypes: using the top-down methodology with consideration of the
initially very cold/dense nature of the surface air mass... the
initial cold air aloft giving way to a warm nose... and the strong
low level warm advection apt to dislodge this surface air mass
gradually from southeast to northwest Monday evening... expect this to start as
mostly light snow with perhaps patchy light sleet Sun night across
the northern and western County Warning Area... followed by a slow steady transition from south-southeast
to north-northwest to freezing rain/sleet then to all rain... with the far northwest
counties including The Triad the last to see an end to the wintry
precipitation Monday evening. Tentative accumulations are up to one to two
hundredths of an inch of icing (trace amounts) for much of the
County Warning Area... and snow totals of 1-3" northwest quarter with an inch or less
elsewhere... all of which should be quickly swept away by moderate
to potentially heavy rainfall late Monday night into Tuesday morning.
Rainfall totals and storm potential: at this time storm total liquid
quantitative precipitation forecast is expected to be 1-2" with locally higher amounts possible...
given the high water content and strong lift Monday night/Tuesday morning.
Based on the antecedent conditions and several rivers and creeks
running high... a Flood Watch may be needed for some portion of the
area. Also... while lapse rates are unlikely to be very
impressive... the strong and focused lift possible with this system
and warming low levels especially in the sandhills and coastal plain
may support a few lightning strikes on Tuesday.
Temps: expect lows Sun night of 22-26. Temperatures should slowly rise Monday
through Monday night... reaching the low 30s northwest to low 40s southeast late
Monday... rising to the middle 30s northwest to middle 40s southeast Monday night... and
peaking at 48-56 Tuesday prior to frontal passage.
Wednesday through Fri: we may see a perturbation swing through the
longwave eastern trough base across Virginia on Wednesday... but models vary on the
strength and latitude of any such wave... and regardless the
moisture will be limited yielding no impacts on central NC other
than some clouds across the north. Otherwise... this period will
feature a transition away from western ridge/eastern trough over the
Continental U.S.... as flat ridging builds over the Gulf/southeast states from
the west... with a net result of dry weather and near to slightly
above normal temperatures for central NC. -Gih
Aviation /00z Saturday through Wednesday/...
as of 730 PM Friday...
24 hour taf period: aside from lingering IFR/MVFR ceilings through 01-
02z at the Fay terminal...VFR conditions will prevail at all
terminals for the duration of the taf period. The only aviation
concern will be gusty northwest winds during the day Saturday (esp
morning)...in the wake of an Arctic cold frontal passage late
tonight. Expect winds to increase to ~15 knots with gusts up to 25 knots
during the strongest cold advection (09-15z)...remaining steady at
12-16 knots for the remainder of the day. Winds will decrease to 5-10
knots after sunset Sat evening.
Looking ahead: VFR conditions will prevail through middle-day Sunday as
an Arctic airmass advects into/over the region. High pressure will
quickly move offshore...with MVFR ceilings returning from west-east
Sunday evening/night in associated/west a strengthening southerly return
flow. Confidence in the forecast decreases significantly early next
week...however...adverse conditions in the form of low ceilings and
precipitation (perhaps mixed ptype) will be possible. -Vincent
Here are the record lows and record low maximum temperatures for Sat
Feb 13th and sun Feb 14th at gso... rdu... and fay:
Rec yr rec yr
low low maximum
02/13 11 1955 31 1986
02/14 6 1905 22 1914
02/13 4 1899 10 1899
02/14 -2 1899 27 1916
02/13 14 1973 32 1955
02/14 12 1968 33 1916