Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
634 am EST Friday Feb 12 2016
high pressure slides offshore this morning. Weak low pressure
will develop along the southeast coast this morning...lifting
northeast off the North Carolina and Virginia coasts later this
afternoon into tonight. Arctic high pressure builds in for the
upcoming weekend...resulting in the coldest temperatures so far
this year. Another storm system will impact the region early next
Near term /through tonight/...
weak hi pressure was right over the forecast area early this morng...providing
dry/cold conditions...with increasing hi and middle level clouds.
The hi will slide offshr later this morning...with attention
quickly turning to weak low pressure developing along the southeast CST...as
shortwave energy digs from the Midwest toward the NC/SC CST. Temperatures early
this morng were ranging from the upper teens to middle 20s across the
region with dewpoints in the single digits to lower teens. The low pressure
area will intensify slightly...as it tracks NE off the NC and Virginia
csts later this afternoon into tonight. Have kept warnings and advisories
in place for NE NC and extreme southeast Virginia...and generally maintained snow
amts for these areas. But...have trimmed back probability of precipitation and thus
decreased snow amts farther north and west into the Piedmont...due to
lack of deeper moisture (qpf amts) and dynamics (lift) in these
locations. Best dynamics (lift/frontogenetic forcing) and deeper
moisture (highest quantitative precipitation forecast amts) remain across extreme southeast Virginia and NE NC for
this event...and thus still could get 2-3 inches of snow (possibly
up to 4 inches) over NE NC counties adjacent to the Albemarle sand
and Atlantic CST...with 1 to 2 inches (possibly up to 3 inches) over
southeast Virginia (hampton roads area) SW into interior NE NC counties. Very
late this afternoon into early this eveng...some sleet may mix in with
the snow near the NC CST. For interior southeast Virginia...NE across the middle
peninsula into the lower Maryland eastern shr and including Accomack
County...snow amts could end up between 0.5 inch and 1 inch.
But...no advsy is in effect for the locations. Please see latest
west-southwest for more information. Snow comes to an end this eveng/early tonight...as
the surface low pushes well east-northeast of the middle-Atlantic CST and the Arctic
boundary pushes through the region.
Short term /Saturday through Sunday/...
closed upper low/energy associated with the polar vortex digs
over New England Saturday. ~1040mb Arctic high pressure builds
over the Midwest...ushering in the coldest air mass of the season
for the upcoming weekend. Windy Sat with northwest winds generally 15 to
25 miles per hour with gusts of 30 to 40 miles per hour (stronger near the coast and
over the eastern shore). Highs Sat forecast to warm only into the
middle 20s northwest to low 30s southeast (-2 Standard dev) under a sunny to mostly
sunny sky. Wind chill values will be in the teens...resulting in a
raw/cold/windy day. Temperatures plummet into the single digits to low
teens Sat night. Winds decouple inland as the high builds into the
region...but wind chills still forecast in the single digits
inland to 0 to 8 below Northern Neck to the Eastern Shore. The high centers
over the local area Sunday with northerly winds 5 to 10 miles per hour. Slightly
colder sun with decreased mixing. Highs generally in the middle/upper
20s (-2 Standard dev) under a sunny to mostly sunny sky.
Long term /Sunday night through Thursday/...
high pressure shifts toward New England Sunday night with attention
turning to a developing system over the deep south Monday. There
remains plenty of uncertainty with respect to the details...although
the 11/12z numerical guidance is trending slower...and warmer for
Monday night and especially Tuesday. The 11/12z GFS continues to
show some light precipitation Monday as a northern stream trough swings across the
area. This would mainly fall as snow or sn/ip...with a transition to
rain closer to the coast by afternoon. Substantial warming aloft would
generally result in a transition to rain Monday night...aside from the
far northwest where mixed precipitation could persist into Tuesday morning with an
in-situ wedge in place. The latest data scours out The Wedge by
afternoon with p-type becoming rain even in the far northwest. Drying occurs
midweek in the wake of the departing system...with a northern stream wave
clipping the area late in the period. This will bring another shot
of cooler air as Canadian high pressure builds into the area
Highs Monday will likely struggle to get out of the low 30s along
and west of I-95...while coastal locations warm into the upper 30s to
low 40s. Temperatures remain steady Monday evening and begin to rise
overnight eventually warming into the 40s to low 50s Tuesday. Highs
Wednesday are forecast to reach the middle 40s to low 50s...followed by
low 40s NE...to upper 40s SW Thursday. Morning lows are forecast to
be in the upper 20s to middle 30s Wednesday morning.
Aviation /12z Friday through Tuesday/...
challenging forecast later today as the latest high res data keeps
the forecast area dry through 18z and shows most of the sgnfcnt moisture with this
coastal low hugs the Outer Banks with little in the way of sprt/quantitative precipitation forecast for
sgnfcnt accums across southeastern Virginia and points to the northwest. Thus...VFR
cndtns will be maintained through 18z. Brought snow into ecg/orf and
phf around 21z with a 2-3 hour prd of MDT snow possible by 00z which is
where any accumls would occur. Kept a snpl mix at ecg as soundings do
show some marine influences occurring before precipitation ends. Latest data
indctg that most precipitation remains east of sby...but did keep a 4 hour
prd of lght snow there this evening. Data also sprtg a possible snow shower
across northern most counties with the actual Arctic front as it crosses
the region tonite. MVFR ceilings expeceted with the snow but IFR visibilities are
likely in any heavier snow bands. Low deep temperatures/dry airmass over the
Piedmont should prevent anything more than scattered flurries at ric.
Outlook...gusty northwest winds develop Saturday morning. VFR and dry
weather will prevail through Sunday night. Precipitation develops Monday as
the next weather system approaches from the SW. Precipitation begins as
snow under a high pressure ridge but this breaks down and warmer
air works in and changes snow to rain from southeast to northwest.
Rain continues into Tuesday as low pressure moves across the area.
Dry weather returns Wednesday.
no headlines today as the marine area winds will gnrly be at or below 15kts
ahead of an area of low prs prognosticated to move off the Carolina coast
tonight. Although this low will not bring any wind related marine
headlines...the assctd precipitation will bring reduced visibilities in snow/sleet
of varying intensities late this afternoon and evening.
As the low lifts to the NE Friday night a strong Arctic cold front
will pass across the region with strong cold air advection developing late Friday
night and continuing through Saturday into Saturday night as Arctic
high pressure builds in from the northwest. A northwest wind will average 25-30kt
with frequent gusts of 35-40kt over the ocean and Bay. Seas build to
5-8ft with 4-5 feet waves in the Bay. Gale flags have been raised for
late tonight through Saturday night. For the rivers and sound...wind
speeds have been capped at high-end Small Craft Advisory at this time.
Expanded the freezing spray window to include Sat...Sat night and Sun
morning given forecasted wind speeds / gusts combined with air temperatures below 30
degrees. Limited the freezing spray to the more open ches Bay and
coastal water areas. Per coordinate with phl...hoisted freezing spray advisory
for this time frame as well. This means light to MDT accumulation of
ice can be expected on vessels.
The wind will diminish Sunday into Sunday night as the high settles
across the area. Low pressure approaches form the SW early next
strong northwest flow associated with an Arctic cold front could produce
blow-out tides / low water advisories Saturday afternoon and night.
NC...Winter Weather Advisory until midnight EST tonight for
Winter Storm Warning until midnight EST tonight for ncz015>017-
Virginia...Winter Weather Advisory until midnight EST tonight for vaz092-
Marine...freezing spray advisory from 7 am Saturday to noon EST Sunday
Gale Warning from 4 am Saturday to 4 am EST Sunday for
Freezing spray advisory from 7 PM Saturday to noon EST Sunday
Small Craft Advisory from 4 am Saturday to 4 am EST Sunday for