Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
741 PM EDT sun Mar 16 2014
low pressure over the lower Mississippi Valley will track east
tonight and Monday. A large and strong area of high pressure will
wedge along the Appalachians tonight. Another strong upper level
disturbance will Dart across the Gulf of Mexico Monday night also
moving along the coast Tuesday. It may take a cold front moving
through our region Wednesday night and Thursday to finally dislodge
Near term /through Monday/...
as of 520 PM EDT Sunday...
Complicated forecast this afternoon into tomorrow with March winter
storm. The initial low pressure center over Tennessee this afternoon
will work east tonight and give way to a coastal low tonight.
Decided to keep winter storm headlines with warnings across the
north and advisories in the south.
Warm advection and isentropic lift are pushing precipitation shield
northward across the forecast area this afternoon into tonight with
drier/cold air pushing south. Evaporative cooling is occurring with
heavier rates. Mostly snow north of the Highway 460 corridor with a
more mixed nature New River and southwest to mostly rain during the
daylight hours in much of northwest North Carolina. A couple of
concerns with precipitation for this evening into tonight are warm
ground...dry slot pushing northward through southwestern North
Carolina...convection to south taking moisture...models having hard
time capturing wedge and temperature profiles tonight.
There is some banding potential across the northern half closer to
the upper deformation axis that will set up tonight into Monday.
This supports the 6 to 10 inches of snow and sleet across the north
and 3-6 roa to Buckingham while having a very sharp cutoff to the
south where more sleet likely as warming aloft develops a bit after
the initial evaporative cooling. Adjusted snowfalls totals across
the southern half allowing for drier air pushing north and warmer
temperature profiles. Some icing is possible overnight along the
eastern slopes when the precipitation becomes lighter.
Deep moisture exits after midnight while low level temperatures fall
to below freezing most spots under the enhanced wedge per low
pressure along the coast. This may allow icing to develop along the
southern Blue Ridge and even into Southside Virginia and the Piedmont of
North Carolina. There is nothing glaring in guidance or observation that
suggests making any changes to the advisory for the south....and
impacts should be limited with just a glaze in trees and elevated
surfaces. Used blend of MOS for low temperatures tonight with values
form the teens in the northwest mountains to the lower 30s in the
south. For probability of precipitation Monday shaped towards the GFS...and used top down
with blend temperatures for ptype/weather. Wedge holds tough Monday
so very chilly for middle March...with even stronger sun angle not
making much of a diurnal for highs. Snow cover may also hold
temperatures down on Monday. High temperatures will range from the
upper 20s in the mountains to the middle 30s in the south.
Short term /Monday night through Wednesday night/...
as of 400 PM EDT Sunday...
Models continue to come into better agreement on there not being
another round of winter weather Tuesday into Wednesday as a result
of another coastal low developing along the baroclinic zone across
the Georgia/SC coast. Latest model trends continue in the direction of
the earlier GFS runs showing any coastal development will be further
southeast with drier air behind the current/Monday system being advected into
the region from the northwest. The upper support for this system is
also further southeast...across GA/FL/SC...moving east out to sea in a
basic zonal flow. However...there is still concern for wrap around
maritime moisture on NE-east surface flow on the back side of this system
as it moves off the coast to result in light -dz...especially along
the east facing slopes of the Blue Ridge. With a cold air wedge
remaining firmly in place east of the Appalachians...temperatures
through the first half of the day will struggle to rise above
freezing. But...as noted...no dynamics to generate anything more
than stratus induced -dz. Given expected surface T...have included
-fzdz through the morning hours Tuesday in areas where surface T is 32f or
less. Elsewhere...just -ra or -dz. Also mentioned -sn in the
northern areas...but this is more of a -sndz nature than dynamically
driven -sn. Probability of precipitation less than 50 percent...so no quantitative precipitation forecast and thus no snow
accumulation in the grids after 00z Tuesday.
For Wednesday...a deep surface/upper trough will pass through the region Wednesday
afternoon. In advance of this Wednesday morning...The Wedge remains with
again the potential for early morning -dz and even a few pockets of
-fzdz through the Greenbrier and southern Shenandoah valleys.
However...by afternoon the associated trough will pass through the
area bringing a modified Canadian/Pacific air mass into the
region...thus milder temperatures into the region with 40s mountains
and 50s Piedmont. Upslope -shra and -shsn toward evening cannot be
ruled out across eastern West Virginia favorable upslope areas.
However...at this point it appears to be very insignificant.
Long term /Thursday through Sunday/...
as of 400 PM EDT Sunday...
Zonal flow will generally dominate much of the long range period. An
upper trough will race through the region Sat with a chance of
-shra. A substantial warmup is expected in advance of this system
with strong SW flow. We should see 60s and perhaps in a few low 70s
across the Piedmont Friday in advance of this system. Depending on the
degree of instability...an isolated thunderstorms and rain cannot be completely ruled
out...but it has not been advertised just yet as the dynamics are
weak and the best instability remains east and south of the County Warning Area.
This system heralds a return to colder northwest flow and a return to
normal or even below normal temperatures for sun into early next
week as a large Canadian high drops southeastward from the Great
Plains and Great Lakes region. Some weak embedded disturbances
appear inevitable...but none have strong enough signals at this
point to include mentionable probability of precipitation or significant upslope -shsn. A
southern stream system at this point is forecast to remain south of
the County Warning Area sun-Mon...but as always will need to be watched closely for
any winter weather potential as it creeps just south of our County Warning Area
Aviation /00z Monday through Friday/...
as of 730 PM EDT Sunday...
Surface low pressure will head northeast along the coast of the
Carolinas tongiht into Monday. An upper low will progress eastward
into the region from the Tennessee Valley. The combination of
these two factors will keep widespread precipitaiton across the
region overnight with lesser coverage during the day on Monday.
IFR or worse visibilities and ceilings are expected with a mix of wintry
weather through the night. While the precipitation will continue
through the day Monday...coverage will be less and is not included
in the prevailing weather section of the tafs past roughly
14z/10am Monday. Surface winds will be northeast with gusts around
20-25kts between klyh-kdan. These will wane by the late morning
Monday. Also round this time...many areas will expiernce visibilities
improving to VFR with ceilings increasing to MVFR.
As of 1250 PM EDT Sunday...
Extended aviation discussion...
Sub VFR conditions will remain in play through Tuesday...the
upper level trough lingering potentially into Tuesday night. A
cold front is expected to cross the area Wednesday...sweeping the
area free of cloudiness by Wednesday night. VFR conditions are
expected to return for the 2nd half of the work week.
Virginia...Winter Storm Warning until 2 PM EDT Monday for vaz018>020-
Winter Weather Advisory until 2 PM EDT Monday for vaz010>017-
Winter Weather Advisory until 2 PM EDT Monday for vaz043-044-
NC...Winter Weather Advisory until 2 PM EDT Monday for ncz001-002-
Winter Weather Advisory until 2 PM EDT Monday for ncz003>006-
WV...Winter Storm Warning until 2 PM EDT Monday for wvz043>045.
Winter Weather Advisory until 2 PM EDT Monday for wvz042.