Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1156 PM EST Thursday Dec 12 2013
cold high pressure will slide south into the Carolinas
tonight. A complex area of low pressure will approach from the
southwest by Saturday and then push across the region Saturday
night. The system exits the coast on Sunday followed by high
pressure for early next week.
Near term /through Friday/...
as of 1000 PM EST Thursday...
Strong high pressure centered overhead will drift southeast
overnight as a weak shortwave aloft passes well north. A very dry
airmass across the region support mainly clear skies through the
overnight...although warming aloft and faint channeled vorticity
may bring a period of middle clouds in from the northwest late.
Expect temperatures to level off some after quick evening falls as
winds starts to pick up mainly along the ridges overnight. Used a
non- diurnal temperature curve to allow temperatures to hold up or
rise in the higher terrain towards Friday morning. Wind chills
will be near Wind Chill Advisory levels across the highest terrain
in the northwest mountains but not enough coverage for any
headlines. Low temperatures tonight will range from the middle teens
in the mountains to the lower 20s along the foothills along the
southern Blue Ridge mountains.
On Friday...high pressure will be shifting east off into the
Atlantic Ocean. This will allow winds to shift from the southwest.
High clouds/moisture will slowly increase Friday ahead of our next
storm system. Dry weather will continue through the daylight hours.
Rising 500mb heights will allow afternoon temperatures to warm
nicely compared to this afternoon. Highs will vary from the middle 30s
across the mountains to the around 50 degrees across the piedmonts.
Short term /Friday night through Sunday night/...
as of 400 PM EST Thursday...
Not much change to the current forecast. Still some question if
there will be a wedge and if one exists...how long will it
survive with strong warm air advection from the SW. Might be a combination of a
traditional/in situ wedge...as precipitation arrives at the perfect time
for this to occur. All models have delayed precipitation almost until
12z/7a Saturday...although precipitation usually breaks out several
hours quicker in this type of overrunning scenario...didn't want
to break out precipitation too early so have most measurable in the west
around 8z/3a Saturday. Expecting rain...then wetbulbing into the
dry air produces a window of snow which then mixes and changes to
sleet before becoming all rain Saturday morning for the New River
valley and northwest NC. Thinking mostly nuisance amounts of sleet/snow
at this time...with maybe a quick burst of snow putting down a coating
late Friday night. With some easterly component up against the
Blue Ridge across northwest NC there could a sneaky hour of freezing
rain right around dawn Saturday. Piedmont/Southside would lean
even more towards all rain with also a quicker changeover in the
blf/jfz corridor to all rain. Southern Shenandoah and the
Greenbrier valley could stay snow longer before mixing with
sleet...and thus there could be some light to moderate
accumulations late Friday night into Saturday afternoon. When
combined with a trace or a few hundredths of freezing rain Sat
afternoon and evening...this could potentially put some of those
counties at warning criteria based upon the snow/ice matrix.
Granted this would be along the higher elevations but something to
consider nonetheless for a potential watch on the next shift.
Although guidance does warm the aforementioned counties above
32f...MOS does keep an easterly wind all day which could keep near
freezing temperatures locked in much of the day. Looks as though any ice
accumulate would be limited by most of the quantitative precipitation forecast racing to the east...so
might just be dealing with several hours of freezing drizzle up
there. Precipitation should finally change to upslope snow showers late
Saturday night and lasting into Sunday.
Long term /Monday through Thursday/...
as of 318 PM EST Thursday...
There is a very low chance for measurable precipitation next week as
high pressure blocks Gulf moisture from advancing northward. If any
one area would see precipitation next week...it may be western
slopes of southeast WV. Models continues to advertise a relatively dry
frontal passage Tuesday. Behind the front...trajectories from the
Great Lakes may bring enough moisture to squeeze out a few flakes
Wednesday morning along western slopes of Greenbrier/Bath counties.
Both the ecm/GFS swing a short wave across northern rnk County Warning Area. If this
short wave remains on this track...bulk of the moisture will remain
north of Greenbrier. If models trend to track this short wave across
the southern Appalachians...probability of precipitation will need to be increased along
western slopes of southeast WV down into SW Virginia. The ecm seems a little
bullish on moisture and therefore leaned forecast toward the GFS/HPC
guidance. Pop chances are under 10 percent.
With no significant precipitation maker for next week...the
challenge with the forecast will be temperatures. On Monday...high
pressure shifts off the middle Atlantic coast. With a cold front coming
across the Ohio Valley...southwesterly flow will bring warmer near
normal temperatures into the region beginning Monday afternoon into
Tuesday. Cold air will then filter in behind the cold front as it
moves to the East Coast Tuesday evening. Colder than normal
temperatures will likely remain until Thursday morning...then
another warm up is possible Thursday afternoon.
Aviation /06z Friday through Tuesday/...
as of 100 am EST Friday...
VFR conditions will prevail during the 24 hour taf period...still
dominated by high pressure. High pressure will be centered just
to our southeast Friday morning...then drift off the southeast coast
Friday night. Dry weather expected Friday...but moisture will
increase quickly Friday night. Winds will become west around 10
miles per hour at the taf sites.
High confidence for ceilings and visibility to remain VFR during
the taf period. High confidence for surface winds to be less than
10 kts overnight and Friday.
Extended aviation discussion... an area of low pressure will move
across Texas Friday...then across the MS valley Friday
night...approaching the middle Atlantic region Saturday. Some light
frozen precipitation may arrive across the mountains of the central
Appalachians by daybreak Saturday. Temperatures are expected to
warm above freezing Saturday...so any wintry mix Saturday morning
is expected to change to rain Saturday afternoon. Regardless of
precipitation type... there is a high probability for MVFR ceilings and a chance
for a period of IFR ceilings/visible by Saturday afternoon. MVFR ceilings may
linger both Saturday night and Sunday. A more tranquil pattern
returns by Monday with high pressure stretching from the Tennessee Valley
into the middle Atlantic.