Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1021 am EDT Friday Mar 14 2014
high pressure will shift off the southeast coast today allowing a
warmer southwest flow across the region. Low pressure passing
across the Great Lakes will drag a cold front across the area
late tonight into Saturday. A larger low pressure system will
bring precipitation back to the region for Sunday and Monday.
Near term /through tonight/...
as of 1015 am EDT Friday...
Quick warm up in store today as high pressure across the Carolinas
slides offshore allowing an increasing SW flow to develop through
the afternoon. This warm advection combined with deeper mixing
should promote a large diurnal swing in temperatures from a very cold
start to a mild/breezy afternoon. Some guidance...mainly the
NAM...trying to bring in a more robust high cloud canopy during
the afternoon ahead of the next system to the northwest but looks too
fast given dry air so keeping mostly sunny trend. This also
supports going closer to the warmer mav MOS which pushes low 60s
Piedmont and overall middle/upper 50s elsewhere.
Next 500 mb trough swings by well to the north overnight with an
associated weak cold front working southeast to near the northwest slopes late.
Lobe of deeper moisture ahead of the boundary...and south of the
wave will arrive across the northwest after midnight with a possible band
of mostly rain showers working into southeast West Virginia. Think mainly
chance probability of precipitation with better moisture/lift to the northwest which will bring
the best coverage into northwest Greenbrier where could be some snow
mixed in. Otherwise partly to becoming mostly cloudy while staying
quite breezy on the ridges with a strong westerly jet just ahead
of the front. This should act to keep the ridges mostly in the 40s
with some 30s in the valleys and out east early on.
Short term /Saturday through Monday night/...
as of 430 am EDT Friday...
Main concern is potential winter system Sunday through Monday. The
entire model suite made a turn towards a more northern track
through the southeastern states...and a weaker/more eastern polar
vortex. Thus...all models came in warmer with the center of the
important surface high closer to the US/Canadian border...and less
cold air to work with in our region. Hesitant to completely
except this warmer and wetter solution just yet...as several times
this winter...as the event nears the models swing back to a colder
regime. However...seems as though air may just be cold enough
across the southern Shenandoah and perhaps also parts of
Greenbrier County...for mostly snow with sleet mixing in at
times...suggested by the GFS and the European model (ecmwf). Best chance for
accumulating snow in those locations would be Sunday night.
Because of this...HPC has some pretty hefty snow probabilities
considering the event is still a few days away...with a 50 to 60
percent chance of 6 inches or more just touching Hot Springs Virginia.
Just north or northeast of hsp is typically the bullseye with
these late season highly elevation dependent events. Will start
out with some light to moderate accums across the far northern
portions of the County Warning Area mostly Sunday night. The New River valley is
by no means out of the Woods yet...as it wouldn't take much of a
southern jog for impactful accumulations there too Sunday night.
As of now models indicate a mix of rain/snow/sleet later Sunday
afternoon into Sunday evening as cold air slowly seeps south with
The Wedge becoming entrenched...then some freezing rain into
Monday morning. However...the model trend is definitely towards a
warmer and wetter outcome for that region. Will remove some of the
severe weather potential statement wording for much of the southern half of the County Warning Area.
Both the European model (ecmwf)/GFS have an impressive jet maximum...with the County Warning Area
perhaps in the right entrance region for Monday. So precipitation on the
backside of this system cannot be ruled out and have increased
probability of precipitation this day. This could be more snow for the southern Shenandoah
and more of a mix further south...but identifying exact precipitation
types Monday is even more complex than Sunday night.
Long term /Tuesday through Thursday/...
as of 355 PM EDT Thursday...
During the day Tuesday...wrap-around moisture with the closed low
may bring an increasing chance for rain and/or snow to the
foothills and Piedmont counties as it tracks off the NC/Virginia coast.
For now...used hpcguide with less than 20 probability of precipitation Tuesday in the
east. We will revisit this scenario tomorrow if the models remain
consistent. Will also need to revisit temperatures following the
exit of this low Tuesday night into Thursday. Models are hanging
on to wedge until the next front sweeps across the region
Wednesday (gfs) or Thursday (ecm).
Aviation /14z Friday through Tuesday/...
as of 715 am EDT Friday...
VFR ceilings/visibilities expected to prevail today as high pressure passes
to the southeast. A weak cold front approaching from the northwest will
begin to spread a high cloud canopy in from the west this
afternoon with some increase in middle deck espcly across the southeast wva
sites this evening. Ceilings will then lower after midnight as a band
of showers heads into southeast wva. This could cause cloud bases to
lower to MVFR espcly around klwb/kblf late when a few showers
could occur. Elsewhere appears ceilings to remain VFR along the Blue Ridge
with mainly middle/high clouds in the east later tonight. The exiting
surface ridge off to the southeast will make for a quick turn around in
SW flow. This combined with heating should cause an abrupt
increase in wind speeds by the afternoon with gusts over 20 kts
likely this morning...and perhaps 25-30 kts from kblf-kroa by middle
or late afternoon.
Extended aviation discussion...
A weak cold front will move through the region Sat with upslope
clouds and possible rain/snow showers across the southeast wva
sites...otherwise mostly VFR expected elsewhere through Sat. A
southern stream system will phase with a northern stream system
Sunday through Monday bringing widespread rain to the area by Sun
afternoon along with MVFR-IFR cigs/vsbys. As cold air spreads
south down the east side of the Appalachians Sun
night/Mon...precipitation will likely change to snow north and a wintry
mix south. Accumulating snow appears possible early Monday. Winds
will also likely be strong and gusty in association with this
weather system. It could be Tuesday or Wednesday before conditions improve
as of 325 am EDT Friday...
Fire weather concerns will be high again today. Winds will shift
southwest...allowing warmer air to enter the region. With little
or no return of Gulf/Atlantic moisture expected... afternoon
humidity values will again fall below critical levels and likely
end up below 20 percent in many spots later today.
The warm and dry conditions...combined with abundant sunshine...will
allow the fine fuels to continue to dry further. Wind speeds will
increase again during the afternoon as low pressure passes across
the Great Lakes...but are overall expected to remain just below
critical levels outside of an hour or two just east of the Blue
Ridge later today.
Thus given the short duration of any expected pure red flag
conditions have opted for a enhanced Fire Danger Statement to
replace the going Fire Weather Watch that was in effect for areas
along and east of the Blue Ridge.