Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1252 PM EDT sun Mar 16 2014
an area of low pressure along the Mississippi River valley will
track through the southeastern states today. The developing
winter aspects of this system will unfold this afternoon and
tonight as the storm moves off the Carolina coast. 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 The Wedge.
Near term /through tonight/...
as of 1205 PM am EDT Sunday...
Youtube briefing posted and linked on facebook and twitter. Made
more adjustments to probability of precipitation and temperatures for early this
afternoon. More changes this afternoon...
As of 1019 am EDT Sunday...
Slowed the onset of the over running rain this morning...with
WSR-88D images and surface observation showing slower advance north. Adjusted
temperatures up this morning with surface observation and model trends. Thus
raised high temperatures in a few locations. Concerns over dry
slot seen on GFS and potential for convection to south hinder
forcing and moisture transport. Will hold with current winter
headlines at this time. More adjustment later today...
As of 305 am EDT Sunday...
Complex March winter storm to affect the region heading into this
afternoon with init low pressure working through the lower miss
valley today before giving way to a coastal low tonight. Leading
batch of arcing heavier precipitation looks to zip NE toward the area this
morning as strong isentropic lift develops along the leading nose of
the upper jet to the SW. At the same time...drier/cold air will
continue to bleed in from the northwest as confluence to the north tends to
block this system farther south. Timing appears a bit slower given
the dry middle levels so slowed down the onset a bit this morning. Otherwise
main batch of lift to pass across from middle afternoon through this
evening then taper some as the upper levels dry under the nose of
the dry slot. Precipitation initially likely to briefly be mostly rain
before strong evaporative cooling quickly cools the column
provided heavier rates.
Guidance remains rather consistent in having mostly snow north of
the Highway 460 corridor with a more mixed nature New River and SW to
mostly rain during the daylight hours in much of northwest NC. However
expect even the northern NC ridges could get in on some snow at the
onset per strong cooling. Amounts remain very tricky given time of
year during the day and potential for the quantitative precipitation forecast to be less with more
of a dry slot per an event a couple weeks back. However profiles
and isothermal nature to forecast soundings suggest some banding
potential espcly north half closer to the upper deformation axis
that will set up later in the day but perhaps just north of the
northernmost County Warning Area. Latest Euro continues to peg the Greenbrier
valley east across The Highlands to north of lyh with 6-10 inches
and 4-6 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. Thus have added a few more
counties in the east to the warning where deeper colder air will
reside while running with an advisory for much of the New River
valley SW into northwest NC to cover both snow/sleet potential early and
some icing overnight along the eastern slopes when the precipitation
becomes lighter. Went in between MOS temperatures with some bump in
values early then quickly falling at the precipitation onset.
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 northwest NC. Although
iffy across the far south...likely enough late tonight to perhaps
cause problems so after coordination with surrounding sites have
hoisted a Winter Weather Advisory elsewhere over the southeast sections for
tonight into Monday.
Short term /Monday through Tuesday night/...
as of 345 am EDT Sunday...
All models have backed off suggestion of another round of
significant snow on Monday...with the exception of Greenbrier/
Bath/Rockbridge/Amherst. Impressive jet maximum and upper level
disturbance arrive but moisture isn't deep enough for more than
perhaps an inch or two across these row of counties. Quantitative precipitation forecast elsewhere
should be light...and the warm nose from late Sunday night will
continue into Monday...such that Highway 460 and points south should
only see light quantitative precipitation forecast which would be a mixture of sleet and possibly
some freezing drizzle. Wedge holds tough so very chilly for middle
March...with even stronger sun angle not making much of a diurnal
for maximum T.
Focus then shifts to late Monday night. Another strong disturbance
moves off the southeast coast with both the European model (ecmwf)/GFS in agreement with
regards to an area of precipitation moving into either northwest NC or the NC
Piedmont. Considering models struggle with the northern extent of
stratiform precipitation...will need to watch to see if this gets shoved a
little further north. Nonetheless...models only kicking out about
0.10" of quantitative precipitation forecast. However...little rise in temperatures Monday followed by
persistent easterly or NE upslope component should push temperatures below
freezing when this precipitation arrives. Thus...there could be some fair
amounts of ice accumulation with freezing rain after midnight Monday
into Tuesday dawn. Pinpointing this area of precipitation is going to prove
difficult but this event could very well merit a Freezing Rain
Advisory. Wedge starts to break across extreme SW Virginia and northwest NC but
New River valley and southern Shenandoah may stay locked in to the
colder temperatures Tuesday. Can foresee a big difference in temperatures between
Wytheville and Blacksburg for highs. Still some easterly flow and
wedge holding barely could produce some freezing drizzle or just
drizzle and fog over the remaining southern Shenandoah
snowpack Tuesday night.
Long term /Wednesday through Saturday/...
as of 330 PM EDT Saturday...
From Wednesday through Friday...model guidance is in fairly uniform
agreement of progressing a closed upper level low pressure system
from the western Great Lakes region eastward to just north of the
Canadian Maritimes. Across our region...low level flow will be such
that a fetch of Atlantic moisture will be in place with the approach
of the upper low/S trough axis. We are expecting some light rain
across mainly northern and eastern part of the area during the day
Wednesday. Some light freezing rain will be possible across these
areas early Wednesday prior to temperature rising above freezing.
Wednesday night into early Thursday...the cold front associated with
the upper system is prognosticated to move through our area. We are
expecting some isolated to scattered rain or snow showers across
Once the front moves through...high pressure will build into the
area and bring milder weather and dry conditions. While the high is
approaching...a tight pressure gradient will keep gusty conditions
across the area on Thursday.
The next chance for precipitation for the region will be on
Saturday. A strong cold front is expected to move through the area
with showers across the area. Convective indices offer the
potential for some isolated thunderstorms Saturday afternoon across
the central and eastern parts of the area.
Temperatures through the period will gradually moderate through the
period. On Wednesday...snow cover across central and northern parts
of the area will continue yield high temperatures below
guidance...likewise Wednesday night. Highs Wednesday will range
from the middle to upper 40s north to the middle to upper 50s south. By
Saturday...highs will range from the upper 50s to lower 60s in the
mountains to the middle to upper 60s across the Piedmont.
Aviation /18z Sunday through Friday/...
as of 1250 PM EDT Sunday...
VFR cloud bases will lower...then transitioning to MVFR this
afternoon and IFR ceilings by Sunday afternoon/evening. Visibility
restrictions will follow with visibilities falling below 3sm later this
afternoon as rain spreads northeast across the region.
Cold air arriving from the north later this afternoon into
tonight will result in a change from rain to snow and sleet for
all terminals along and north of Highway 460. Based on latest
guidance...slowed down the arrival of snow a few hours...and some
IFR ceilings may be experienced Sunday afternoon. A combination of
snow and or drizzle along with low ceilings will then result in
IFR/LIFR conditions from Sunday night into Monday. Warming and
drying aloft may transition much of the precipitation for roa/bcb/lyh to
freezing drizzle near dawn Monday...as precipitation slows after midnight
into Monday morning.
Low to medium confidence in ceilings and visibilities during the
taf period. Medium confidence in wind forecast.
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 from 8 PM this evening to 2 PM EDT
Monday for vaz043-044-058-059.
NC...Winter Weather Advisory until 2 PM EDT Monday for ncz001-002-
Winter Weather Advisory from 8 PM this evening to 2 PM EDT
Monday for ncz003>006-019-020.
WV...Winter Storm Warning until 2 PM EDT Monday for wvz043>045.
Winter Weather Advisory until 2 PM EDT Monday for wvz042.