Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
644 am EST Sat Nov 28 2015
a frontal boundary moves southeast through the middle Atlantic and upper
Ohio Valley today...reaching our area Sunday. This boundary
situates itself across the Virginia/North Carolina region into
Monday. High pressure builds into the northeast setting up a wedge
by Monday night.
Near term /through tonight/...
as of 252 am EST Saturday...
Models in decent agreement with respect to frontal boundary
sagging southeast toward the area today into tonight. Really
seeing lower probability of precipitation than earlier forecast for today...due to slower
movement. WV loop shows a train of moisture from the Baja California NE
through Texas and into the Ohio Valley/northeast. As far as radar
GOES...bulk of decent precipitation exists over western Tennessee southwest
to Texas where precipitable waters range from 1.5 to 2.0 inches which is over
200 percent of normal for this time of year.
For US...the frontal boundary shifts southeast and faces westerly flow in
the low levels...which given this setup of weaker forcing...favors
lower precipitation total and lower probability of precipitation east of the mountains. Better lift
to reside north of the frontal boundary tonight from the Mason-
Dixon...west-southwest into KY/WV. Have higher probability of precipitation...likely to categorical
pushing as far east as the Alleghany Highlands of Virginia southwest into
the mountain Empire of SW Virginia...tapering probability of precipitation to slight to low chance
southeast of the Blue Ridge...with <15 probability of precipitation from Keysville to
Yanceyville to the NC triad.
Prior to this some fog will be patchy at times across the Piedmont
where middle/high clouds thin out at times. Overall will see skies
becoming broken/overcast through the morning...of mainly middle deck.
Sunshine at times appears favorable later this morning into
afternoon east of lyh/Dan line. With a westerly low level flow
expect temperatures will jump into the upper 60s to lower 70s east...with
lower to middle 60s west.
Clouds tonight and increasing rain chances will limit temperatures falling
too far...but with dewpoints in the middle 40s to lower 50s...lows
should range close to this...which is about 15 to 20 degrees above
Short term /Sunday through Tuesday night/...
as of 330 am EST Saturday...
The split upper level pattern will be dominated by moist southern
stream energy with short waves rippling through the flow ahead of a
large closed low moving across the Midwest. This will allow strong high
pressure at the surface to move into the northeast and push a front
through the region as it sets up a strong wedge down the eastern
Seaboard for the first part of next week. This will establish
isentropic lift in a moist environment and keep the area in
precipitation for most of the short term period from later on Sunday
Temperatures will remain above normal through Sunday but as The Wedge
builds in and precipitation spreads across the region Sunday night...
most locations will see temperatures languish in the 40s on Monday with
a slight improvement on Tuesday.
Long term /Wednesday through Friday/...
as of 330 am EST Saturday...
Timing of a surface cold frontal passage remains iffy given the
slowness of the associated upper low across the Great Lakes to move
east. GFS a bit faster now with the boundary crossing later Tuesday
night into Wednesday but per ensembles trends and latest European model (ecmwf) not
going that fast with perhaps another wave along the front into
Wednesday afternoon. This supports continued high probability of precipitation at times into
Wednesday before possibly tapering late Wednesday as the flow turns
more west/SW along/behind the front. Does appear that by Wednesday
evening that most other than perhaps the far south and northwest will be
drying out with clouds decreasing. Temperatures to remain cool before
rebounding into the 50s all sections and closer to 60 east Wednesday.
Surface boundary wont go too far to the east Thursday with trailing
upper energy and possible Pacific tropical moisture along the tail end
back over the SW generating another wave that looks to emerge somewhere
off the southeast coast by day7. Just how far north the precipitation shield with
this feature gets remains in question as well as the track/intensity of
the system per differences between operational models and
Either way without linkage of the upper cold pool to the surface
system and only a weak wedge to the north...appears wont be enough
cooling at this point to produce any snow espcly during Friday
even if precipitation is farther north. Thus leaving out mention based
on latest forecast soundings and wpc forecasts. Also looks like temperatures
may be able to rise just enough to preclude any early icing issues
at this point as well even if some rain does occur. Otherwise
other than for brief upslope northwest where could be a few snow showers
Wednesday night...Thursday looks dry/seasonal with some increase in
clouds late...with probability of precipitation possibly arriving far south late Thursday
night. Best chances Friday mainly south/southeast but given latest
offshore shift in the coastal low via the 12z European model (ecmwf) only running
with low chance to slight probability of precipitation Friday for now.
Aviation /12z Saturday through Wednesday/...
as of 640 am EST Saturday...
Middle deck to settle over the region today...with some lower
stratocu moving into the mountains by sunset. Fog has been in and
out and with cloud cover think threat of fog at taf sites will be
negligible at 12z today...though allowed for MVFR tempo at lyh
given some thin spots in the overcast.
Tonight...should see ceilings lower but stay VFR through
midnight...with MVFR ceilings and light rain working into blf/lwb
about 04-05z...then dropping toward IFR ceilings at blf by the end of
the taf period as better coverage of rain moves in. Further
east...think VFR will prevail until the end of this taf period.
Winds through the period will be light/calm..and generally SW to
Extended aviation discussion...
The cold front will finally sag south into the Carolinas Sunday.
Moisture moving from the Tennessee Valley and over a cool wedge
will bring several days of rain/drizzle/fog and low clouds to the
region into Tuesday night. Another cold front will clear The Wedge
out of the area with improving flight restrictions on Wednesday.
Following this front...breezy and gusty west winds are likely
Wednesday and Wednesday night.