Area Forecast Discussion
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FXUS61 KRNK 141737
Area Forecast Discussion
National Weather Service Blacksburg VA
1237 PM EST Sat Jan 14 2017
A weak cold front has drifted south of the region and will
remain south of the area until Monday at which time it will
drift back north of the area. Meanwhile, a series of
disturbances aloft will track over the region keeping clouds
and periods of precipitation across the region for several days.
Finally, a stronger cold front is slated to move through the
region by the middle of next week.
.NEAR TERM /THROUGH TONIGHT/...
AS OF 1147 AM EST Saturday...
Cancelled the Freezing rain advisory because the threat for
widespread freezing rain and icing has ended. Surface
temperatures have climb above freezing mark at most locations
and will continue to rise this afternoon.
Adjusted isc temperatures and trimmed back pops for early this
afternoon. More changes this afternoon.
AS OF 1005 AM EST Saturday...
Canceled the freezing rain advisory for Southeast West Virginia
with temperatures above the freezing mark and threat for
widespread icing problems ended.
Continue the Freezing Rain Advisory for northern portions of
CWA with colder air pushing south along the Mountains. Posted a
SPS for Isolated pockets of freezing rain in elevations mainly
above 3000 feet this morning. Adjusted temperatures with the
latest obs and trends, then blended towards the nam for late
morning into this afternoon. Made some changes in pops and
weather for this morning with ptype and precipitation tapering
off. more changes later...
As of 400 AM EST Saturday...
Wedge front has drifted as far south as northern SC and into
western NC. Models do not support it drifting much further
south, but also now keep it south of our area until Monday, at
which time a stronger short wave approaching from the west
moves it back north. Temperatures have been rather slow to fall
and as of this hour all areas remain above freezing. While,
there is plenty of light rain drifting across the region per
series of weak upper disturbances in zonal flow aloft, with
temperatures still above freezing, freezing rain has yet to
materialize. NAM and ECMWF still insist that temperatures will
drop toward 30 degrees as far south as Craig and Monroe counties
in the 12Z-15Z time frame, then hold there until mid-afternoon
today. Historically, once a wedge of cold air gets in place, it
is very difficult to dislodge. Thus, will not make any changes
in the configuration or timing of the Freezing Rain Advisory at
this point, although was strongly tempted to do so earlier
seeing the reluctance of temperatures to drop below freezing. By
the same token, was also tempted to pull out some of the
southern counties, but the cold air has more efficiently spread
down toward the New River Valley than the Greenbrier Valley, so
will leave Craig/Monroe/Botetourt as is as well. If conditions
fail to materialize or end earlier than 4 pm, which appears
likely, day shift can cancel early or remove counties as needed.
Otherwise, have used a NAM/ECMWF blend for the temperatures
today as the GFS appears too warm again. Used more of a
consensus model blend for tonight. All-in-all, a non-diurnal
temperature trend is in order for today.
With regard to precipitation, timing will be difficult, but
all models suggest that another wave of rain will develop,
mainly across western/northern areas later today, then focus
back more into the TN valley overnight/early Sunday. At any
rate, there will likely be drizzle when it is not raining, so
have included drizzle throughout the CWA in addition to the
light rain. Pops range from categorical west/north to chance
.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
As of 315 AM EST Saturday...
Initial low level wedge across the region to start Sunday will weaken
as the flow turns more northwest behind a weak exiting wave offshore.
This may bring about some drying across central/eastern sections for
much of Sunday before another transient but weaker surface high starts
to build in from the north again with yet another wedge ensuing. In
addition another faint mid level shortwave will approach along the
residual baroclinic zone from the west allowing more backing
aloft to take shape. Latest forecast soundings suggest that this will
be enough to saturate the column again with early low rain chances far
west to start becoming more widespread from west to east by late
Sunday. Highs perhaps a bit warmer espcly south and east given weak
downsloping and possibly some sun. Otherwise staying on the cooler
side of MOS with 40s north to low/mid 50s south.
Weak wave aloft crosses the area Sunday night with possible drier air
to the north aiding in cooling as the wedge deepens while being
overrun by 850 mb warm advection. Models again differ on the
degree of low level cooling within the wedge with the Nam again the
coldest in showing a rather impressive cold nose just off the surface
while other solutions keep boundary layer temps above freezing across
the northwest. Since this CAD episode appears a bit weaker as the
surface high is not quite as strong, may only leave in a brief freezing
rain mention late Sunday night into early Monday in the LWB-HSP
vicinity at most. Otherwise appears another rather low QPF event but
enough coverage to go with some low likely pops northwest with at least
chance elsewhere. Lows mostly 30s north to 40s south but more in line
with the slightly warmer Mav/EC mos.
Warm advection regime will finally start to win out later Monday into
Monday night as more in the way of shortwave ridging takes shape ahead
of the next upstream cold front. With the surface high shifting from
eastern sections Monday morning to offshore by Monday night would
expect the cooler 40s to linger east Monday with warmer 50s far west.
Pops likely more scattered to isolated given less forcing and
deeper moisture to the west with perhaps little shower coverage by
Monday night when should be well into the warm sector.
.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
As of 300 PM EST Friday...
Frontal boundary lifts north into New York Tuesday and reaches Maine
by Tuesday night as strong upper low moving across the central U.S.
amplifies ridge downstream. Cold front approaches from the west on
Wednesday and moves into the CWA on Thursday. On Thursday night into
Friday, the boundary slowly moves north across the region. There are
differences in timing of frontal systems with GFS faster than
ECMWF. Leaned towards superblend for Medium range. High temperatures
will run about 10- 20 degrees above normal Tuesday into Friday.
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 1236 PM EST Saturday...
Overall poor flying conditions will continue this afternoon into
tonight as a wedge of high pressure locks in along and east of
the mountains. Low clouds with patchy light rain and drizzle
will combine to produce IFR/LIFR cigs and MVFR/IFR vsbys
in the mountains and MVFR out east where cloud bases should
remain higher and rainfall less. There is the potential
for pockets of freezing rain or drizzle in the coldest locations
aside from at the terminals. Pilots should prepare for icy
areas and Mountain Obscurations this afternoon into Sunday.
Light southerly winds will continue this afternoon, then become
west to northwest under 10 kts tonight.
Some potential to see some improvement in cigs later this
afternoon once the easterly flow starts to veer and rainfall
fades but still thinking overall sub-VFR at this point across
the region. Expect conditions may flop back into more IFR in
fog/stratus this evening before drying aloft on weak northwest
flow arrives overnight. This could allow bases to rise although
some fog likely to persist overnight. Low level wedge should
gradually redevelop on Sunday as a second area of high pressure
builds to the north and eventually wedges south again along the
mountains by late Sunday. Easterly flow around the high will
again bring lowering cigs Sunday afternoon with an increasing
threat for light rain mainly mountains by the end of the day
into Sunday evening.
Medium to low confidence with cigs and vsbys through Sunday
given varying conditions in and out of the wedge through the
weekend. Spotty nature of fog and drizzle is also problematic.
Higher confidences that east to southeast winds will prevail on
Extended Aviation Discussion...
A baroclinic zone will remain anchored across the region
sandwiched between a strong upper ridge over the southeast
states and an active jet stream from the southwest U.S. into the
northeast U.S. Thus, an unsettled, wet weather pattern is
expected to remain in place Monday into Tuesday. The frontal
boundary may lift north enough by Monday night for a brief
period of mainly VFR, but a stronger front will arrive By
Tuesday with more showers including widespread sub-VFR.
Generally looking at MVFR much of the period, although periods
of VFR as well as IFR- LIFR can be expected at times. Passing
cold front from later Tuesday should clear the region on
Wednesday allowing for a return to VFR across the region for
midweek. Moisture may return from the southwest Thursday
afternoon into Thursday night.