Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 132347
Area Forecast Discussion
National Weather Service Blacksburg VA
647 PM EST Fri Jan 13 2017
A cold front will move south, then stall across northern North
Carolina Saturday before returning north as a warm front late
Saturday night. This front will then oscillate north and south
across the region into early next week keeping an unsettled and
wet weather pattern in place. By the middle of next week, a
stronger frontal system will finally approach from the west and
move the pesky front out of the area.
.NEAR TERM /THROUGH SATURDAY/...
-- Changed Discussion --As of 640 PM EST Friday...
Forecast updates this evening are focusing on the very near term
of the forecast. Will leave any portion of the forecast
dedicated to the time period of the Freezing Rain Advisory alone
for now. May revisit closer to 10pm when additional model data
are available. For this evening, have made only minor tweaks
regarding cloud cover, temperature and dew point. Have adjusted
values based upon the latest observations and expected trends
through the evening. Light rain is arriving across parts of the
western sections of the region. The ongoing precipitation timing
forecast looks on track.
As of 310 PM EST Friday...
A cold front will slowly move into North Carolina this evening.
Cooler temperatures will be felt behind this front but
temperatures will remain warmer than normal with morning lows
ranging from the upper 20s from the Greenbrier and Southern
Shenandoah Valleys to the upper 30s towards the NC/VA border.
The coldest air associated with this front will remain with the
center of high pressure currently located over the Great Lakes.
This high pressure center will track east keeping the very cold
air north of the Mason-Dixon line. Some freezing temperatures
will move south once the core of the cold air moves east of the
Appalachains tonight. These freezing temperatures are expected
to move into the Greenbrier and Southern Shenandoah Valleys and
Allegheny Highlands early Saturday morning. Winds will remain
out of the east through the day Saturday, so these areas will
only warm into the mid to upper 30s. These easterly winds will
also keep areas east of the Blue Ridge cool with temperatures
closer to normal values (low to mid 40s). Looking at forecast
soundings, this cold air will be shallow, possibly 2000 feet
thick. Therefore this cold air in easterly flow will not move
west across the mountains Saturday. With no cold air intrusion,
southwestern Virginia and northwestern North Carolina will
likely warm into the the lower 50s Saturday.
There remains a baroclinic zone from the Ozarks to the Southern
Ohio Valley tonight and Saturday. Weak impulses along this zone
will bring rain into the mountains late tonight into Saturday.
Most of the models have the higher rainfall amounts through the
period north of I64. This just so happens to be the area where
temperatures will drop below freezing, thus creating a threat
for freezing rain Saturday morning. First of all, models are
moving moist warm air over cold temperatures possibly over doing
amounts. Also, this type of signature could be an area where
more snow or sleet falls as compared to freezing rain. Looking
at forecast soundings, the cold air will be shallow south of
I64, approximately 2000 feet. North towards Charlottesville, the
depth of the cold air is around 3000 feet thick. With this in
mind, we are thinking Ptype south of I64 will be predominately
rain changing to freezing rain with a light glaze on elevated
surfaces to include overpasses. North of I64, a snow/sleet
mixture changing to freezing rain by sunrise with accretions
possibly up to a tenth of an inch on elevated surfaces and
overpasses. We are not thinking much will coat the roads with
our recent warmer than normal weather the past couple of days.
Now lies our problem within the freezing rain advisory. The GFS
is the warmer model and keeps all precipitation as rain. Low
level thicknesses are above 1315m and 85H temperatures are +2C.
The NAM is the coldest model with 85h temperatures near 0C and
low level thicknesses ranging from 1295 to 1310 in the advisory
area. The NAM also has a strong warm nose, pushing 7C air over
surface temperatures in the upper 20s. The ECM is in between the
GFS and NAM.
With differing models, RNK, WPC and neighboring offices are
leaning towards the colder NAM. Our thinking is, it is better to
have an advisory and nothing happen than have something happen
and no headlines. Therefore we will keep the current freezing
rain advisory for tonight and Saturday as is.
-- End Changed Discussion --
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As OF 300 PM EST Friday...
The high amplitude split upper flow will remain across the
nation during the weekend. Trough in the southwest continues
with a ridge in the Southeast. A wavy frontal boundary will
remain across our region Saturday night through Sunday night. In
general, the cooler temperatures associated with the boundary
will prevail in the north and on the east side of the
Appalachian Divide. Meanwhile, warmer air over the Tennessee
Valley will push north. An isolated pocket of freezing rain may
be possible Saturday night into Sunday morning in Northwest
Greenbrier county. Coverage will be limited and only on the
coldest elevated surfaces. But overall, Sunday morning is
forecast to be a few degrees warmer compared to Saturday. Low
temperatures will range from the lower 30s in northwest
Greenbrier county in Southeast West Virginia to near 50 degrees
in the southwest mountains in North Carolina. During the day on
Sunday, the front lifts northward with the best chance of rain
in the west. High temperatures on Sunday will warm to near 40
degrees in the northern mountains to the lower 50s along the
southern Blue Ridge. The NAM continues to hint that slightly
cooler air will drift back into the area Sunday night as the
front gets a little nudge to the south. If this turns out to be
the case, then some of the higher elevations along and north of
I-64 could see some freezing rain/drizzle Sunday night. It would
be low QPF and mainly on elevated surfaces. Low temperatures
Sunday night into Monday morning will range from the lower 30s
in the northern Mountains to the mid 40s in the southwest
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As OF 300 PM EST Friday...
Frontal boundary across the area Monday morning 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. Monday will
average near normal to 15 above in the west, then high
temperatures will run about 10- 20 degrees above normal Tuesday
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 1215 PM EST Friday...
Generally deterioriating to poor aviation conditions expected
through the TAF valid period as a backdoor front sags southward
through the region, then stalls just south of the NC/VA border,
returning northward slowly Sat-Sun.
An upper disturbance and stalled front will return rain to the
region later this evening and overnight. Cigs will remain/trend
toward IFR-LIFR in the west and become generally MVFR in the
east as this area of rain spreads east overnight. As cold air
spreads southward from the northeast overnight, a brief period
of freezing rain will be possible at KLWB early Saturday
morning. Winds generally WNW-NW this afternoon becoming NE-ENE
this evening into Saturday.
Medium to high confidence in ceilings through the TAF valid
Medium to high confidence in visibilities through the TAF valid
Medium to high confidence in wind speed/direction through the
TAF valid period.
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 through the extended periods. The
frontal boundary may lift north enough by Monday for a brief
period of mainly VFR, but a stronger front will arrive By
Tuesday with more showers. Generally looking at MVFR much of the
period, although periods of VFR as well as IFR-LIFR can be
expected at times through the period. Overall, not the best
weather for aviation.
VA...Freezing Rain Advisory from 4 AM to 4 PM EST Saturday for
WV...Freezing Rain Advisory from 4 AM to 4 PM EST Saturday for