Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 251143
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
743 AM EDT WED MAY 25 2016

.SYNOPSIS...
High pressure will continue to build off the southeast coast and push
warmer and more humid air into the region. This will bring well above
normal temperatures to the appalachians and central mid Atlantic
region...along with a chance for afternoon showers and
thunderstorms...into the weekend. Then...a developing area of low
pressure off the coast will begin moving in our direction and bring
greater chances for precipitation for the latter portion of the
Memorial Day weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 430 AM EDT Tuesday...

High pressure off the southeast coast will continue to push warmer and
more humid air in our direction today. A combination of orographic
effects from the Blue Ridge westward along with some upper level short
wave energy looks like it will be enough to generate some low chance
POPs for a late day shower. Meso guidance has trended these chances
upward of late but do not have enough confidence in these wetter
solutions at this time to go with higher POPs far west so will wait and
see if the trend sticks around in later model runs and adjust upward if
needed. However there does appear to be enough support to add a slight
chance of thunder to the mix with this grid package.

For tonight it looks like any convection will be tapering off early but
there are indications that another impulse will keep some showers going
overnight with some additional development spreading eastward into the
piedmont. Will keep chance/slight chance pops going through the
overnight period for most locations.

With the influx of warmer air high temperatures will reach the middle
and upper 80s east of the Blue Ridge with upper 70s/around 80 more
common to the west. Lows tonight will generally be in the upper 50s to
lower 60s.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
As of 400 am EDT Wednesday...

Synoptic pattern will continue to feature a deep and highly diffluent
upper trough in the southwestern U.S. This system is not expected
to move much at all through the period. Meanwhile...a downstream
upper ridge will be located across the eastern half of the
country. For Thursday...the main focus for our region will be on a
short wave that is slated to eject northeast from the western U.S.
upper low into the Ohio Valley Thursday...then toward New England
by Friday. Ample moisture and instability will be present by
Thursday afternoon to support scattered showers and
thunderstorms...with the best focus west of the Blue Ridge closer
to the upper support and better thermodynamics. Dynamics are weak
at best...so expecting non-severe pulse thunderstorms. There is
the potential for showers to be ongoing/developing early in the
day Thu across the northwest...but the best coverage/intensity
will be during the afternoon into the early evening.

The aforementioned short wave moves northeast of the region
Friday. The southwest U.S. upper low drifts slightly further east
into the TX/OK region. As a strong short wave rounds the base of
the upper trough...the upper flow amplifies with the flow becoming
more meridional across the central and eastern U.S. Thus...it
appears that this next short wave will largely lift northwest of
the RNK CWA with upper ridging the dominate feature across our
region. Showers/thunderstorms Friday will be highly diurnally
driven and mainly focused across the Alleghanys and mountains of
southwest VA/northwest NC. Areas east of the Blue Ridge may see a
decrease in convection Friday as that area comes under increasing
subsidence on the northwest side of a developing low pressure area
across the Bahamas.

For Saturday...the western U.S. upper low continues with a strong
short wave lifting almost due north through the Midwest...thus
having little to no effect on the RNK CWA. Our attention will be
increasingly turning toward the southeast and a potential
developing tropical system across the Bahamas. All models indicate
strong potential for a tropical or subtropical system to develop
across the Bahamas and drift northwest toward the SC/NC coast. The
GFS remains one of the most aggressive models with this
development...pushing deep tropical moisture well northwest into
the RNK CWA by Sunday with PWATS into the 2+ inch range. The other
models remain less aggressive with this deep moisture...tending to
focus the effects of such closer to the NC/SC coast. This is in
agreement with WPC thinking at this time. For
Saturday...subsidence to the northwest of this developing low
pressure area will likely suppress convection for much of the
CWA...outside the Alleghanys and southeastern sections late in the
day.

One thing for sure during this period...our extended cool weather
of recent will be gone. This entire period will feel much more
like August with increasingly high humidity and temperatures in
the 70s mountains and 80s elsewhere. Steadily increasing
dewpoints/PWATS/RH values will result in some of the muggiest
conditions we have experienced so far this year and will be in
sharp contrast to the well below normal temperatures we have
experienced most of May to this point. Low temperatures will tend
to average 8-10 degrees above normal with max temps 5-8 degrees
above normal. The increase in humidity will be the most notable
part...however.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 430 am EDT Wednesday...

This period will be dominated largely by the aforementioned
tropical system slated to drift northwest into or near our region
Sunday into Monday. The upper flow will remain quite stagnant with
an upper high to our north and a broad upper low continuing in the
western U.S. Therefore...if the tropical system does drift into
the GA/SC/NC area as most models suggest...although there are
notable differences in the distance it will track inland...it will
likely linger for several days with non-existent steering
currents and blocked upper flow. The upper high to the north could
keep the system lingering in place for several days. Rainfall may
become a concern depending on how far inland the system tracks.
The ECMWF continues to paint the least ominous solution...keeping
the bulk of the precipitation and higher PWATS closer to the
coast. At a minimum...we can expect scattered diurnal convection
with warm/humid conditions through the period. Max temps will
remain mostly in the 70s mountains and 80s elsewhere...with lows
mainly in the 60s. Have not made any drastic changes to the
extended pops as there is still considerable uncertainty in
exactly how much precipitation we will see.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
As of 735 AM EDT Wednesday...

Generally VFR conditions expected through the TAF valid
period...with a few exceptions...mainly in the form of late
night/early morning fog. Fog this morning limited to the
Greenbrier Valley with KLWB briefly seeing IFR-LIFR vsbys. Any fog
will dissipate quickly in the 13Z-14Z time frame.

Through the day...main focus will be on short wave ejecting from
broad upper low in the southwest U.S. Moisture and instability
will increase in advance of this system through the
afternoon...which may support scattered showers and isolated
thunderstorms across the Alleghanys...far southwest VA...and
northwest NC mountains late afternoon. Any activity could linger
through the evening and overnight as the disturbance tracks
northeast through the OH valley...so will carry VCSH
KBLF...KLWB...and KBCB through the night. Will refrain from
mentioning TSRA at this time as confidence in such given limited
instability is low. Fog development early Thursday
questionable...but late night rainfall and light winds could
contribute to such in the KLWB and KBCB area.

For the most part...cigs are expected to remain aoa050 through the
TAF valid period...but BKN050 cigs a good bet west of the Blue
Ridge this afternoon and overnight in association with upstream
disturbance.

Winds...mostly SW 5-8kts daytime...3-5kts or less at night.

Medium to High Confidence in cigs through the TAF valid period.
Medium to High Confidence in vsbys through the TAF valid period.
High Confidence in wind dir/spd through the TAF valid period.

Extended discussion...

Wind flow through Friday will be out of the southwest with the
weather pattern more reflective of summer conditions, primarily
VFR except for widely scattered afternoon and evening showers
during the peak heating part of the day. Nightime fog also
possible in the mountain valleys, but mainly after midnight up
until an hour or two after daybreak.

Potential wind flow change is advertised by the models this
weekend per development of a storm system off the southeast
Atlantic Coast. Models differ quite a bit on timing and movement
of this feature so low confidence forecast beyond Saturday attm.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...MBS
NEAR TERM...MBS
SHORT TERM...RAB
LONG TERM...PM/RAB
AVIATION...DS/MBS/RAB


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