Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 201134
Area Forecast Discussion
National Weather Service Blacksburg VA
734 AM EDT FRI MAY 20 2016
Low pressure over the lower Mississippi Valley will deepen and
move northeast into the Tennessee Valley today and tonight. At the
same time, another low develops off of South Carolina and tracks
northeast along the coast. By Sunday, these systems transition to
a strong low well off of the New Jersey coast.
.NEAR TERM /THROUGH TONIGHT/...
As of 430 AM EDT Friday...
Low pressure will develop over the Tennessee Valley today. This
will enhance a wedge of high pressure over the forecast area as a
second low forms off the Carolina coast. Models were in good
agreement spread clouds northeast across the region followed by
rain. Have slowed the onset of the rain in the northern and
eastern county warning area until late afternoon. Best forcing and
isentropic list as well as strong upslope will be from 00Z/8PM
through 06Z/2AM. 850MB southeast low level jet increases to
around 40KTS which will enhance the upslope and precipitation
amounts on the eastern slopes of the Blue Ridge. Have raised wind
speeds and gusts in the western downslope area overnight. Expect
the smallest rise in temperatures in the southwest county warning
area, especially once the rain begins. Took a blend of guidance
for lows tonight.
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 330 am Friday...
A Miller B type system expected with parent low weakening over the
Ohio Valley and the energy is transferred to the coastal low. The
upper level trough will move out of the Great Lakes and push the
moderate to heavy rain east of the area Saturday. The challenge in
the forecast is how long does it rain hard before the secondary low
becomes the primary low Saturday afternoon, pulling bulk of the
precipitation out to sea. Several shortwaves will rotate around the
upper trough generating scattered convection afternoon into
Saturday evening. High temperatures Saturday will range from the
upper 50s in the northern mountains to the lower 70s in the
Piedmont. We may see warmer than expected temperatures Saturday
depending on when the bulk of the rain exits.
The Coastal surface low lifts northeast along the coast Saturday
night. The upper level trough will pivot over the region Saturday
night, keeping the chance for rain showers especially over the
mountains. A few showers may overcome northwest flow and push east
of the Blue Ridge overnight. Low temperatures Saturday night will
drop into the mid 40s in the mountains to the mid 50s in the
Cold pool remains over the region Sunday and with afternoon heating,
scattered showers and isolated thunderstorms are possible into the
evening. Sunday afternoon high temperatures will remain below normal
with readings from lower 60s in the west to the lower 70s in the
The upper trough becomes a closed low Sunday night off the Mid
Atlantic coast. As the low moves away, the chance of rain will
decrease with our area in a subsidence region. The locations of this
feature is similar on both the ECMWF and GFS. Low temperatures on
Sunday night into Monday morning will generally be from the mid 40s
in the west to the lower 50s in the east.
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 330 AM EDT Friday...
An upper level low in the vicinity of the Mid Atlantic will keep a
chance for showers and a few afternoon thunderstorms in the area
Monday. If this low wobbles offshore, the area will be in the
subsidence zone and with high pressure building east, the chance for
rain will decrease for a few days. Once this low departs, upper
level ridging will increase, which means warmer temperatures are on
the way. However, with warmer temperatures, the threat for
thunderstorms will increase which looks to begin Wednesday. The
threat of convection may hang around through the end of the week.
Temperatures will moderate to near normal on Monday, then above
normal for the remainder of the workweek.
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --As of 730 AM EDT Friday...
Leading northern edge of 4000-6000FT ceilings was advancing
north across Virginia and will cover KLWB and KLYH just after the
12Z start of the TAF forecast period. Patchy dense fog with LIFR
visibility had developed overnight. Visibility will improve this
morning as mixing begin but only meduim confidence on the timing
of this improvement.
Ceilings will gradually lower today as a low pressure system
approaches from the southwest. Models, including the GFS and
variations of the WRF showed good consistency with the timing of
the MVFR ceilings and arrival time of light to moderate rain.
Still high confidence there will be widespread moderate to heavy
rain across the region ceilings lowering to IFR between 00Z and
06Z. A low level jet from the southeast tonight will produce some
wind gusts of 25 to 35 knots along the ridges. Gusts up to 30
knots are possible at KBLF.
Saturday, the precipitation will trend more showery as the axis of
the upper trough draws close and the surface low passes overhead.
Flight conditions will improve as the low level winds become
northwest and the lee side wedge erodes. Isolated afternoon
thunderstorms cannot be ruled out as surface instability increases,
especially in the west.
Sunday, mainly VFR conditions are expected along with some hit or
miss showers as the axis of the upper trough passes across the
region. The best potential for MVFR conditions will be across
southeast West Virginia where northwest upslope cloud cover is
expected. Monday into Tuesday, most areas will be VFR.
-- End Changed Discussion --
As of 450 AM EDT Friday...
Consistent forecast from the models and the Weather Prediction
Center with one to two inches of rain expected across the forecast
area from this afternoon through late in the day Saturday. A bulk
of this precipitation will fall this evening into Saturday
morning. There is still a potential that this longer duration
rainfall will lead to localized minor flooding along streams and