Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 200226
Area Forecast Discussion
National Weather Service Blacksburg VA
1026 PM EDT THU MAY 19 2016
High pressure will be over the region tonight into Friday. Low
pressure will advance towards the region Friday and move through the
area Friday night into Saturday. An upper trough of low pressure
will progress across the area on Sunday with area of high pressure
close behind it for Monday.
.NEAR TERM /THROUGH FRIDAY NIGHT/...
-- Changed Discussion --As of 1000 pm EDT Thursday...
Don`t blink. Skies have partially cleared for some of the forecast
area, primarily north of Highway 58 into central/northern VA and
across WVA. Moon was visible, albeit briefly, at 9PM this evening
in Blacksburg. Clouds lurking across North Carolina and just
across the border into VA are poised to move back north as wind
flow becomes southeasterly overnight.
High pressure is centered to our north, thus providing a clearing
tease for our northern CWA. This will be short lived as clouds
advance back into the area from the south and southwest per low
pressure along the Gulf Coast region.
Through the overnight hours, anticipate the lee side wedge from
the High pressure to our north to gradually become more
entrenched. Anti-cyclonic flow around the High, plus the influence
of an approaching area of Low pressure, will bring wind around to
the southeast across much of the region. The resultant flow will
allow for cloud covers to redevelop where they had cleared earlier
today. Areas with clouds currently, will remain cloudy. Also,
patchy light rain will start to work its way back into the
southwest portion of the area and spread slowly northeast. Light
fog development is also anticipated for much of the region. Lows
tonight will range from the mid 40s to around 50 across the
mountains with upper 40s to lower 50s across the piedmont.
Friday into Friday night we are still expecting widespread rain to
overspread the region from southwest to northeast. Plenty of Gulf of
Mexico moisture will be advected into the region in advance of an
approaching area of low pressure. Moderate to heavy rain is still
very likely late Friday afternoon through Friday night. At this time
however, the amount of forecast rainfall does not warrant a flash
flood or flood watch. Please reference the HYDROLOGY section of this
discussion for more details. We will continue to discuss the
expected moderate to heavy rain in the Hazardous Weather Outlook.
High temperatures on Friday will range from the upper 50s to lower
60s across the mountains to the lower 60s to upper 60s across the
piedmont. Lows Friday night will be a mix of the lower 50s across
the mountains to the mid 50s across the piedmont.
-- End Changed Discussion --
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 330 pm Thursday...
An upper level trough will swing out of the Great Lakes and kick the
heavy rain east of the area Saturday. The parent surface low is over
the Ohio Valley with a secondary low forming off the Virginia coast.
This may delay the exit of moderate to heavy rain Saturday morning,
therefore left high PoPs. The secondary low becomes the primary low
Saturday afternoon, pulling bulk of the precipitation out to sea.
However, that does not end our rain chances. The upper level trough
coming across the Ohio Valley will pivot over the region Saturday
night, keeping the chance for rain showers over the mountains. A few
showers may overcome northwest flow and push east of the Blue Ridge
Cold pool remains over the region Sunday and with afternoon heating,
scattered showers and isolated thunderstorms are possible into the
evening. This trough is expected to become a closed low Sunday
night. If this low is off the Mid Atlantic coast, then the forecast
area will be in a subsidence region keeping our chance for showers
low. If the low remains closer to the shore or inland, showers
chances will remain Sunday night into Monday.
We may see warmer than expected temperatures Saturday depending on
when the bulk of the rain exits. Cooler air is not expected to enter
the area until the trough pivots east. For now, temperatures will
remain below normal and in the lower to mid 60s. Some areas across
northern North Carolina may make it to 70F late Saturday. Sunday may
be a little warmer with more chances to see the sun. Sunday
afternoon will remain below normal with highs in the mid to upper
60s west to lower 70s east.
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 330 pm Thursday...
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 drop to zero 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 /02Z FRIDAY THROUGH TUESDAY/...
As of 720 pm EDT Thursday...
Overnight, low level moisture will condense into IFR/MVFR
ceilings with some light fog possible as well in spots under a
developing wedge of high pressure. After about 14Z/10am Friday,
flight categories will again improve to VFR as the nocturnal
inversion breaks. Rain will again start progressing into the area
by the late morning across southwest portions of the forecast
area. At this time, none of the TAF locations are expected to be
impacted by 21Z/5pm.
Rain will overrun the region Friday afternoon into Friday night on
the east side of an approaching upper level trough and surface low.
This rain will help to strengthen the lee side wedge. Anticipate
cloud cover to trend to IFR/MVFR ceilings with MVFR visibilities
for rain and light fog.
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
Monday into Tuesday, most areas will experience VFR conditions as
an upper level shortwave ridge noses itself into the area.
As of 335 pm EDT Thursday...
The latest WPC quantitative precipitation forecast for the time
period of Friday through Saturday places an average of 1.25 to 2.00
inches across our region, with 75 to 85 percent of that occurring
Friday night. The latest flash flood guidance from the river
forecast center offer anywhere between 1.50 to 4.00 inches of rain
in six hours to prompt flash flooding with similar values forecast to
be required to prompt flash flooding in three hours. Our
largest forecast six hour precipitation forecast Friday night is on
the order of 0.80 to 0.90 inches in six hours.