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FXUS61 KRNK 241154

Area Forecast Discussion
National Weather Service Blacksburg VA
754 AM EDT Sat Jun 24 2017

The remnants of former T.S. Cindy, located over northern
Virginia this morning will accelerate northeast of the Mid-
Atlantic coast by evening as upper troughing deepens across the
Great Lakes. A weak cold front will push slowly southeast
through the day, then southeast of the area by Sunday morning.
Upper troughing will remain in place through much of the
upcoming week, but at the surface weak high pressure will hold
until late week, leaving the area with mostly dry conditions
until late week with slightly below normal temperatures.


As of 415 AM EDT Saturday...

Surface pressure analysis shows that the remnants of T.S. Cindy
tracked through the heart of the CWA overnight and early this 
morning were located over Loudon county VA, just west of D.C. 
Any area of showers and gusty winds moved quickly through the 
CWA just after midnight blowing a few trees down in the Henry 
County VA/Rockingham County NC area, but other than that it was 
just a breezy and muggy night, albeit about 10 degrees cooler 
with the passage of the showers and Cindy.

So, we are done with problems associated with Cindy now as it is
progged to continue racing off quickly to the east-northeast
amidst strengthening 500mb flow thanks to a trough deepening
over the Great Lakes. A trailing cold front, will be much slower
to push south of the area, as the flow aloft is largely parallel
to the front. With the trough deepening, the front will
eventually sag south of the CWA later tonight and early Sunday.
Convective allowing models in addition to most of the synoptic
scale models, indicate good potential for showers and
thunderstorms to develop across eastern TN/western NC and
perhaps even into far southwest VA, such as the Grayson/Carroll
county area, this afternoon, before drifting east-southeast
through the evening. Brooks-Craven parameters suggest that there
is even some potential for a few severe storms, but mainly
closer to the I-40 corridor just south of the CWA. SPC has
indicated a marginal risk for severe this afternoon/evening, but
has kept it just south of our CWA with general thunder indicated
to the northwest into most of the areas previously mentioned.
With the wind fields much weaker than was the case earlier with
the passage of the remnants of T.S. Cindy, main threat would be
locally heavy downpours, CG lightning, and perhaps small
hail/localized wind gusts.

Any threat of convection will end very quickly after sunset with
the boundary shifting southeast of the area under the deepening
upper trough. Cooler/drier air will start to filter further
southeast overnight and Sunday morning will start off quite a
bit cooler than we have seen in the past few days with lows
ranging from the 50s in the northwest to the 60s in the
southeast with dewpoints dropping into the 50s northwest to the
60s southeast. This will end the daily thunderstorm threat for
the next few days.

The passing remnants of T.S. Cindy and the deepening upper
trough/lower heights will lead to fairly breezy conditions
today, so some wind gusts into the 20-25 mph range not out of
the question at all. But for most of us, especially north and
west of the Blue Ridge, it will be a very pleasant Saturday.


As of 330 AM EDT Sunday...

A broad upper level trough will reside over the eastern half of the 
US through early next week. Northwest winds will usher in cooler 
drier air both Sunday and Monday. Besides some fair weather cumulus 
clouds forming in the afternoon, both days look very comfortable. 
Afternoon temperatures will average 3F-5F cooler than normal. Dew 
points will range from the upper 40s across the mountains to upper 
50s in the piedmont. No rain is expected until Tuesday afternoon.


As of 339 PM EDT Friday...

The long range models are in good agreement with the overall upper 
air pattern during this period with an anomalously deep upper trof 
over the eastern U.S. early in this period, with 500mb heights 2-3 
standard deviations below normal,transitioning to a zonal flow by 
mid week, with ridging building by the end of the week. 

The 12Z GFS is still fastest with the eastward progression of the 
upper trof Tuesday night into Wednesday, but this has little impact 
on the tranquil weather expected during this time. A weak frontal 
boundary moving through early Tuesday morning may generate some 
spotty showers in the mountains, but forecast RAOBS indicate there 
will be very little moisture available. Otherwise, PWAT values will 
remain below average until Thursday night/Friday so expect a 
prolonged period of dry weather. By late in the week...a deep 
southwest flow developing on the west side of an upper ridge and 
ahead of an approaching upper trof in the upper mid west will 
increase moisture and provide the opportunity for weak upper level 
disturbances to pass over our area. This will result in increase 
chances for scattered thunderstorms during this period.

As for temperatures, forecast 850mb temps from the GEFS are 2-3 
standard deviations below average, which will lead to some cool 
mornings Tuesday and Wednesday. Adjusted low temperatures down a 
couple of degrees below guidance during this period. Temperatures 
will moderate late in the week.


As of 745 AM EDT Saturday...

Remnants of T.S. Cindy have moved well northeast of the area and
its effects, which moved through very rapidly overnight, are
gone and it will no longer be a factor in our weather going
forward. Concern through the day today is a weak cold front
sagging slowly southward being supported by increasing broad
upper troughing across the Great Lakes. The front will combine
with residual moisture and afternoon heating to likely support
thunderstorms across northwest/north central NC and Southside VA
later this afternoon. HRRR supports some pretty robust
thunderstorm development in those areas after 17Z, moving
southeast of the area after 00Z. Included a VCTS at KDAN, but
this is the only TAF site that could potentially be impacted.

Otherwise, lingering upslope MVFR to briefly IFR cigs across
eastern WV, with mostly VFR cigs elsewhere. Would expect cigs to
improve to MVFR or better in eastern WV after 16Z with VFR
conditions holding in most areas from mid-afternoon onward. Air
mass is drying, so do not expect fog development overnight or
Sunday morning.

Winds will be WSW veering more toward the WNW with time as high
pressure builds southeast from the Midwest and the remnants of
T.S. Cindy move further away. Low end gusts can be expected in
the 16Z through 22Z time frame at most sites. On average, look
for speeds of 7-10kts with gusts 18-20kts.

Medium to high confidence in ceilings through the TAF valid 
High confidence in visibilities through the TAF valid period. 
Medium to high confidence in wind direction/speed through the 
TAF valid period.

Extended Aviation Discussion...

VFR conditions expected to prevail most of the Sun through Wed 
period. A weak front may provide a few clouds early in the week,
but little sensible weather. Potential for radiation fog and 
related visibility restrictions will increase later in the week
as moisture levels increase. Showers and thunderstorms will
return in earnest late in the week as southwest flow returns to
the area.





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