Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 240826

Area Forecast Discussion
National Weather Service Blacksburg VA
426 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 Loudoun 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 150 AM EDT Saturday...

Following the HRRR as a guideline for events over the next
several hours since it matches well with current radar trends,
would expect bands of showers and isolated thunderstorms
associated with remnants of T.S. Cindy to translate many east of
the Blue Ridge through the morning hours, exiting the CWA before
daybreak. Generally looking at still VFR cigs with this
activity, worst case scenario low end VFR cigs as air mass is
very tropical. Visibilities could be briefly reduced into the
MVFR category. The exception will be KDAN as activity developing
along the Blue Ridge south of U.S. 460 could be somewhat more
intense, and may reach KDAN as a TS or VCTS. Will need to watch,
otherwise, just looking for VCSH/SHRA at this point.

Through the daylight hours, generally looking at improving
conditions as the remnants of Cindy track well northeast of the
area. Looking at VFR cigs throughout the day with scattered CU
and some SCT-BKN CI. Visibility will not be an issue through
the daytime or into the evening. The exception will be KBLF
where upslope clouds will result in several hours of IFR to LIFR
cigs through the mid-morning, then improving to VFR there as

Will need to watch for thunderstorm development across the NC
Piedmont near a lingering frontal boundary and tail of moisture
from Cindy. These could translate into the KDAN area before
shifting southeast during the evening. Otherwise, not expecting
any precipitation at the TAF sites after 12Z.

Gusty winds associated with a 850mb core of strong winds
traversing the area at the current time and associated with
Cindy will move east of the area before daybreak. Looking for
SSW-SW winds 15-25kts through the next few hours to generally
diminish to 10-20kts overnight and through the daytime hours
Saturday, veering more to the northwest with time as well.

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

Extended Aviation Discussion...

VFR conditions to then prevail Saturday night through Sunday night.
Potential for radiation fog and related visibility restrictions
Sunday night.

A cold front passing on Monday may produce VFR/possible MVFR
conditions and breezy northwest winds behind it. VFR then lasts
through Wednesday.




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