Area Forecast Discussion
Issued by NWS Blacksburg, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS61 KRNK 231349

Area Forecast Discussion
National Weather Service Blacksburg VA
949 AM EDT Fri Jun 23 2017

Tropical Depression Cindy was over Arkansas this morning and by
Saturday morning will be over Maryland with a cold front
trailing into the Southern Plains. High pressure builds in
Sunday and Monday from the west behind the front and by Tuesday
will cover much of the eastern United States.


As of 948 AM EDT Friday...Regional composite radar mosaic shows
lighter showers over Charlotte and Halifax Counties exiting
eastward, while another area of steady showers essentially arcs
parallel to I-40/I-81 corridor in eastern TN/western VA moving
to the northeast. Could see some brief, embedded localized
downpours from these given the humid air mass in place.
Essentially nowcasted these in the PoP/Wx grids through 17z
using the 11z HRRR and a consensus blend of finer resolution
guidance. This keeps scattered showers mainly west of I-81 and
then eastward across Rockbridge into Amherst Counties. There
have been some breaks in the clouds; while I`ve lowered cloud
cover some, we probably will struggle to fully clear so kept sky
cover partly to mostly cloudy at best.

Question for the afternoon is if any thunderstorms can develop,
still contingent on sufficient clearing to destabilize the
atmosphere. Recent CAM guidance isn`t really that steadfast in
indicating much thunderstorm development this afternoon. Left
PoPs for the afternoon as is for now and will closely monitor
forthcoming guidance for possible adjustments. Greater/heavier
showers and thunderstorms projected into the later evening,
hours as we await Cindy`s remnants, now over the mid-Mississippi
Valley, with progressing cold front now over the Great Lakes.

Previous near-term discussion issued at 345 AM Friday follows...

It will take 6 to 12 hours for the former tropical system and cold
front to cross through southern West Virginia and southwest
Virginia. Good diffluence aloft tonight, partially with the tropical
feature, but moreso with the strong upper level jet in the northern
stream. Some differences in the short range models with how much
precipitation there will be following the North Carolina wave and
before the tropical/frontal precipitation arrives. Wildcard may be
the band of showers in eastern Tennessee to southeast Mississippi
and the location of this feature by this afternoon. Will be trimming
back probability of precipitation for today but will retain
categorical probability tonight. Limited coverage of showers and
thunderstorms will also limit severe threat prior to 00Z/8PM, but
with surface dew points in the lower 60s to lower 70s, leading to
increased CAPE and 0-3KM helicity forecast to be up to 400 m2/s2,
the threat for severe thunderstorms is still present.

850mb reach about +19 this afternoon. Should get some sun following
the cluster of showers tracking out of North Carolina. Took a blend
of MET /MAV guidance. Front does not completely clear the Virginia
and North Carolina piedmont before 12Z/8AM. Will keep minimum
temperatures mild ahead of the front.


As of 330 AM EDT Saturday...

Remnants of TS Cindy will get absorbed into a cold front coming
across the Ohio Valley early Saturday morning. This cold front will
slide across the mountains during the morning, but may not clear
Southside until Saturday evening. Strong ridging off the southeast
coast will slow the southern movement of the front, which will stall
across the Carolina coast on Sunday. Rain showers will clear the
mountains by early afternoon then move south into North Carolina
during the evening. Subsidence behind the front will also bring
breezy/gusty winds to the mountains through the evening.

This front will remove the tropical air mass but humidities will
remain slightly elevated until the dew point front moves across the
region on Sunday. Dry high pressure will then take control of our
weather starting Sunday afternoon. Saturday`s afternoon temperatures
will warm to near normal levels. Cooler and drier air will arrive
Sunday with temperatures 3F-5F cooler than normal.


As of 125 PM EDT Thursday...

Fairly quiet wx this period with cooler temperatures as 5h trough
digs across the eastern U.S. A few shortwaves in the Monday-Tuesday
time frame may fuel a few showers, but overall it looks dry.

Toward Thursday the upper trough exits to the east with shortwave
ridging building across the Appalachians. Highs and lows Monday-
Wednesday should run 5 to 10 degrees below normal, then edge close
to normal by Thursday.


As of 740 AM EDT Friday...

An area of light to moderate showers will move across the
mountains this morning as another batch of showers will move
east of KDAN. Pockets of MVFR ceilings this morning that will
improve back to VFR by 14Z/10AM. Could see an isolated shower
or thunderstorm develop in the afternoon but coverage should be
limited and confined to the mountains.

Showers and thunderstorms associated with the remnant tropical
depression and approaching cold front will reach West Virginia
and Virginia late today. High confidence in the arrival time of
this precipitation, with models in good agreement. Have
brought precipitation with MVFR visibility back into the central
Appalachians, including at KBLF, KLWB, and KBCB between 02Z/10PM
and 06Z/2AM. The precipitation will move east throughout the
night with MVFR ceilings expanding across the mountains behind
the front after midnight.

Extended Aviation Discussion...

A cold front will move through central and eastern Virginia and
North Carolina Saturday morning. There may be thunderstorms
along the front which will produce heavy rain and gusty winds.
West to east clearing anticipated through the day Saturday east
of the Blue Ridge with VFR conditions and a wind shift to
northwest. VFR conditions appear to continue until Monday
afternoon with possible VFR/MVFR conditions in the mountains
Monday night/Tuesday associated with a upper-level disturbance.


As of 735 AM EDT Friday...

Rainfall forecast/models/ensemble river forecasts suggests greater
threat for flooding will be west and north of our forecast area.
Average rainfall amounts of 1 to 2 inches expected from the NC
mountains to Mountain empire of SW VA to southeast WV with 2 to 3
inches further west into the KY/TN/OH corridor.

Not seeing enough signals to warrant a watch, but given efficient
rainfall rates, any convective elements or training will increase
the threat. Timing of heavy rain will be this evening into
Saturday morning.

In summary, based on models looking wet, but still not high enough
confidence in a flood/flash flood watch.




HYDROLOGY...AMS/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.