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NWS Area Weather Forecast Discussion
County Warning Area [CWA]: RNK
Regional NWS Weather Office: Blacksburg, VA

000
FXUS61 KRNK 231426
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1026 AM EDT Tue May 23 2017

.SYNOPSIS...
A weak stalled front over northern North Carolina will remain in
place today as ripples of low pressure slide northeast along
the boundary resulting in added rainfall into tonight.  Yet
another area of low pressure will arrive midweek with added
showers likely for Wednesday and Thursday. Weak high pressure
will follow this system for Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1020 AM EDT Tuesday...

Moderate to heavy rainfall mainly east of the Blue Ridge earlier
today has moved out of the area, causing streams and creeks to
run near bankful and drainage into the mainstem Dan river has
prompted flood warnings from Danville through South Boston.
There is a lull in the action at the moment, but the frontal
boundary is lingering in our far eastern counties and the upper
jet structure continues to generate large scale ascent as
additional waves slide northeast along the front. Meso guidance
and an early glance at 12Z data coming show a resurgence in
rainfall with precipitation moving up from the southwest this
afternoon. The flood watch continues to look on target and no
changes will be made.

Previous discussion...

Convection along the NC/VA border and points south continues to
evolve slowly north into the developing wedge north of the
residual front that remains across the far southern counties
attm. This in advance of main shortwave energy that will round
through the southeast states within strong southwest flow aloft this
morning before exiting with a final surface wave passing
offshore this evening. Increasing low level easterly flow along
with a surge in PWATS to over an inch south/east beneath a 6-8
hour window of good upper diffluence, supports widespread
showers/rain through much of the day as overrunning of the
boundary persists. However exactly where the axis of heaviest
rainfall sets up still iffy given potential for more convection
to the south and overall lighter rates per more stratiform
rainfall over our region. This supported by the latest HRRR that
has multiple rounds of steadier rainfall while keeping heavier
totals to the south and west. Latest flash flood guidance has
become much lower over the far south given rounds of heavier
showers in the past few days and where higher QPF totals appear
likely into this evening.

Thus have opted to hoist a flood watch across the VA/NC border
counties into tonight given ongoing deeper convection and likely
lingering light/moderate rainfall later on. Just how far north
some of the elevated/embedded convection gets key to heavier
amounts elsewhere espcly east so something to watch. Otherwise
trend of ramping pops up to likelys up to Highway 460 on track
through daybreak, followed by likely to categorical coverage for
rain at times through the day all sections. Will be much cooler
within the developing wedge with potential for temps to stay in
the 50s in spots today, with only low/mid 60s at best most
locations.

Expect rainfall to linger espcly eastern half this evening
before seeing drying aloft kick in behind the departing wave
overnight. This should allow pops to trend back to chance or
lower through the night as the region slips in between this
exiting system and the next upstream closed low that will be
approaching by morning. Will remain cool with lows overall in
the 50s as the wedge remains.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 300 AM EDT Tuesday...

Any reprieve in rainfall will be short as a strong upper low
across the Midwest teams with associated surface low pressure to
drive another axis of deep moisture ahead of a cold front into
the area Wednesday. Appears enough of a remnant wedge will
linger ahead of this feature to limit instability and convective
development, but good isentropic lift and dynamic support will
make for increasing rainfall and some possibly some embedded
thunder from lift over the stable layer. Also, there may be a
very narrow window just ahead of the front, espcly far southern
sections where the wedge has weakened that may allow for just
enough surface based instability to support deeper convection
in a highly sheared environment. Other issue will be with
another round of heavy rainfall that this time looks to occur
mainly over western sections with higher rainfall rates possible
within elevated convection. This combined with rainfall from
today could prime things up even more that another watch may be
needed. Thus will address in the HWO for possible flooding into
Wednesday evening behind the first event today.

Bands of showers rotating around the upper system may linger
into Wednesday evening before some semblance of a dry slot aloft
arrives overnight. This along with loss of heating and best lift
passing to the north/east should allow for decreasing pops
overnight. However may not be until late before coverage wanes
given wrap around potential far west and diffluence elsewhere
ahead of the cold pool that will still be west of the mountains
through daybreak Thursday. Should be a little milder Wednesday
given strong warm advection aloft and a gradual breakdown of the
wedge which supports highs mostly in the 60s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 330 AM EDT Tuesday...

Active and very unsettled weather to continue through the
period. A deep 552dm upper low will be overhead early Thursday,
rotating northeast to off the Mid-Atlantic coast line by Friday
morning. With the upper low over the area Thursday, expect
scattered to numerous convection with steep lapse rates and
ample low-level moisture in place. After an active day Thursday,
convection will diminish fairly quickly after sunset Thursday
evening as the upper low lifts off to the northeast.

Friday, will bring a brief break from the active weather as the
area is briefly sandwiched between the departing upper low and
yet another upper low digging southeast from the Northern
Plains. Can`t completely rule out a few afternoon
showers/thunderstorms across the western mountains, but in
general pops are below 15% for much of the CWA during the
daytime hours Friday.

Saturday, a baroclinic zone develops across the area as the
upper low to the northwest very slowly sags southward into the
Midwest. This pattern brings about a concern for more heavy
rainfall from convection as well as a greater severe threat
than we are seeing with the near term/short term convection. The
first round of convection will arrive into the region Friday
night, then redevelop along the baroclinic zone during the day
Saturday. Another round is likely Sunday as the upper low shifts
slowly eastward. Both days there appears to be at least some
threat for severe with strong instability along the baroclinic
zone. SIG SVR values are in the 20,000 to 25,000 range on
several models both Sat and Sun afternoon.

Temperatures will be warmer and closer to or even slightly above
normal during the extended periods with highs 70s west to lower
80s east and lows in the 50s west to the 60s east.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
As of 645 AM EDT Tuesday...

Will see a gradual deterioration in flying conditions from south
to north this morning as bands of light to moderate rain shift
north. However appears the majority of the heavier rainfall will
stay in the KDAN/KLYH corridor this morning. This will result in
sub-VFR along/east of the Blue Ridge with ocnl IFR/LIFR cigs and
periodic MVFR to IFR vsbys mainly around KDAN. A bit more
uncertainty exists from KBCB westward where cigs will be slower
to lower within the wedge with perhaps KBLF-KLWB staying VFR
until late morning. Expecting all to fall below VFR this
afternoon with widespread IFR possible as moisture deepens and
another round of rain slides northeast. Steadier rain should
taper off this evening leaving IFR/MVFR cigs and vsbys in fog
espcly after midnight.

Another low pressure system will arrive Wednesday with
additional showers and storms likely espcly in the afternoon.
Sub-VFR conditions should again accompany this area of
rainfall with better chances of thunderstorms across southern
and perhaps eastern sections Wednesday afternoon/evening.

Extended Aviation Discussion...

Rainfall should become a bit more showery by Thursday with
sub-VFR mainly associated with the showers while periods of
afternoon VFR possible outside of the convection. Friday will
be drier with a better chance of VFR ceilings and visibilities.
Another front reaches the area for Saturday with more showers
and thunderstorms including sub- VFR conditions.

&&

.HYDROLOGY...
As of 405 AM EDT Tuesday...

1 to 2 inches of rain with locally up to 3 inches can be
expected especially across southern and eastern sections today into
tonight. FFG along parts of the southern Blue Ridge remains in
the 1.5 to 2.5 inch range with the ground nearly saturated in
spots from heavy rainfall over the past couple of days. This
additional rainfall through tonight combined with locally
heavier rainfall rates due to showers and storms could result in
possible flooding of streams and creeks. Thus a flood watch has
been issued for counties along and south of the VA/NC border
excluding the NC mountains into tonight. Flooding along the
lower reaches of the Dan River could also occur tonight into
late week pending the amount of rainfall today and subsequent
runoff.

More rainfall is expected Wednesday and Thursday, which could
lead to additional small stream and river flooding. Models
continue to favor areas along/west of the Blue Ridge, possibly
resulting in another 1 to 3 inches of rain which could pose more
widespread flooding issues in the wake of heavier rainfall from
today.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch through late tonight for VAZ016-032-043-044-058.
NC...Flood Watch through late tonight for NCZ003>006-019-020.
WV...None.

&&

$$
SYNOPSIS...JH
NEAR TERM...MBS/JH
SHORT TERM...JH
LONG TERM...RAB
AVIATION...AMS/JH/WP
HYDROLOGY...AMS/JH

Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather