Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 221153
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
753 AM EDT Sun Oct 22 2017

.SYNOPSIS...
High pressure will finally move east of the area by tonight. A
strong cold front and upper trough will move into the region
from the west late Monday, crossing the area through early
Tuesday. The front will bring widespread rain followed by much
cooler temperatures for the later half of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 515 AM EDT Sunday...

The large high pressure area, both surface and aloft that has
been over the region the past several days will drift east and
be located just off the VA/NC coast by Monday morning. As the
high moves east, a deepening upper trough will move slowly east
from the Midwest and intensify, moving into the Mid-Atlantic
region late Monday. Today will still be dry, although with
considerable high cloud cover as it increases in advance of the
deepening upper-level system. Light rain will begin to develop
along the Blue Ridge in northwest NC around or shortly after
midnight, then spread northeast, especially along the Blue
Ridge, during the morning hours. The bulk of the rainfall will
arrive after the near term period.

Temperatures will still be warm today as 850mb readings hover
around +15C and remain very mild tonight with increasing warm,
moist southerly flow across the region. Some areas will be hard
pressed to fall below 60 degrees Monday morning. High
temperatures today will be mostly in the 70s, except 60s high
terrain in the west.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
As of 215 AM EDT Sunday...

The item of interest during this portion of the forecast continues
to be the first substantial rainfall for the entire forecast area in
over a week`s time, Monday into Tuesday.

A cold front will approach the region on Monday through IN/KY/TN/AL.
In advance of this feature, southeast isentropic and orographical
lift, that started Sunday night, will increase through the day. The
result will be the development of an increasingly expansive area of
showers, with the greatest coverage across the western half of the
region. Model guidance has been trending more quickly with the
spread of the heaviest precipitation into the area, now most
probably by the afternoon in the southwest sections. Surface wind
gusts will be on the increase during the day especially at the
higher elevations of the Northern Mountains of North Carolina and
neighboring sections of the Mountain Empire region of southwest
Virginia. Here, a few gusts may reach 40 to 45 mph by the late
afternoon

This same quicker guidance likewise brings the cold front into and
across the area Monday night. The result will be the Monday evening
time frame as the period for the heaviest precipitation in
association with the front, across the north and northeastern
sections of the region. A combination of weak surface based
instability and substantial increase in low level shear supports
isolated thunderstorms coincident to the leading edge of the cold
front across the southern half of the region Monday afternoon
through Monday evening. The latest Day 2 Convective Outlook by SPC
places this region within a Marginal risk of severe thunderstorms
with damaging winds the greatest threat.

By late Monday night into Tuesday, most of the latest guidance has
the front and associated precipitation east of the region. The NAM
is a bit slower, with activity lingering in the east until about
midday Tuesday. Our latest forecast will reflect the faster departure
with a hint of lingering activity in the east Tuesday morning.

By Tuesday afternoon through Wednesday night, our attention for any
additional precipitation turns to the western sections of the
region. Gusty northwest flow behind the front, and the approach of
its parent upper level low/trough, will help maintain cloud cover
and isolated to scattered showers across the preferred upslope
regions of southeast West Virginia, and to a lesser extent, the
neighboring first tier of counties of southwest Virginia. As colder
air works its way into the area, some of these isolated rain showers
may transition to isolated snow showers across this same
geographical area Wednesday night. QPF numbers will be minimal at
this point with little if any in the way of accumulation.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 415 PM EDT Saturday...

All of the extended models have trended much more progressive with
the upper trough, lifting it out Thursday, west to southwest flow
aloft returning to the area and allow temperatures to moderate
quickly. Wednesday looks like it will be the coolest day of the
week, then moderating for Thursday and Friday.

Models are now hinting at another upper level long wave trough for
the weekend with the potential for showers and bonafide cold frontal
passage. The GFS brings clouds/showers into the area as early as
Saturday whereas the ECMWF is 24 hours slower holding off on any
appreciable QPF until Sunday. Attm will introduce low chance threat
for showers Saturday, but nothing more until models can resolve the
timing.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
As of 750 AM EDT Saturday...

The strong high pressure area that has been over the region for
the past several days will slide just to our east and just off
the coast today. A strong southern stream short wave will begin
to approach the region from the southwest late tonight and
Monday.

Extensive high clouds will overspread the area today in advance
of the approaching upper trough. However, ceilings are expected
to remain VFR outside of very patchy early morning fog (e.g.,
KLWB and KBCB) in the 09Z-13Z time frame. Most of the day,
conditions will be BKN250 throughout the CWA. After 00Z,
southerly flow will begin to increase in advance of the short
wave and bring deeper Gulf moisture into the region from the
southwest. Ceilings should begin to lower into the MVFR range,
especially across northwest NC into southwest VA after 04Z, then
into the low end of the MVFR range or potentially even the IFR
range after 09Z, especially west of the Blue Ridge.

Winds will become southeast 5-8mph with low end gusts possible
in the KBLF area during the afternoon/evening. Southeast winds
will continue overnight and early Monday with speeds mostly in
the 5-10mph range, with low end gusts continuing around KBLF.

Medium to high confidence in ceilings and visibilities
throughout the TAF valid period.
Medium confidence in wind direction, high confidence in wind
speed throughout the TAF valid period.

Extended Aviation Discussion...

A deep upper trough and associated strong cold front will move
into the region from the west Monday night/early Tuesday with
sub- VFR conditions in rain/showers along with increasing wind.
Colder, blustery, unsettled weather with perhaps largely MVFR
conditions across the mountains will linger through the later
half of next week. MVFR showers may return by early next week.

&&

.HYDROLOGY...
As of 230 AM EDT Sunday...

Latest model trends place the bulk of the precipitation pre- and
concurrent to the approaching cold front across the area Monday
afternoon and evening. The latest QPF numbers from WPC offer a
solution that gives the region one to two inches of rain from early
Monday morning through Monday night. Higher amounts are noted along
the higher elevations along and west of the Blue Ridge from roughly
Roanoke, VA southwest into the Northern Mountains of North Carolina.
Amounts of two to three inches are more likely during this same time
period, with amounts immediately along the crest of the Blue Ridge a
little shy of four inches. The latest Day 3 Excessive Rainfall from
WPC places the entire forecast area within a Slight Chance of
exceeding flash flood guidance. While the expected rainfall amounts
are decent, they are trending lower than the flash flood guidance
provided by the corresponding RFCs. At this time, a minor flooding
concern will continue to be placed in the HWO and eHWO, but no
headlines will be hoisted at this time.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...RAB
NEAR TERM...RAB
SHORT TERM...DS
LONG TERM...DS/PM/RAB
AVIATION...RAB/RCS
HYDROLOGY...DS



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