Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 240503
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
103 AM EDT Mon Sep 24 2018

.SYNOPSIS...
A wedge of high pressure will keep overall cool and damp
conditions overnight into Tuesday morning. Temperatures will
begin to warm Tuesday afternoon before the next frontal passage
Wednesday.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1130 PM EDT Sunday...

Decided to drop the flash flood watch. Short range models keep
threat of light showers, possibly moderate over the WV mountains
overnight but not expecting any rates that would lead to flash
flooding. The rest of the forecast was adjusted to keep higher
pops in the mountains, but overall amounts will be around a
tenth of an inch or less thru dawn. Will revisit any hydro
watches for Monday during the early morning shift.

Previous discussion from early this evening...

Didn`t make many changes to the going forecast. Wedge front
Current radar mosaic shows scattered heavy showers from Bland,
Tazewell and Smyth County southwestward, which have prompted
some short- fused flood advisories with rain rates at times up
to an inch an hour. This activity looks to slowly progress
northeast and likely weaken as it does so. Looks to be a break
in the rain further to the west, as we await the next wave of
rain now over western Tennessee. Some uncertainty if this
actually makes it this far east as recent higher resolution
guidance suggests this wave may peel more north versus east as
primary mid-level vort max moves from Arkansas into the
Louisville KY area. Otherwise, a cloudy evening with mist and
fog as wedge conditions are well entrenched. Temperatures not
likely to fall much from current readings tonight in the 60s.

Previous discussion from 145 PM...

Significant rains occurred across southside Virginia Saturday
has cause significant rises on the Roanoke and Dan Rivers and
tributaries. A modest rise is expected on the James River.
Rivers should crest by tonight and fall below flood stage on
Monday.

The cold front, which moved across the area this morning, will
continue to wedge south into the Carolinas tonight. Meanwhile, a
stalled frontal boundary is draped from eastern Kentucky to
eastern Texas. Waves riding along this boundary will track over
West Virginia into northern Virginia tonight into Monday. Warm
moist air associated with these waves will overrun the surface
wedge hanging over the Mid Atlantic region. These weather
features will interact over the area bring extensive cloud
cover, periodic light rain or drizzle, and continued advection
of cooler air into the forecast area from the northeast. The
best isentropic lift is expected to occur north of I-64 tonight
which keeps any additional heavy rain north of the area. There
is still a chance for heavy rain to skirt over southeastern West
Virginia this afternoon and evening. Therefore, we will keep
the Flash Flood Watch into tonight. The rest of the area does
not have the threat for heavy rain and will see creeks, streams,
and rivers levels recede to within their banks over the next
6-12 hours.

The cloudy, cool, damp wedge will hang around for the next
couple of days. Temperatures over the next 24 hour will not
fluctuate much with readings range from the upper 50s to lower
60s tonight to the low to mid 60s tomorrow.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
As of 115 PM EDT Sunday...

Long wave trough deepens over the central United States through
Wednesday night. Models in good consensus with the synoptic
pattern through Wednesday morning. Leading edge of the best lift
ahead of the front and diffluence with the upper jet now slower
on the guidance arrive in the central Appalachians Wednesday
morning.

Main forecast challenge is what happens with the wedge on
Tuesday. Wedge become shallow and may erode on western slopes of
the Appalachians and in the piedmont. This may lead to a late
day high in the 70s. all other locations will stay in the upper
50s to mid 60s. Wind across the region come around to the
southwest Wednesday ahead of the front. Will be leaning toward
the MAV/MOS guidance which is cooler than NAM for Tuesday and
warmer than NAM on Wednesday for most locations.

Seeing some indications of a potential for heavy rain along the
front which will be stalling out Wednesday night. Precipitation
potential placement and precipitable water values approaching
two inches also support higher rainfall amounts. Will be raising
the probability of precipitation for Wednesday night.

Confidence was average for all elements.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 1210 PM EDT Sunday...

Upper pattern becomes zonal by Friday with mid Atlantic region
between the northern jet stream across the Great Lakes and
northeast United States and a retrograding upper ridge over the
Gulf of Mexico and southeast United States.

The ECMWF was the slower than GFS and Canadian with the passage
of the surface cold front on Thursday. Short-lived period of
weak cold air advection and northwest winds on Friday, then back
to west to southwest 850 mb winds for Sunday. High pressure and
drier air, with precipitable water values potentially below one
inch, also come in behind the front for Friday and Saturday.

Confidence was average for all elements.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
As of 101 AM EDT Monday...

Poor flying conditions to prevail overnight into Monday as a
wedge of cool air keeps low clouds and fog including periods of
light rain or drizzle around. Only exception perhaps around KBLF
where cigs may oscillate up to high end MVFR or better at times
by Monday afternoon. Also left in a mention of -RA at times at
KBLF where best chance for steady rain will prevail but
restrictions would be more from mist and ceilings than lowered
visbys from rain. Otherwise looking at mostly IFR/MVFR with
mountain obscurations in the low cigs into Monday morning at
least. Winds east to northeast around 4-10 kts, but will become
more southeast at KBLF on Monday.

Low cigs and vsbys look to persist into Monday night but may
improve by early Tuesday as the wedge weakens. However still
mostly sub-VFR at this point.

High confidence in winds and flight categories, but low on
timing ceiling category changes.

Extended Discussion...

Stationary front over the southern Appalachians will be the
focus for widespread cloud cover through mid week with potential
for rain, low cigs/vsbys. May see brief improvement to VFR/MVFR
later Tuesday into Wednesday before another period of likely
sub- VFR with cold front late Wednesday into Wednesday night.
Unlikely to see improvement Thursday or Friday with continued
sub-VFR as front may stall near or just south of the area with
weak low pressure keeping low cigs/vsbys within rain around.

&&

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

&&

$$
SYNOPSIS...JH/RCS
NEAR TERM...AL/RCS/WP
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...JH/RCS


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