Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 231456
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1056 AM EDT Mon Oct 23 2017

.SYNOPSIS...
An intense strong cold front will move through the region today
and tonight and will move off the East Coast on Tuesday. A
similar scenario will play out next weekend with a warming trend
Thursday and Friday, followed by a cold frontal passage
Saturday and Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 250 AM EDT Monday...

GOES 16 Water vapor loops showed a short wave developing over the
northern Gulf of Mexico and Florida panhandle in advance of the
closed upper low moving into the western Tennessee Valley. The
Florida wave reaches northwest North Carolina by 18Z/2PM and may
back the low level winds and enhance what will already be healthy
shear over the area. As SPC pointed out the amount of CAPE and
instability is very questionable. Will have the scattered coverage
of thunderstorms along the front with less potential in the pre-
frontal precipitation. Will increase wind gusts today when the low
level jet peaks near 70 knots from the south-southeast, with the
most favorable location for strong wind from Mercer County, WV
through Grayson County, VA to Watauga County, NC.

All the clouds today will also limit heating but until the front
goes through will have a small rise in temperatures this afternoon.
Behind the front models have been consistent showing cold air
advection. Upslope clouds will fill in late tonight over the
mountains.

Precipitable water values rise to around 1.8 inches today, which is
excessively high for this time of the year. Will stay close to WPC
QPF values which have been increasing every run, similar to what is
shown in the synoptic guidance. Still seeing a potential for
isolated flooding in the southern Blue Ridge and adjacent foothills
where rainfall amounts will be the highest. Previous dry conditions
will limit areal coverage, but leaf clogged storm drain may result
in better chance of nuisance flooding in urban/suburban areas and
high rates when the front comes through also favor an increased
flooding risk. In coordination with surrounding offices, will hold
off on any Flash Flood Watch and continue to highlight in the
Hazardous Weather Outlook.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
As of 215 AM EDT Monday...

By Tuesday morning, the influence of the front will be east of the
region, and any precipitation immediately associated with it will
likewise be to our east. However, the parent upper low/trough will
still be to our west. The center of this upper low will be situated
near the upper peninsula of Michigan with its trough axis extending
south along the Mississippi River Valley. During the course of the
day, these features will make slow progression eastward, still
poised west of the forecast area by sunset. The bulk of the energy
associated with the low is progged to remain farther north than
earlier forecast. As such, our latest forecast will back down on the
coverage of any associated showers in the west. At best we will now
advertise isolated showers between the Northern Mountains of North
Carolina and southeast West Virginia.

As we progress through Tuesday night into Wednesday, the upper
low/trough continues its slow progression toward/into the area. By
Wednesday afternoon, the axis is progged to be overhead, while at the
surface a sw-ne oriented ridge axis noses into the area from the
Deep South. Moisture will be lacking, and the best dynamics will
continue to north of the region. Therefore, very few, if any,
showers are forecast across the western half of the region.

A trend that will start on Tuesday night, and continue into at least
Wednesday will be advection of colder air into the region. Tuesday
night, low temperatures of the low to mid 30s will be common across
the mountains with lows around 40 to the lower 40s across the
Piedmont. By Wednesday night, anticipate readings about three to
five degrees colder on average across the area as mostly clear clear
skies are forecast, along with light winds, as the center of the
surface high pressure settles overhead. High temperatures will also
trend cooler. On Tuesday expect upper 50s to lower 60s across the
mountains with upper 60s to around 70 across the Piedmont. On
Wednesday, subtract about ten degrees from Tuesday`s numbers for the
expected high temperatures.

The last day of the growing season across the mountains is October
25th. While a few spots across the mountains will experience
temperatures at or a little below freezing Tuesday night, the
presence of cloud cover and light winds will limit the degree to
which frost develops. By Wednesday night, conditions are more
favorable for a frost/freeze across the mountains, but at this
point, the morning of the 26th, the growing season will have ended,
and thus frost will not mentioned in any forecast products or
headlines. The same is not true of parts of Rockbridge County, VA.
Here, and points eastward, the growing season ends November 15th.
With temperatures around freezing, limited cloud cover, and light
winds, patchy frost will be forecast late Wednesday night into early
Thursday morning for parts of that county, including areas in and
around the cities of Covington and Buena Vista. This period is still
too far out it time for contemplating any headlines.

Thursday into Thursday night, the center of the surface high
pressure will shift east of the area. Aloft, southwest winds will
start to increase in advance of an approaching upper trough across
central CONUS. High temperatures on Thursday and low temperatures
Thursday night will be about five degrees milder across the
mountains as compared to Wednesday and Wednesday night`s readings.
Highs and lows across the Piedmont will be similar to Wednesday and
Wednesday night`s readings.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 345 PM EDT Sunday...

High pressure will continue build back across the southeast United
States for the end of the week promoting warming temperatures
through Saturday with high confidence for fair dry weather
associated with sunny skies Friday.

For the weekend it looks like we are going to repeat the current
scenario with the development of an amplified upper level trough
over the central United States which will move east pushing a cold
front through the area over the weekend.

The GFS is still the faster of the models bringing the front through
Saturday night whereas the ECMWF is 24 hours slower holding off on
any appreciable rainfall until later Sunday. Attm will maintain
threat for showers Saturday through Sunday, but nothing more or less
until models can resolve the timing.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
As of 800 AM EDT Monday...

Ceilings will quickly deteriorate this morning with widespread
MVFR-IFR conditions developing. Rain will become widespread this
morning and continue through the afternoon.

Strong lift associated with a cold front will cross the area
this afternoon and evening. This intense front will move from
from west to east across the area between Noon-Midnight.
Periods of heavy rain with embedded thunderstorms will precede
and accompany the front. The stronger showers/storms may
produce gusty surface winds. Of more concern will be the strong
low level jet. Models indicate a 60 knot low level jet 3-5kft
above ground level from the south will precede the frontal
passage.


Extended Aviation Discussion...

The region will be in the dry slot late Monday night and Tuesday
with conditions east of the Blue Ridge improving back to VFR. In
the mountains little to no improvement in expected. Much colder
air comes in for Tuesday and Wednesday. Scattered showers with
possible MVFR ceilings and visibilities are expected on
Wednesday across the region. Upper troughing remains over the
eastern United States keeping temperatures cool but with VFR
flying weather.

&&

.HYDROLOGY...
Localized areas through the mountains of northwest North
Carolina and southwest Virginia have seen in excess of 2 inches
of rain since midnight. An additional 2 to 3 inches can be
anticipated before frontal passage around 8 PM this evening.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flash Flood Watch from 2 PM this afternoon to 8 PM EDT this
     evening for VAZ015-016.
NC...Flash Flood Watch from 2 PM this afternoon to 8 PM EDT this
     evening for NCZ001-002-018.
WV...None.

&&

$$
SYNOPSIS...AMS
NEAR TERM...AMS/JR/PM
SHORT TERM...DS
LONG TERM...DS/PM
AVIATION...AMS/PM
HYDROLOGY...JR/PM



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