Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 091503

Area Forecast Discussion
National Weather Service Blacksburg VA
1003 AM EST Fri Dec 9 2016

High pressure will build across the Mid-Atlantic region today
through Saturday. The associated cold airmass will remain over the
area through early Sunday before beginning to moderate. A cold
front will approach the area late Sunday night and  promoting
cold A strong push of cold air will overtake the region tonight
behind the passage of an arctic front. This cold airmass will
stick around through Saturday before beginning to moderate ahead
of a cold front that will approach late Sunday Night.


As of 1000 AM EST Friday...

Adjusted pops for snow showers and snow flurries for this morning
into the afternoon. A heavier snow band could produce up to an
inch. Made changes to temperatures for late morning into this
afternoon. more later changes this morning.

As of 500 AM EST Friday...

Forecast area is now entirely under the influence of an arctic
airmass. We are still much better off than our neighboring states
to the northwest where combination of single digit temperatures
and lake effect snow is ongoing. For our region, just flurries
for the mountains and temperatures in the teens and 20s, but still
bone chilling enough to wear a heavier layer or two and add a
little heavier BTU producing wood to the fire.

Will continue to advertise an inch or two of snow for the
mountains of WVA...mainly northwest of Lewisburg, otherwise mainly
trace amounts elsewhere, and no activity east of the Blue Ridge
where skies will remain clear. Temperatures today will struggle to
get much above freezing east of the Blue Ridge, and remain below
freezing in the west. Highest ridges, above 3500 feet are progged
to remain in the teens... I think we have 15 degrees forecast for
the high temperature on Mount Rogers today, after a low of 8 or 9
last night. Wind chills at these respectively colder higher
elevations will also dip into the minus 5-10 degree range.
Elsewhere winds will still be a factor with apparent temperatures
in the single digits and teens.

Blustery northwest winds today will gradually subside tonight.
This in combination with mostly clear skies will allow for ideal
radiational cooling conditions, promoting temperatures in the
teens for most of the CWA, and upper single digits for the highest
elevations, such as Mount Rogers and similar elevation.


As of 500 AM EST Friday...

Large, sprawling anticyclone associated with moderating Arctic-
origin cold airmass will be centered over the Appalachians on
Saturday before shifting eastward later in the day. As that occurs,
southwesterly return flow begins overnight Saturday with initially
light/variable winds becoming more southeasterly with time. Sky
conditions trend mostly clear and dry with highs ranging from the
upper 20s in western Greenbrier County to the upper 30s to lower 40s
east of the Blue Ridge and northwest North Carolina mountains.
Evening lows in the upper teens for the Alleghany Highlands and far
southwest Virginia to the lower 20s from the New River, Roanoke
Valleys east.

For Sunday, clouds begin to increase as high pressure builds off the
Chesapeake with lingering ridging building back into the foothills
of Virginia and North Carolina. 850 mb temperatures continue to
climb back to values a couple degrees either side of 0C through
Sunday; however limited insolational effects should keep highs only
in the upper 30s to mid 40s.

Moving into Sunday night, pressure gradient begins to increase
particularly in western sections in advance of a developing surface
low over northern IL. Both GFS and ECMWF begin to overspread some
light precip eastward into what appears to be an in-situ or hybrid
cold air damming type setup. Given that the airmass is still dry I
opted to confine the highest PoPs through midnight across the
Alleghany Highlands and into far southwest Virginia. Effect of
clouds and increasing winds should allow for only a slow fall in
temperatures, which stand to fall to lows in the low to mid 30s.

Cold front then pushes eastward across the region during the day on
Monday with PoPs increased into the Likely range. There`s still some
question as it pertains to the low-level thermal structure on
precipitation type and have therefore maintained cold rain or snow
as weather types for now. The forecast calls for any frozen precip
to change to rain by the mid/late morning. However, given the cold
airmass now in place over our area, it`s possible road surfaces are
marginally cold enough to produce some slippery travel even in cold
rain, if for a short period of time. Something to keep in mind.
Front clears our area later Monday with skies trending partly to
mostly cloudy by evening. Shown highs in the 40s west of the Blue
Ridge (except upper 40s/low 50s in southwest flow in Smyth county),
to the lower 50s east of the Blue Ridge...with evening lows in the


As of 500 AM EST Friday...

No sooner does this system exit our region do we turn our eyes
southwest again with the approach of yet another potentially wintry
system starting either late  in the day Tuesday or late Tuesday
night. There are notable differences on timing, storm path,
precipitation coverage and amount between the GFS and ECMWF. Given
the differences, our forecast will favor more of a persistence
forecast with the model blend.

A wintry mix will again be possible during this onset window of
opportunity. However, for now given the uncertainties, a snow versus
rain forecast is more practical. By Wednesday afternoon, the
associated trough axis, regardless of model, is expected to be east
of the area and we switch again to a gusty northwest flow regime.
Our precipitation will transition to rain or snow showers, with the
best coverage of snow showers across the mountains, winding down
Wednesday night.

Thursday looks to be drier with less cloud cover.

Temperatures during this portion of the forecast will start the
period around ten degrees above normal, and cool to reading around
normal by the end of the period.


As of 600 AM EST Friday...

A mix of VFR and MVFR ceilings will persist in the mountains
through the TAF period with scattered flurries. Little or no
visibility restriction is expected, but can`t rule out chc/lcl
MVFR vsby due to a more modest snow shower. This would impact
routes mainly across WVA.

Cold temperatures will persist through the forecast period,
remaining below freezing west of the Blue Ridge. Winds will
gradually subside over the next 24 hours as high pressure finally
builds overhead for Saturday.

Categorical Forecasts from 091200-101200...

BCB...VFR. Tempo MVFR CIG before 15z/10AM this morning.
BLF...MVFR CIG/VSBY through noon. Becoming VFR CIG.
LWB...VFR. Tempo MVFR CIG before 15z/10AM this morning.

Extended aviation discussion...

High pressure will pass overhead Saturday promoting light winds
and clear skies.  Next weather system to follow will be a cold
front, models suggesting a Sunday Night arrival which will likely
produce sub-VFR conditions at times, and possibly wintry mix in
the mountains. The cold front crosses the area Monday with
continued threat of showers and sub-VFR at times, then somewhat of
a break Monday night, with possibly more precip Tuesday, a pattern
that will promote sub-VFR conditions attms.




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