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FXUS61 KRNK 230943

Area Forecast Discussion
National Weather Service Blacksburg VA
443 AM EST Thu Feb 23 2017

Weak high pressure off the Mid Atlantic coast will cover
Virginia and North Carolina today and tonight. A front across 
the Great Lakes into the southern Plains shifts slowly southeast
to the Ohio Valley by Friday. The main cold front approaching 
from the Midwest will pass through our area Saturday.


As of 430 AM EST Thursday...

No changes planned to Dense Fog Advisory. Numerous locations
reported visibility of one half mile or less. The few exceptions
were on the western slopes from Bluefield to the Mountain 
Empire area and along the peaks of the Blue Ridge which were
higher than the depth of the fog. 

Models showed a modest improvement in visibility after 10AM. A
few breaks in the clouds are possible from Charlotte County
Virginia to Yadkin County North Carolina late this afternoon.
With little to no heating today...temperatures rise will be
limited. Have trimmed maximum temperatures today and may still
need them lower depending on cloud cover. 

Some isentropic lift forecast today from Kentucky into western
Pennsylvania. Otherwise little forcing so have lowered 
probability of precipitation. 

Bufkit forecast soundings and visibility guidance showed
reformation of fog again late tonight. Have added larger
coverage of fog after midnight.


As of 300 AM EST Thursday...

Weak shortwave ridging will build over our area Friday, as a mid-
level trough/low is forecast to move into the Great lakes and Ohio 
Valley. It will remain unseasonably mild and generally rain free.
The only exception is a few locations near the crest of the Blue 
Ridge thanks to local upslope flow. trimmed back pops a little 
friday and shaped towards the NAM. High temperatures Friday 
afternoon will range from the lower 60s in the mountains to the mid 
70s in the Piedmont. 

A cold front will approach the region from the west Friday night and 
reach the mountains Saturday morning. Showers and a few 
thunderstorms will develop along and ahead of the cold front. The 
Day two convective outlook brings general thunderstorms into western 
portions of the forecast area. The marginal threat clips a few far 
western counties. It still looks like the best instability will 
remain north of the Ohio River. Low temperatures Friday night into 
saturday morning will vary from the mid 40s in the northwest 
mountains to the the 50s in the Piedmont.  

A cold front will move east across our area Saturday with scattered 
showers and thunderstorms. The mention of thunderstorms remains 
support by the sfc best lifted index and computed cape values.
The latest Day 3 Convective Outlook places portions of cwa in a
5 percent chance of severe weather, Marginal threat. The main 
threat is for convective lines with damaging winds. High 
temperatures on Saturday will warm to the mid 50s in the 
mountains to the lower 70s in the Piedmont. 

By Saturday night, the front will be to our east, and northwest 
winds will be on the increase. The northwest winds will yield some 
gusts approaching 40 to 45 mph at the highest elevations. At this 
time, it appears that winds will remain below wind advisory levels. 
With colder air pushing into our region, any lingering upslope rain 
showers across parts of southeast West Virginia, south into the 
northern mountains of North Carolina are expected to transition
to snow showers by Sunday morning. Little or no accumulations 
expected with any snow showers. Low temperatures Saturday night 
will be near normal with readings from the lower 20s in the 
mountains to the mid 30s in the Piedmont.


As of 300 AM EST Wednesday...

Gusty winds will continue into early Sunday behind Saturday's cold 
frontal passage. These winds will weaken quickly during the day and 
back southwest as the next upper level trough deepens across the 
Central Plains. 

This same upper trough will move east and be over the Ohio Valley by 
mid-day Monday. A warm front in advance of this system will head 
north through our region, bringing a return of patchy light 
precipitation to the area during the day Monday. There may be an 
issue of a brief period of a wintry mix across the northwest section 
of the area early Monday as a potential warm nose develops over a 
sub-freezing boundary layer and surface. For now, will keep things 
simple by reflecting a rain versus snow forecast based solely on 
whether the forecast surface temperatures is above or below 

Monday night the system's associated cold front is expected to cross 
the area. Look for the precipitation to become more showery Monday 
night into early Tuesday.

Model guidance for the remainder of Tuesday into Tuesday evening is 
not clear. The GFS is progressive with the cold front making 
significant headway east of the region. The ECMWF is not 
progressive, stalling the feature over the area, all while 
suggesting another wave will move northeast along this boundary, 
keeping a generous coverage of rain across the area Tuesday 
afternoon into Tuesday night. Our forecast will reflect a blend of 
these solutions. While rain will be forecast Tuesday afternoon and 
evening, it will not be to the degree offered by the ECMWF.

For late Tuesday night into Wednesday, model agreement improves with 
solutions bringing yet another upper low/trough from the Central 
Plains states into the Ohio Valley. Warm frontal rain is expected 
late Tuesday night into early Wednesday, with a generous coverage of 
showers and some isolated thunderstorms across the area Wednesday 
afternoon coincident to the cold frontal passage. Behind the cold 
front in the northwest flow, a few rain and snow showers may linger 
in the western mountains Thursday.

Temperatures Sunday and Monday will be normal for this time of year. 
Reading moderate through mid-week with temperatures some ten to 
fifteen degrees above normal expected.


As of 1030 PM EST Wednesday...

Dense fog advisory along and just east of the Blue Ridge through 
10am Thursday. In spite of clearing aloft, a very moist 
boundary layer with RH values of 100% has allowed for the
formation of dense fog with widespread visibilities under 1/2SM
Lack of wind will allow this fog to persist through mid-morning 
Thursday before daytime heating begins to mix the boundary layer
and allow for improvement. Until then expect Widespread LIFR.
This is a situation where the valleys and lowland areas will
contain more stratus and fog as compared to the ridges. Ridge
tops will likely remain above the stratus layer.  

The fog/stratus looks to burn off Thursday morning with a 
return to VFR conditions by the afternoon. However, a weak 
frontal boundary will brush the region as an area of low 
pressure moves through the Great Lakes region tomorrow. This may
bring a shower to locations west of the Blue Ridge so will 
include VCSH after 18Z all sites except KDAN and KLYH. Winds 
will be light through the period.

Extended Aviation Discussion...

Thursday night-Friday, we will be well into the warm sector 
with VFR conditions and much above normal temperatures. Surface 
wind gusts of 20 to 30 kts possible across the higher terrain.

Band of showers and isolated thunderstorms with MVFR conditions arrive
late Friday night into early Saturday along and ahead of a 
strong cold front. Drier weather and increasing northwest winds
follow behind the front on Saturday afternoon through Sunday.

Approach of another front Monday will provide increasing clouds
and possibly showers and MVFR cigs to BLF/LWB late in the day.


As of 245 PM EST Wednesday...

Warm temperatures set to occur again Thursday with increase in 
westerly flow in the low levels. Question will be cloud cover. At 
the moment with some sunshine look for highs and lows to approach or 
break records for Feb 23rd.

Thursday 02/23/2017
Site        Record High/Year  Record Warm Low/Year
Bluefield       74 1975          51 1975
Danville        73 1980          50 1981
Lynchburg       74 1943          52 1925
Roanoke         76 1943          54 1925
Blacksburg      69 1980          46 1990


As of 440 AM EST Thursday...

The automated observation system at Lynchburg(LYH)had multiple
sensor failures. Electronics technicians will be performing
repairs on the system this morning. 


VA...Dense Fog Advisory until 10 AM EST this morning for VAZ007-
NC...Dense Fog Advisory until 10 AM EST this morning for NCZ001>006-
WV...Dense Fog Advisory until 10 AM EST this morning for WVZ042>044-



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