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FXUS61 KRNK 160907

Area Forecast Discussion
National Weather Service Blacksburg VA
407 AM EST Sat Dec 16 2017

High pressure will build across the Southeast U.S. today.
This will result in fair weather and warming temperatures.
A weak disturbance will move northeast from Texas and into 
the Ohio Valley Sunday. This feature will result in increasing
cloud cover and a chance for a few showers across the mountains 
late Sunday into early Monday.


As of 345 AM EST Saturday...

Persistent Western CONUS Ridge and Eastern CONUS trough which
has been the predominant set-up for the past week is now in the
process of changing. As the break-down of the pattern takes
place, the cold air in the eastern U.S. will retreat north with
a slow but steady moderation of temperatures over the next
several days. 

Today will start off cold, but unlike yesterday, lack of
meaningful cloud cover and increasing warm air advection will 
lead to a wholesale increase in temperature this afternoon, 
highs a full 10 degrees warmer than yesterday. Winds will
continue to be a bit breezy, so there will still be a bit of a
wind chill to contend with.

No threat of precip through Noon Sunday.


As of 330 AM EST Saturday...

On Sunday, upper level shortwave energy will eject out of the 
southern plains to our north late on Sunday with our area 
positioned on the northern periphery of an upper level ridge. There 
still is uncertainty with regard to the depth of moisture that will 
be in place, but confidence is high that any precip that does 
materialize will be light with most ensemble members generating less 
than 0.10 of an inch through 06z (1 AM) Sunday night. Despite cloudy 
skies, backing low level winds should push temps toward the warmer 
side of guidance values.

Precipitation should be liquid for a large portion of the forecast 
area through Monday, but some guidance suggests  very light freezing 
or frozen precipitation in the Alleghany Highlands when/if light 
precipitation falls into low level dry air Sunday evening,and early 
Monday morning. GFS forecast soundings are cooler in the low levels, 
with little warm nose aloft suggesting the potential for light 
rain/snow mix, while the NAM (which regional studies show is better 
at forecasting low level warm noses), shows warmer low level temps, 
but a more pronounced warm nose aloft,keeping precip liquid. 
Considering the amount of warming that is expected Sunday afternoon, 
feel chances for wintry precip is very low. For now, a couple of 
hours of a rain/snow mix is mentioned, but even if colder than 
forecast temps occur Sunday night/early Monday morning, precip 
amounts will be so light, no adverse impacts to travel are expected.

Zonal flow Monday with a deep westerly/downslope flow should bring 
warmer temps to the region, especially along and east of the Blue 
Ridge will clearing is expected. Bumped up high temps a couple of 
degrees for highs Monday. Lingering low level moisture along the 
western slopes and upslope flow may spawn a a few showers in 
southeast WV.

On Tuesday, an upper level trof begins to deepen across the Great 
Lakes into the northeast, but we remain in deep western flow will 
continue to bring mild temperatures. Again, a stray shower or two in 
southeast WV is not out of the question, but a large majority of our 
area will be dry. Gusty winds will be possible, which were bumped up 
in the forecast for Tuesday. 

While there are timing differences in the models, a cold front 
crosses Tuesday night, but the cold air behind this front is short-


As of 330 AM EST Saturday...

High pressure builds in from the west Wednesday night and quickly 
offshore Thursday, but there is good agreement in the medium range 
models that a southern stream system move across our region late 
Wednesday into Thursday. There is considerable uncertainty about 
how much moisture will be place for this system, but trends are 
wetter for the 00Z ECMWF and Canadian models, so introduced small 
precipitation chances during this time. 
Ridging to work farther east Friday  ahead of the next cold front 
that could bring some chance of showers to mainly western sections 
pending timing on Day 7. 

Main aspect will be with the mild temperatures including highs that 
will be 10-15 degrees above normal espcly Tuesday per warmth aloft 
and ahead of the front on Friday. Some cooling in between behind the 
passing cold front but still a bit warmer than average for


As of 1151 PM EST Friday...

Will see upslope MVFR cigs wane toward dawn behind departing
shortwave, with all sites VFR after 12z. Winds will be gusty at
times early mainly Roanoke west then diminish by dawn.

VFR conditions anticipated for Saturday with winds west- 
southwest 4-12 kts.

Forecast confidence high thru the period except medium on cigs
this evening.

Extended Discussion...

VFR conditions continue through Sunday afternoon. A weak frontal
system approaching from the west may induce a brief period of 
VFR/MVFR with light rain showers mainly for western terminals 
Sunday night. 

Better opportunity for sub-VFR is Monday as ceilings lower 
ahead of another disturbance coming out of the Gulf of Mexico.
Should start seeing some showers Monday night through Tuesday
night in association with this system. 

VFR then returns for Wednesday.





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