Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 krnk 160907 

Area forecast discussion
National Weather Service Blacksburg Virginia
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.


Near term /through tonight/...
as of 345 am EST Saturday...

Persistent western Continental U.S. Ridge and eastern Continental U.S. 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.


Short term /Sunday through Tuesday night/...
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-


Long term /Wednesday through Friday/...
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 European model (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


Aviation /09z Saturday through Wednesday/...
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.


Rnk watches/warnings/advisories...



National Weather Service Glossary of Abbreviations