Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Blacksburg Virginia
359 PM EDT Sat Aug 30 2014

an upper level system moves from Mississippi to the Ohio Valley
through Sunday. The area will remain in a typical Summer airmass
into Tuesday. A front arrives from the north by Thursday.


Near term /through Sunday/...
as of 300 PM EDT Saturday...

Just isolated convection this afternoon along a nose of higher
thetae and deep moisture convergence that runs from the NC mountains
northeast to the Alleghany Highlands of Virginia into southeast WV. Still not
expect much coverage through the evening.

Will keep the slight chance of showers across the far west
overnight...increasing them 40 probability of precipitation by morning as strong upper
shortwave moves from the lower MS valley to the Ohio Valley. Main
flux of moisture will stay west of our County Warning Area but looking at increased
SW flow and convergence along with outflow will bring shower chances
as far east as Interstate 81 by 8 am Sunday.

Lows tonight with increasing clouds and higher dewpoints will be
muggy...from the middle 60s to around 70 areawide.

Sunday...models in similar agreement on track of upper shortwave but
differ on eastward extent and amount of precipitation. The 12z NAM overall
looked to bullseyeish with fingers of higher quantitative precipitation forecast across the NC mountains
into SW leaned the forecast toward the 12z ECMWF/GFS...which
for the most part take the higher probability of precipitation across the northwest NC/SW Virginia/southern WV
area into the Shenandoah Valley tomorrow...with less threat of
showers and storms east of the Dan/lyh corridor. Temperatures will be
tempered by the cloud cover so looking at humid conditions with
highs ranging from the upper 70s-lower 80s middle to
upper 80s east.


Short term /Sunday night through Tuesday night/...
as of 315 PM EDT Saturday...

Scattered showers and a few thunderstorms will persist through
Sunday night into Monday morning...with greatest rain chances found
west of Interstate an upper level disturbance shifts across
the Great Lakes from the Ohio River valley. With a very moist
atmosphere in place...may see a few areas of excessive rainfall...
but believe the flooding threat will be low due to a week of dry

May see a few showers redevelop Monday afternoon as we approach
maximum heating...but believe this activity will be more
disorganized due to drier conditions as high pressure moves in from
the well as a lack of upper level support. Rainfall will
diminish quickly as the sun sets and should see dry...albeit warm
and muggy...conditions persist through Monday night.

Rain chances will increase again on Tuesday as another low pressure
system moving across eastern Canada will drag a cold front south of
the Great Lakes. Better chances for rain will be found across the
mountains...where stronger upper level support will be located.
Believe models are too aggressive in pushing the front into North
Carolina per the 30/12z runs...and expect the cold front will stall
further north due to the upper level ridging in place across the
southeast states...perhaps somewhere between the Interstate 64 and
Highway 460 corridors during Tuesday night.

Temperatures will remain slightly above normal for the early half of
the week...with highs ranging from the upper 70s/low 80s across the the low 90s across the Southside. Lows will fall into
the middle 60s to low 70s.


Long term /Wednesday through Saturday/...
as of 330 PM Saturday...

Upper level ridging will shift northward from the southeast states
over the middle Atlantic during the second half of the week...resulting
in both warmer temperatures and weaker winds aloft. This will make
for more stable conditions that will keep shower and thunderstorm
activity disorganized through the period. Any rainfall which
develops will be driven mainly by daytime heating...which will allow
this activity to fizzle after sunset.

Expect widely scattered showers and perhaps a thunderstorm or two to
develop Wednesday afternoon along the stalled frontal boundary...
wherever it is located. High pressure passing across the Great
Lakes should keep the northern half of our area dry.

High pressure will pass off the New England coast on Thursday...
resulting in a weak wedging pattern with easterly flow off the
Atlantic. This will likely be the driest day of the period.

Winds will shift southwesterly again on Friday as another cold front
sinks south from the Great Lakes. Stronger flow off the Atlantic
will result in increased moisture...and will expect spotty shower
and thunderstorm activity during the afternoon and evening.

Expect temperatures to remain slightly above normal for the period.


Aviation /20z Saturday through Thursday/...
as of 130 PM EDT Saturday...

Automated observation showing more cloud cover than reality per Sat/web
cams. Mainly scattered field of cumulus this times broken. Not
really seeing any taf site threatened by sub VFR or convection.
Best chance of any rain showers/thunderstorms and rain would be near roa/lwb...but given
lack of vertical structure will not highlight any in the tafs.

Tonight...models showing the upper shortwave that is over the
lower MS valley this move into the Ohio Valley
overnight. Will not really see any good threat of showers until
Sunday morning after 12z west of a lwb/blf line...and added vcsh
at blf by 14z. Overall will see VFR though some fog and/or low
clouds could form near Dan/lwb/roa/bcb late...but confidence
overall is low.

Extended discussion...

Sunday an area of low pressure will head eastward through the
southern Quebec. Its associated cold front will sweep through the
region bringing a generous coverage of showers and some storms.
Sub-VFR conditions are expected to accompany the system and

Another cold front is expected to produce similar conditions Tuesday
into Wednesday. However...model guidance for this one offers
precipitation in a more scattered distribution. As such...the
magnitude of sub-VFR conditions may be less.


as of 730 am EDT Friday ...

The visibility sensor at kdan...Danville Regional Airport...will
be out of service until further notice. A part has been back-ordered.


Rnk watches/warnings/advisories...


near term...wp
equipment...air mass

National Weather Service Glossary of Abbreviations