Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS61 KRNK 160838
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
338 AM EST Mon Dec 16 2019

.SYNOPSIS...
Low pressure passes to our north along the Ohio Valley Monday 
into Tuesday, with its associated cold front coming through our 
region on Tuesday. High pressure will settle in behind the front
by Wednesday and provide dry weather into Friday. This weekend 
will bring the next chance of active weather.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 330 AM EST Monday...

Low pressure currently in the Tennessee 
Valley approaches our area, with an associated east-west warm 
front splitting the region around the Highway 460 corridor. 
Southerly flow will enhance milder temperatures and advect Gulf 
moisture towards the front throughout the day today. The front 
then lifts away to the north tonight. 

No major changes in this update in regards to precipitation coverage 
today or the winter weather in Greenbrier and Bath counties this 
morning.

Lows this morning will be in the 30s for most of the CWA, with lower 
30s across the mountains and the southside staying in the upper 30s. 
South of the warm front boundary, highs reach into the upper 50s. 
North of the boundary cloud cover and precipitation will keep high 
temperatures relegated to the mid-upper 40s.


&&

.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
As of 330 AM EST Monday...

A cold front should cross overhead on Tuesday and provide a line of 
moderate rain across the Mid Atlantic. Although the latest GFS still 
pushes the cold front eastward toward the coast faster than the 
other models, the timing consistency between the models is getting 
better. A non-diurnal temperature pattern will take place as 
temperatures should fall behind the frontal boundary, which will 
occur during the morning hours west of the Blue Ridge and later in 
the afternoon across the Piedmont. As temperatures fall below 
freezing, the rain will change to snow showers across the higher 
elevations west of the Blue Ridge. Snow accumulations up to an inch 
are anticipated for western Greenbrier County with maybe a dusting 
to a half an inch west of a line from Bluefield to Boone.

Behind the cold front, winds will increase from the northwest. Model 
soundings indicate 850 mb winds increasing to near 45 knots by 
midday Tuesday and persisting into Wednesday. These wind gusts may 
let up a little during Tuesday night as a nocturnal inversion forms, 
but boundary layer mixing on Wednesday should eliminate this 
inversion and allow more gusts to occur. The highest ridgetops could 
possibly see up to wind advisory criteria, so this threat has been 
highlighted in the HWO for Tuesday afternoon through Wednesday.

With good cold air advection expected due to the aforementioned 
northwest flow, low temperatures for Wednesday morning and Thursday 
morning were dropped a few more degrees. High pressure should arrive 
over the Appalachian Mountains by Wednesday night and keep 
conditions dry through Thursday night. The upper air pattern will 
flatten and become more zonal by Thursday as an upper level trough 
in the northern stream heads offshore. Some ridging appears to take 
place overhead on Thursday night ahead of an approaching shortwave 
trough in the southern stream that crosses over the Plains.&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 350 PM EST Sunday...

High pressure will move over the area Thursday into Friday
providing dry conditions with seasonably cool to cold
temperatures overall. Temperatures will be a bit below normal
with lows in the teens west to 20s east and highs in the 30s
west to 40s east.

The weekend remains very questionable with regard to
precipitation chances and type. GFS and ECMWF continue to flip-
flop on the track of a strong southern stream system. As such,
have not made any significant changes to this period leaving in
slight chance pops for a rain/snow mixture. The latest GFS has
trended toward the ECMWF, keeping the threat for any more
significant amounts of precipitation well south/southeast of our
area. This is far from being resolved at this point and
conditions for the weekend should be monitored closely during
the next few days to address the potential for any winter
weather over the weekend. Solutions continue to range from a
significant snow event to a zero event. However, it should be
noted that the preponderance of evidence at this time is toward
a non-snow event and litte precipitation overall. There is also
a question with regard to the temperatures in place at that time
as models show a warming with the northern stream lifting out of
the area. It should also be noted that WPC favors the the
northern and southern streams remaining out of phase with regard
to this event, which would also support the southern solution.
Stay tuned!

/Confidence in Forecast Parameters/
Temperatures - Moderate,
Precipitation Probabilities - Low
Winds - Moderate.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
As of 1201 AM EST Monday...

Cloud bases will gradually lower overnight with transition to 
MVFR/IFR overnight into Monday morning. Clouds and precipitation
will increase, spreading across the area from north to south. 
Between roughly 06Z/1AM and 12Z/7AM Monday, ceilings across the 
area will range from IFR to MVFR with light rain expected south 
to roughly a KBLF-KROA-KFVX line. Some of the higher locations 
between roughly KLWB-KHSP may see a light wintry mix from late 
tonight until mid-morning Monday.

The precipitation will slowly expand southward Monday morning 
with IFR ceilings becoming more commonplace along with sub-VFR 
visibilities for the precipitation and some light fog.

A strong southwest low level jet is expected to develop
overnight above relatively weaker surface winds. Low level wind
shear looks promising for parts of the region during the 06Z/1AM
through 18Z/1PM Monday portion of the current valid TAF forecast
period.

Some improvement is expected Monday afternoon as warmer air
moves up from the south. This improvement will be brief, with
lowering conditions again after sunset Monday.

Confidence in the above aviation forecast is moderate. 

Extended Aviation Discussion...

Sub-VFR conditions will continue across the region through
Tuesday ahead and immediately behind the passage of a cold
front. Winds will also become very gusty behind the cold front.

A return to VFR is expected Wednesday and Thursday but with 
winds remaining gusty. 

VFR conditions and light winds are expected Friday. Some
moisture may try and return Saturday from the south with Sub-
VFR conditions possible. 

Confidence in the above aviation forecast is moderate to high.
The biggest question is the timing, and for some locations
precipitation type, with Monday/Tuesday system.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Winter Weather Advisory until 10 AM EST this morning for 
     VAZ020.
NC...None.
WV...Winter Weather Advisory until 10 AM EST this morning for 
     WVZ507-508.

&&

$$
SYNOPSIS...AMS/VFJ

National Weather Service Glossary of Abbreviations