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FXUS61 KRNK 140455

Area Forecast Discussion
National Weather Service Blacksburg VA
1155 PM EST Fri Dec 13 2019

Low pressure off of South Carolina will track up the East Coast
tonight and Saturday and will be well into southeast Quebec by
Sunday morning. High pressure will cover the eastern United 
States on Sunday. Another low pressure system will track across 
the central and eastern United States on Monday and Tuesday,
followed by high pressure on Wednesday and Thursday.


As of 950 PM EST Friday...

No major changes are needed for this update. Fog is rather
robust across the area, but the rain showers have at least
pushed visibilities upward from a quarter of a mile a few hours
ago to where readings are now ranging from a half mile to one

Surface low pressure will move along the coast from South Carolina 
coast to New York overnight. Upslope low level flow from the 
southeast, deep isentropic lift in the 290-295K layer and upper 
diffluence will promote areas of rain/drizzle/fog through early
Saturday. Temperatures will be steady or slowly rising through
the overnight. 

The low gets far enough north by Saturday afternoon to bring surface 
and low level winds around to the west and northwest. This will be 
the start of cold air advection. Precipitation will be ending east 
of the Blue Ridge by afternoon but will continue in the mountains, 
especially in the typical upslope areas. Rain will change to snow 
throughout the day. The low level jet will be in the 40 to 45 knot 
range and the Bufkit forecast of momentum transfer was suggesting 
gusty wind, particularly along the southern Blue Ridge. Will have 
wind gusts just short of advisory level for Saturday afternoon.


As of 245 PM EST Friday...

For Saturday night, while the cold front will already be east of the 
region, a trailing 850mb shortwave trough axis is expected to cross 
the region during the overnight hours. This feature will bring a 
reinforcing push of colder air and winds increase a bit from the 
already gusty conditions from Saturday afternoon. These winds and 
residual low level moisture will help produce some isolated to 
scattered upslope snow showers across southeast West Virginia, south 
into the Northern Mountains of North Carolina. For a short period 
Saturday evening, some isolated rain/snow showers may work their way 
as far east as the I-81 corridor of southwest Virginia, north of I-
77.  As drier air works its way into the region, and as low level 
winds slow and start to back, the isolated rain/snow showers will 
dissipate by Sunday afternoon.

Our next weather maker will be associated with an area of low 
pressure that will make its way eastward through the mid-Mississippi 
River Valley on Monday. We can expect increasing southwest flow 
ahead of this system which will bring a return of Gulf of Mexico 
moisture to the region, along a warm nose above colder surface and 
shallow boundary layer temperatures. This overrunning precipitation 
is expected to work its way into western sections Sunday evening and 
farther eastward by daybreak Monday. Initially, the warm nose aloft 
will still be to our southwest, and we should have a rain versus 
snow forecast, with the areas of snow mainly across southeast West 
Virginia and neighboring counties of southwest Virginia. By late 
Sunday night, we are expecting enough of a warm nose aloft to allow 
for some areas of freezing rain or sleet along and near the I-64 
corridor. By mid-morning Monday, more of the area will be covered 
with the precipitation, but as temperatures rise at the surface, 
light rain become the only precipitation type expected. Coverage of 
the rain will continue to expand eastward as the day progresses 
with he approach of the cold front. Coverage and the amount of the 
rain increases even more Monday night as the cold front draws 
even closer, on our western doorstep by daybreak Tuesday.

Temperatures during this portion of the forecast will average close 
to ten degrees above normal.

Confidence in this portion of the forecast is moderate.


As of 200 PM EST Friday...

On Tuesday, the cold front will cross the region during the morning 
hours. We are still forecasting likely to categorical coverage of 
showers across the region coincident to, and just in advance of, the 
the progressing front. In the wake of the frontal passage, look for 
winds to turn sharply northwest and increase during the afternoon 
and continue to increase Tuesday night and remain very gusty on 
Wednesday and Wednesday evening. Residual moisture across western 
sections of the region will be lifted upslope across the mountains 
of southeast West Virginia. This will allow for isolated snow shower 
across this area Tuesday night. By Wednesday, enough drier air is 
expected to have arrived to both end the light snow showers and also 
clear out the remaining cloud cover.

High pressure will head eastward through the southeast U.S. 
Wednesday into Thursday, with our region experiencing no 
precipitation and little to no cloud cover. Once the center of the 
high reaches the GA/SC coast on Friday and low pressure moves east 
into the mid-Mississippi Valley, look for a return of southwest 
winds and both increasing temperature and moisture advection. At 
this time, no precipitation is forecast for Friday. However, cloud 
cover is expected to be on the increase. Any precipitation 
associated with the approaching low looks more likely to impact our 
forecast Friday night into Saturday, but that will be past the valid 
time of our current forecast.

Temperatures during this portion of the forecast will average about 
ten degrees above normal Tuesday (thanks to a mild Monday night 
low). However Wednesday through Friday, temperatures are expected to 
average five degrees below normal.

Confidence in this portion of the forecast is moderate to high.


As of 1155 PM EST Friday...

Widespread LIFR ceilings and MVFR visibility with fog and light
rain will continue through Saturday morning. Conditions are 
expected to gradually improve Saturday afternoon.

Above average confidence for ceilings, wx and visibility. 
Average confidence for wind. 

Extended Aviation Discussion... MVFR ceilings along with rain 
and snow showers are expected in the mountains Saturday night,
otherwise a return to VFR can be expected, with VFR expected
areawide Sunday. Another storm system will impact the region 
Monday into Tuesday. Mainly rain is expected with this system
for our area with temperatures above freezing.

Forecast confidence is moderate to high.





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