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FXUS61 KRNK 231152

Area Forecast Discussion
National Weather Service Blacksburg VA
752 AM EDT Mon Oct 23 2017

An intense strong cold front will move through the region today
and tonight and will move off the East Coast on Tuesday. A 
similar scenario will play out next weekend with a warming trend
Thursday and Friday, followed by a cold frontal passage 
Saturday and Sunday.


As of 250 AM EDT Monday... 

GOES 16 Water vapor loops showed a short wave developing over the 
northern Gulf of Mexico and Florida panhandle in advance of the 
closed upper low moving into the western Tennessee Valley. The 
Florida wave reaches northwest North Carolina by 18Z/2PM and may 
back the low level winds and enhance what will already be healthy 
shear over the area. As SPC pointed out the amount of CAPE and 
instability is very questionable. Will have the scattered coverage 
of thunderstorms along the front with less potential in the pre-
frontal precipitation. Will increase wind gusts today when the low 
level jet peaks near 70 knots from the south-southeast, with the 
most favorable location for strong wind from Mercer County, WV 
through Grayson County, VA to Watauga County, NC. 

All the clouds today will also limit heating but until the front 
goes through will have a small rise in temperatures this afternoon. 
Behind the front models have been consistent showing cold air 
advection. Upslope clouds will fill in late tonight over the 

Precipitable water values rise to around 1.8 inches today, which is 
excessively high for this time of the year. Will stay close to WPC 
QPF values which have been increasing every run, similar to what is 
shown in the synoptic guidance. Still seeing a potential for 
isolated flooding in the southern Blue Ridge and adjacent foothills 
where rainfall amounts will be the highest. Previous dry conditions 
will limit areal coverage, but leaf clogged storm drain may result 
in better chance of nuisance flooding in urban/suburban areas and 
high rates when the front comes through also favor an increased 
flooding risk. In coordination with surrounding offices, will hold 
off on any Flash Flood Watch and continue to highlight in the 
Hazardous Weather Outlook.


As of 215 AM EDT Monday...

By Tuesday morning, the influence of the front will be east of the 
region, and any precipitation immediately associated with it will 
likewise be to our east. However, the parent upper low/trough will 
still be to our west. The center of this upper low will be situated 
near the upper peninsula of Michigan with its trough axis extending 
south along the Mississippi River Valley. During the course of the 
day, these features will make slow progression eastward, still 
poised west of the forecast area by sunset. The bulk of the energy 
associated with the low is progged to remain farther north than 
earlier forecast. As such, our latest forecast will back down on the 
coverage of any associated showers in the west. At best we will now 
advertise isolated showers between the Northern Mountains of North 
Carolina and southeast West Virginia.

As we progress through Tuesday night into Wednesday, the upper 
low/trough continues its slow progression toward/into the area. By 
Wednesday afternoon, the axis is progged to be overhead, while at the 
surface a sw-ne oriented ridge axis noses into the area from the 
Deep South. Moisture will be lacking, and the best dynamics will 
continue to north of the region. Therefore, very few, if any, 
showers are forecast across the western half of the region.

A trend that will start on Tuesday night, and continue into at least 
Wednesday will be advection of colder air into the region. Tuesday 
night, low temperatures of the low to mid 30s will be common across 
the mountains with lows around 40 to the lower 40s across the 
Piedmont. By Wednesday night, anticipate readings about three to 
five degrees colder on average across the area as mostly clear clear 
skies are forecast, along with light winds, as the center of the 
surface high pressure settles overhead. High temperatures will also 
trend cooler. On Tuesday expect upper 50s to lower 60s across the 
mountains with upper 60s to around 70 across the Piedmont. On 
Wednesday, subtract about ten degrees from Tuesday's numbers for the 
expected high temperatures.

The last day of the growing season across the mountains is October 
25th. While a few spots across the mountains will experience 
temperatures at or a little below freezing Tuesday night, the 
presence of cloud cover and light winds will limit the degree to 
which frost develops. By Wednesday night, conditions are more 
favorable for a frost/freeze across the mountains, but at this 
point, the morning of the 26th, the growing season will have ended, 
and thus frost will not mentioned in any forecast products or 
headlines. The same is not true of parts of Rockbridge County, VA. 
Here, and points eastward, the growing season ends November 15th. 
With temperatures around freezing, limited cloud cover, and light 
winds, patchy frost will be forecast late Wednesday night into early 
Thursday morning for parts of that county, including areas in and 
around the cities of Covington and Buena Vista. This period is still 
too far out it time for contemplating any headlines.

Thursday into Thursday night, the center of the surface high 
pressure will shift east of the area. Aloft, southwest winds will 
start to increase in advance of an approaching upper trough across 
central CONUS. High temperatures on Thursday and low temperatures 
Thursday night will be about five degrees milder across the 
mountains as compared to Wednesday and Wednesday night's readings. 
Highs and lows across the Piedmont will be similar to Wednesday and 
Wednesday night's readings.


As of 345 PM EDT Sunday...

High pressure will continue build back across the southeast United 
States for the end of the week promoting warming temperatures 
through Saturday with high confidence for fair dry weather 
associated with sunny skies Friday. 

For the weekend it looks like we are going to repeat the current 
scenario with the development of an amplified upper level trough 
over the central United States which will move east pushing a cold 
front through the area over the weekend. 
The GFS is still the faster of the models bringing the front through 
Saturday night whereas the ECMWF is 24 hours slower holding off on 
any appreciable rainfall until later Sunday. Attm will maintain 
threat for showers Saturday through Sunday, but nothing more or less 
until models can resolve the timing.


As of 800 AM EDT Monday...

Ceilings will quickly deteriorate this morning with widespread
MVFR-IFR conditions developing. Rain will become widespread this
morning and continue through the afternoon.

Strong lift associated with a cold front will cross the area 
this afternoon and evening. This intense front will move from 
from west to east across the area between Noon-Midnight.
Periods of heavy rain with embedded thunderstorms will precede
and accompany the front. The stronger showers/storms may  
produce gusty surface winds. Of more concern will be the strong
low level jet. Models indicate a 60 knot low level jet 3-5kft
above ground level from the south will precede the frontal 

Extended Aviation Discussion...

The region will be in the dry slot late Monday night and Tuesday
with conditions east of the Blue Ridge improving back to VFR. In
the mountains little to no improvement in expected. Much colder
air comes in for Tuesday and Wednesday. Scattered showers with
possible MVFR ceilings and visibilities are expected on 
Wednesday across the region. Upper troughing remains over the
eastern United States keeping temperatures cool but with VFR 
flying weather.





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