Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 270533

Area Forecast Discussion
National Weather Service Blacksburg VA
133 AM EDT Mon Mar 27 2017

Low pressure near Chicago will move northeast through the Great
lakes and weaken as it passes into Ontario tonight and Monday.
A second area of low pressure will move northeast out of the
southern Plains crossing the Mid-MS Valley Monday, and across
the Ohio Valley into the northern Mid-Atlantic Monday night and
Tuesday. These weather features will result in unsettled weather
across the central and northern Appalachians through Tuesday.
Temperatures will remain well above normal through mid week.


As of 659 PM EDT Sunday...Radar and METARs continue to indicate
ongoing, though weakening rain showers from Roanoke to
Reidsville NC eastward into western portions of Appomattox
County. These showers stand to dissipate per recent HRRR/NAMNest
output. Also watching stronger convective development to the
the west and south of our forecast area, primarily in central
West Virginia, associated with vort max pinwheeling northeast
into southern Ohio around parent upper trough extending
southeastward from the upper Midwest. Past couple HRRR runs,
which have generally handled the spatial coverage of convection
to our west the best since it partly initializes off radar,
continues to suggest that some possible scattered
showers/possible rumble of thunder may slip into Mercer, Summers
and western Greenbrier Counties in WV as well as our southwest
Virginia Tennessee Valley counties next couple hours. As we
progress toward midnight, upper trough lifts to our northeast,
leaving us in shortwave ridging overnight. As forcing becomes
nebulous at best, except for some additional upslope convergence
along the southern Blue Ridge, PoPs should be at their lowest
overnight with shower coverage being even more isolated than
they presently are. Given rather saturated air mass would expect
skies to stay at least mostly cloudy. Lows only fall into the
50s tonight.

Previous near-term discussion issued at 300 PM follows...

Radar indicated a 30 mile wide band of rain showers propagating
east across the central CWA. As of 3PM the leading edge was
along the 220 corridor from Clifton Forge to Martinsville.
Movement was to the east at 20 mph.

Leading rain band was associated with a front aloft, arcing from
NW to SE from Low pressure moving through the Great Lakes.
The actual surface front was over western KY/TN, with additional
bands/clusters of showers and thunderstorms scattered across the
Ohio Valley. The initial rain band over our CWA has outrun any
surface instability and has been weakening with time. Rainfall
amounts have been averaging between a tenth to a quarter of an
inch, but as this band of showers continues to move east, the
overall qpf will diminish with amounts of a tenth of an inch or
less. Timing suggests these showers will reach Highway 29
corridor...Charlottesville, Lynchburg, Danville, between 5-6PM.

Behind the front aloft, some partial clearing was taking place,
the rain only lasting a couple hours in duration. Once this
initial rain area moves east, will have to wait for the
instability driven showers over KY/TN ahead of the actual
surface front to move east. Models suggest most of this activity
will dissipate during the overnight, but until then will
threaten our western CWA (primarily west of I-77 in VA/NC and
west of Lewisburg or highway 219 in WV) this evening with
potential for both showers and thunderstorms and an additional
tenth or two of rainfall before midnight.

As the main upper level low slides by to our northwest overnight,
dynamic support will decrease. The actual surface front is
forecast to wash out before crossing the mountains so this will
maintain a persistent mild southerly flow across the forecast
area overnight. As such, there will be a continued chance of
showers mainly along and west of the Blue Ridge overnight,
although nothing severe per waning instability. Some patchy fog
is also possible, but cloud cover should prevent it from
becoming widespread.

On Monday, a second storm system will be moving northeast out
of the southern Plains, crossing the Mid MS valley during the
day and into the OH Valley Monday evening. Response will be the
development of more showers and thunderstorms with focus
primarily to our west across the OH/TN valleys. Model soundings
suggest some instability driven activity may develop over our
CWA during the afternoon associated with weak convergence near
the Blue Ridge. Attm will advertise chance threat for
showers/storms Monday, but coverage generally less than 50
percent and no mention of severe attm. Certainly can`t rule out
a stronger storm or two if temperatures rise into the 70s permitting
surface based CAPE in the 1000-1500 range.

Temperatures through Monday will remain mild with readings 10
to 15 degrees above normal, and remaining well above freezing.


As of 300 PM EDT Sunday...

During this portion of the forecast, a Pacific based system is
expected to impact the region. Guidance among the models is in good
agreement of bringing a shortwave trough eastward along the Ohio
Valley and then into the New York City region Monday night into, and
through Tuesday. This track will keep the region on the mild side of
the system until the passage of its associated cold front Tuesday
morning into the afternoon hours.

Scattered showers and isolated storms across the area Monday
afternoon, will lingering into Monday evening. The scattered showers
will continue through the overnight, with coverage increasing
towards daybreak in the west. There may be an initial increase in
coverage across eastern parts of the area through the evening hours,
but decrease to isolated coverage early Tuesday morning.

As the front crosses the region on Tuesday, showers will be in
greatest concentration coincident and just in advance of the cold
front. Instability is progged to increase enough to warrant isolated
to scattered thunderstorms in this same general area, with the best
potential shifting eastward during the course of the day.

Coverage will quickly decrease Tuesday evening with the departure of
the cold front to the east. Some lingering northwest flow upslope
isolated showers are possible across portions of southeast West
Virginia, neighboring counties of southwest Virginia, and south into
the Northern Mountains of North Carolina. Coverage will be greatest
during the evening hours with decreasing coverage as the nigh

Wednesday into Wednesday night, an upper level shortwave ridge is
progged to build over the area, all while surface high pressure
noses south along the lee of the Appalachians. Look for any
lingering isolated showers in the west to end by noon. Limited cloud
cover is forecast for all of the region by Wednesday afternoon. As
Wednesday night progresses, low level flow on the west side of the
surface ridge will allow for moisture levels to increase. Anticipate
increasing cloud cover, and eventually some patchy light rain across
areas mainly near the crest of the Blue Ridge from roughly Roanoke,
VA southwest into the Northern Mountains of North Carolina.

Temperatures during this portion of the forecast will trend from
roughly fifteen degrees above normal Monday night into Tuesday to
around five to ten degrees above normal Wednesday into Wednesday night.


As of 300 PM EDT Sunday...

The lee side ridge of surface high pressure will continue to prevail
on Thursday, although low level flow not too far above the surface
will start to increase as a closed upper low heads eastward through
the central U.S.  Look for light rain to increase across the area on
Thursday, especially western and central parts of the region. The
activity will take on more of a showery nature Thursday night as the
upper system draws closer.

On Friday, showers will be likely across most of the region with
isolated thunderstorm possible across the western and southern parts
of the area. The main system will track north of the area Friday
night into Saturday, with its associated cold front across our
region early Friday night. Look for an end of the shower activity
for much of the area by Saturday morning. Lingering upslope showers
on the backside of the system will be possible across southeast West
Virginia and neighboring counties of southwest Virginia.

Saturday night into Sunday, an upper level ridge will build over the
area, allowing for a gradual decrease in the upslope showers in the
west, and limited cloud cover in the east.

Temperatures during this portion of the forecast will be around or
slightly above normal Thursday and Friday, but trend to readings
about ten degrees above normal for Saturday and Sunday.


As of 119 AM EDT Monday...

There is a backdoor boundary situated from eastern WV north of
LWB to FVX and this has allowed for some low level clouds in
the IFR range to move as far south as ROA/LYH. At the same time,
isolated to scattered showers continue to move northeast with
best coverage approaching DAN/BLF/LWB as of 0515z. Satellite
and high-res models favor a mix of VFR to IFR cigs and at times
vsbys this morning. Usually a backdoor front will not retreat
back to the north at night, and should keep places like ROA/LYH
stuck in the IFR or lower cigs through at least 10-13z.

Given the scattered/isolated nature to showers there will be
some tempo groups in for these through 12z, then as we head into
Monday the flow should increase out of the southwest taking the
warm front north and seeing all sites go to VFR cigs. Appears
next threat of showers and isolated storms will arrive late this
afternoon but should be isolated with best chance in the
mountains near BLF. Better threat overnight, with one wave
moving toward DAN but this after this taf period. Still looking
at VFR through Monday evening.

Extended Aviation Discussion...

Front moves into the mountains after 12z Tuesday with best
threat of showers/some thunder and sub-VFR in the 09z-18z
Tuesday time frame. Cold front exits the piedmont by 00z
Wednesday with lingering sub-VFR cigs in BLF/LWB with VFR east.

High pressure builds in from the north Wednesday into Thursday
with next storm system moving into the MS Valley. A threat for
sub-VFR cigs appears likely as the high wedges southwest Wed
night-Thursday for most sites. Better chance of rain Thursday
night into Friday.




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