Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 290513
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
113 AM EDT Sat Apr 29 2017

.SYNOPSIS...
High pressure offshore will maintain a warm and humid southerly
flow of air across the region through the weekend. A strong
cold front will move through the area Monday with showers and
thunderstorms, followed by some cooler, but near seasonal
temperatures through the first part of next week.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1127 PM EDT Friday...

Forecast was updated to increase sky cover a little over the
northwest as outflow from upstream convection pushes eastward in
stronger westerly upper flow. A couple questions overnight will
be fog and shower/thunderstorm threat.

The latest hi-res models and 00z synoptic models still trying to
develop showers further southeast toward our area than what is
currently indicated on radar. The airmass is still unstable, but
at the same time already getting night time subsidence which can
squelch thunderstorms.

Based on upstream conditions and track of line of convection
should see this stay upstream of us most of the night with some
showers possible at times reach Southeast WV, but overall looks
isolated. Corfidi vectors suggest convection to mainly stay
along/north of the Ohio River into Western PA.

As for fog will see less than last night but with dewpoints in
the mid 50s to mid 60s, moist ground and lighter winds along the
river valleys, think will see at least fog in the river valleys
overnight, mainly patchy to patchy dense.

Otherwise not much change to the temps with lows running 15-20
degrees above normal in the lower to mid 60s, with some upper
50s mountains. These lows are more typical of late June into
July.

Previous forecast discussion from early evening...
Forecast looks to remain on track. Thunder in western Greenbrier
later tonight looks even less favorable than earlier anticipated
as showers currently pushing toward the region are having
trouble clearing the terrain. Made slight adjustments up for
overnight lows as temps are not falling as fast as previously
forecast and newer guidance is trending warmer.

As of 215 PM EDT Friday...

Satellite imagery showing a Cu field mainly east of the
mountains with some cirrus over the top, but the radar is quiet
and expect it to remain that way into tonight. There is some
uncertainty as to the chances for showers/thunderstorms tonight
mainly along and north of the Interstate 64 corridor as
convection develops upstream and slides along a warm front. The
majority of guidance is keeping the frontal boundary and
associated convection to our north, but some meso guidance has
the convection clipping the northern portion of the area.
Believe the most likely scenario is for the warm front and
convection to remain to our north, but an outflow boundary from
this convection will sink into the region and may trigger a
showers or thunderstorm in a small time window around Midnight.
Will use some low chance POPs extreme north for a 3 to 4 hour
period around Midnight to cover this and keep an eye on trends
to see if fine tuning is needed.

Conditions tomorrow will be quite unstable in the hot and humid
airmass but there is significant capping aloft. In the absence
of synoptic forcing to break the cap, will have to rely on
orographic effects/differential heating to enhance convergence
and do not expect this to be overly effective. So aside from
some slight/low chance POPs for a shower/storm late in the day
mainly in the mountains, expecting a dry day.

Temperatures will be quite summer-like with lows tonight in the
mid/upper 60s east to upper 50s/around 60 west. Highs on
Saturday will be near 90 east to mid/upper 80s west. Since this
our first taste of real warmth, make sure air conditioning units
are clear of debris before turning them on, and be sure to take
frequent hydration breaks when outdoors on Saturday.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
As of 215 PM EDT Friday...

Large upper ridge off the southeast coast through Sunday night. Low
pressure tracks across Missouri on Sunday with a warm front
extending into Pennsylvania and a cold front over the central and
southern Mississippi Valley. This puts the Mid Atlantic region well
into the warm sector. No organized lift or forcing so will keep
probability of precipitation low through Sunday night.

Models still showing some differences with the timing of the cold
front on Monday. Will keep the highest probability of precipitation
on Monday along with a mention in the Hazardous Weather Outlooks of
strong to severe thunderstorms threat due to a 50-60 knot low level
jet.

Minimum temperatures will be mild on Sunday night with increasing
moisture and mixing from a south wind ahead of the front. Have
stayed just above MAV guidance for lows Sunday night. Front will not
be reaching the foothills and piedmont until Monday afternoon and
evening. This should give enough time, depending on the cloud cover
from upstream, for heating ahead of the front. Raised maximum
temperatures east of the Blue Ridge on Monday.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 215 PM EDT Friday...

Upper low moves through the Great Lakes on Monday night and high
amplitude eastern trough in reinforced Tuesday through Thursday.
00Z ECMWF closes off a low over the Gulf Coast states by Friday
morning, while the GFS is much deeper in the northern stream.

Surface boundary becomes east-west oriented on Tuesday and
Wednesday. Weak waves of low pressure will track east along the
front. will carry a dry forecast Tuesday through Wednesday with near
normal temperatures.

The 00Z ECMWF brings one of these waves and the associated
probability of precipitation into the Mid Atlantic region on
Wednesday night and Thursday. WPC leaned toward the ensembles in
this time frame, tracking a low from the Tennessee Valley Thursday
through the Mid Atlantic states on Friday. This pattern favors below
normal temperatures for both of those day.

&&

.AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
As of 105 AM EDT Saturday...

Area remains in between deeper moisture with the front just to
the northwest and return low level moisture around high pressure
to the southeast tonight. This should allow for mainly VFR
conditions into the overnight before seeing some patchy
fog/stratus develop across the valleys including possible
influx of lower cigs across the southeast due to advection of
the low level moisture. This mainly shown via the latest Nam
which appears likely overdone but given satellite trends in
seeing low clouds over eastern NC will include more MVFR cigs
around KDAN along with patchy fog into early Saturday morning.
Otherwise given more mixing and increase in high clouds from the
northwest will cut back on dense fog coverage around
KBCB/KLWB/KLYH and run with more of a TEMPO nature toward
daybreak at this point. Any thunder overnight at KLWB is still
possible, but will likely pass far enough to the north as
the latest HRRR and most other solutions keep coverage training
farther north but something to watch as a weak wave passes.

Unstable conditions will exist tomorrow as temperatures and dew
points will be more reminiscent of summer rather than of April,
however a strong cap should suppress most convective
development. If there will be any thunder it will likely be very
isolated and terrain induced, therefore would only be in the
higher elevation. Due to the isolated nature of this convection,
has for the time being not been mentioned in the TAFs. Winds
will be generally light and southerly during the TAF period.

Extended Aviation Discussion...

High pressure should build off the Southeast coast during this
weekend. Other than the potential for MVFR/IFR morning fog at
the usual river valley locations, VFR conditions should prevail
Saturday and Sunday. As a low pressure system approaches from
the west late Sunday and Sunday night, the potential for
afternoon showers and thunderstorms will increase. The cold
front associated with this system should reach the Appalachian
Mountains by Monday and depart offshore by Tuesday morning. As
such, expect the best chance of MVFR conditions during the
frontal passage.

&&

.CLIMATE...
Potential for high temperature records to be broken Saturday,
April 29, as well as record warm lows for the 29th

 Current record/yearForecast
Roanoke89/191589
Lynchburg88/197489
Danville91/198189
Bluefield83/199685
Blacksburg83/197485


 Current record/yearForecast
Roanoke63/195666
Lynchburg66/195664
Danville65/195666
Bluefield63/199165
Blacksburg59/196262

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...JH/MBS
NEAR TERM...JR/MBS/WP
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...JH/JR/MBS
CLIMATE...JR/WP


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