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000
FXUS61 KRNK 281736
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
136 PM EDT Fri Jul 28 2017

.SYNOPSIS...
Low pressure along a front across the Midwest will track east
crossing the Mid-Atlantic region later today into this evening.
A trailing cold front from this system should pass east into
the area later this afternoon before exiting to the east of the
region overnight. High pressure follows behind the front
bringing drier and cooler weather from later Saturday into
early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 130 PM EDT Friday...

A murky weather pattern ahead of a slow moving cold front creating a
challenging forecast through this evening. Clouds have been
thick this morning from weak waves of rain tracking across the
mountains. This has kept instabilities rather low and thus no
convection so far. However, as these areas of rain move east
across the mountains, clouds have been thinning and raising to
about 10kft. A few areas are seeing breaks in the clouds and
CAPE values are increasing to moderate levels. Very little rain
has fallen since sunrise east of the Blue Ridge and especially
over the piedmont. CAPE values are quickly on the rise with
skies becoming mostly sunny.

A couple of weak surface lows are expected to form along the front
this afternoon and track east. Most models are showing one across
the Ohio Valley moving east to the Mid Atlantic region. This wave
will interact more with the closed low coming out of the Great
Lakes. The majority of the stronger convection and heavy rain threat
will reside in northern Virginia and southern Pennsylvania.

A second low tracks east along the TN/VA-VA/NC border this afternoon
and evening. This low will bring a chance for strong to severe
storms to areas along the NC/VA border. With instabilities on the
rise along with synoptic forcing, the best coverage of stronger
storms will be over the piedmont and moreso east of hwy 29 later
this afternoon into the evening. Right now, the areas is under a
marginal risk for a few severe storms which may come from short line
segments.


As of 300 AM EDT Friday...

Rather complicated forecast continues today with strong shortwave
energy seen in water vapor across the western Great Lakes set to dig
southeast while deepening a surface wave that looks to track just
north of the area into tonight. However before this feature
consolidates by this evening, forecast remains uncertain due to
pieces of fragmented upper waves that will scoot east ahead of the
trailing cold front and subsequent closing off upper system aloft.
Models remain quite overdone with showers early this morning since
the region remains basically in between a mid level wave to the
southeast from Tuesday, and pockets of better defined lift south of
the front across KY/TN attm. This seems handled best by the GFS
which holds better coverage to the west through midday before
enhancing lift along the front over the west this afternoon, and out
east late into early evening perhaps along a lead pre-frontal type
outflow band. Thus trimmed pops back a bit this morning, although
expect some increase by daybreak, at least with coverage of more mid
deck showers.

Questions remain with severe/flooding potential this afternoon as
most guidance less impressive with severe parameters per projected
weaker instability given degree of early clouds/showers around. Does
appear best severe threat across the west if can get more multicell
clusters early on, and then possibly with a more organized band by
this evening east pending the degree of any heating as shear aloft
still decent. Overall flooding threat mainly from southeast WVA
across the far north where coverage may be more widespread closer to
the front/surface low. However given uncertainty with just how far
south the more organized belt of deeper convection will be, and
overall dry antecedent conditions expect flooding more of the
isolated nature, so holding off on any watch for now. Otherwise kept
pops similar to previous with values ramping up to likely/categorical
from west to east this afternoon including a heavy rain mention
given moist PWATS. Highs tricky per early clouds and timing of
more widespread convection which supports staying with a cooler
Mos consensus for now.

Upper low closes off just to the north overnight with the trailing
surface cold front swinging through mainly after midnight. Expect
best convective coverage over the east/north during the evening
before dry slotting aloft from the southwest overnight. However
potential wrap around/upslope flow likely to keep bands of showers
going most sections overnight as cool advection increases late.
Therefore trend of diminishing pops looks good after this evening
with winds turning blustery along the ridges by daybreak. Appears
this mixing and clouds to limit temp falls despite strong cool
advection so kept most in the 60s overnight.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
As of 315 AM EDT Friday...

The combination of the closed upper low dropping south through the
Appalachians and the surface low pulling off toward the coast will keep
some lingering showers across the region Saturday with our chances for
precipitation decreasing throughout the day. The closed upper low will
then then take up residence over the mid Atlantic coast through the
weekend and nudge the surface low a bit further offshore with the last
of the lingering showers tapering off Saturday night. A large area of
high pressure will then build in from the upper midwest with fair
weather expected into the first part of next week.

With a cool north to northeast wind this weekend, expect temperatures
to be 5 to 10 degrees below normal on Saturday and Sunday with highs
generally in the low to mid 70s west of the Blue Ridge and upper
70s/around 80 to the east. Nights will be notably cooler as well with
lows by Monday morning in the lower 50s west to upper 50s east. Expect
a gradual warming trend through the first part of next week with highs
Monday in the middle 80s east to middle 70s/near 80 west.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 1245 PM EDT Thursday...

Upper low opens up and lifts northeast back into the northern jet
stream through Tuesday with 500MB heights rising Tuesday and Wednesday
over the Mid Atlantic region. Still under long wave troughing over the
eastern United States through the end of the week with models showing
some signs of through amplifying by Friday. 850MB temperatures
gradually warm Monday through Wednesday back close to +18 to +20 for
Wednesday and Thursday. Will maintain dry forecast through Thursday.
Once surface high moves offshore on Friday a slight chance of
precipitation will return to the mountains.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
As of 125 PM EDT Friday...

Low confidence TAF forecast continues today with showers
spreading across the west early followed by redevelopment this
afternoon as showers/storms increase ahead of a cold front to
the west. However timing, strength and extent of stronger more
widespread thunderstorms highly contingent on sufficient cloud
breaks. For now will continue with a VCTS mention at most
locations from west to east this afternoon, and TEMPO in a
period of sub-VFR as perhaps a more organized area shifts east
from the western terminals early this afternoon and into eastern
sections by late afternoon/early evening. Any thunderstorm may
be capable of torrential downpours and associated IFR to LIFR
visibility and lightning.

Expect coverage to gradually exit the east after sunset but
lingering wrap around likely to produce low cigs and lingering
shower bands across most of the region until around midnight.
Appears most rainfall will be along and north of a KLWB-KLYH
line by daybreak Saturday with patchy fog possible despite
increasing northerly flow late.

Appears Saturday will start out mainly dry under low cigs.
However given upslope northwest flow across the KBLF/KLWB
vicinity, and the upper low dropping south across eastern
sections, expect a return of periodic return of showers until
late in the day. Should see cigs rise some as drying aloft
gradually works in but still appears will stay sub-VFR for much
of the day espcly western mountains and east of the Blue Ridge.

Aviation Extended Discussion...

Expect widespread VFR to return Sunday-Tuesday under high
pressure following the front/upper low.

&&

.HYDROLOGY...
As of 122 PM EDT Friday...

More in the way of widespread showers and storms can be expected
ahead of a strong cold front this afternoon into tonight.
Locally heavy rainfall could accompany any of the stronger
showers and storms with rainfall rates of better than 2-3
inches per hour possible. This heavy rainfall could lead to at
least isolated flooding or flash flooding especially if rainfall
tends to train across the same locations. However lingering
antecedent conditions remain quite dry with only the far
northwest sections having seen more widespread heavier rainfall
from Thursday. This combined with very high flash flood
guidance and low stream flow supports less in the way of
widespread flooding issues, especially given the uncertainty in
projected rainfall through this evening. Thus will hold off on
any watches with this package and handle with short fuse
products if needed later today for now.

&&

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

&&

$$
SYNOPSIS...JH/RCS
NEAR TERM...JH/RCS
SHORT TERM...MBS
LONG TERM...MBS
AVIATION...RCS
HYDROLOGY...JH