Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 221903 AAA
AFDRNK

Area Forecast Discussion...UPDATED
National Weather Service Blacksburg VA
303 PM EDT Tue May 22 2018

.SYNOPSIS...
A warm front lifts north into the mid-Atlantic this afternoon,
followed by a cold front shifting southeast across our area
late tonight into Wednesday. High pressure noses down from the
Ohio Valley and Mid Atlantic Wednesday night into Thursday, then
off the coast by Friday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Update as of 250 PM EDT Tuesday...

Quick update for the inclusion of severe thunderstorm watch 116
until 9 PM for a few counties across the far northeast including
LYH.

Previus update as of 1030 AM EDT Tuesday...

Warm front has basically lifted northeast of the area this
morning with the region in a lull within the moist warm sector
well ahead of the cold front northwest of the Ohio Valley.
Morning soundings show a bit stronger steering aloft today with
more of a west/southwest trajectory ahead of the upstream front
that should allow cells/bands to move a bit faster. Latest
short term solutions show some development near and just west of
the Blue Ridge before perhaps a more organized broken band of
convection slides into the region by this evening as seen via
the latest HRRR. This may allow for stronger storms to work
farther south as depicted with the new SWODY1 so bumped up pops
central sections a bit sooner while increasing coverage heading
east later in the day. Otherwise some small adjusts to remove
fog and reduce clouds some as expect a decent amount of heating
given breaks off latest visible satellite pics to support going
highs of 70s west to 80s east before convection becomes more
widespread.


Previous discussion as of 250 AM EDT Tuesday...

Showers still lingering along warm frontal boundary from central WV
to the Alleghanys and into the area north of Lynchburg, with even
isolated coverage per some moisture convergence and weak wave aloft
in central NC.

Fog has developed given higher moisture at the sfc and in the low
levels. However, extensive cloud cover at least over the northeast
3/4ths of the forecast area is limiting coverage of dense fog.
Meanwhile, clearing taking place in the southwest CWA may act to
enhance the fog here through the morning. May have to issue an dense
fog advisory if coverage increases for low vsbys. Otherwise, a
special wx statement will cover it.

Today, models in reasonable agreement on keeping our area in the
warm sector as the warm front lifts north into the mid-Atlantic.
Expect storm motion this afternoon to be more from the west to east
ahead of the front and a little faster, around 15 to 20kts. Still
high pwats around 1.25 to 1.5 inches will lead to localized flash
flood threat, especially if storms line up in a wsw to ene
orientation and train over the same area. Coverage is not enough to
warrant a flash flood watch but folks should be alert to torrential
downpours and be prepared to act if flooding is observed.

As for severe threat, we have a marginal risk roughly north of U.S.
60 from Lewisburg WV to Buckingham VA.

High-res models suggest enough clearing to allow for
destabilization, with better low and mid lapse rates further north
over Northern VA, west northwest to the Ohio Valley. Looking at
SBCAPEs of 1000-1500 J/KG in this area, so cannot rule out some
damaging winds from wet microbursts.

The models diverge this evening in terms of coverage of storms, with
high-res and 00z ECM drying things out east of the mountains while
the GFS and to an extent the NAM hang onto the convection a little
longer in the east. With a west-northwest flow aloft expect some
drying but will not completely erode pops out east until late, with
all models keeping a secondary surge of showers over the mountains
of WV/far SW VA by 12z ahead of the front.

As far as temperatures go, not much change with highs in the mid 70s
to around 80 west, to mid 80s east, possibly upper 80s if enough
sunshine occurs.

Tonight, still sticky with lows in the 60s.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
As of 225 AM EST Tuesday...

As center of large ridge shifts westward toward the mid-Mississippi
Valley Wednesday, northwest flow aloft will become carved out across
the mid-Atlantic and Northeast. At the surface, a slow-moving cold
front should extend central and eastern Virginia. Convergence along
the front looks pretty good and daytime heating should help to
develop showers and thunderstorms. There is some level of
uncertainty on the exact position of the front, as 12z NWP guidance
has sped up the front`s southeastward push a little sooner. Its
position also will likely depend on convective developments from the
today/tonight period. MUCAPE values approach 2000 J/kg with
effective shear values around 30 kts supporting some potential
loosely organized multicells or short line segments given along-
front forcing. Given the damp ground from recent rains, potential
would exist for localized flooding in thunderstorms with the best
chance east of the Blue Ridge. However I could see at least a small
corridor of potential strong storms along/south of the front (best
chance from Farmville to Wilkesboro southeast). Where the front is
positioned early Wednesday would significantly influence the
forecast in a big way; if the front is slower to advance southeast,
it would put more of the area in a greater chance at seeing stronger
storms than presently envisioned; likewise, frontal position closer
to the VA/NC border would keep any convective threat rather limited
spatially. So still some important details to iron out, but
Wednesday offers some potential for an active day. In the Day-2
convective outlook, SPC maintains a 5%/Marginal Risk for mainly
Southside. This seems reasonable given aforementioned uncertainties
in frontal position. Southward push of the front with more northwest
surface winds should stabilize things quickly around late
afternoon/early evening.

Behind the front, a sprawling high pressure area centered over New
England then wedges into the region overnight Wednesday through
Friday. This will force a drier northerly flow into the region, with
cooler 850 mb temperatures (around +11 to +13C) and shifts the axis
of higher precipitable water air further south into central North
Carolina. This appears to be our best chance at at least a day or
two of much needed dry days after nearly daily rains. Best chance
for any rain is in the southern Blue Ridge, and it is pretty
limited. Given the very wet soils, there may be a greater potential
for fog if winds stay light/calm enough but not much confidence to
place in the grids attm.

Wednesday projects to be the warmest and most humid of the period
with highs mid 70s to mid 80s. Highs Thursday and Friday should be a
couple degrees cooler but about 5-7 degree lower dewpoints leading
to more comfortable conditions. Lows Wednesday and Thursday nights
in the 50s to lower 60s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 300 PM EST Tuesday...

Coverage of showers and thunderstorms will increase during the
weekend as a warm front lifts northward through the mid
Atlantic, bringing a return of deeper moisture from the Gulf
coast region. Afternoon temperatures will range from the mid 70s
to the mid 80s each day, while overnight lows will generally be
in the 60s areawide.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
As of 1245 PM EDT Tuesday...

Clusters of showers and storms developing across the western
mountains will shift slowly east reaching the Blue Ridge by
19-20Z/3-4PM, and eastern locations between 20-23Z/4-7PM.

Will likely see more of a scattered coverage west to start with
most Taf sites having at least thunder in the vicinity but will
likely include a Tempo period of thunder from northwest to
southeast into this evening. Potential to see at least a broken
line along and east of the Blue Ridge later this afternoon so
boosting thunder mention east later on.

Looks like activity wanes in the evening with some clearing
taking place to allow for fog, dense at times to form. Should
see at least MVFR fog to IFR stratus at most sites, with dense
fog at KLWB/KBCB late.

Appears any low clouds/fog will fade by mid morning Wednesday
leading to more in the way of VFR across the region through
early afternoon. Added sub-VFR conditions will be possible
mainly southeast of a line from KLYH- KDAN with most activity
likely south of the region later in the afternoon.


.Extended Aviation Discussion...

Conditions are will be drier and are expected to be VFR
Thursday and Friday. Tropical like moisture streams back north
as a warm front moves through Saturday with a return to
showers/storms and potential sub-VFR conditions and heavy rain
by Saturday afternoon/evening.

&&

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

&&

$$
SYNOPSIS...WP
NEAR TERM...JH/WP
SHORT TERM...AL
LONG TERM...NF
AVIATION...AMS/JH/RCS/WP


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