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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 231737
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
137 PM EDT Thu May 23 2019

.SYNOPSIS...
Low pressure over the Great Lakes will pull a warm front north
through the Ohio Valley and Mid Atlantic region this morning, then
bring a cold front into Virginia and the Carolinas tonight and
Friday. Another low taking a similar track across the northern
United States will repeat the pattern Saturday through Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1213 PM EDT Thursday...After reviewing the 12z guidance
and assessing mesoscale environment, sent a quick update to the
forecast to add enhanced wording for gusty thunderstorm winds
through 00z from a line from Bluefield- Blacksburg-Roanoke-
Lynchburg north/west.

Ongoing convective line continues to move across central WV -
and across our area, the air mass has destabilized rather
substantially with CAPEs for a surface-based parcel between
2500-3000 J/kg per SPC`s mesoanalysis. This has led to cumulus
in the western third of the CWA, a few of which started to
deepen a bit further. It seems highly probable that ongoing
storms will move into this favorable juicy/unstable air mass and
strengthen. 12z convective-allowing guidance suite has now come
around to the idea of bringing this initial line of storms into
southeast WV between 1-3 PM, then into the Alleghany
Highlands/southern Shenandoah to the I-81/Route 460 areas
between 3 and 7 PM. It`s this area that a few storms may
produce sporadic instances of severe weather, capable of gusty
to localized damaging winds especially as downdraft CAPEs
continue to amplify (currently just under 1000 J/kg). Hail may
be possible but it would take a really robust updraft to do so
given the high freezing levels.

Otherwise, no other changes made attm.

Previous discussion from 315 AM...

Upper low over Minnesota early this morning moves east across
southeast Canada today and will be off the Maine coast by Friday
morning. This in turn shifts the upper ridge west which results in
northwest flow over the Mid Atlantic region tonight.

Bufkit forecast soundings from the HiResNMM and ARW, along with the
NamNest showed the stratus diminishing after sunrise with enough
heating by noon to overcome any cap/warm air aloft.

Models bring two main bands of showers and thunderstorms across the
Mid Atlantic region. One from Pennsylvania into central Virginia
this afternoon and the next over West Virginia tonight. Enough shear
that strong storms may develop but better forcing and dynamics are
confined to the north. Inverted-V sounding suggest the potential for
evaporative cooling and enhanced downdrafts with any of the stronger
storms. Downdraft CAPES from the SPC SREF are forecast to be in
the 500 to 1000J/KG range this afternoon and evening.

At the surface the parent high moves farther offshore this morning
but a piece of the ridge remains over the Carolinas which will
produce west to southwest winds over the area and continue advect in
higher dew points. Southwest Virginia, northwest North Carolina and
southeast West Virginia will stay in the warm sector for the rest of
the day. A cold front will approach from the north tonight and may
be as far south as Hot Springs by Friday morning.

Due to the clouds this morning, and especially north of the warm
front will be staying on the cooler side of guidance for maximum
temperatures today. Warmer air mass and surface dew points well into
the 60s tonight will keep lows mild.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 310 AM EDT Thursday...

A broad upper level ridge, centered over the Gulf States, will cover
the eastern half of the United States on Friday. With the area being
on the northeast corner of this ridge, our wind flow will be out of
the northwest. Any storms developing/tracking over the mountains
will drift into the foothills through the day. However, deep
northwest flow will have storms decaying very quickly moving east of
the Blue Ridge. Friday`s 85h temperatures averaging around +19C
which translates to surfaces temperatures across the mountains in
the 80s. Out east, warm temperatures aloft and downsloping flow will
produce temperatures in the lower 90s.

With the lose of heating Friday night, a weak cold front is expected
to slide across the region. Behind the front, winds become
northeasterly through the morning. If low clouds and northeasterly
winds can hang on into the afternoon, temperatures will be a little
cooler Saturday compared to Friday. However, weak wedges in late May
tend to not stick around for long. Temperatures should warm back
into the 80s across the mountains to the mid to upper 80s east of
the Blue Ridge. A Theta-E ridge is expected to replace the wedge
Saturday afternoon and evening, allowing dew points to creep into
the low to mid 60s. With increasing moisture, scattered diurnal
showers and thunderstorms are possible across the mountains Saturday
afternoon and maybe an isolated thunderstorm over the foothills in
the evening.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 229 PM EDT Wednesday...

Waxing and waning of the eastern upper ridge will allow energy
sliding along surface fronts to periodically affect the Appalachians
and central mid Atlantic region through the first part of next week,
while keeping us locked in to temperatures well above normal.

Outside of scattered diurnal convection, there may be a chance for
enhanced thunderstorm activity with an upstream MCS developing late
Sunday/Sunday night. Thereafter, uncertainties in handling of the
upper ridge into next week make for low confidence in identifying
any specific potential periods of concern for severe weather. Will
have to monitor this closely over the next several days to see
exactly what degree of severe threat materializes.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 113 PM EDT Thursday...

Lingering low stratus has finally started to thin out away from
Southside into the NC Piedmont; but the main concern for the
remainder of the afternoon is for scattered strong/severe
thunderstorms. Threat appears greatest for most TAFs except
Danville, and have included SHRA VCTS in association with a
likely line of storms progressing eastward from central WV now
through 00z. Storms may be capable of lightning, gusty winds
capable of localized turbulence, and brief IFR visby from heavy
rainfall. Storms should weaken as instability wanes after
sunset, though a few additional showers capable of brief
restrictions toward Lewisburg late this evening. Kept TAFs at
mainly VFR, but will be quick to issue TEMPOs for any convective
threat this afternoon/tonight. Winds outside of thunderstorms
mainly southwest 6-10 kts.

Should see mainly VFR conditions through 18z Friday. May see
isolated thunderstorms build up southwest of I-77 into the
mountains of northwest NC very late in the 18z TAF period, but
not likely to affect any TAFs. Winds west to northwest 6-9 kts.

Forecast confidence is moderate on thunderstorm potential, and
moderate to high on aviation categories outside of thunder.


EXTENDED AVIATION DISCUSSION...

VFR conditions are expected across the region Friday thru
Sunday. Exception is with evening/overnight fog but confidence
low on development attm. SCT MVFR showers and thunderstorms are
possible Monday in the west.

&&

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

&&

$$
SYNOPSIS...AMS
NEAR TERM...AL/AMS
SHORT TERM...RCS
LONG TERM...MBS
AVIATION...AL