Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 201345

Area Forecast Discussion
National Weather Service Blacksburg VA
945 AM EDT Sun May 20 2018

A southerly flow will continue to push warm and humid air into our
region today and tonight. Scattered showers and thunderstorms will
develop this afternoon and become more numerous for Monday.


As of 945 AM EDT Sunday...

Drew back the PoPs significantly for the next several hours as
short range guidance such as the HRRR and Conshort are much more
bearish than previously forecast. Will hold on to the more
widespread PoP after 21Z to wait and see how convection plays
out this afternoon. This also mandated a change to forecast
weather and QPF grids. Otherwise, minor adjustments made to
match current temp trends. Nothing else significant enough to

As of 420 AM EDT Sunday...

An upper level disturbance rotating east across the region this
morning creating a few lingering showers and isolated thunderstorms.
This convection will dissipate as the shortwave shifts farther
to the north and away from the area. Southerly flow will
continue to advect warm, moist and unstable air into our
region. Scattered showers and thunderstorms will develop this
afternoon. The HRRR and NAM showed limited coverage, while
HiResw-ARW-East indicated better coverage with convection
starting along the southern Blue Ridge initially after 18z,
then increasing coverage by 00z. The ECMWF and GFS had s
scattered storms by 00z. The Day One Convective Outlook placed
our forecast area in general thunderstorms with a marginal
threat of severe to our west.

With a saturated ground and rich moisture, there remains the
potential for flooding. However, the coverage will be less than
recent days and more localized. Please continue to monitor for
river flood warnings and localized flooding problems and heed
remaining road closures. High temperatures this afternoon will
range from the lower 70s in the northwest mountains to the mid
80s in the Piedmont. Any convection should move east this
evening. It will turn out partly to mostly cloudy and mild
tonight. Low temperatures tonight will vary from the upper 50s
in the mountains to the upper 60s in the Piedmont.


As of 600 AM EDT Sunday...

Continued wet and unsettled through much of the period. A
Bermuda ridge will remain in place to our southeast keeping a
steady, warm, moist flow of Gulf air into the region while a
weak upper-level disturbance approaches from the Ohio Valley.
This disturbance will push yet another weak front into the area
that will stall Monday into Tuesday near the NC/VA border.
A convective complex tracking across the Ohio Valley Sunday
night will drift into the far western portions of the CWA early
Monday before dissipating, but leave outflow boundaries along
with the front draped across the area Monday afternoon to result
in scattered to numerous showers and thunderstorms once again.
Locally heavy rainfall and renewed flooding would be the main
concern. Cannot rule out an isolated strong to severe
thunderstorms, but with limited dynamics, not expecting anything
organized and SPC has pulled the marginal outlook back to the
west out of our area with the latest update.

The boundary or baroclinic zone will linger across the area
Tuesday, most likely near the NC/VA border and continue to serve
as a focusing mechanism for convective development. Weak
upper-level disturbances in the westerlies will drive the time
frames over the more widespread convective coverage, along with
diurnal heating. There is also evidence of yet another weak
disturbance tracking north from the eastern Gulf of Mexico into
the southeast and southern Appalachians that will serve to keep
deep tropical moisture across the region and as noted above the
main concern through the period of heavy rainfall and possible
renewed flooding. Additional Flash Flood Watches may be needed
if these forecast trends continue given that most of the
forecast area is completely saturated from this past week of
heavy rainfall.

Little change in temperature is expected through the period with
maximum temperatures just above normal in the mid 70s to lower
80s and minimum temperatures well above normal in the 60s.


As of 630 AM EDT Sunday...

Global models point to the later part of the week being a bit
drier than the first half of the week as upper troughing drifts
to the northeast of the area and an upper ridge builds over the
southeast U.S. Initially this will bring a drier northwest flow
aloft to the area and a large surface high drifting across OH/PA
and the northern Mid-Atlantic region. This should confine the
best chances for precipitation across the southern parts of the
CWA. This should hold until the weekend when there is some
potential for a tropical disturbance/system to move north from
the eastern Gulf of Mexico renewing the threat for rain across
our region.

Temperatures will be a bit cooler, yet very close to normal, at
the start of the period thanks to the Canadian high pressure
drifting across the Ohio Valley and northern Mid-Atlantic
region. By the weekend conditions should return to slightly
warmer and more humid conditions once again.


As of 545 AM EDT Sunday...

MVFR/IFR SCT to BKN clouds will continue east of the mountains
this morning. The greatest concentration of the lower clouds is
located in the northeast. West of the mountains outside of the
showers ceilings were VFR. IFR/LIFR clouds are pushing into far
southwest Virginia. Isolated showers and thunderstorms are
diminishing as they moved eastward this morning. Plenty of low
level moisture and light winds will have resulted in pockets of
fog this morning. Any morning fog will be shallow and burn off
or lift by mid morning.

As weak high pressure builds over the Mid Atlantic region
today, moisture will decrease. Southwest Virginia, northwest
North Carolina and southeast West Virginia will become VFR by
late morning, with medium confidence in this timing.

Diurnally driven isolated MVFR/IFR showers and thunderstorms
will develop this afternoon into tonight. Patchy fog will form
Sunday night into Monday morning, especially where it rains

Medium confidence in ceilings, visibilities and winds during
the taf period.

.Extended Aviation Discussion...

Another weak cold front will bring increasing coverage of
showers and thunderstorms again on Monday. Scattered MVFR
showers and thunderstorms are possible Monday night into Tuesday
with another round likely Wednesday. Conditions are expected to
improve later in the week.




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