597
FXUS61 KRNK 181359
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
959 AM EDT Wed Sep 18 2024

.SYNOPSIS...
Low pressure centered over the southern Appalachians this
morning will drift northeast today and Thursday bringing more
clouds and precipitation. The low moves offshore by Friday,
lowering the probability of precipitation. Dry weather and
seasonal temperatures are expected for Saturday and Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 955 AM EDT Wednesday...

Key Message:

1) Light rain and drizzle this morning will give way to
additional showers/isolated storms this afternoon and evening.

2) Localized urban and small stream flooding possible, with a
lower flash flood threat compared to yesterday.

Little change to the forecast this morning, with an upper level
low centered near Greenville, SC, and a surface low located
along the TN/NC border. Moisture from the Mid Atlantic continued
to be drawn towards the Appalachians, but for now there was a
more NE surface component which was running parallel to much of
the terrain, so no significant showers yet. Otherwise, short
wave energy and higher level moisture was rotating around the
upper low, and was responsible for some light returns on radar
this morning near Roanoke and Lynchburg.

Precipitable water had backed off some here (1.23 inches on this
morning`s RNK sounding) and shifted east, and current
mesoanalysis showed a pocket off instability over eastern VA
and just nudging into our eastern counties. This is where
isolated lightning is more likely this afternoon and evening as
we see some breaks in cloud cover there, along with better low
level moisture. Cool high pressure wedging will keep any strong
storms out of the forecast however. Temperatures will only
increase a few more degrees today.

Adjusted PoPs and hourly temperatures slightly for this update.


As of 315 AM EDT Wednesday...

Key messages:

    - Thunderstorms isolated this morning, scattered this afternoon

    - Lower threat of flooding today

The upper low and occluded surface low were stacked over the
southern Appalachians early this morning. This system will drift
northeast today and tonight with little change in intensity.

Satellite water vapor images showed a small short wave rotating
around the upper low into central Virginia. Slightly colder air
aloft and surface convergence from a decaying occluded front were
providing enough lift for isolated thunderstorms. Will be adding
some thunderstorms in for this afternoon since the models were
showing an increase in Convective Available Potential Energy from
noon through 8 PM.

Abundant low level moisture remains in place across the region today
and tonight. There should be some breaks in the clouds this
afternoon across the mountains, southern Virginia, and northern
North Carolina. Areas north of Route 460 in Virginia may see
little, if any sunshine. Clouds fill back in tonight. Will stay
below guidance for most areas for highs today and close to NBM
numbers for lows tonight.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
As of 240 AM EDT Wednesday...

Key Messages:

1) Confidence is moderate for the chance of showers to slowly
decrease by the end of the week.

2) Temperatures should gradually rise back to near normal values
for this time of year.

An upper level trough will slowly drift eastward on Thursday as
an upper level ridge builds from the west. Enough moisture and
instability remains to produce scattered showers with a couple
thunderstorms on Thursday afternoon. The upper level trough
should finally head offshore during Thursday night, and drier
will arrive by Friday. The increase in heat from more sunshine
along with orographical lift may still overcome the drier air
mass to spark an isolated thunderstorm along the southern Blue
Ridge on Friday afternoon. High pressure will take more control
by Saturday with temperatures peaking in the mid 70s to the
lower 80s.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 240 AM EDT Wednesday...

Key Messages:

1) Confidence is moderate for high pressure wedging against the
eastern slopes of the Blue Ridge on Sunday.

2) A low pressure system could approach from the west to bring
an increasing chance of showers by early next week.

High pressure could wedge against the eastern slopes of the Blue
Ridge by Sunday to bring a cool easterly flow. This flow may
persist into Monday. The models diverge significantly beyond
Monday due to increasing uncertainty on when a low pressure
system could approach the Appalachian Mountains from the west.
Some models hold the wedge firm and slow the advance of the low
pressure system, while others weaken the wedge and allow the
system to arrive sooner. The slower scenario seems to be the
more logical choice, but the chance of showers should steadily
rise west of the Blue Ridge during Monday and Tuesday. If the
flow can be swung around towards the south more quickly on
Tuesday to weaken the wedge, then instability could increase to
push thunderstorm chances higher.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
As of 945 AM EDT Wednesday...

Primarily LIFR to IFR ceilings continue across the region. The
southern edge of the cloud shield around the upper low was
approaching the Virginia/North Carolina border from the south.

Ceilings will lift back to MVFR this afternoon. Clouds may also
becoming scattered west of the Appalachians, including for a few
hours at KBLF and KLWB. Scattered showers and isolated
thunderstorms are possible in areas that get some heating and
some better instability.

Stratus and fog will redevelop across the region this evening
with fog and LIFR ceilings. LIFR fog is likely at KLWB and
potentially at KBCB and KBLF.

Winds will be from the east to northeast this morning, with a
few gusts up to 20 knots. By this afternoon and evening, wind
speeds will be less than 10 kts.

Average confidence for ceiling and wind.
Below average confidence for coverage of any thunderstorms this
afternoon and LIFR fog overnight.


EXTENDED AVIATION OUTLOOK...

Thursday and Friday less coverage of showers is expected.
Ceilings will improve to VFR by Friday.

VFR conditions and dry weather is expected to return for
Saturday and Sunday.

&&

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

&&

$$

SYNOPSIS...AMS
NEAR TERM...AMS/SH
SHORT TERM...PW
LONG TERM...PW
AVIATION...AMS/DS/SH