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000
FXUS61 KRNK 031412
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1012 AM EDT Mon Aug 3 2020

.SYNOPSIS...
Tropical Storm Isaias will track northward along the East Coast
during today and Tuesday to bring bands of showers and
thunderstorms to the Mid Atlantic. A cold front should cross
overhead by Tuesday night but stall along the coast for the
remainder of this week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 345 AM EDT Monday...

Bands of showers and thunderstorms are moving northward toward
the Mid Atlantic. Some of the stronger storms have produced
frequent lightning, heavy rainfall, and gusty winds. Patchy fog
has been added for the remainder of the overnight hours given
the moist boundary layer and recent rainfall. Meanwhile,
Tropical Storm Isaias will churn northward along the Florida and
Georgia shoreline today. An approaching cold front will enter
the Ohio River Valley by this afternoon. The resulting moisture
convergence will result in increasing coverage of showers and
thunderstorms.

The showers and thunderstorms present several hazards with the
potential for severe due to damaging winds and flooding due to
heavy rainfall. As a result, no changes have been made to the
Flash Flood Watch due to an anticipated predecessor rain event,
or PRE, that typically occurs well away from landfalling
tropical cyclones when moisture interacts with some kind of
frontal boundary. There is the potential for isolated amounts
of one to two inches of rain along parts of the Blue Ridge
before the day is done. High temperatures should reach the 70s
in the mountains and the low to mid 80s in the Piedmont.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/...
As of 330 AM EDT Monday...

Heading into Monday evening, the axis of heaviest rainfall
associated with the wave of energy (PRE) passing across the
lower Mid-Atlantic is expected to be situated across the
Piedmont and foothills of the Blue Ridge, lifting gradually
northeast. Meanwhile, Isaias will make landfall near the North
Carolina/South Carolina border and advance quickly northward
toward the mouth of Chesapeake Bay.

Isaias is a rather compact and fast-moving storm, with its
greatest impacts expected to remain confined east of a
Danville to Lynchburg line. After a brief lull in rain in the
wake of the departing wave of energy, the main bands of Isaias
will enter Halifax County shortly before dawn Tuesday. Northerly
windflow on the western half of the storm will draw drier air
across the Piedmont to counteract the moisture radiating outward
from the core of Isaias. The result will be a tight gradient in
rainfall accumulations as the storm passes, with 4+ inch
amounts expected across portions of Buckingham and Charlotte
Counties, with accumulations diminishing by about an inch
roughly every 30 miles to the west. The wind threat associated
with the storm is expected to be marginal at best, 25 to
occasional 35 mph gusts across Buckingham and Charlotte Counties
during the morning.

By noon Tuesday, the center of Isaias is expected to be near the
Chesapeake Bay, with dry air quickly working its way in from the
northwest in the wake of the storm as a trailing cold front
passes across the Appalachains chain. Clearing skies can be
expected across the Piedmont during the afternoon as winds shift
northwesterly and downslope. Cannot rule out a few showers
developing across the mountains during the afternoon, but
believe this activity will be spotty and disorganized, and will
fade toward sunset with the loss of afternoon heating.

Widely-scattered showers and thunderstorms will return for
Wednesday as the frontal boundary stalls across the Piedmont,
serving as the focus for afternoon convection. May see a few of
these storms become severe for brief periods of time, capable of
producing localized damaging wind gusts.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 300 PM EDT Sunday...

Weather pattern returns to more typical for summer time. Will
again be repetitive forecast of daily chances for afternoon
and evening thunderstorms, along with heat and humidity typical
of summer. No major deviation from long range synoptic scale
guidance.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
As of 210 AM EDT Monday...

Outside of periods of heavy rainfall/storms, conditions will be
VFR. This AM`s band of showers and storms have eroded and are being
replaced by a new line of thunderstorms stretching from western
TN, into SWVA through far east WV. These storms will obviously
produce sub VFR conditions when over TAF sites through today and
into this evening. As the day progresses, this line of
convection will traverse eastward while another band of storms
makes there way northward from central NC. These two bands will
ultimately provide a prolonged period of storm chances for all
TAF sites along and east of the Blue Ridge.

Eventually the storm move out of the region, ushering in the
next focus of the forecast, Isaias. Due to its proximity moving
up the coast, light to moderate rainfall will spread over the
eastern part of the region, bringing rainfall for LYH and DAN.
This also places BCB and ROA on the edge between light
rainfall/BR producing low ceilings, or gusty conditions as
downslope occurs with the wind shift associated with the system,
resulting in better flight ceilings. For now, leaning toward
the low ceilings lighter winds. Sites in WV will drop tonight,
but terrain influences combined with winds will determine
whether BLF and LWB drop sub VFR, or remain VFR with windy
conditions.

Extended Aviation Discussion...

Poor flying conditions are expected into Tuesday due to
Tropical Storm Isaias passing over eastern Virginia. Showers and
thunderstorms will continue through this time until a cold
front sweeps the moisture away by Tuesday night. Conditions
should improve to VFR on Wednesday and generally remain this way
through Friday, but some early morning patchy fog and scattered
afternoon showers and thunderstorms could temporarily restrict
flight conditions during this time.

&&

.HYDROLOGY...
A frontal boundary stalled near the spine of the Blue Ridge
will support bands of showers and thunderstorms that will pass
across the region through the day. Moisture will continue to
increase as Tropical Storm Isaias continues its approach, which
will cause some storms to produce 2 to 3 inch per hour rainfall
rates this afternoon and evening. In addition, training of
storms across the same locations is probable, leading to
prolonged periods of heavy rain and possibly localized flash
flooding. A few locations could receive 3 to 4 inches locally.

Just as this system exits to the northeast late this evening,
Tropical Storm Isaias is expected to make landfall near the
border of North Carolina and South Carolina tonight, and pass
rapidly northward to near the mouth of Chesapeake Bay by early
Tuesday afternoon. This will bring the potential of 3 to 5
inches of rain to areas east of a Danville to Lynchburg line.
Rainfall associated with Isaias will exit during early
afternoon, with rapidly clearing conditions expected thereafter.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flash Flood Watch from 2 PM EDT this afternoon through Tuesday
     evening for VAZ022>024-033>035-043>047-058-059.
     Flash Flood Watch through Tuesday evening for VAZ015>017-032.
NC...Flash Flood Watch from 2 PM EDT this afternoon through Tuesday
     evening for NCZ004>006-020.
     Flash Flood Watch through Tuesday evening for NCZ001>003-018-
     019.
WV...None.

&&

$$
SYNOPSIS...PW
NEAR TERM...PW
SHORT TERM...NF
LONG TERM...AMS
AVIATION...PW/RR
HYDROLOGY...NF