703
FXUS61 KRNK 250106
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
906 PM EDT Tue Sep 24 2024

.SYNOPSIS...
A slow-moving frontal system will meander along the Ohio River
Valley over the next several days, triggering rounds of showers
and thunderstorm activity through much of the workweek. Helene
is forecast to move northward from the Gulf of Mexico toward
the end of the work week, and may bring more widespread
rainfall to the region.

&&

.NEAR TERM /NOW THROUGH WEDNESDAY/...
Issued at 905 PM EDT Tue Sep 24 2024

Overall, the ongoing forecast is on track this evening.

Convection continues to thrive this evening, mainly from the
Southside into northern North Carolina. MLCAPE values between
500 and 1000 J/kg, combined with sufficient values of effective
bulk shear will allow this to be the favored region for
strong/severe storms over the next couple of hours. The airmass
behind this batch of convection has stabilized somewhat,
especially the farther north you go from the Virginia state
border. But effective bulk shear values remain greater than 40
knots in this region, so additional convection cannot be totally
ruled out overnight.

There`s plenty of boundary layer moisture for the convection to
work with. Our 25/0000 UTC sounding from Blacksburg has a
precipitable water value around 1.5 inches. The values farther
east are greater, averaging 1.9 inches. (This is well above
normal, by the way.) When combined with strong low-level
moisture transport vectors, this will result in thunderstorms
being efficient rain producers. As such, the risk of heavy
rainfall and flooding will continue overnight.

As of 200 PM EDT Tuesday

Key message:

1) An upper level trough and associated cold front will
approaching the region today will lead to continued shower and
thunderstorm activity overnight tonight and into the early
morning hours on Wednesday before becoming more isolated in
nature through Wednesday afternoon.

An upper level trough that has been digging southward today is
expected to separate from the main northern flow by Wednesday, and
become quasi-stationary across northeastern Arkansas and western
Tennessee. As this happens, upper level ridging is expected to build
across the southeastern coastal plain, and off the southeast
coastline. While This happens throughout the day on Wednesday, a
strengthening jet streak in a southwest to northeast orientation is
expected to develop from the lower Mississippi valley towards West
Virginia. This 250mb jet orientation coupled with upper level
divergent flow through the 500mb level will lead to scattered
shower and thunderstorm activity across the region for much of the
morning on Wednesday, with a possible break in the mid morning
before additional storms develop through the afternoon hours across
the I-77 corridor into West Virginia.  While much of the eastern
half of the area will dry out through the afternoon and evening,
cloud cover is expected to be plentiful across the region as mid and
upper level clouds from the south and southwest stream north. This
will keep temperatures in the low to mid 70s across higher terrain,
and in the upper 70s to near 80 across the Piedmont. Lows Wednesday
morning will generally fall into the low to mid 60s areawide.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
Issued at 135 PM EDT Tue Sep 24 2024

Key Messages:

1: Outer bands of TS Helene will cause showers as early as Thursday

2: Heaviest and most widespread rainfall will be Friday and Friday PM


Moisture convergence over a weak wedge will continue to cause
showers and embedded storms Wednesday night. TS Helene will still be
in the Gulf, but entering the influence of a closed 500mb low near
the Arklatex and MS. This low will accelerate Helene quickly
northward, going from the FL panhandle to western Carolina in the
span of just 12 hours. This could place the outer bands of tropical
moisture and rain in our NC counties as early as Thursday afternoon.
Friday looks to be the most active day, with rain expected for most
of the day throughout the CWA. Flooding will be a definite concern
as we expect 3-4" along the southern Blue Ridge and in the High
Country, and 1-3" across the remainder of the CWA. As always with
banding in tropical systems, due to the nature of banding there
could be higher amounts in localized areas.

Flooding concerns will be exacerbated by the enhanced winds,
particularly near and south of the NC/VA border. Above 3kft
elevation, winds could gust up to 30kt. This will blow down early
dead leaves, serving to clog up drains, culverts and sewers.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 200 PM EDT Tuesday...

Key Messages:

1) Lingering moisture from Tropical Storm Helene will remain in the
area through the forecast period, with showers possible each day.

2) High pressure wedges back into the region on Sunday, decreasing
rain chances and keeping below average temperatures through midweek.

As Tropical Storm Helene begins to dissipate over the Appalachian
mountains early on Saturday, remnant moisture and breezy conditions
will remain across the area. Rain chances decrease significantly on
Saturday but remain possible. High temperatures will be in the 70s,
with eastern piedmont locations around 80. For Sunday, surface high
pressure over New England will begin to wedge back into the RNK CWA,
pushing drier and cooler air southward. Residual moisture from
Helene will continue to ride over top of this wedge, leading to
light showers and cloudy conditions continuing into early next week.

Due to the cloud cover and high pressure wedge, temperatures are
expected to remain below normal beginning on Sunday. Highs will be
in the 60s and 70s, with lows in the 50s to around 60 degrees
through midweek. Winds also remain slightly elevated due to the
wedge. There is some model disagreement with where the remnant low
and associated moisture will go early next week. The Ensemble
Situational Awareness Table continues to keep precipitable water
values around 1.5 inches for early next week. Due to this, PoPs are
kept modest through the forecast period, with showers possible each
day.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Issued at 905 PM EDT Mon Sep 24 2024

SHRA/TSRA will continue to bring flight restrictions to
terminals across Central VA into N NC into the early morning
hours, with a break expected in terminals W of this region.
Additional SHRA/TSRA are expected to affect terminals in SE WV
and SW VA toward 25/0400 UTC and could bring restrictive CIGs
and VSBYs overnight.

MVFR to LIFR conditions look to return to all terminals beyond
0900 UTC Wednesday, and linger through 12-15 UTC on Wednesday
before conditions start to improve to MVFR to VFR levels as
visibilities increase, and CIGs lift.

EXTENDED AVIATION OUTLOOK...

MVFR/IFR stratus and fog are expected to occur in rounds through
at least the middle of the week, and increasingly likely to
persist through the end of the workweek. Rounds of showers and
thunderstorms will also continue to pass across the lower Mid-
Atlantic.

Low pressure lifting northward from the Gulf of Mexico toward
the end of the week may bring more widespread rainfall and sub-
VFR conditions to the region.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch through Wednesday morning for VAZ016-017-032>034-
     043>046-058-059.
NC...Flood Watch through Wednesday morning for NCZ003>006-020.
WV...None.

&&

$$

SYNOPSIS...DB/EB
NEAR TERM...DB/EB
SHORT TERM...VFJ
LONG TERM...JCB
AVIATION...DB/EB