167
FXUS62 KRAH 070717
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
316 AM EDT Tue May 7 2024

.SYNOPSIS...
A series of mid to upper-level disturbances will interact with an
unseasonably moist airmass as they move across NC through Thursday,
while sub-tropical high pressure will otherwise extend across the
South Atlantic states. A cold front will move across the region on
Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 935 PM Monday...

An area of showers and isolated thunderstorms that tracked across
much of the northern half of the forecast area is currently falling
apart around Rocky Mount, while another broken line of showers and
thunderstorms extending from Myrtle Beach to Charlotte and eastern
Tennessee is now approaching from the west. An increasing low-level
temperature inversion should reduce the amount of instability for
thunderstorms, but still think that thunderstorms will be a
possibility through the night, although severe potential is minimal.
The observed precipitable water value from the 00Z GSO sounding was
1.18 inches, just over the 75th percentile for the date, meaning
that the showers/thunderstorms could be efficient rain makers as
well. Expect another muggy night with overnight temperatures in the
low to mid 60s.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 340 PM Monday...

Tuesday and Tuesday night: Aloft, as the s/w moves east and off the
mid-Atlantic coast, a brief period of omega blocking will set up as
the sub-tropical ridge builds northward through the Southeast US,
central Appalachians, OH Valley and western Great Lakes. To the east
of the block, a low will progress eastward through Quebec and
Newfoundland Tue, then out over the northern Atlantic Tue night. To
the west, a large low will sit over the northern Plains as several
s/w disturbances rotate around it. The eastern low progressing
eastward Tue night will weaken the block, allowing a leading s/w
moving through the OH Valley around the western low to push the
ridge slightly eastward and suppress it southward. At the surface, a
warm front will lift newd through the area early Tue, with a
Piedmont trough setting up east of the mtns and strengthening
through Tue night as a low develops over the southern Great Lakes.
Expect continued advection of warm, moist air into the area, with
PWATS starting the day around 1.7 inches, decreasing slightly with
daytime mixing, but remaining largely in the 1.4-1.6 inch range. The
12Z NAM and 12Z GFS both have MLCAPE values of about 1000-2000 J/Kg
(GFS lower than the NAM) across all of central NC Tue aft/eve, with
effective shear around 30 kts. The SPC has included just about all
of central NC in a marginal risk for Tue. The big question will be
the presence of a forcing mechanism to get storms firing. Look for
showers/storms to largely form along the developing lee trough
and/or differential heating boundaries if they are present. An
isolated strong to severe storm is possible, with the primary threat
of damaging wind gusts and possibly hail. As for temperatures, highs
should top out in the mid to upper 80s, while lows in the mid 60s to
around 70 degrees are expected.

Wednesday and Wednesday night: Aloft, the leading s/w will continue
eastward through the Northeast US toward the eastern low, while the
western low finally begins to migrate slowly eastward. A second s/w
will swing through the Plains and the MS Valley Wed/Wed night. At
the surface, the surface low will move slowly eastward through the
Northeast US Wed and offshore Wed night. Another low will develop
along the front over the southern Plains early Wed, lifting newd
into the upper MS Valley through Wed eve before drifting eastward
into the OH Valley Wed night. The trough over central NC will weaken
and lift northward out of the area as the low move east and offshore
Wed night. The frontal zone between the two lows should generally
remain north of the area through Wed night, with continued swly flow
over the area. Expect continued advection of warm, moist air into
the area, with PWATS largely in the 1.4-1.7 inch range. The 12Z NAM
and 12Z GFS both have MLCAPE values of about 1500-2500 J/Kg across
all of central NC Tue aft/eve, maximized over the eastern Piedmont
and Coastal Plain, with effective shear again around 30 kts. The SPC
has included all of central NC in a marginal risk for Wed. The
forcing mechanism will likely be the lee trough as it moves eastward
through the area. An isolated strong to severe storm will once again
be possible. As for temperatures, highs should be about a category
higher than Tue, topping out in the upper 80s to low 90s. Lows
should be in the upper 60s to low 70s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 316 AM Tuesday...

The main impacts in the extended will focus on Thu/Fri with a
continued threat of severe weather (mainly Thu) ahead of a strong
cold front. Drier conditions and seasonal to below normal
temperatures are still favored for the weekend into early next week.

A messy and complex weather pattern is shaping up for the period Thu
and Fri. Confidence on specifics is low given the latest trends in
the suite of guidance products and overall synoptic pattern. Broadly
speaking, while the specifics are not clear cut, troughing over the
Midwest to Great Lakes/OH valley Thu is forecast to move east across
the Mid-Atlantic Fri aftn/night before exiting sometime Sat off the
NE US coast. At the surface, low pressure over the OH valley Thu is
forecast to move into the NE US Fri, allowing a cold front to push
through sometime Fri night.

What happens Thu may partially depend on what evolves Wed night to
early Thu morning. Models, particularly the GFS, indicate impulses
of energy tracking across the region on the nose of the left-exit
region of a jet streak near upstate SC. This energy, if it verifies,
would inherit a favorable kinematic and thermodynamic environment
for showers/storms overnight Wed night. This activity could lay an
outflow boundary to start Thu morning. A secondary uncertainty is
upstream convection that will advance into western NC and the
Piedmont Thu morning ahead of the cold front over the TN valley.
Both of these uncertainties could have implications on the coverage
and intensity of storms Thu aftn/evening due to potential rain-
cooled air and convective debris clouds. That said, the environment
in the absence of these competing factors still supports a risk of
damaging winds, large hail, and a few tornadoes with strong low/deep
layer shear and high instability/DCAPE. The CSU/CIPS severe analogs
continue to indicate a wide swath of severe potential from the SE US
into VA. SPC has kept a slight risk (Level 2 out of 5) across the
region. A lee trough will be in place ahead of the front Thu,
favoring a gusty/warm SW flow. Highs could be tricky given the above
considerations, but for now have low 80s NW to near 90 SE.

The severe risk should subside overnight into Fri morning as the
effective front pushes into SE SC. Meanwhile, the cold front looks
to get hung up along the spine of the Appalachians, not moving
through until Fri night. Deterministic/ensemble data still shows
uncertainty on the strength of a secondary shortwave rounding the
base of the main trough, which could bring a secondary shot of
showers/storms Fri aftn/eve. The GFS is particularly robust with
this feature relative to other solutions, tracking a secondary low
along the cold front over eastern NC. We kept showers in the
forecast Fri as a result, but retained the thunder chances mainly
along/east of US-1 as the main instability axis should be confined
along SE NC. Severe weather is not anticipated with this potential
wave. Shower activity should end Fri night as the front pushes
through.

The rest of the period looks to favor more dry time than rain
chances, although precipitation cannot be fully ruled out. It
appears ensemble data is still not in agreement on the placement and
timing of a series of troughs that could impact the region over the
weekend with the NW flow aloft. Rain chances are possible Sat and
Sun, but with lack of consensus in the guidance, we kept most of the
forecast dry with very low-end shower chances at this stage.
Temperatures should return closer to normal and even slightly below
average with highs in the 70s and lows generally in the 50s.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 140 AM Tuesday...

Several small clusters of showers and thunderstorms
extend from the NC mtns to the western and central Piedmont.
The general model consensus is for the convection to drift
east into central and eastern NC overnight and into the early/mid
morning hours. While associated MVFR to IFR restrictions will be
possible at just about any of the TAF sites, confidence is the
exact timing and location is low.

Additionally, continued unseasonably moist/humid air will also favor
the redevelopment of areas of IFR-MVFR stratus late tonight-Tue
morning. Associated ceilings should then lift and scatter and yield
to a gusty swly surface wind by ~14-16Z Tue.

Some additional convection is possible this afternoon and evening,
but should be more isolated/widely scattered in nature and
potentially limited INVOF KINT and KGSO.


Outlook: There will be a chance of mainly afternoon-evening showers
and storms throughout cntl NC through Thu, then ahead of a passing
cold front, mainly at FAY, on Fri.

&&

.CLIMATE...

Record High Minimum Temperatures:

May 8: KGSO: 66/1938 KRDU: 68/1930 KFAY: 70/2003

May 9: KGSO: 68/2002 KRDU: 70/1936 KFAY: 71/2009

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...MWS
NEAR TERM...Green
SHORT TERM...KC
LONG TERM...Kren
AVIATION...CBL/MWS
CLIMATE...RAH