392
FXUS62 KRAH 070752
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
350 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 350 AM Tuesday...

...There is a Marginal/Level 1 Threat for Isolated Severe Storms
This Afternoon and Evening...

A low-amplitude shortwave trough currently moving through the area
will move off the southern mid-Atlantic coast during the late
morning. Accompanying weakening cluster of showers and embedded
thunderstorms over the western Piedmont will shift eastward through
mid morning. Hi-res guidance has struggled in this convective
environment. Thus, it`s difficult to predict how much further
weakening, or not, will occur before the convection exits the area.
Rainfall amounts will be light, generally between one to two tenths
in the more organized showers.

In the wake of the exiting trough, synoptic scale subsidence will
overspread the area as ridging builds overhead. Additionally, 925-
700mb winds will become increasingly W-NWLY, a favorable downslope
regime will should favor substantial clearing and ample sunshine for
the afternoon. Temperatures will respond according, with highs
warming into the mid 80s north to upper 80s/near 90 south.

Though more isolated/widely scattered in nature, some additional
late day showers and storms are possible. PWATS will remain
exceptionally high as strong insolation fuels moderate instability
across the area. While weak sfc convergence along a lee side trough
could spur some pop up storms, hi-res guidance favors a scenario of
upstream convection over the higher terrain moving into the NW
Piedmont late in the day, potentially related to PV anomaly
associated with the southern tail end of the ongoing convection
moving in the mid MS Valley. If storms do develop or move into the
area, sufficient deep layer shear of 30-35 kts amidst moderate
buoyancy of 2000-2500 J/KG and a favorable high DCAPE environment
would support a threat of damaging wind gusts and possibly large
hail. The severe threat appears greatest over the NW Piedmont,
between 4-10 pm.

Any convection should eventually weaken as it drifts east into the
central Piedmont through midnight. Mild overnight lows 65-70.


&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 350 AM Tuesday...

...Summer-like Heat Returns...

...Another Marginal/Level 1 Threat for Severe Storms during the
afternoon and evening...

Upper ridge centered over the SE US will flatten and shift east and
offshore during the day, which should make the Carolinas more
susceptible to some upper disturbances moving into the region as a
70-80kt subtropical jet punches in from the SW. At the surface, a
lee sfc troughiness will sharpen over western NC.

The first weather headline will be the summer-like heat. Low-level
thicknesses of will be comparable to late June than early May and
will support afternoon highs ranging from upper 80s across the north
to lower 90s over the remainder of the forecast area. When coupled
with the humid BL dewpoints in the mid to upper 60s, heat indices
over the central and eastern portions will be in the mid 90s.

The second weather headline will be another marginal/level 1 threat
for severe storms. Confidence is below average regarding convective
evolution/details Wednesday. However, there appears to be the
potential for two round of storms during the forecast period; 1)
during the early afternoon/early evening which could develop along
old outflow boundary from the previous night; 2) potentially
followed by another round late Wednesday night and into early
Thursday morning from upstream convection moving into the area.

The summerlike heat and humidity will result in moderate to strong
destabilization with MLCAPE of 2500-3500 forecast across the area.
Strong shear of 30-35kts and another favorable high DCAPE
environment will support a primary threat of damaging winds. Large
hail is also possible, given the robust/fat CAPE profiles.

Lows Wednesday night could challenge for the warmest on record with
temperatures in the upper 60s to lower 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...CBL
SHORT TERM...CBL
LONG TERM...Kren
AVIATION...CBL/MWS
CLIMATE...RAH