-- Discussion containing changed information from previous version are highlighted. --
047
FXUS62 KRAH 041817
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
217 PM EDT Sat May 4 2024

.SYNOPSIS...
A series of upper level disturbances will move through the area
through Sunday. Meanwhile, a backdoor cold front will stall across
the area through tonight, before lifting north into Virginia early
Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 933 AM Saturday...

Showers and a few embedded thunderstorms continue to move north-
northeast across a semi-stationary front extending along the
southern, western, and far northern Piedmont this morning.  A pocket
of enhanced dew points over the southern Piedmont have fed some weak
instability promoting continued lightning activity over Stanly,
Cabarrus, and Union counties.  Elsewhere in this corridor, stable
conditions have mostly precluded thunder.  Regardless, a swath of
>1.6 inches of PWAT extends through this region, which has allowed
for brief heavy downpours and associated isolated pockets of higher
rain rates. Additionally, the mean-layer flow is light and oriented
quasi-parallel to the frontal boundary promoting slow, n-s moving
cells. As such, we`ve seen some training (and hints of backbuilding)
which has prompted a few flash flood warnings this morning.

An additional series of weak perturbations aloft will traverse over
central NC through this evening promoting continued scattered
showers and storms. While areas south and east of Raleigh may stay
dry through noon, high-res guidance does suggest an uptick in
coverage over the Sandhills/southern Coastal Plain early to mid
afternoon.  Some clearing is already occurring in that vicinity
which should enhance instability some later today. Additionally, the
plume of anomalous PWAT should extend further east in this period as
well. Models do also simulate a weak sfc wave moving through the
Sandhills/central Piedmont this afternoon which could also enhance
coverage in this vicinity later today/tonight.

Given the slow n-s oriented storm motion embedded within an
anomalously moist environment, can`t rule out continued chances for
isolated instances of flash flooding continuing through tonight.
Don`t think we`ll see widespread flooding by any means, but given
tall-skinny CAPE profiles, warm cloud depths >10,000 ft, and mean-
layer flow conducive to slow-moving cells and potential training,
isolated instances of flash flooding (especially urban areas) seems
plausible today and tonight. Additionally, a stronger vort max
currently over GA will ride over central NC late tonight which
should continue to promote higher chances for showers and a few
storms through early Sunday morning. However, given weak shear not
expecting any severe storms to develop today or tonight.

Temperatures today will range between the lower to mid 70s along the
NC/VA border (which should stay north of the boundary and locked
into cooler enely sfc flow) and lower to mid 80s elsewhere. Warm
overnight lows in the mid 60s are expected.

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
-- Changed Discussion --
As of 215 PM Saturday...

Aloft, the sub-tropical ridge will shift offshore and breakdown
Sun/Sun night as the increasingly sheared shortwave disturbance
moves through the mid-Atlantic and Northeast US. Another southern
stream s/w will strengthen over the southern Plains on Sun, then
move eastward into the lower/mid-MS Valley through Sun night. At the
surface, high pressure will move off the New England coast and
eastward over the northern Atlantic as a low moves through the Great
Lakes and into the Northeast Sun/Sun night. An attendant cold front
draped swwd from the low will become more W-E oriented through the
OH Valley by Sun night. Meanwhile over central NC, the quasi-
stationary front that had lingered over the area will lift northward
as a warm front, with warm, moist southerly return flow over the are
in its wake.

Precipitation/Convection: Showers and storms will likely still be
ongoing Sun morning, most prevalent over the Piedmont. PWATs will
remain anomalously high, in the 1.6 to 1.8 inch range, through the
afternoon. Surface-based instability should increase with daytime
heating, although the latter may be somewhat inhibited by the
ongoing convection and extensive cloud cover. Bulk shear is also
expected to be weak again on Sun. As a result, slow-moving, widely
scattered showers and storms will be possible through the aft/eve
Sun, with the main threat of some isolated heavy rainfall and
localized flooding, although most locations may only receive a few
hundredths of an inch of rain.

Temperatures: Widespread overcast skies and ongoing convection
should somewhat limit heating early, but temps could recover during
the afternoon. For now expect highs to range from the mid 70s along
the NC/VA border to around 80 degrees SE. Lows Sun night mainly in
the low to mid 60s expected.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 250 AM Saturday...

The extended forecast will feature a continued chance of unsettled
weather to start the week Mon, followed by somewhat drier and hot
temperatures by the middle of the week. A potent late-week
system/trough looks to increase storm chances again by week`s end.

On Monday, models continue to show a shortwave over the TN valley
tracking east across the region in the afternoon/evening, before
exiting along the coast by Tue morning. A surface Piedmont trough
will be in place and combined with 200-percent of normal PW`s should
favor another day of scattered to perhaps numerous showers and
storms, maximizing during peak heating. Instability is between 500-
1000 J/kg but shear is weak, so severe chances are not expected,
though slow-moving storms could bring heavy rain. Activity should
wane overnight with loss of heating and as the trough slides toward
the coast. Highs should hover in the low/mid 80s with higher rain
chances and cloud cover.

As the trough moves to our east Tue, weak ridging starts to build
in, although the CMC/GFS show a weak perturbation riding along the
ridge. With a lack of large-scale forcing, confidence on coverage of
storms, if any, is low, such that storm activity should be
isolated/scattered in nature and focused along differential heating
boundaries and/or the sea-breeze. Highs should warm to the low to
upper 80s.

A drier pattern still appears to be favored midweek Wed and part of
Thu as ridging and southwest flow builds back into the region. This
will also be when the airmass will warm quite a bit with a lee
trough setting up east of the Appalachians and low-level thicknesses
well above average and highs some 12-15 degrees above normal in the
upper 80s to low 90s. The NBM still indicates a 60-80 percent chance
of 90 or greater maxT values across portions of the Sandhills,
Triangle region, and Coastal Plain during this period. Heat index
value could reach the mid 90s over these areas, making for an early
taste of summer. While this period looks drier, most guidance shows
a developing trough over the upper MS valley Thu, with solutions
indicating a decent plume of moisture tied to a perturbation
advecting ahead of a cold front draped over the OH valley. This
would favor better chances of isolated/scattered storms Thu aftn/eve
with higher instability coupled to higher shear.

Although model solutions diverge by late in the week with a frontal
system location, there is broad consensus that chances of storms
appear to remain elevated to close out the week as the trough slides
closer to the TN/OH valley and Great Lakes region with
instability/shear still favorable over the Carolinas.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 127 PM Saturday...

Under anomalously moist conditions, LIFR ceilings persist at
KINT/KGSO this afternoon. Elsewhere, terminals have largely
scattered to VFR with some clearing of the cloud shield.  Scattered
showers and a few storms will continue to stream from south to north
through early Sunday morning. If any heavier cells interact with our
terminals, brief periods of gustiness and sub-VFR conditions are
likely.  As we progress into early Sunday, additional scattered
showers and a few isolated storms will be possible as well.  LIFR to
IFR ceilings are then likely to sock back in across central NC
starting around 03Z and persisting through early to mid Sunday
morning.

Outlook: MVFR to IFR ceilings are likely to sock back in Sunday and
monday night with additional scattered showers/storms possible.
Drier conditions are expected mid-week.

&&

.CLIMATE...

Record High Minimum Temperatures:

May 4:
KGSO: 65/2022
KRDU: 68/1938
KFAY: 68/1942

&&

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

&&

$$
SYNOPSIS...CBL/Green
NEAR TERM...Luchetti
SHORT TERM...KC
LONG TERM...Kren
AVIATION...Luchetti