Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 270529

Area Forecast Discussion
National Weather Service Raleigh NC
125 AM Sat EDT May 27 2017

A weak surface trough will be located over the Piedmont this
afternoon through Sunday. An upper level disturbance will cross the
region this afternoon and early evening, followed by another
disturbance Sunday afternoon.


As of 825 PM EDT Friday...

A rare pristine/unmodified elevated mixed layer characterized by H7-
H5 lapse rates on the order of 8.5-9.0 C/km will advect eastward
across the southern Appalachians into the Carolinas tonight.
Marginal nocturnal destabilization will occur as mid-level lapse
rates become nearly dry-adiabatic, however, poor low-level moisture
will maintain considerable CIN and preclude significant
destabilization through 12Z Sat. With clear skies and calm winds,
expect overnight lows ranging from the upper 50s to lower 60s,
warmest in the S/SW.

Severe Potential on Saturday: The aforementioned EML will set the
stage for strong to extreme diurnal destabilization Sat afternoon in
the N/NW Piedmont as rich low-level moisture advects beneath it from
the W/SW. With central NC firmly embedded in the westerlies and
equilibrium levels approaching ~13km, effective deep-layer shear (0-
8km) will likely reach 40-45 knots Sat aft/eve. Diurnal heating and
low-level moisture advection are expected to erode the CAP across
the N/NW Piedmont by late afternoon, however, significant
uncertainty persists with regard to whether or not convection will
develop since the magnitude/timing of forcing will highly depend on
the evolution of upstream convection overnight and early Sat. The
latest convection allowing models suggest at least isolated
development will occur north of Hwy 64 late Sat aft/eve. If deep
convection develops over or propagates into central NC late Sat
afternoon, thermodynamic/kinematic profiles would support intense
supercells capable of producing destructive hail (1.75-2.75") and
wind (65-75 mph). -Vincent


As of 350 PM Friday...

Low amplitude shortwave disturbances riding atop the flat
subtropical ridge in place across the southern U.S. will set the
stage for scattered upstream convection to move into the area within
a west-southwesterly WAA belt spreading east into the southern
Appalachians late tonight/early tomorrow morning and then into
central NC on Saturday. The convection should align closely to a
wavy west-east frontal zone that will initially push east into VA
during the afternoon, and then gradually sag south into central NC
during the evening and overnight, likely aided by the expected
convective and associated outflow. While an EML plume advecting into
the area may help to bolster destabilization across the area, it may
also serve to limit convective coverage especially south of US 1.
Will keep a good/high chance across the far north with only slight
chance pops across the south, with a decrease in pops with cooling
after sunset.

A strong mid-level wind field will result in favorable deep layer
shear of 30 to 35 kts, along with moderate instability to support a
cluster or two of severe storms capable of producing large hail and
damaging straight-line winds, mainly along and north of HWY 64.

Warming H8 temperatures to 15 C tomorrow(+ 5C from Friday) with a
corresponding 20 meter rise in low-level thicknesses to 1420 meters
will support a quick return to above normal temperatures. Highs in
the mid to upper 80s north to lower 90s south. Lows tomorrow night
in the mid to upper 60s with some patchy fog possible where any
heavy rain falls.


.LONG TERM /Sunday through Friday/...
As of 300 PM Friday...

A short wave trough over the TN valley Sunday morning will move east
and across the Carolinas by late day.  Scattered showers/tstms are
expected along and ahead of it, developing over the mountains around
mid-day and moving east across our cwa during the late afternoon
into early evening.  With 2000+ J/kg cape and 40+ kt of deep layer
shear forecast in the models, the environment would appear to
support at least isolated strong to severe tstms.  Given the
position of an old boundary along and north of hwy 64, look for the
best chance for such activity to be across the northern half of our

Short wave ridging behind the aforementioned short wave will provide
a break in the weather Sunday night into Monday morning, but the
next short wave moving through the longwave trough centered over the
Great Lakes will move across the Carolinas late day Monday into
Monday night, helping to push a weakening cold front across our
area.  This system will provide the next chance for showers and
tstms Monday afternoon through Monday night.

For the rest of the long term period, will keep pops near or above
climo each day as the aforementioned cold front will stall across
the region and a series of mid level short waves embedded in the
broad cyclonic flow move across the region.  Above normal temps
forecast through the period.


As of 125 AM Saturday...

A disturbance aloft will bring a chance of thunderstorms to most
areas this afternoon into the early evening. Otherwise, VFR
conditions are expected through 06z/Sunday.

Outlook: A series of upper level disturbances along the frontal zone
will nudge the front south into the area Sunday. There be a chance
of mainly late day storms on Sunday, and again on Monday through
Wednesday as a cold front slowly approaches from the west and
potentially stalls over the area.





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