Severe Thunderstorm Warning 92, NWS Raleigh, NC

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
1230 PM EDT Thu Jun 20 2019

.SYNOPSIS...
A vigorous mid level disturbance will cross the Carolinas this
afternoon. A surface cold front will cross the region tonight,
followed by high pressure and a drier and more stable air mass for
Friday into Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1040 AM Thursday...

...Severe thunderstorms appear likely this afternoon through early
evening across central NC...

A significant early summer severe weather event appears likely this
afternoon through early evening across central NC. The main severe
weather hazards will be damaging wind gusts as high as 65 mph, large
hail and frequent lightning strikes.

12Z upper air analysis depicts a decent low-mid level jet crossing
the Deep South/TN Valley with a 40-45kt jet crossing MS/AL this
morning and a 40kt mid level jet overhead. The kinematics are in
place to support organized convection with effective bulk shear
expected to be 35-40kts this afternoon/early evening. Strong
insolation this morning through early afternoon will prime the
atmosphere with surface based CAPE projected to be as high as 3000
j/kg and mixed layer CAPE 1200-1500 J/kg. With sfc temperatures
warming into the low-mid 90s, anticipate low level lapse rates on
the order of 8.5-9 deg C/km, highly supportive of damaging
convective wind gusts. Additionally, model soundings for this
afternoon depict CAPE in the favored hail growth zone as high as 700-
800 J/kg. This suggest a decent threat for large hail along with
frequent cloud-to-ground lightning strikes. Finally, synoptic lift
will be increasing this afternoon as central NC will be in the right
entrance region of a 110+kt upper jet lifting newd across the
central Appalachians.

Expect main convective mode to be broken bands of convection with an
isolated supercell or two possible out ahead of the banded
convection.

Current PoP forecast appears to have a good handle on the coverage.
May adjust the timing (slightly slower than earlier forecast) though
the bulk of the convective activity will occur in the 4 PM-9 PM time
frame.

A broken band of convection will depart our eastern periphery prior
to 03Z. A surface cold front will drift across the region overnight
through early Friday. Cannot rule out an isolated shower or two
along the front though the atmosphere will be drying out in the
mid/upper levels of the atmosphere after 06Z.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 515 AM Thursday...

A longwave ridge will amplify across the MS Valley, with related
nwly flow aloft developing across NC through early Sat. Associated
height rises aloft and subsidence will yield the development of a
strong capping inversion that should suppress convective development
through most of the period. The exception, however, will be the
potential remnants of upstream convection/MCSs in nwly flow, which
may cross the Appalachians and affect the NC Foothills and NW
Piedmont in a weakened state by daybreak Sat. At the very least
convective blow-off/mid to high-lvl cloudiness will cause skies to
become mostly cloudy to cloudy through the same time, after a sunny
Fri. It will be less hot, and near average, in post-frontal high
pressure, with highs ranging from mid 80s across the nrn Piedmont to
90-92 degrees across the srn Piedmont and Sandhills, and with low
temperatures in the 60s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 1230 PM Thursday...

Not much structural changes to the long term portion of the
forecast. 06z models have trended a bit further east with the
possible MCV type system, forecast to spill southeast out of the
Ohio valley, crossing central NC around peak heating Saturday. Have
trended POPs further east in response, with showers/storms likely
lingering into early Sunday, especially across the western zones. If
this scenario were to come true, temps would struggle to reach the
80 degree mark across much of the area due to persistent cloud cover
and lingering precipitation. With inherent uncertainties in MCV type
forecasts 48 hours+, have sided closer to climatology with my high
Ts on Saturday, topping out in the mid to upper 80s (north) with low
90s (south). This could, however, be on the magnitude of 6 to 10
degree too warm depending on the ultimate track and intensity of the
MCV. Elsewhere, have trended a bit drier early next work-week with
mid to upper level ridging winning out. Most of next week, however,
the mid Atlantic region will remain in the battle ground region
between the western periphery of the ridge (centered to our SE) and
the best upper-level jet support (to our N). Thus, slight changes in
either direction could shift the forecast considerably.

Previous valid discussion...

Saturday morning a strong upper level low will be located over
Newfoundland and Labrador with mid-level heights quickly rising over
the Great Lakes. For central North Carolina a leftover cold front
will be stalled near the SC/ NC border. The main question for
Saturday morning remains vorticity that is scheduled to break off
from an upper level low located near ND. The overall thinking is for
this wedge of PV to dive southeast towards NC/ SC Saturday. The
ECMWF, GFS, NAM, and CMC all show this happening in one form or
another. The general track of the PV and some type of MCS appears to
be anywhere from GA to NC. The current predictability with this
event remains extremely low at this point, so for now have kept
mostly chance PoPs Saturday.

Saturday evening into Sunday morning another weak disturbance is
forecast to push across the area in the NW flow with even lower
confidence on the eventual track and strength of this wave. Monday
into Tuesday mid-level ridging will move overhead as the next
shortwave approaches the Great Lakes. Out ahead of this next wave
precipitation chances will decrease slightly as mid-level ridging
temporarily increases. Forecast soundings for both days show a low
level CAP forming with a skinny CAPE profile. 850 mb temperatures
Monday and Tuesday also rise to around 20 degrees C which will
support high temperatures in the low to mid 90s. The above likely
means that Monday and Tuesday will be relatively warm with lower
chances of convection. Tuesday into Wednesday the wave will eject
northeast into Canada with temperatures continuing above normal for
central NC.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
As of 800 AM Thursday...

Patches of MVFR stratus will lift and scatter through 14Z. VFR
conditions, and a breezy and gusty swly surface wind, will otherwise
prevail through early this afternoon. However, the approach of a
vigorous mid level disturbance will cause initially discrete storms
to develop over the wrn Carolinas between 16-19Z. These storms will
subsequently spread enewd across cntl NC, with some merging into
fast-moving clusters with 45-60 kt surface wind gusts, and others
remaining discrete with large hail, through 00Z. A cold front will
cross the region late tonight, with following nwly winds and drier
and more stable air that will yield VFR conditions through Sat.

Outlook: NW flow aloft, and low level moisture return into a
lingering frontal zone over the srn Appalachians and Carolinas, will
direct clusters of showers and storms across the region this weekend
into early next week.

&&

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

&&

SYNOPSIS...MWS
NEAR TERM...WSS
SHORT TERM...MWS
LONG TERM...JJM/BAH
AVIATION...MWS

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Special Weather Statement
National Weather Service Raleigh NC
123 PM EDT Thu Jun 20 2019

NCZ021-201815-
Forsyth NC-
123 PM EDT Thu Jun 20 2019

...A STRONG THUNDERSTORM WILL MOVE INTO AND AFFECT FORSYTH COUNTY
UNTIL 215 PM EDT...

At 121 PM EDT, Doppler radar was tracking a strong thunderstorm over
Yadkinville, moving east at 45 mph. This storm may strengthen,
requiring a future Severe Thunderstorm Warning Issuance.

Nickel size hail, wind gusts of 50 to 55 mph, and heavy rainfall
will be possible with this storm.

Locations impacted include...
Winston-Salem, Kernersville, Clemmons, Bermuda Run, Huntsville,
Lewisville, Walkertown, Rural Hall, Pfafftown and Belews Creek.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Seek shelter in a nearby building or vehicle. Wind gusts as high as
50 mph are capable of knocking down small or weakened trees and
blowing around trash cans, potted plants, lawn furniture and other
light outdoor objects.

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

If on or near Belews Lake, get out of the water and move indoors or
inside a vehicle. Remember, lightning can strike out to 10 miles
from the parent thunderstorm. If you can hear thunder, you are close
enough to be struck by lightning. Move to safe shelter now! Do not
be caught on the water in a thunderstorm.

&&

LAT...LON 3611 8051 3612 8046 3614 8044 3621 8045
      3622 8043 3624 8045 3626 8045 3626 8004
      3601 8005 3603 8021 3600 8022 3600 8032
      3597 8040 3599 8042 3601 8042 3606 8046
      3604 8049 3605 8051 3609 8052
TIME...MOT...LOC 1721Z 275DEG 37KT 3614 8068

MORROW