Severe Thunderstorm Warning 157, NWS Raleigh, NC

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
405 PM EDT Tue Sep 29 2020

.SYNOPSIS...
A cold front will move across central NC tonight and then off the
Carolina coast Wednesday morning. High pressure will build into the
area on Wednesday. A cold front will move across the area on
Thursday and Thursday night with chilly high pressure building into
the region on Friday into the weekend.
&&

.NEAR TERM /TODAY AND TONIGHT/...
As of 320 PM Tuesday...

Latest surface analysis shows the cold front has pushed into the
Foothills and is entering the western Piedmont with a west to
northwest wind at Mount Airy, Statesville, and Charlotte. A
southerly low level flow is noted east of the front across central
and eastern NC. Visible satellite imagery shows a decent amount of
sunshine mixing in the with strato-cumulus across the eastern
Piedmont and Coastal Plain. Latest meso-analysis shows a weakly
unstable airmass with MLCAPE values of around 600 to 1300 J/Kg
across central NC with dew points in the the upper 60s to lower 70s.
Mid-level lapse rates are rather anemic and range between 5.5 and 6
deg/Km. Precipitable water values continue to increase from the
south and range between 1.5 to 2.0 inches and should further
increase this evening.

As the vigorous upper trough axis approaches and becomes neutrally
tilted, a belt of 75+ kts winds at 500 hPa will approach and then
move across western and central NC late this afternoon and evening
pushing the surface front eastward. A weak and broad surface wave
will develop along the front in response to the upper disturbance
and lift north across the western Piedmont late this afternoon and
evening. A band of showers and thunderstorms just ahead of the cold
front will move east this evening with individual cells along the
front racing northeast. Given the weakly unstable air mass, strong
mid and upper level flow, and notable forcing for ascent, some
strong to severe thunderstorms are possible. The primary threat will
be damaging winds. With the upper flow parallel to the front and
potential for some cells to repetitively hit the same locations,
localized flooding is possible. Given the potential for a stronger
storm to sustain its updraft and capture the shear aloft and some
slightly backed surface flow, an isolated tornado is possible. The
greatest severe weather threat will be from 4 to 7pm in the Triad, 6
to 10pm in the Triangle and Fayetteville area and 8 to 11pm in
Goldsboro and Rocky Mount.

A trailing band of showers behind the front will push east as the
upper trough axis moves into central NC by Wednesday morning. Mainly
dry conditions should arrive in the Triad by around midnight and the
Coastal Plain before daybreak. Lows will range in the lower 50s in
the Triad to the lower 60s across the southeast. -Blaes

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 335 PM Tuesday...

The cold front will reach the coast by daybreak Wednesday and then
move further offshore during the day. Weak high pressure centered
across the northern Gulf of Mexico will extend into the Carolinas.
While the initial elongated short wave trough will move across
central NC on Wednesday morning, broad eastern U.S. troughing will
persist through Wednesday night with a couple of weak disturbances
moving across the region. Generally fair weather is expected with
some lingering low level moisture and clouds across the Piedmont and
Coastal Plain during the morning along with a few periods of some
high clouds. Highs will range in the upper 60s to low 70s and lows
in the low to mid 50s. -Blaes &&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 405 PM Tuesday...

A short wave trough extending from the Upper Great Lakes
southwestward into the Central Plains on Thursday will slightly
amplify south and easterly as it moves over our region on Friday.
The short wave trough will then exit the region to the northeast
Friday/Friday night. Saturday a dry short wave will move quickly
along the long wave trough axis across Central NC. After the trough
moves over the region, south-southwesterly flow aloft will develop.
Sunday night a shortwave will move across the area with a zonal flow
in its wake through the rest of the forecast period.

At the surface, high pressure over the Northern Plains Thursday
morning will quickly move southeast near the Lower Mississippi
Valley and then follows a cold front over central NC Thursday night.
This front could produce some precipitation across the NW Piedmont,
with high confidence that other areas will remain dry. As the cold
front moves off shore by early Friday afternoon, high temperatures
will remain around 10 degrees below normal and remain below normal
for the rest of the forecast period. Friday night/Saturday morning
winds will be northerly bringing in cool and dry air and this will
be the coldest temperatures of the forecast period (lows will be in
the mid to upper 40s).

Sunday afternoon into Monday evening there is a slight possibility
of precipitation across most of the region as a coastal low slowly
moves up the coast from Florida and a upper level short wave moves
across NC. While most recent runs (29/12z) of the GFS and ECMWF both
have precipitation developing over the area, only the ECMWF model
deepens the coastal low offshore to create a greater area of
precipitation over NC. After the low exits the region,Tuesday is
expected to be dry.

&&

.AVIATION /18Z MONDAY THROUGH SUNDAY/...
As of 240 PM Monday...

24 hour TAF period: A mix of VFR and MVFR conditions with
restrictions in areas of strato-cumulus early this afternoon will
give way to a period of widespread adverse aviation conditions as a
band of showers and thunderstorms sweeps east across central NC late
this afternoon and through the evening hours. A period of heavy
rain, reduced VSBYS and CIGS along with locally gusty winds can be
expected with the band of convection. The most hazardous conditions
are expected at KINT and KGSO from 20 to 23Z, KRDU and KFAY between
22 and 02Z and KRWI from 00 to 03Z. A period of light to moderate
rain is expected to continue for a few hours behind the front before
conditions become VFR from west to east late tonight. Some shallow
stratus may linger into the daybreak hours on Wednesday before VFR
conditions and west to northwest winds at around 10 kts arrive for
the late morning and afternoon.

Looking ahead: A period of predominately dry and fair weather is
expected for late Wednesday through the weekend. A dry cold front
will move across the area Thursday and Thursday night, otherwise
high pressure will extend across the region.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
.none...

&&

SYNOPSIS...Blaes
NEAR TERM...Blaes
SHORT TERM...Blaes
LONG TERM...CC/JJT
AVIATION...Blaes

Hazardous Weather Outlook
National Weather Service Raleigh NC
104 PM EDT Tue Sep 29 2020

NCZ007>011-021>028-038>043-073>078-083>086-088-089-301715-
Person-Granville-Vance-Warren-Halifax-Forsyth-Guilford-Alamance-
Orange-Durham-Franklin-Nash-Edgecombe-Davidson-Randolph-Chatham-Wake-
Johnston-Wilson-Stanly-Montgomery-Moore-Lee-Harnett-Wayne-Anson-
Richmond-Scotland-Hoke-Cumberland-Sampson-
104 PM EDT Tue Sep 29 2020

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...This afternoon and tonight.

A band of showers and thunderstorms will pose a risk of strong to
locally damaging wind gusts, localized flooding and an isolated
tornado late this afternoon and evening. The greatest severe weather
threat will be from 4 to 7pm in the Triad, 6 to 10pm in the Triangle
and Fayetteville area and 8 to 11pm in Goldsboro and Rocky Mount.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

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