Severe Thunderstorm Warning 33, NWS Raleigh, NC

Area Forecast Discussion
National Weather Service Raleigh NC
1035 AM EDT Fri Apr 19 2019

.SYNOPSIS...
Enhanced southerly flow will continue to strengthen this morning
between a Bermuda high to our east and a strengthening mid latitude
cyclone to our west. A related cold front will cross central NC
Friday night, spreading strong to severe thunderstorms. A mid and
upper level low will then linger over the central Appalachians and
middle Atlantic states through the weekend with surface high
pressure set to push in from the southwest on Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM Friday...

...Significant severe weather event likely late morning through
this evening...

Very few changes to the forecast this morning as a moderate risk
remains in place. Emergency Action plans should already be in
place. Know where your safe place is! If a warning is issued
for your location take shelter! Also, have multiple ways to
receive watches and warnings. Please check on your nearby
family members and neighbors to ensure they are also prepared.
The last time we had a moderate risk out for the area is
February 24th, 2016.

Ahead of an approaching squall line this morning discrete cells
will be likely with isolated tornadoes, damaging winds, and
hail all possible. Between 2 PM and 6 PM the squall line will
approach the Triad. Widespread damaging winds and isolated
tornadoes will be possible in the squall line. An isolated
strong to long track tornado can't be ruled out. Between 6 PM
and 10 PM the squall line will be crossing the triangle. The
squall line will then likely exit the eastern zones just before
midnight tonight.

Heavy rainfall will also be possible in any stronger storms and
across urban areas. If you observe water over the roadways,
PLEASE TURN AROUND. Heed all road closures by local, county, and
state officials.

Prev Discussion->
Confidence continues to grow with respect to the severe weather
potential Friday afternoon and evening. The latest update from the
Storm Prediction Center has upgraded the risk for all of
central North Carolina into a Moderate Risk (4 of 5) for severe
weather today, the first of it's kind in our forecast area in
over three years (Last time: February 24th, 2016). Primary
threats with today's setup are widespread damaging winds, hail,
tornadoes (possibly long-track tornadoes), and localized Flash
Flooding. This severe setup has the potential to be a very
dangerous situation, with several severe ingredients rarely seen
across the eastern seaboard coming together over portions over
central North Carolina. NOW IS THE TIME TO FINALIZE EMERGENCY
PLANS, REPLENISH YOUR EMERGENCY SUPPLIES IN YOUR SAFE PLACE, AND
ENSURE YOU HAVE A RELIABLE WAY TO RECEIVE WATCH/WARNING
INFORMATION. Once you are completely prepared, check on your
nearby family members and neighbors to ensure they are also
prepared and aware.

Overview: A strong mid to upper level trough is expected to deepen
this morning with a rapidly strengthening area of low pressure
beginning to migrate north and east out of the lower Mississippi
valley. East of the Low and associated cold front, a rapidly
increasing pressure gradient will work to enhance southerly flow
east of the Appalachians, further enhancing the WAA regime,
resulting in additional formation of pre-frontal convective showers
and storms in two primary areas (1) along the southeastern facing
slopes of the Appalachians via upslope flow just west of our
forecast area, and (2) across the eastern Sandhills and Coastal
Plain, spreading northeastward through the lunchtime hours. A few
rumbles of thunder will be possible in these showers, but the severe
threat should be minimal. Some uncertainty remains on the coverage
and impact of these pre-frontal WAA regime showers, but they will
likely establish several differential heating boundaries across
central North Carolina that will need to be watched closely for
future interaction with the more organized line of strong to severe
convection, likely to march east of the mountains after 12z/8am
Friday, this stronger line of storms will be the epicenter for
severe impacts, likely influencing the Triad region shortly
after (18z/2pm - 00z/8pm), the Triangle between (21z/5pm
- 02z/10pm) and points along and east of Interstate 95 through
roughly 04z/12am.

Environmental conditions ahead of the front look dangerous to say
the least, with efficient enough instability (1000 - 1500 J/KG ML
CAPE), dangerous shear (Bulk: 45 to 55kts; SFC -> 1km: 20 - 30kts)
and helicity values, and near record PWat values (1.6 inches
+). In terms of limiting factors, few exist, other than the
uncertainty of just how much surface heating will be allowed
throughout the day, however, with such a strong WAA regime in
place, the atmosphere should be allowed to destabilize pretty
efficiently without many breaks in the sunshine. The environment
looks prime for a very active and potentially destructive
weather day across the Carolinas. A quick overview of each
threat is below.

Winds: A wind advisory has been issued for areas along and east of
US-1, beginning at 11am this morning and continuing through 10pm.
This Wind advisory was issued to highlight the southerly flow
regime, which will likely produce sustained winds as high as 25mph
with intermittent gusts approaching 45 mph ahead of the frontal
boundary. In terms of the front/convection impacts, damaging winds
will remain the primary and most widespread impact thanks to the
predominantly linear storm mode and the line of storms passage
occurring during peak atmospheric heating. The strongest cells will
be capable of producing wind gusts as high as 60 to 70mph, with
locally stronger gusts possible in a wet-microbursts type regime.
This will be more than enough to cause damage to trees, unsecured
objects, and even some structures.

Tornadoes: High-resolution model ensembles continue to spit out some
alarming low and mid-level shear values across central NC which, if
realized, would easily support the formation of a few tornadoes
across our region. Still some uncertainty on favored locations at
this point, likely dependent in large part to the progression of
surface heating ahead of the line and the eventual strength and
placement of the meso-low and attendant triple point. With the
primary storm mode remaining linear in nature, often times, the
embedded Tornadoes in these storm structures can spin of very
quickly, which could greatly reduce lead time ability. Also,
ensemble mean updraft helicity values remain high, indicating that a
few long-track strong tornadoes can't be ruled out across the area.

Flash Flooding: With seasonably high precipitable water values
present and already saturated soils abundant across central NC,
Flash Flooding will certainly be a concern again with this system,
especially in and around urban centers. Have decided against a Flash
Flood Watch for now, as I think the primary threat here is more
centered within urban centers, however, a future watch issuance may
be required down the road. The Weather Prediction Center has placed
most of central NC in a Slight Risk (2 of 5) for excessive rainfall.
Areas that see training storms will be of primary concern.
Eventually, the 1 - 1.5 inch areal average QPF with this system will
transition into the already swollen rivers/lakes, causing additional
or at least prolonging river flooding across central NC into the
weekend. This is generally supported by both GEFS/NAEFS Ensemble
River Forecasts, which continues to advertise additional flooding
along the Neuse and Haw Rivers through the weekend, possibly lasting
into next week.

Hail: With only modest mid to upper-level lapse rates present, large
hail 1"+ shouldn't be commonplace. However, with the parent low not
too far displaced from the region, and the possibility of some
sustained updrafts, can't completely rule out a few storms capable
of producing some isolated quarter to half-dollar sized hail
stones.

A diminishing chance of showers will linger overnight, as we remain
under the influence of the dynamic upr low/trough, but any severe
risk should move east of cntl NC by 10-11 PM. Post-frontal flow will
also be swly, so the incoming air mass will not be particularly
cool, and instead characterized by lows generally in the low-mid
50s.

&&

.SHORT TERM /SATURDAY/...
As of 320 AM Friday...

The closed mid/upper low over the southern Appalachians will jog
slowly ENE across the southern Mid-Atlantic States through Sunday.
As the core of the cold(-20 to to -22 C) temps aloft pivots NE moves
through the area, isolated to widely scattered showers are expected
mainly across the northern portions of the forecast area where the
deeper moisture extends. With the core of the cold air aloft and
associated cloud cover/moisture centered over the area, expect below
normal temps through the weekend. Highs Saturday and Sunday
generally in the 60s, potentially cooler in the mid to upper 50s
across the northern portions where the best chance of showers exist.
It will be breezy on Saturday as well with gradient winds of 20 to
25 in the mixed layer. Lows in the 40s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
As of 320 AM Friday...

Heights aloft rebound in the wake of the low lifting up the Mid-
Atlantic and New England Coast on Monday with shortwave ridging
building across the area on Tuesday. At the surface, weak surface
high pressure centered over the GOM will briefly build north over
the area Monday and Monday night and will shift offshore on Tuesday
with the development of a lee side sfc trough across western
portions of the state. Convective rain chances return Wednesday and
Wednesday night as a northern stream shortwave trough passage
through the NE US and Mid-Atlantic region will drive a cold front SE
into the Carolinas. Front looks to push south of the area by
Thursday morning, with mostly dry conditions on Thursday.
Significant rain chances look to hold off until Friday and possibly
even into the weekend, depending on the eastward progression of yet
another vigorous storm system across the southern CONUS.

Near seasonable high temperatures in the mid to upper 70s on Monday
will warm into the lower 80s to mid 80s Tuesday and Wednesday in
advance of the cold front. Temperatures cool return to more
seasonable temps behind the cold front on Thursday.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
As of 630 AM Friday...

24 hour TAF period: MVFR conditions continue across all TAF sites as
of 11z/7am Friday. Expecting aviation conditions to remain MVFR to
IFR for much of the day with some localized improvement not out of
the question in between lines of convection. Expect intermittent
showers to begin filling in rapidly after sunrise, especially at
KFAY/KRWI/KRDU. Otherwise, southerly surface sustained winds should
remain elevated, likely between 10 - 15kts with gusts becoming more
frequent/intense after sunrise, reaching into the 30 - 40kt range by
lunchtime, especially across the eastern TAF sites.

The big forecast question will be the timing and location of the
showers and thunderstorms, of which two rounds are expected. The
earlier showers and storms will occur mainly at KRDU, KFAY and KRWI
in the 10Z-16Z range, ahead of the more pronounced and much stronger
line of storms. The second round will push across central NC from
west to east between 18Z and 03Z or so. Best guess of timing is as
follows; 18Z-22Z at KINT and KGSO, 19Z-02Z at KFAY and 20Z-03Z at
KRDU and KRWI. These storms could be strong to severe with the
chance of producing wind gusts to 45 kts or more and possibly
tornadoes. Expect the usual reduced visbys and cigs to accompany
them as well, possibly reaching LIFR CATs a time or two.

Looking ahead: A cold front will cross cntl NC early Fri night, with
a wind shift to swly and continued breezy conditions for much of the
night. In such, somewhat atypical regimes of post-frontal swly flow,
low level drying is not as significant as the climatologically more
typical wly or nwly post-frontal flow regimes; and as such, some
patchy MVFR ceilings may linger through early Sat. Otherwise, the
lingering presence of a mid-upr level low in the vicinity of the
Appalachians will maintain a risk of mainly diurnal showers and
storms Sat-Sun. -MWS

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 10 PM EDT this evening for NCZ009>011-
026>028-041>043-077-078-085-086-088-089.

&&

SYNOPSIS...Haines/JM
NEAR TERM...Haines/JM
SHORT TERM...CBL
LONG TERM...CBL
AVIATION...JM/MWS

Hazardous Weather Outlook
National Weather Service Raleigh NC
1039 AM EDT Fri Apr 19 2019

NCZ007-008-021>025-038>040-073>076-083-084-201445-
Person-Granville-Forsyth-Guilford-Alamance-Orange-Durham-Davidson-
Randolph-Chatham-Stanly-Montgomery-Moore-Lee-Anson-Richmond-
1039 AM EDT Fri Apr 19 2019

...TORNADO WATCH 88 IN EFFECT UNTIL 5 PM EDT THIS AFTERNOON...

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Tornado Watch.

Winds on Friday will be quite strong well ahead of the storms.
Gusts between 30 and 35 mph from the south will be common.

Severe thunderstorms will be likely this afternoon and evening,
primarily between 12 PM and 10 PM. The main severe weather hazards
will be damaging straight-line winds, large hail, torrential
downpours, and a few tornadoes. An isolated strong and long track
tornado can't be ruled out.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed.

NCZ009>011-026>028-042-043-078-088-089-201445-
Vance-Warren-Halifax-Franklin-Nash-Edgecombe-Johnston-Wilson-Wayne-
Cumberland-Sampson-
1039 AM EDT Fri Apr 19 2019

...WIND ADVISORY IN EFFECT UNTIL 10 PM EDT THIS EVENING...

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

Severe thunderstorms will be likely this afternoon and evening,
primarily between 12 PM and 10 PM. The main severe weather hazards
will be damaging straight-line winds, large hail, torrential
downpours, and a few tornadoes. An isolated strong and long track
tornado can't be ruled out.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed.

NCZ041-077-085-086-201445-
Wake-Harnett-Scotland-Hoke-
1039 AM EDT Fri Apr 19 2019

...TORNADO WATCH 88 IN EFFECT UNTIL 5 PM EDT THIS AFTERNOON...
...WIND ADVISORY IN EFFECT UNTIL 10 PM EDT THIS EVENING...

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Tornado Watch.
   Wind Advisory.

Severe thunderstorms will be likely this afternoon and evening,
primarily between 12 PM and 10 PM. The main severe weather hazards
will be damaging straight-line winds, large hail, torrential
downpours, and a few tornadoes. An isolated strong and long track
tornado can't be ruled out.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed.

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