- Day Three
acus01 kwns 262001
Storm Prediction Center ac 262000
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0300 PM CDT sun Mar 26 2017
Valid 262000z - 271200z
..there is a moderate risk of severe thunderstorms across central
OK and far north-central Texas...
..there is an enhanced risk of severe thunderstorms across
central/eastern OK and North Texas...
..there is a slight risk of severe thunderstorms across portions of
the Southern Plains...
..there is a marginal risk of severe thunderstorms from central Texas
to the Ozarks...
..there is a marginal risk of severe thunderstorms across the upper
Numerous severe storms with very large hail, tornadoes, and damaging
winds are expected after 4 PM CDT especially across central and
eastern Oklahoma and North Texas through evening.
The overall forecast philosophy remains relatively unchanged, with
an expectation for severe thunderstorms to rapidly develop late this
afternoon along a dryline across central Oklahoma southward into
North Texas. Initial elevated convection that developed over central
Oklahoma early this afternoon continues to advance east/northeast in
tandem with a low-level jet. These cells may continue to briefly
pose a marginally severe hail threat, but are expected to weaken
with northeastward extent.
Farther southwest, despite pockets of stronger mixing, dew points in
the mid/upper 50s to lower 60s have streamed north ahead of the
dryline, resulting in MLCAPE values around 1000-1500 j/kg across far
southern Oklahoma and North Texas. As stronger large-scale ascent
continues to overspread this corridor, storms should expand in
coverage, with supercell modes capable of all very large hail,
damaging winds, and a few tornadoes. The most notable change with
this outlook is the expansion of higher hail and tornado
probabilities southward across North Texas. Recent visible satellite
imagery and hi-res guidance suggest a relative maximum in severe
potential near and perhaps just south of the Red River. Cells
developing to the west/southwest should mature as they enter this
corridor of relatively greater low-level moisture. For more
information on the threat, reference mesoscale discussion 335.
Previous discussion... /issued 1130 am CDT sun Mar 26 2017/
Embedded within a moderately strong belt of southern-stream
westerlies, a relatively compact shortwave trough over the
south-Central High plains at late morning will continue eastward and
reach the Ozarks by late tonight. Within the base of this trough,
12z upper-air analysis featured a 50 kt belt of mid/high-level (500
mb and above) southwesterly winds that extend from southern/eastern
nm into the Texas Panhandle/far western OK/southwest Kansas. Given that
less that 48 hours has passed since the prior system (now over the
midwest) at this general latitude/longitude, moisture
return/availability across the Southern Plains remains a Point of
uncertainty, especially regarding the magnitude of the tornado risk
in an otherwise very favorable early-Spring Southern Plains setup.
Beneath an eastward-advecting elevated mixed plume (sampled across
the south-Central High plains at 12z), surface observations feature
around 60f dewpoints into southern parts of dfw metroplex as of 16z.
These near-60f dewpoints should reach parts of south-central OK by
21z-00z. Visible satellite imagery shows a band of higher-level
cloud cover that will overspread the increasingly moist warm sector
this afternoon. While not typically a severe-favorable factor, this
cloud cover should at least partially shield the boundary layer and
somewhat deter mixing while otherwise supporting a gradual increase
in near-surface moisture through the afternoon/early evening.
Current trends/short-term guidance suggest this cirrus should
overspread/progress east of the dryline toward/after roughly 21z.
Ahead of the slow-eastward-mixing dryline, near-60f surface
dewpoints should generally result in around 1500-2000 j/kg of MLCAPE
by peak heating from south-central OK into western parts of North
Texas. Weaker near-surface destabilization is expected farther north
into northwest/north-central OK and extreme southern Kansas.
As forcing for ascent and deep-layer shear (effectively 40+ kt)
increase, late-morning thinking is that semi-discrete supercells
will begin to develop by mid-afternoon (around 21z/4pm cdt) across
west-central OK into western north TX, initiating just west of the
I-35 corridor. Potentially very large hail is likely along with at
least some tornado risk, which should at least somewhat increase
through 23z-01z toward/east of the I-35 corridor, especially across
south-central OK and far North Texas as low-level moisture continually
increases and low-level hodographs enlarge.
Sustained warm advection should contribute to an eventual clustering
and bowing of storms by late evening as storms persist generally
eastward especially across southeast OK and extreme northeast Texas.
Accordingly, damaging wind potential may increase for a time late
this evening before updraft/downdraft intensities wane overnight as
storms progress into Arkansas/arklatex vicinity.
..upper Ohio River valley...
A shortwave trough centered over northern/central Illinois late this
morning per water vapor satellite imagery will continue
east/northeastward today, with a weakening/opening trend expected
tonight. Moderately strong winds aloft (12z upper-air data and more
contemporary WSR-88D vwp data) just ahead of this trough will
overspread the upper Ohio River valley vicinity through the
afternoon/evening. Modest moisture (lower to middle 50s f surface
dewpoints aside), prevalent cloud cover and multiple ongoing bands
of showers suggest that overall destabilization should remain
limited. Even so, locally damaging winds, marginally severe hail and
possibly a brief tornado could occur presuming at least modest
diurnal destabilization. Parts of southern OH, northeast Kentucky into
western/northern WV currently appear most susceptible to a
severe-storm risk this afternoon/early evening.
acus11 kwns 262214
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 262213
Mesoscale discussion 0336
National Weather Service Storm Prediction Center Norman OK
0513 PM CDT sun Mar 26 2017
Areas affected...parts of central/eastern Oklahoma and north central
Concerning...Tornado Watch 86...
Valid 262213z - 262345z
The severe weather threat for Tornado Watch 86 continues.
Summary...severe thunderstorm potential will continue to increase
across parts of north central Texas into south central Oklahoma
through the 7-9 PM CDT time frame.
Discussion...discrete storm development is now underway across parts
of south central Oklahoma into north central Texas, where low-level
convergence has become locally enhanced near a pre-cold frontal
confluence zone in the vicinity of the dryline. Further
intensification is likely during the next few hours within a
strongly sheared environment characterized by at least modest
Even within a narrow corridor of relatively higher moisture content
ahead of the dry line, moisture remains somewhat marginal for
intense convective development. However, thermal profiles are
relatively cool at mid-levels with generally steep lapse rates that
appear quite favorable for severe hail in strongest storms.
A zone of enhanced mid-level forcing for associated associated with
a short wave impulse pivoting east of the south Central High plains
may augment storm development and perhaps support
consolidation/upscale growth of initially discrete storms into an
evolving line as early as the 00-02z time frame. As this occurs
potentially damaging wind gusts may become a more prominent threat.
Until then, large hail appears the primary severe threat. The
extent of the tornadic potential remains a bit more unclear, but the
leading edge of a corridor of better low-level moisture return that
now appears to be spreading across the Dallas/Fort Worth metroplex
may contribute to more favorable boundary layer conditions as it
gradually continues to advect northward into the Red River vicinity
through early evening.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 35509662 35619569 35019512 32999633 32299727 32569842