LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1241 AM CDT Thu May 04 2023
Valid 041200Z - 051200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL
TEXAS TO OKLAHOMA AND FAR SOUTHERN KANSAS...
...SUMMARY...
Severe thunderstorms capable of large hail, strong/damaging wind
gusts, and a couple of tornadoes are possible across parts of the
southern Great Plains this afternoon and evening. More isolated
strong to severe storms capable of severe wind and large hail are
possible across parts of the central Plains and the Pacific
Northwest.
...Synopsis...
Omega blocking over the southern/central Plains is expected to break
down over the next 24 hours as a sub-tropical shortwave trough,
noted over Baja California and northwest Mexico in latest
water-vapor imagery, shifts northeast. This will result in modest
lee cyclogenesis over the TX Panhandle and northwest OK this
afternoon, which will help northward moisture advection through the
day, and the establishment of a warm sector ahead of the approaching
ascent. A weak surface trough/stationary front across the central
Plains will likely focus thunderstorm development this afternoon
within an otherwise weakly forced environment. Across the Pacific
Northwest, broad ascent over eastern WA and northern ID may support
a few isolated strong to severe thunderstorms.
...Southern Plains...
Mid 50s to upper 60s dewpoints, currently spread across central to
southern TX, are expected to gradually advect north into central OK
as the lee cyclone deepens through the day. Broad ascent ahead of
the approaching shortwave trough is noted in recent satellite
imagery, and is expected to maintain a swath of high-level cloud
cover over the region. This will modulate diurnal warming over much
of TX/OK/KS to some degree, but temperatures warming into the upper
70s should be adequate to support a corridor of around 1000 J/kg
MLCAPE across central OK with increasing buoyancy into central TX.
40-50 knot mid-level flow associated with the wave should overspread
much of the region, and somewhat weak low-level flow will result in
elongated, nearly straight, hodographs across the warm sector.
While the environment appears adequate to support organized
convection, storm coverage and mode remain uncertain, especially
across north TX into OK and far southern KS. Overnight convection
ongoing across the TX Panhandle may persist into central OK/north TX
by the start of the period. This could reinforce the existing
diffuse warm frontal zone across north TX, which could then be a
focus for convective initiation this afternoon. Several CAMs also
depict sufficient isentropic ascent ahead of the wave for broad rain
showers/isolated elevated thunderstorms during the morning hours,
which may hinder destabilization. Predictability of these scenarios
is low given spread in high-res model solutions. Thunderstorm
initiation appears most probable along a sharpening dryline across
western OK to central TX where initial storm modes should be
discrete to semi-discrete supercells given off-boundary storm
motions/deep-layer shear vectors. While confidence in exact
evolution of the warm sector is somewhat low across OK/KS, backed
low-level winds in the vicinity of the surface cyclone may support
adequate low-level shear for a couple of tornadoes if discrete
supercells can be achieved.
...Central Plains...
Although moisture advection into the central Plains is expected to
be modest, ensemble guidance shows a reasonably strong signal for
dewpoints in the low 50s to reach NE by late afternoon. This,
coupled with 8 C/km mid-level lapse rates, should be adequate for a
swath of MLCAPE values approaching 1000 J/kg. The central Plains
will be well displaced from stronger synoptic ascent to the south,
but focused lift along a surface trough/stationary front should
support thunderstorm development by late afternoon. Effective bulk
shear values near 25-30 knots will allow for organized convection,
but mean-wind vectors and storm motions roughly along the initiating
boundary may favor upscale growth, limiting the coverage/duration of
the severe threat.
...Pacific Northwest...
Recent surface observations are sampling a pocket of dewpoints in
the upper 40s to low 50s across eastern WA into adjacent areas of
OR/ID. This moisture will support a regional pocket of 500-1000 J/kg
MLCAPE this afternoon, which may allow for a few more intense cells
as lift ahead of a broad West Coast low overspreads the region.
While the spatial coverage of this threat is expected to be limited,
adequate deep-layer shear may allow for robust convection capable of
posing a hail/wind risk. This scenario appears to be captured well
by latest CAM ensembles, which show a somewhat stronger UH signal
across the region compared to previous days.
..Moore/Broyles.. 05/04/2023
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