700
ACUS01 KWNS 061945
SWODY1
SPC AC 061943

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0243 PM CDT Mon May 06 2024

Valid 062000Z - 071200Z

...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS FROM CENTRAL AND
NORTHERN OKLAHOMA INTO SOUTH-CENTRAL KANSAS...

...SUMMARY...
A regional outbreak of severe weather with multiple intense (EF3+),
long-tracked tornadoes, as well as very large hail and severe
thunderstorm gusts, is expected over parts of the south-central
Plains from this afternoon through evening.

...20Z Update...

Recent surface analysis places a low over far southeast MT, with an
occluded front arcing southeastward to the triple point near far
southwest SD/far north-central NE Panhandle. A cold front extends
southward from this triple point across far eastern CO and then back
south-southwestward across eastern NM. A dry line also extends
southeastward from this triple point into south-central NE before
arcing back more southward/south-southwestward across western KS,
the eastern TX/OK Panhandles, and into TX Trans-Pecos.

Thunderstorms developed quickly along the dryline from south-central
NE into north-central KS, as well as ahead of the occluded front in
southwest SD. General expectation outlined in the previous
discussion (appended below) remains, with thunderstorm coverage and
intensity expected to increase as the shortwave trough continue to
progress northeastward into the central High Plains. Eventual
organization into more of an eastward-progressing convective line is
anticipated, with the resulting line moving across southern NE and
northern KS. Primary threat with this line will be severe wind gusts
up to 80 mph. Some line-embedded QLCS tornadoes are also possible,
particularly as the line enters southeast NE and northeast KS later
this evening amid a strengthening low-level jet. STP values from 3
to 5 appear likely across southeast KS ahead of the line this
evening.

Farther south (from south-central/southeast KS into most of OK), the
airmass continues to destabilize ahead of the dryline. Upper 60s
dewpoints are now approaching the KS/OK border, with low 70s
dewpoints now moving into central OK. Visible satellite imagery
continues to show relatively limited vertical development across OK,
with some stable undulations noted as well, both of which are
indicative of a capped airmass. This is verified by the 18Z OUN
sounding, which showed that notable capping remains in place. This
capping is a few degrees higher than estimated by the 12Z guidance.
Even so, deepening cumulus has been noted along the dryline across
the eastern TX/OK Panhandle, and recent initiation has occurred in
southwest KS, both of which suggest initiation of additional storms
farther south is probable around 20 to 22Z.

Overall scenario for a potentially volatile afternoon and evening
remains for south-central KS into western and central OK. An
isolated storm could also develop in far northwest TX. Supercells
capable of all severe hazards are still expected, with the
environment becoming more favorable with time and eastern extent.
All guidance continues to indicate STP values around 10 are likely
in the 00 to 06Z timeframe across western and central OK. Giant hail
up to 4" in diameter, severe gusts up to 80 mph, and long-track,
intense tornadoes are all possible. Particularly Dangerous Situation
(PDS) Tornado Watch #189 was recently issued to cover this threat.

..Mosier.. 05/06/2024

.PREV DISCUSSION... /ISSUED 1102 AM CDT Mon May 06 2024/

...NE/KS/OK to north TX...
Water-vapor imagery late this morning shows a potent mid- to
upper-level trough/low over the central Rockies with a speed max
moving through the base of the trough and into the southern and
central High Plains.  This negatively tilted mid level trough will
continue northeast to near the Black Hills by this evening while its
southern portion overspreads the KS/OK corridor.  The 12z Amarillo,
TX raob showed the leading edge of stronger 700-600 mb southwesterly
flow nosing eastward into the High Plains.  A cyclone near the NE
Panhandle this morning will deepen as it moves north-northeast to
the SD/ND border early Tuesday morning.  An associated Pacific front
will push east into the High Plains and overtake the northern
portion of the dryline across parts of the central High Plains this
afternoon into this evening.  Farther south, a dryline will mix east
into western OK by late this afternoon with a broad moist/unstable
warm sector across the southern Great Plains and becoming
increasingly pinched in spatial width farther north into the
north-central Great Plains.  An attendant warm front will advance
northward from OK into the lower MO Valley by early evening and
later into the mid MS Valley.

Visible satellite imagery shows considerable low stratus and
stratocumulus from north TX into the central Great Plains.  The 12z
Fort Worth, TX raob sampled the richer low-level moisture (15 g/kg
lowest 100mb mean mixing ratio) compared to areas farther north.
Surface analysis late this morning shows rapid northward transport
of moisture into OK with 65-70 deg F dewpoints advecting northward
through OK to the KS border.  This plume of richer moisture will
continue northward today beneath an EML and lead to moderate
destabilization over NE with a very to extremely unstable airmass
forecast to develop farther south over the southern half of KS into
OK and adjacent north TX.

Initial thunderstorm development is likely as the upper forcing
impinges on the northwestern periphery of the moist/unstable sector
across the central High Plains (western KS/NE) and northward into SD
with time.  Steep 700-500 mb lapse rates and strengthening flow
becoming more meridional with time will favor organized storms,
including supercells and bands of storms with an associated isolated
to scattered risk for hail/wind and perhaps a few tornadoes.
Farther south, the erosion of the cap is expected initially over the
KS portion of the dryline and perhaps into northwest OK by the mid
afternoon.  Strengthening flow through the column combined with
strong to extreme buoyancy (2500-4500 J/kg MLCAPE) --from I-70 in
central KS to I-40 in central OK-- will strongly favor supercell
development.  Strong upper-level diffluence across the central Great
Plains and intensifying southwesterly to westerly 250-mb flow, which
will result in very long hodographs, will strongly favor discrete
storm modes, at least initially.  Large to giant hail (3-4 inches in
diameter) is possible with the more robust supercells.  The LLJ is
forecast to be strongest over KS northward into the north-central
Plains through 21z.  During the 21-00z timeframe, the flow
associated with the LLJ will strengthen over OK acting to enlarge
hodographs.  Climatologically large combinations of deep-layer
shear, buoyancy, and SRH will result in extreme values of composite
indices (STP 6-12) during the 22z-06z timeframe across the Moderate
to High Risks.  Several discrete supercells are expected to traverse
across a large portion of the Moderate and High-Risk equivalent
tornado probabilities.  Tornadoes, some of which can be intense
(EF3+), are forecast late this afternoon and well into the evening.
Some model guidance shows regenerative supercell development across
central OK this evening.  Have extended the High Risk slightly
farther south to account for this possibility.

...Lower MO Valley/Ozarks/mid MS Valley late...
As greater storm coverage and merging occurs this evening across KS
into northern OK, large-scale ascent will further promote upscale
growth into a severe squall line across eastern KS and moving into
the lower MO Valley and western part of the Ozarks.  Have upgraded
severe-wind probabilities and this resulted in a slight spatial
extension of the Moderate Risk to the east across southeast
KS/northeast OK.  A severe risk will probably continue east to the
MS River overnight with an attendant wind risk and perhaps an
isolated risk for a tornado.

...Northern Plains...
No appreciable change from previous forecast thinking for severe
potential across the northern Plains.  A prefrontal corridor of
favorable moisture and diurnal destabilization will become quite
narrow with north and northwestward extent.  Nonetheless, it should
support scattered thunderstorms in northward-shifting plume, curving
from the western Dakotas (and perhaps parts of extreme northeastern
WY and southeastern MT) southeastward to central NE, and connecting
to the northern part of the central Plains severe threat.  With
strong large-scale lift, cooling aloft, rapidly weakening MLCINH,
and robust low-level mass response/shear expected ahead of the
ejecting shortwave trough, confidence is growing that an arc of
strong-severe thunderstorms will develop, offering large hail,
severe gusts and at least marginal tornado potential.  Even with 50s
to low 60s F surface dewpoints and limited time for substantial
diabatic heating, the net steepening of low/middle level lapse rates
should support peak MLCAPE near or slightly above 1000 J/kg.  Deep
shear may not be particularly intense in a regime of strongly
difluent flow aloft, but still should be adequate for supercell
potential given large lowest-km hodographs possible, and effective
SRH in the 150-300 J/kg range.  Severe potential should diminish
after about 00Z.

...West-central/southwest TX...
Model guidance continues to indicate isolated thunderstorms are
possible in mid/late afternoon along/ ahead of the dryline over
northwest to southwest TX.  Although large-scale/mid-upper forcing
will be negligible (displaced to the north), any pockets of
relatively persistent/maximized low-level lift may aid in local
erosion of the cap and convective initiation.  Mid/upper 60s to low
70s F surface dewpoints and steep low/middle-level lapse rates will
contribute to 3000-4000 J/kg MLCAPE amidst enough deep shear for
supercells.  A conditional significant-hail and marginal tornado
threat exists with sustained supercell(s) -- if any can form.
Coverage concerns preclude more than marginal categorical outlook at
this time.

...Mid South/TN Valley into the southern Appalachians...
A mid-level shortwave trough over TN this morning will continue to
move east into the southern Appalachians today.  An enhanced belt of
westerly mid-level flow accompanying this impulse will overspread
this general region.  In wake of decaying morning convection over
the southern Appalachians, ample heating of a moist boundary layer
will result in moderate destabilization by early-mid afternoon.
Storm redevelopment is forecast this afternoon along and north of a
trailing/diffuse convective boundary over the TN Valley.  Scattered
thunderstorms will probably develop by early to mid afternoon.
Effective shear magnitudes 25-30 kt will support  some organization
in the form of clusters and perhaps transient supercells.  Marginal
Risk equivalent severe probabilities have been added to highlight
this isolated severe threat.

$$