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LU9DCE > ALERT 20.11.19 07:03z 137 Lines 7810 Bytes #999 (0) @ WW
BID : 2607_LU9DCE
Read: GUEST
Subj: Storm Prediction Center 20 11
Path: HB9ON<IW2OHX<IR2UBX<DB0RES<DB0ERF<OK0NAG<OK0NBR<OK2PEN<N3HYM<N7HPX<
LU9DCE
Sent: 191120/0700Z 2607@LU9DCE.TOR.BA.ARG.SOAM LinBPQ6.0.19
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SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130
PM CST Tue Nov 19 2019
Valid 201200Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
ACROSS PARTS OF THE TEXAS SOUTH PLAINS...
...SUMMARY... A couple of strong storms are possible across parts
of the Texas South Plains this afternoon, which could pose at least
some risk for large hail or a strong wind gust.
...Synopsis... Downstream of amplified ridging within the
westerlies across the mid-latitude eastern Pacific into western
Canada, flow has split, with a closed mid-level low now in the
process of developing in the southern stream, near the central into
southern California coast. As a significant upstream short wave
approaches the ridge axis, the northern portion of the ridging is
forecast gradually shift across and east of the Canadian Rockies
during this period, with downstream troughing digging toward
Hudson Bay and the northern U.S. Plains. At the same time, the
southern branch low appears likely to shift inland across southern
California, before gradually weakening/broadening over the southern
Great Basin/Colorado Valley by 12Z Thursday. And the increasingly
deformed remnants of a preceding mid-level closed low are forecast
to continue accelerating northeastward across the southern Rockies
through the south central Plains and mid/lower Missouri Valley.
An influx of mid/high level moisture emanating from the lower
latitude eastern Pacific will precede the lead southern stream
impulse across and northeast of the southern Rockies. Models also
indicate that forcing for ascent will support at least modest
surface cyclogenesis from the lee of the Colorado Rockies into
parts of the Upper Midwest by the end of the period. This will be
accompanied by a strengthening southerly return flow across the
southern Plains toward the Upper Midwest. However, in the wake
of mid-level troughing shifting east of the mid/south Atlantic
Seaboard, boundary layer modification over the western Gulf of
Mexico is only slowly underway, and it appears that boundary layer
moistening inland into the lee surface trough will remain fairly
modest through at least this period.
...Southern Plains northward into Missouri Valley... Models are
suggestive that thunderstorm activity will generally occur in
response to elevated moisture return. Even this may be hindered
by precipitation from preceding higher-level convection, but
initially steep lower/mid tropospheric lapse rates, associated with
elevated mixed-layers, may still allow for at least weak CAPE and
thermodynamic profiles at least marginally sufficient for lightning.
Even in close proximity to the lee surface trough across the
central/southern high Plains, the extent to which cloud cover,
associated with low-level moistening beneath the capping elevated
mixed-layers, restricts boundary layer destabilization remains
unclear. This will considerably impact any severe weather potential,
as the operation NAM, for example, suggests that storms will remain
rooted above the boundary layer, where weak CAPE and cloud-bearing
layer shear will minimize severe weather potential, despite the
presence of rather strong lower/mid tropospheric wind fields.
With at least the Rapid Refresh continuing to indicate the possible
development of modest boundary-layer based CAPE across parts of
the Texas South Plains, low severe weather probabilities will
be maintained at least for now. However, even this risk may be
limited to an isolated storm or two, which could pose potential
for severe hail or a strong surface gust, as the southern stream
impulse overspreads the central/southern High Plains during the
mid to late afternoon.
...Arizona... As the exit region of a 70-90 kt 500 mb jet
overspreads Phoenix and the surrounding lower deserts, associated
mid-level cooling, forcing for ascent, and strengthening deep layer
shear could potentially contribute to an environment conducive to
an isolated supercell or two late this afternoon. However, model
forecast soundings continue to raise considerable uncertainty
concerning the evolving thermodynamic profiles, which currently
seem likely to only become very marginally favorable at best.
As a result, severe weather probabilities are being maintained at
less than 5 percent.
..Kerr/Cook.. 11/20/2019
SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1223
AM CST Wed Nov 20 2019
Valid 211200Z - 221200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM NORTH
TEXAS INTO THE ARKLATEX REGION...
...SUMMARY... A few strong storms are possible from north Texas
to the Arklatex Thursday night.
...North Texas through the Arklatex region...
Low-amplitude shortwave trough initially over the middle MS Valley
will accelerate through the Great Lakes as it interacts with a
southeast-advancing, northern-stream shortwave trough. Farther west
a synoptic upper low will move through the Southwestern States. A
significant vorticity maximum is forecast to move through the base
of this feature and into the southern Plains Thursday evening
and overnight. By 12Z Thursday a cold front will extend from a
low pressure area over the upper MS Valley, southwestward through
central OK into west TX. This boundary will advance southeast and
likely stretch from the lower Great Lakes into the lower MS Valley
and central and southwest TX by the end of the period.
Partially modified Gulf air with low to mid 60s F dewpoints will
return through the Southern Plains pre-frontal warm sector. But
widespread clouds and weak lapse rates should limit MUCAPE to at or
below 800 J/kg. Showers and thunderstorms are expected to develop
primarily along the southeast-advancing cold front with the arrival
of deeper ascent during the evening. Tendency should be for most
storms to be undercut by the front. However, a few storms based near
the surface will be possible along and just ahead of the front. The
approaching upper trough and resulting increase in the southwesterly
low-level jet will contribute to a kinematic environment favorable
for organized storms with 45+ kt effective bulk shear and 200-300
m2/s2 storm relative helicity. Some threat will exist for a few
strong storms and bowing segments capable of mainly damaging wind
and a brief tornado. However, tendency for most storms to be undercut
by the cold front and the marginal thermodynamic environment should
serve as limiting factors for a more robust severe event.
...West Texas...
A few instance of small to marginally severe hail will be possible
with storms developing in post-frontal zone and in closer proximity
to the upper low circulation where colder air aloft will support
steeper (6.5-7 C/km) mid-level lapse rates. However, overall threat
will likely remain limited by weak instability.
...MAXIMUM RISK BY HAZARD... Tornado: 2% - Marginal Wind:
5% - Marginal Hail: <5% - None
..Dial.. 11/20/2019
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Hark, Hark, the dogs do bark The Duke is fond of kittens He likes to take
their insides out And use them for his mittens
From "The Thirteen Clocks"
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