03/06/2017 Severe Weather Threat

Primarily focused in the Ozarks region, and along Missouri I-44, mid to late afternoon. Large hail, wind and few tornadoes likely. Keep your head on a swivel if you're traveling through this area and things start boiling. Even outside of the Enhanced risk area, hail and high winds will accompany any discreet storm cells that can develop ahead of the advancing dry line. Spring is coming and these early season storms are previews of things to come.


From the Springfield, MO Wx office ...

.DAY ONE...Today and Tonight.

Weather hazards expected...

Elevated Tornado risk.
Elevated Hail risk.
Elevated Thunderstorm wind damage risk.
Significant Lightning risk.
Elevated Non thunderstorm wind risk.

DISCUSSION...

Strong southerly sustained winds of 20 to 30 mph and gusts of 35
to 45 mph will be possible today ahead of the next storm system.
The strongest winds will be over central Missouri and extreme
southeast Kansas where a wind advisory is in effect from late
morning through the afternoon.

Gulf moisture will continue to increase today ahead of a cold
front which should aid in increasing instability during the
afternoon. A thermal cap will be in place for a good portion of
the day, but should erode by the late afternoon. Thunderstorms
will be possible from mid to late afternoon through the night.
Most of the thunderstorms will occur along a cold front which will
push through from the evening into the overnigh period.

All modes of severe weather will be possible, with damaging
straight line winds and large hail the main severe weather risks.
A few isolated tornadoes will be possible, especially if some
supercells can develop in the unstable air mass in advance out
ahead of the front.
...
http://www.spc.noaa.gov

 

SPC AC 061301

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0701 AM CST Mon Mar 06 2017

Valid 061300Z - 071200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER THE OZARKS
REGION OF MISSOURI...OKLAHOMA AND ARKANSAS...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ELSEWHERE FROM
EASTERN OKLAHOMA AND ARKANSAS TO CENTRAL MINNESOTA AND WESTERN
ILLINOIS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK FROM THE ARKLATEX TO NORTHERN/WESTERN MINNESOTA...

...SUMMARY...
Severe thunderstorms are expected starting late this afternoon and
expanding across the upper and middle Mississippi Valley to the
Ozarks and Mid-South. Damaging wind gusts, large hail and a few
tornadoes are possible.

...Synopsis...
The upper-air pattern begins with synoptic-scale troughing from the
AK Panhandle to the northern Rockies, Four Corners and northwestern
MX. A strong/basal shortwave trough now located over UT will phase
with another currently over portions of eastern MT, WY and CO, as
they collectively shift eastward across the central/northern Plains
through the period. By 00z, the northern perturbation should evolve
into a closed 500-mb cyclone over central/eastern ND, with the
combined shortwave trough arching southeastward over the FSD area
then southwestward across western KS. By 12Z, the cyclone should
eject northeastward to northwestern ON near the MB border, with
associated vorticity lobe arching across Lake Superior, eastern WI,
northern MO, and eastern KS. The height trough will extend
southwestward over west TX by that time.

At the surface, the main low was analyzed at 11Z between PIR and
HEI, with a Pacific cold front southward across the NE Sandhills
then southwestward over central NM. An arctic front extended
southwestward over western WY. A dryline was drawn from
east-central SD to west-central KS, the eastern TX Panhandle, the
southeastern corner of NM, and northern Coahuila. By 00Z, the
surface low should deepen to around 978-980 mb and move to near the
northern terminus of I-29 where MB, MN and ND join. The arctic and
Pacific fronts will merge from north to south, with arching
southeastward from the low over MN and northern IA, then
southwestward over eastern KS, northwestern OK and the TX Panhandle,
having overtaken some of the dryline into eastern KS. The dryline
should extend from there south-southwestward across central OK to
the Edwards Plateau of TX. By 12Z, the surface cyclone will be
stacked with its manifestation aloft, and the cold front should
extend from lower MI across IN, southeastern MO, central AR, and
central TX.

....Ozarks, mid/upper Mississippi Valley to Mid South...
Scattered thunderstorms should develop along and ahead of the cold
front late this afternoon between eastern KS and central/western MN,
increasing in coverage and backbuilding southward into eastern OK
this evening, while an initially separate area of convection
develops in a low-level warm-advection/confluence zone from eastern
OK/western AR at least into northern MO. Each will shift eastward
with time, offering the potential for all severe modes.

The CAPE/shear parameter space should become favorable this
afternoon and evening in a narrow, triangular corridor of warm
sector, tapering with northward extend from eastern OK and AR
northward to southern MN and western WI. Surface dew points are
expected to reach the 50s F over the upper Mississippi Valley area,
with 60s from the lower Missouri Valley region southward. This, in
conjunction with diurnal heating, boundary-layer warm advection, and
cooling aloft preceding the shortwave trough, should support MLCAPE
from around 2000 J/kg in the western Ozarks region to around 500
J/kg in north-central MN. Forecast soundings reasonably suggest
that, amidst strengthening deep-layer winds with time, 55-65-kt
effective-shear magnitudes should become common along/ahead of the
cold front, with effective SRH commonly in the 250-400 J/kg range.

Within that corridor, the two regimes discussed above should support
at least a short temporal window of discrete-supercell potential:
1. Along the front for a brief maturation period before the frontal
convection evolves to more of a QLCS configuration, or (on the
northern/MN end) the mean-wind vector is less parallel to the front,
but activity moves quickly across the very narrow warm sector into
more stable air. The steepest lapse rates and largest buoyancy will
be available to this process, with any sustained/discrete cells
offering the most large-hail and tornado risk.
2. The prefrontal warm-advection plume, which will develop near the
eastern rim of the surface-based effective-inflow parcels in weaker
but still sufficient surface-based instability. This activity also
will exit the favorable buoyancy sooner than in the frontal regime.

Collectively, the greatest concentration of severe should be in or
near the enhanced risk, corresponding to the most probable area
affected by both regimes over the longest period of time.

Overnight, as the main band of thunderstorms moves eastward past the
Mississippi Valley, it should overtake the northern part of the
warm-advection band and weaken on the northeastern end; then the
zone of weakening zippers southward with time. This will take place
as the eastern theta-e/CAPE gradient effectively collapses southward
down the Mississippi Valley, on the western fringes of more poorly
modified continental/polar trajectories, and convection outruns
favorable surface-based buoyancy. With the northern warm sector
getting "pinched off" in such a manner late tonight and early
tomorrow morning, the zone of most favorable severe potential will
shift into southeastern OK, southeastern MO, AR, the Arklatex
region, and the Mid South. Damaging wind will become the main
threat with a mostly linear mode, though
embedded/short-lived/small-scale circulations may be capable of a
brief tornado or two.

..Edwards/Peters.. 03/06/2017

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