Case (Chase) Study: 04 May
2007
Supercells, Supercells, and more
Supercells
Us
23214 SW ARNETT ELLIS OK
MULTIPLE MEDIA REPORTS...NSSL EMPLOYEES...EMERGENCY
MANAGEMENT OFFICIALS REPORTED THE TORNADO. BEGAN AT 621 PM...STILL OCCURRING AT 627 PM.
(OUN)
00153008 W SHARON WOODWARD OK
REPORTED BY NSSL EMPLOYEE. (OUN)
Preliminary Forecast
• Why did we choose Woodward, OK?
– Model output
• Forecast soundings, forecast upper air, forecast surface
• CAPE, Helicity, low level moisture, low level convergence
• GFS, NAM, WRF all in good agreement
– Observations
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Observed upper level divergence
Obvious dryline
Lee cyclogenesis
Good agreement with model initialization
The Morning Of
• Still kept Woodward, OK as ‘target’
– Again, good model initialization
– Dryline setup was as progged
– SPC gave some good reassurance
http://www.spc.noaa.gov/
– All in all, not much change
• That made us happy
INTO OK...WITH MID-UPPER 60S INTO THE DRYLINE OVER KS...NWD INTO
SCNTRL NEB. GIVEN THIS MARKED INCREASE IN MOISTURE MDT-HIGH
INSTABILITY WILL DEVELOP ACROSS THE ENTIRE WARM SECTOR BY LATE
AFTERNOON. SBCAPE VALUES COULD EASILY EXCEED 4000 J/KG ACROSS MOST
OF THE SRN PLAINS INTO PORTIONS OF KS...HIGHER THAN MODELS WOULD
SUGGEST. ADDITIONALLY...STRONG SFC HEATING ALONG/WEST OF THE
DRYLINE OVER THE TX SOUTH PLAINS INTO THE OK PANHANDLE WILL
CERTAINLY REMOVE ANY INHIBITION ACROSS THIS REGION. IT SEEMS
REASONABLE THAT SUPERCELLS SHOULD DEVELOP DURING THE 21-00Z TIME
FRAME FROM SWRN KS...SWD INTO SWRN TX WHERE DEEP LAYER SHEAR WILL
ONLY INCREASE AS UPPER TROUGH ADVANCES EWD.
AS LLJ STRENGTHENS DURING THE EVENING HOURS SCATTERED SUPERCELLS
SHOULD BE MAINTAINED
WITHIN HIGH QUALITY AIRMASS ACROSS THE PLAINS...WHILE LARGE SCALE
FORCING/ASCENT GRADUALLY INCREASE AFTER DARK. ALTHOUGH DRYLINE
SHOULD BE THE INITIAL INSTIGATOR FOR SUPERCELLS...ADDITIONAL
DEVELOPMENT IS POSSIBLE DURING THE OVERNIGHT HOURS AS UPPER SPEED
MAX EJECTS INTO THE CNTRL HIGH PLAINS. AT THAT TIME WIDESPREAD
CONVECTION SHOULD EVOLVE WITHIN STRONG WARM ADVECTION REGIME
ACROSS MUCH OF NEB/SD. VERY LARGE HAIL MAY ACCOMPANY HIGH
INSTABILITY SUPERCELLS...ALONG WITH A FEW STRONG TORNADOES.
THE INTERSECTION OF DRY LINE/COLD FRONT OVER WRN KS FOCUSES ANOTHER
AREA OF ENHANCED CONVERGENCE AND CONVECTIVE INITIATION BY MID/LATE
AFTERNOON. WITH THE HIGH INSTABILITY AND ENHANCED VEERING SHEAR
PROFILES VICINITY FRONTAL ZONE/DRY LINE...SUPERCELLS WOULD RAPIDLY
BECOME SEVERE WITH VERY LARGE HAIL AND TORNADO POTENTIAL. STRONG
TORNADOES CERTAINLY A POSSIBILITY IN WRN KS GIVEN THE HIGH
CAPE/SHEAR ENVIRONMENT EXPECTED TO BE IN PLACE BY LATE AFTERNOON.
FURTHER SOUTH ALONG DRY LINE FROM SRN KS ALONG TX/OK BORDER INTO
SWRN TX...THE THREAT OF STORM INITIATION WILL BE BOTH MORE
CONDITIONAL AND LATER. BY EVENING WITH CAP WEAKENING AND INCREASING
UPPER DIFFLUENCE AHEAD OF APPROACHING WIND MAX...AT LEAST ISOLATED
INITIATION IS LIKELY VICINITY/JUST E OF DRY LINE. WITH MLCAPES AOA
4000 J/KG...STORMS THAT AREA ABLE TO FORM WILL QUICKLY BECOME
SEVERE/SUPERCELLS WITH LARGE HAIL AND TORNADO THREAT.
AFTER 00Z SEVERE THUNDERSTORMS WILL LIKELY CONTINUE AND BECOME
MORE
WIDESPREAD AS THEY SPREAD NEWD ACROSS CENTRAL PLAINS AS FAR N AS
SRN
SD. THIS SUPPORTED BY CONTINUED DEEPENING OF SURFACE LOW NEWD THRU
CENTRAL HIGH PLAINS AS S/WV IMPULSE ROTATES NEWD FROM SRN ROCKIES.
On the Road
• We left Norman, OK around 11:00
– Gave us time to get to where we needed to
– ‘Northwest Passage’
• Arrived in Woodward at ~1:30pm
– Sat at random hotel for Wifi internet
• Also got free cookies and coffee!
• http://www.spc.noaa.gov/exper/mesoanalysis/
– Decided to head farther North towards
‘Random Junction’
On the Road
• At Random Junction we played lots of
football, hacky sack, throw rocks at
garbage can, etc.
• Started seeing TCu going up to our SW
– Very hazy, tough to tell, determined it was our
‘go’ time, I didn’t necessarily agree!
– Made our way to Fargo and on to Arnett, OK.
– Passed through one storm that split– not what
we wanted.
• Finally saw the storm
– Drove up on the pendent funnel
• You tube Reed Timmer
What did we learn?
• Chasing is about being mobile with
current, up to the minute information
• Always watch the sky– it still tells you
more than any weather map
• Listen to your chase partners and be
open-minded
• Always call in your storm reports to the
NWS