DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 122003
SWODY1
SPC AC 122000

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT WED JUN 12 2013

VALID 122000Z - 131200Z

...THERE IS A HIGH RISK OF SVR TSTMS FROM EXTREME ERN IA...NRN
IL...NRN IND...EXTREME SWRN MI AND EXTREME NWRN OH...

...THERE IS A MDT RISK OF SVR TSTMS FROM ERN IA...CNTRL AND NRN
IL...SRN WI...SWRN MI...IND...AND WRN OH...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MS VALLEY INTO
THE OH VALLEY...SRN GREAT LAKES AND MID ATLANTIC REGION...

...THERE IS A SLGT RISK OF SVR TSTMS CNTRL AND ERN MT INTO NERN
WY...

...UPPER MS VALLEY SRN GREAT LAKES AND OH VALLEY REGION...

ONLY MINOR CHANGES HAVE BEEN MADE TO ONGOING FORECAST. THREAT FOR A
SIGNIFICANT WIDESPREAD DAMAGING WIND EVENT STILL APPEARS ON TRACK
FROM SRN PORTIONS OF THE GREAT LAKES INTO THE OH VALLEY REGION HIGH
AND MODERATE RISK AREAS.

STORMS ARE IN PROCESS OF DEVELOPING FROM NERN IA INTO SRN WI WITHIN
ZONE OF DPVA AND ASCENT ACCOMPANYING A PROGRESSIVE SHORTWAVE TROUGH
GENERALLY NE OF SFC LOW AND NORTH OF E-W QUASI-STATIONARY FRONT. THE
INITIAL SFC BASED STORMS DEVELOPING EAST OF SFC LOW MAY ORGANIZE AS
DISCRETE SUPERCELLS WITH AN INITIAL TORNADO THREAT. STORMS SHOULD
EVENTUALLY CONSOLIDATE AND TRANSITION TO A FORWARD PROPAGATING MCS
WITH AN INCREASING THREAT FOR SIGNIFICANT WIND DAMAGE AS IT MOVES
ESEWD THROUGH THE SRN GREAT LAKES AND OH VALLEY DURING THE EVENING
AND OVERNIGHT.

...MT AND NERN WY...

REF SWOMCD 1042.

..DIAL.. 06/12/2013

.PREV DISCUSSION... /ISSUED 1126 AM CDT WED JUN 12 2013/

...SYNOPSIS...
A SIGNIFICANT SEVERE WEATHER OUTBREAK APPEARS INCREASINGLY LIKELY
ACROSS PORTIONS OF THE UPPER MIDWEST/LOWER GREAT LAKES FROM THIS
AFTERNOON THROUGH THIS EVENING. INTENSE STORM DEVELOPMENT IN A VERY
UNSTABLE AIRMASS...COINCIDENT WITH A COMPACT AND INTENSIFYING
SURFACE LOW SHOULD RESULT IN NUMEROUS DAMAGING WIND EVENTS AS WELL
AS SCATTERED...POSSIBLY STRONG TORNADOES.

...ERN IA/NRN IL/NRN IND/NWRN OH AND ADJACENT AREAS OF EXTREME SRN
WI AND SWRN LOWER MI...

SIGNIFICANT SEVERE WEATHER INGREDIENTS HAVE CONGEALED AHEAD OF A
COMPACT AND PROGRESSIVE MID/UPPER TROUGH AND ASSOCIATED 50-60KT MID
LEVEL WLY FLOW CURRENTLY TRACKING EAST FROM THE NRN/CNTRL PLAINS. AN
EXPANSIVE WARM/MOIST SECTOR EXISTS AHEAD OF THE UPPER FORCING AND
DEVELOPING SURFACE CYCLONE WITH 2M DEWPOINTS WELL INTO THE 60S AND
LOWER 70S F AND PW VALUES IN EXCESS OF 1.25 INCHES ACROSS MUCH OF
THE MIDWEST FROM IA EAST ACROSS IL/IND/OH. MORNING SOUNDINGS ACROSS
THIS SAME REGION INDICATE A PRONOUNCED EML ADVECTING EAST FROM THE
SRN HIGH PLAINS WITH 700-500MB LAPSE RATES APPROACHING 9C/KM.

DESPITE RELATIVELY STRONG CAPPING ACROSS THE WARM SECTOR...DEGREE OF
HEATING AND LARGE SCALE ASCENT AIDING SURFACE CYCLONE
INTENSIFICATION ACROSS ERN IA BY LATE AFTERNOON WILL PROVE ADEQUATE
FOR SURFACE-BASED STORM INITIATION. ADDITIONAL NEAR-SURFACE-BASED
DEEP CONVECTION WITH BOTH HAIL AND WIND POTENTIAL MAY PRECEDE TRULY
SURFACE-BASED STORMS TO THE NORTH OF THE SURFACE LOW AND
QUASI-STATIONARY FRONT SITUATED FROM NERN IA ACROSS SRN WI TO LOWER
MI. GIVEN DEGREE OF CAPPING AND MAGNITUDE OF INSTABILITY...EXPECT
POTENTIALLY EXPLOSIVE STORM DEVELOPMENT TO OCCUR IN THE PRESENCE OF
MODEST TO LOCALLY STRONG STORM-RELATIVELY HELICITY /SRH/. ANY
CONVECTION INITIATING NEAR THE SURFACE LOW AND FRONT WILL QUICKLY
ACQUIRE SUPERCELL CHARACTERISTICS GIVEN DEGREE OF EFFECTIVE VERTICAL
SHEAR OF 35-55KT. POTENTIALLY STRONG TORNADO THREAT MAY BE MAXIMIZED
DURING THIS EARLY DEVELOPMENT PHASE /21Z-00Z/ NEAR THE LOW AND FRONT
WHILE STORMS REMAIN DISCRETE AMIDST HIGH INSTABILITY AND EFFECTIVE
SRH IN EXCESS OF 200 M2/S2.

ORGANIZING INFLUENCE OF THE DEEPENING SURFACE CYCLONE RIPPLING EAST
ALONG THE WARM/QUASI-STATIONARY FRONT...IN CONCERT WITH 50-60KT
MID-LEVEL JET STREAK DIRECTED PREFERENTIALLY INTO/ACROSS THE
DEVELOPING MASS OF CONVECTION SUGGESTS UPSCALE PROGRESSIVE MCS
/POSSIBLE DERECHO/ EVOLUTION THROUGH THE EVENING HOURS. GIVEN
ANTECEDENT AIRMASS CHARACTERISTICS...STRENGTH OF LARGE SCALE
FORCING...AND DEPICTION OF CURRENT CONDITIONS...RELATIVELY HIGH
CONFIDENCE EXISTS IN A NUMBER OF STORM-SCALE MODEL SIMULATIONS
SHOWING MCS/DERECHO EVOLUTION WITHIN THE HIGH RISK AREA THROUGH THE
EVENING HOURS. WRF-ARW SIMULATION FROM 00Z TAKES THE APEX OF THE
PROGRESSIVE MCS FROM CHICAGO TO DETROIT IN UNDER 6 HOURS WITH A
FORWARD SPEED IN EXCESS OF 40KT. SHEAR AND INSTABILITY WITHIN AND
AHEAD OF THIS CONVECTION WILL REMAIN SUPPORTIVE OF BOTH HIGH WINDS
POSSIBLY WELL IN EXCESS OF 60KT...AS WELL A FEW TORNADOES POSSIBLY
ASSOCIATED WITH SUPERCELL STRUCTURES EMBEDDED WITHIN THE SQUALL
LINE/QLCS.

...OH EAST TO EAST COAST/SOUTHEAST...
WARM MOIST AIRMASS ALSO EXISTS WELL EAST OF THE STRONGER FORCING
ACROSS FROM OH EAST ACROSS THE APPALACHIANS TO EAST COAST. SOME
MODEL SIMULATIONS DEPICT THE POSSIBLE EVOLUTION OF SMALL CONVECTIVE
COMPLEXES DEVELOPING FROM INITIALLY MULTICELLULAR STORMS ACROSS THE
HIGHER TERRAIN THIS AFTERNOON. LARGE SCALE FORCING AND SHEAR REMAIN
SUBTLE/WEAK ACROSS THESE AREAS UNTIL LATE IN THE PERIOD.
HOWEVER...DEGREE OF ANTICIPATED INSTABILITY COULD RESULT IN A FEW
HAIL/WIND EVENTS THROUGH THE EVENING AND POSSIBLY INTO LATE
TONIGHT/EARLY FRIDAY ACROSS THESE PARTS OF THE SLGT RISK AREA.

...MT/NERN WY...
STRONG IMPULSES ROTATING THROUGH THE BASE OF LARGER TROUGH ACROSS
THE PACIFIC NORTHWEST WILL AID ASCENT ACROSS THE NRN ROCKIES THROUGH
THE AFTERNOON. STEEPENING LOW THROUGH MID-LEVEL LAPSE RATES AND
STRENGTHENING SHEAR SHOULD CONTRIBUTE TO A NUMBER OF SUPERCELL
STORMS POSING BOTH HAIL AND WIND THREATS. AN ISOLATED TORNADO MAY
ALSO EVOLVE FROM INITIAL DISCRETE CELLS GIVEN RELATIVELY HIGH
BOUNDARY LAYER MOISTURE AND SUFFICIENT DIRECTIONAL SHEAR IN THE
STORM UPDRAFT LAYER.

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