[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 182209
SWODY1
SPC AC 182207

DAY 1 CONVECTIVE OUTLOOK AMEND 1
NWS STORM PREDICTION CENTER NORMAN OK
0507 PM CDT SUN JUN 18 2006

VALID 182205Z - 191200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS ERN NEB/SRN-ERN IA/NRN
IL/SRN-ERN WI...

...THERE IS A SLGT RISK OF SVR TSTMS LOWER OH INTO LOWER TN
VALLEYS...

AMENDED TO ADD A SLIGHT RISK ACROSS ERN IA/NWRN IL INTO PARTS OF
SRN/ERN WI

...ERN IA/NWRN IL INTO WI...
REGIONAL RADARS/SATELLITE IMAGERY INDICATED A FEW THUNDERSTORMS HAVE
DEVELOPED ALONG A SURFACE BOUNDARY EXTENDING FROM CENTRAL U.P. OF MI
SSWWD THROUGH CENTRAL-SWRN WI INTO ERN IA.  AIR MASS ALONG/E OF THIS
BOUNDARY HAS BECOME MODERATELY UNSTABLE WITH MLCAPE VALUES UP TO
1000-1500 J/KG.  LARGE SCALE ASCENT AHEAD OF UPPER TROUGH DIGGING
SEWD INTO UPPER MS VALLEY AND IN ADVANCE OF MID LEVEL IMPULSE...NOW
LOCATED OVER NRN IA...WILL LIKELY SUPPORT ADDITIONAL THUNDERSTORM
DEVELOPMENT ALONG THE SURFACE BOUNDARY.  STRENGTHENING WLY MID LEVEL
WINDS ASSOCIATED WITH THE AFOREMENTIONED MID/UPPER LEVEL FEATURES
WILL RESULT IN INCREASING EFFECTIVE BULK SHEAR FOR STORMS TO BECOME
ORGANIZED WITH STRONG GUSTY WINDS AND HAIL THE PRIMARY THREATS INTO
THE EVENING.  WSR-88D VAD AT DVN INDICATED LOW-LEVEL DIRECTIONAL
SHEAR SUPPORTIVE FOR STORM ROTATION SUGGESTING A POTENTIAL FOR AN
ISOLATED TORNADO.  GIVEN TIME OF DAY AND THE EVENTUAL ONSET OF
BOUNDARY LAYER STABILIZATION...THE THREAT FOR SEVERE STORMS ACROSS
THIS REGION SHOULD BEGIN TO DIMINISH BY 02-03Z.

...PREVIOUS 20Z DISCUSSION...

...MID MS/LOWER OH VALLEYS...
WATER VAPOR IMAGERY INDICATED A SHORT WAVE TROUGH OVER IL/SERN MO
WITH THIS FEATURE PROGGED MOVE EWD THROUGH THE OH VALLEY THIS
FORECAST PERIOD.  AT THE SURFACE...A WEAK TROUGH EXTENDED SWD FROM
SERN WI THROUGH CENTRAL IL TO SERN MO AND CENTRAL/SWRN AR.  AIR MASS
HAD BECOME MODERATELY UNSTABLE /MUCAPE 1500-2000 J/KG/ IMMEDIATELY
DOWNSTREAM OF MID LEVEL IMPULSE FROM CENTRAL IL INTO SERN MO.  30 KT
OF DEEP LAYER SHEAR SUGGESTS STORMS WILL LIKELY REMAIN MULTICELLULAR
WITH THE POTENTIAL FOR DAMAGING WINDS AND HAIL.  SUFFICIENT LOW
LEVEL DIRECTIONAL SHEAR FROM IL INTO WRN KY INDICATES POTENTIAL FOR
LOW LEVEL STORM ROTATION AND ATTENDANT ISOLATED TORNADO THREAT. 
THUNDERSTORMS WILL SPREAD EWD IN ADVANCE OF SHORT WAVE TROUGH WITH
SEVERE THREAT DIMINISHING THIS EVENING AS THE AIR MASS STABILIZES. 

MEANWHILE...ONGOING CONVECTIVE COMPLEX EXTENDING FROM SWRN IND INTO
NWRN TN WILL PROGRESS ENEWD INTO NRN TN/CENTRAL KY TO SWRN OH AIDED
BY ESTABLISHED COLD POOL AND ASCENT AHEAD OF MID MS VALLEY IMPULSE. 
WEAK INSTABILITY WILL CONTINUE TO MINIMIZE SEVERE THREAT. 
HOWEVER...40 KT WLY WINDS AT 1-2 KM AGL PER FORT CAMPBELL WSR-88D
VAD SUGGESTS POTENTIAL FOR LOCALLY DAMAGING WIND GUSTS.

...LOWER MS/TN VALLEYS...
SRN EXTENT OF MS VALLEY TROUGH WILL CONTINUE TO WEAKEN THIS FORECAST
PERIOD AS IT MOVES SLOWLY EWD ACROSS THE LOWER MS VALLEY.  STRONG
SURFACE HEATING E OF THIS TROUGH OVER MS WITH SURFACE TEMPERATURES
CLIMBING TO AROUND 90 WITHIN A VERY MOIST AIR MASS WILL CONTRIBUTE
TO FURTHER DESTABILIZATION /MLCAPE 1500-2000 J/KG/...GIVEN MODEST
LAPSE RATES /6.5 C/KM/.  GENERALLY WEAK DEEP LAYER SHEAR IS EXPECTED
TO LIMIT SEVERE POTENTIAL.  HOWEVER... MODERATE INSTABILITY
EXTENDING FROM MS INTO SWRN TN MAY ALLOW FOR A FEW DAMAGING WIND
GUSTS THROUGH THE EARLY EVENING...PRIOR TO THE ONSET OF BOUNDARY
LAYER STABILIZATION THIS EVENING.

...NEB/IA...
EARLY AFTERNOON SURFACE ANALYSIS INDICATED A TROUGH/COOL FRONT
EXTENDING FROM THE UPPER MS VALLEY WSWWD THROUGH CENTRAL NEB TO A
MESOLOW NEAR LBF.  SURFACE HEATING S OF THIS TROUGH WITHIN AXIS OF
SURFACE DEWPOINTS IN THE MID-UPPER 50S WILL CONTINUE TO DESTABILIZE
AIR MASS WITH MLCAPE VALUES UP TO 1500 J/KG...WITH RECENT OBJECTIVE
ANALYSES SUGGESTING INHIBITION IS BECOMING WEAKER.  40-50 KT WNWLY
MID LEVEL JET ACCOMPANYING MID MO VALLEY IMPULSE AND AHEAD OF UPPER
TROUGH DEVELOPING SEWD INTO UPPER MS VALLEY IS RESULTING IN STRONG
DEEP LAYER SHEAR SUPPORTING ORGANIZED STORMS.  18Z RUC SUGGESTS
THUNDERSTORM INITIATION WILL BE POSSIBLE BY AROUND 21Z IN VICINITY
OF MESOLOW WHERE LOW LEVEL CONVERGENCE IS MAXIMIZED.  FOR ADDITIONAL
SHORT TERM MESOSCALE INFORMATION...PLEASE REFER TO SPC MESOSCALE
DISCUSSION 1233.

INITIAL STORMS WILL DEVELOP EWD ALONG THE SURFACE FRONT WITH THE
POTENTIAL FOR UPSCALE GROWTH INTO AN MCS THIS EVENING/TONIGHT ACROSS
ERN NEB/SWRN IA INTO NRN MO PER INCREASING WAA ALONG NOSE OF
STRENGTHENING SSWLY LLJ.  HAIL SHOULD BECOME THE PRIMARY THREAT 
TONIGHT AS THE BOUNDARY LAYER DECOUPLES WITH THE LOSS OF DAYTIME
HEATING.

..PETERS.. 06/18/2006