DAY1SVR: Day 1 Convective Outlook Amend 1

ACUS01 KWNS 222153
SWODY1
SPC AC 222151

DAY 1 CONVECTIVE OUTLOOK AMEND 1
NWS STORM PREDICTION CENTER NORMAN OK
0451 PM CDT MON OCT 22 2012

VALID 222000Z - 231200Z

...NO SVR TSTM AREAS FORECAST...

AMENDED TO ADD 2 PERCENT TORNADO CONTOUR

THE OUTLOOK IS AMENDED TO ADD A 2 PERCENT TORNADO PROBABILITY TO
PARTS OF THE SACRAMENTO VALLEY. ROTATING STORMS HAVE DEVELOPED NORTH
OF SACRAMENTO IN A LOW-LEVEL SHEAR ENVIRONMENT THAT MAY SUPPORT A
MARGINAL TORNADO THREAT.

TWO CHANGES HAVE BEEN MADE TO THE OUTLOOK AT 20Z. THE FIRST CHANGE
IS TO REMOVE THE 5 PERCENT WIND DAMAGE AND HAIL PROBABILITIES FROM
PARTS OF THE UPPER MS VALLEY AND SRN GREAT LAKES REGION WHERE
MINIMAL DESTABILIZATION HAS OCCURRED. THE AREA THAT MAY DEVELOP A
MARGINAL SEVERE THREAT APPEARS TO BE FURTHER SOUTH IN THE ST LOUIS
AREA WHERE MODERATE INSTABILITY IS CURRENTLY LOCATED. THE SECOND
CHANGE IS TO TRIM THE 5 PERCENT WIND AND HAIL PROBABILITIES FROM SW
OK AND NW TX WHERE CONVECTION IS NOT EXPECTED TO REDEVELOP THIS
AFTERNOON.

..BROYLES.. 10/22/2012

.PREV DISCUSSION... /ISSUED 1113 AM CDT MON OCT 22 2012/

...SYNOPSIS...

MORNING WATER VAPOR IMAGERY AND RADAR MOSAIC DATA SHOW A
WELL-DEFINED MCV OVER ERN IA AND A MORE SUBTLE SHORTWAVE TROUGH ON
IT/S HEELS OVER THE LOWER MO VALLEY. LATEST MODEL GUIDANCE SUGGESTS
THAT THESE FEATURES WILL LIKELY WEAKEN TODAY WHILE PROGRESSING NEWD
THROUGH A LOW-AMPLITUDE RIDGE AXIS SITUATED OVER THE ERN THIRD OF
THE NATION. MEANWHILE...AN UPSTREAM SHORTWAVE TROUGH OVER ERN
NM/WRN TX IS FORECAST TO MAINTAIN ITS INTENSITY WHILE TRANSLATING
NEWD INTO MO/AR BY TONIGHT.

AT THE SURFACE...LOW PRESSURE OVER NERN KS/SERN NEB AS OF 15Z IS
EXPECTED TO DEVELOP NWD THROUGH THE MID MO VALLEY IN TANDEM WITH A
WARM FRONT LIFTING NWD THROUGH THE MIDWEST. A TRAILING COLD FRONT
CURRENTLY FROM THE SURFACE LOW SWWD INTO NWRN OK AND THE TX PNHDL
WILL STALL TODAY AND SUBSEQUENTLY DEVELOP NWD AS A WARM FRONT IN
RESPONSE TO FALLING MIDLEVEL HEIGHTS AND LEE CYCLOGENESIS OVER THE
NRN HIGH PLAINS.

...MID MS VALLEY INTO THE OH VALLEY/SRN GREAT LAKES THIS AFTERNOON
AND EVENING...

BACKBUILDING STORM DEVELOPMENT OBSERVED NEAR STL IS LIKELY BEING
FORCED BY LOW-LEVEL WAA/ISENTROPIC ASCENT LOCATED AT THE TERMINUS OF
A 30-35 KT LLJ. EXPECT SIMILAR PROCESSES TO MAINTAIN REGENERATIVE
STORM GROWTH OVER THE MID MS VALLEY TODAY...WHILE THE NRN EXTENSION
OF CONVECTIVE BAND OVER SRN WI INTO CNTRL IL ADVANCES EWD IN CONCERT
WITH THE MCV AND SYNOPTIC-SCALE SHORTWAVE TROUGH. THIS ACTIVITY
WILL REMAIN ALONG THE ERN EDGE OF STEEPER MIDLEVEL LAPSE RATES AND
RICHER LOW-LEVEL MOISTURE WITH AFTERNOON MLCAPE VALUES RANGING FROM
AOB 500 J/KG OVER ERN IL/NWRN IND TO 1000-1500 J/KG ACROSS PORTIONS
OF ERN MO/WRN IL.

IN THE PRESENCE OF A VERTICALLY VEERING WIND PROFILE WITH 40-45 KT
OF DEEP WLY SHEAR...THE POTENTIAL WILL EXIST FOR ROTATING STORMS
CAPABLE OF SOME MARGINALLY SEVERE HAIL AND/OR LOCALLY STRONG WIND
GUSTS. CURRENTLY...IT APPEARS THAT A ROBUST SEVERE WEATHER THREAT
WILL BE LIMITED BY THE TENDENCY FOR THE STRONGER FORCING FOR ASCENT
TO BECOME PROGRESSIVELY DISPLACED FROM THE PRIMARY INSTABILITY AXIS.
THEREFORE...THE LOW SEVERE WEATHER PROBABILITIES WILL BE MAINTAINED
IN THIS FORECAST.

FOR ADDITIONAL NEAR-TERM GUIDANCE...SEE MCD 2082.

...SRN OK/NRN TX THIS AFTERNOON AND EVENING...

A RECENT INCREASE IN STORM INTENSITY HAS BEEN NOTED NW OF MWL ON THE
LEADING EDGE OF A NOCTURNAL MCS EXTENDING FROM NWRN TX INTO THE TX
BIG COUNTRY. THE 12Z SOUNDINGS FROM OUN AND FWD SHOWED THE PRESENCE
OF A MOIST BOUNDARY LAYER /I.E. LOWEST 100-MB MEAN MIXING RATIOS OF
AROUND 14 G PER KG/ BENEATH A PRONOUNCED CAP AT THE BASE OF AN EML.
FORCING FOR ASCENT ATTENDANT TO UPSTREAM SHORTWAVE TROUGH COUPLED
WITH DAYTIME HEATING AND LOW-LEVEL UPLIFT ALONG MCS COLD POOL WILL
LIKELY FOSTER AN INCREASE IN STORM DEVELOPMENT THROUGH THE PEAK OF
THE DIURNAL HEATING CYCLE. AS SUCH...ISOLATED OCCURRENCES OF SEVERE
HAIL AND DAMAGING WIND GUSTS WILL BE POSSIBLE INTO THIS EVENING.
HOWEVER...THE TENDENCY FOR STRONGER UPDRAFTS TO BECOME UNDERCUT BY
SURGING OUTFLOW AND MARGINALLY STRONG DEEP-LAYER SHEAR ARE EXPECTED
TO LIMIT THE POTENTIAL FOR A MORE WIDESPREAD SEVERE WEATHER EVENT.

FOR ADDITIONAL NEAR-TERM GUIDANCE...SEE MCD 2083.

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