National Weather Service Weather Forecast Office

Severe Storm Outlook Narrative (ac)

693
ACUS01 KWNS 031239
SWODY1
SPC AC 031236

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0736 AM CDT THU OCT 03 2013

VALID 031300Z - 041200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE MID MO VALLEY
THIS AFTERNOON INTO TONIGHT...

...SYNOPSIS...

THE EQUATORWARD DEVELOPMENT OF MID AND UPPER-LEVEL JET STREAKS FROM
THE PACIFIC NW COAST INTO THE FOUR CORNERS REGION WILL PROMOTE
AMPLIFICATION OF THE WRN U.S. TROUGH PROGRESSING EWD INTO THE
ROCKIES.  THIS PATTERN EVOLUTION WILL RESULT IN STRENGTHENING SWLY
FLOW ALOFT AND A RENEWAL OF AN ELEVATED MIXED LAYER /EML/ ACROSS THE
GREAT PLAINS.  A NUMBER OF WEAKER PERTURBATIONS ARE EMBEDDED WITHIN
THIS SYNOPTIC-SCALE PATTERN...ONE WHICH WILL TRACK FROM THE TN
VALLEY TO MID ATLANTIC COAST...ANOTHER MOVING FROM THE LOWER MO
VALLEY INTO THE OH VALLEY...AND PERHAPS ANOTHER IMPULSE WHICH MODEL
GUIDANCE INDICATES WILL TRANSLATE FROM THE SRN HIGH PLAINS INTO THE
MID/LOWER MO VALLEY.

IN THE LOW LEVELS...A LEE CYCLONE OVER ERN CO/WRN KS WILL DEEPEN
TODAY BEFORE DEVELOPING NEWD INTO CNTRL NEB BY 04/12Z.  THIS SURFACE
LOW WILL TRACK NEWD ALONG A WARM OR STATIONARY FRONT STRETCHING NEWD
THROUGH THE MID MO VALLEY INTO THE GREAT LAKES.  MEANWHILE...A
DRYLINE WILL STRENGTHEN OVER THE CNTRL/SRN HIGH PLAINS WHILE A COLD
FRONT PUSHES EWD/SEWD THROUGH ERN PORTIONS OF THE GREAT BASIN INTO
THE CNTRL ROCKIES.

...MID/LOWER MO VALLEY THIS AFTERNOON INTO TONIGHT...

REMNANTS OF A NOCTURNAL MCS ARE ONGOING TO THE SOUTH OF THE SYNOPTIC
FRONT --ALONG AN ACTIVE COLD POOL-- FROM CNTRL IA TO NERN KS.
MOREOVER...RADAR DATA SHOW SOME SUGGESTION OF AN MCV OVER NWRN IA
WHICH SHOULD CONTINUE ENEWD.  A NUMBER OF CONVECTION-ALLOWING MODELS
SUGGEST THAT FORCING FOR ASCENT ATTENDANT TO THE MCV --AS WELL AS
THE WEAK MIDLEVEL IMPULSE MENTIONED IN THE SYNOPSIS-- WILL AUGMENT
LOW-LEVEL UPLIFT ALONG THE RESIDUAL MCS COLD POOL TO MAINTAIN ACTIVE
TSTM CLUSTERS EWD TOWARD THE MS RIVER.  GIVEN THE OVERLAP OF A
MOIST...MODERATELY UNSTABLE AIR MASS WITH MODEST AMOUNTS OF
CLOUD-BEARING SHEAR...THE POTENTIAL WILL EXIST FOR LINE
SEGMENTS/BOWING STRUCTURES CAPABLE OF LOCALLY DAMAGING WINDS AND
SOME HAIL.

IN THE WAKE OF THESE INITIAL STORMS...LINGERING CLOUDS AND CONTINUED
OUTFLOW GENERATION FROM DEVELOPING ELEVATED STORMS OVER THE
SANDHILLS INTO PARTS OF CNTRL NEB AS OF 12Z CAST UNCERTAINTY ON THE
DEGREE OF AIR MASS DESTABILIZATION AND THE ULTIMATE LOCATION OF THE
SYNOPTIC FRONT-OUTFLOW COMPOSITE BOUNDARY BY THE PEAK OF THE DIURNAL
HEATING CYCLE.  WHERE STRONGER INSOLATION CAN OCCUR...THE
COMBINATION OF 60+ F BOUNDARY LAYER DEWPOINTS AND STEEP MIDLEVEL
LAPSE RATES WILL YIELD MODERATE AMOUNTS OF INSTABILITY WITH MLCAPE
VALUES APPROACHING 1500-2500 J/KG.

IN THE ABSENCE OF APPRECIABLE FORCING FOR ASCENT AND A GRADUALLY
STRENGTHENING CAP...CONFIDENCE IN SURFACE-BASED AFTERNOON/EVENING
STORM DEVELOPMENT REMAINS LOW.  LATEST MODEL GUIDANCE SUGGESTS THE
MOST PROBABLE SCENARIO IS FOR THE DEVELOPMENT OF ELEVATED TSTMS TO
THE NORTH OF THE EFFECTIVE SURFACE FRONT AFTER 04/00Z AS WAA AND
ISENTROPIC ASCENT ARE ENHANCED BY THE FORMATION OF A NOCTURNAL
LOW-LEVEL WIND MAXIMUM.  THE PRESENCE OF 40-50 KT EFFECTIVE BULK
SHEAR AND AMPLE INSTABILITY WILL BE SUPPORTIVE OF ORGANIZED STORM
MODES INCLUDING SUPERCELLS WITH A RISK FOR LARGE HAIL AND PERHAPS
DAMAGING WIND GUSTS WITH THIS THREAT CONTINUING INTO THE OVERNIGHT
HOURS.

..MEAD/MOSIER.. 10/03/2013