Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 120601
SWODY2
SPC AC 120600

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT SAT JUL 12 2014

VALID 131200Z - 141200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE OHIO VALLEY
AND NORTHEAST...

...SUMMARY...
SEVERE THUNDERSTORMS WILL BE POSSIBLE OVER PARTS OF THE OHIO VALLEY
AND NORTHEAST ON SUNDAY. MORE ISOLATED STRONG TO SEVERE STORMS WILL
ALSO BE POSSIBLE ACROSS FRONT RANGE AND CENTRAL PLAINS...THE
SOUTHWEST...AS WELL AS OREGON.

...SYNOPSIS...
A STRONG POSITIVE-TILT MID/UPPER TROUGH AND ASSOCIATED DEEP-LAYER
CYCLONE WILL UNDERGO AMPLIFICATION/DEEPENING FROM JAMES BAY
SOUTHWEST TO THE NORTHERN PLAINS/UPPER MS VALLEY REGIONS THROUGH
SUNDAY. A LEADING SHORTWAVE TROUGH ON THE EASTERN FLANK OF THE
AMPLIFYING UPPER LOW WILL TRACK FROM THE GREAT LAKES ACROSS THE
NORTHEAST AND SOUTHERN QUEBEC AS A STRONGER SHORTWAVE IMPULSE PIVOTS
AROUND THE WESTERN FLANK OF THE UPPER LOW AND DIGS SOUTH ACROSS THE
NORTHERN PLAINS AND UPPER MS VALLEY THROUGH MONDAY MORNING. BETWEEN
THESE TWO SHORTWAVES...A BELT OF MODEST CYCLONIC AND DIFLUENT FLOW
ALOFT WILL EXTEND FROM THE DAKOTAS ACROSS THE GREAT LAKES TO
NORTHERN NEW ENGLAND...COINCIDENT WITH A LEADING SURFACE COLD
FRONTAL SURGE. A WARM/MOIST CONVEYOR BELT WILL EXIST AHEAD OF THIS
LEADING FRONT...FROM THE MIDWEST/OH VALLEY NORTHEAST TO NY/NEW
ENGLAND.

A SECONDARY COLD FRONT ASSOCIATED WITH AFOREMENTIONED STRONGER
SHORTWAVE TROUGH AND DEEPENING UPPER LOW WILL SPREAD SOUTH AND EAST
FROM THE UPPER MS VALLEY AND IA TO THE UPPER MIDWEST THROUGH EARLY
MONDAY. ELSEWHERE...A MID-LEVEL ANTICYCLONE WILL REMAIN CENTERED
ACROSS THE GREAT BASIN WHILE A COMPACT SHORTWAVE TROUGH ACTS TO
BREAK DOWN THE UPPER RIDGE ACROSS THE PACIFIC NORTHWEST.

...NORTHEAST...
THE WARM/MOIST CONVEYOR BELT WILL BE CHARACTERIZED BY A 30-40KT
SOUTHWESTERLY LOW-LEVEL JET AHEAD OF A STRONG MID/UPPER JET EXIT
REGION ARCING FROM LAKE HURON TO THE ONTARIO/QUEBEC BORDER. MODEST
MASS TRANSPORT AND ISENTROPIC ASCENT WILL RESULT IN A NUMBER OF
SHOWERS/STORMS AND DEBRIS CLOUDS THAT MAY LIMIT STRONGER
DESTABILIZATION FROM PA NORTHEAST ACROSS ERN NY AND INTO VT THROUGH
THE AFTERNOON. HOWEVER...FORECAST SOUNDINGS FROM NAM AND PARALLEL
NAM INDICATE WEAK TO MODEST SURFACE-BASED INSTABILITY WILL EVOLVE IN
THE SLGT RISK AREA WITH SURFACE TEMPERATURES AROUND 80F AND
DEWPOINTS 65-70F CONTRIBUTING TO SBCAPE OF 1000-1500 J/KG. EFFECTIVE
DEEP-LAYER VERTICAL SHEAR OF 35-40KT WILL BE ADEQUATE FOR UPDRAFT
PERSISTENCE WHILE LOW-LEVEL JET ACTS TO ENHANCE 0-3KM STORM-RELATIVE
HELICITY. BOTH LINE SEGMENTS AND SUPERCELLS MAY EVOLVE THROUGH THE
AFTERNOON AS LEADING COLD FRONTAL SURGE SPREADS EAST INTO THE WARM
SECTOR. EXPECT THE POSSIBILITY OF STRONG TO SEVERE STORMS WITH
MARGINAL HAIL...STRONG TO DAMAGING WINDS...AND PERHAPS A COUPLE OF
TORNADOES. HIGHER SEVERE PROBABILITIES MAY BE WARRANTED IN LATER
OUTLOOKS DEPENDING ON TIMING AND GREATER CONFIDENCE IN DEGREE OF
DESTABILIZATION.

...OH VALLEY...
AN AXIS OF STRONGER INSTABILITY /MLCAPE 1500-2500 J PER KG/ BUT
WEAKER FLOW/SHEAR WILL EXIST FARTHER SOUTHWEST AHEAD OF THE FRONTAL
SURGE...FROM WESTERN PA WESTWARD ACROSS THE MIDWEST AND OH VALLEY.
NONETHELESS...HEIGHT FALLS WILL CONTRIBUTE TO ASCENT ACROSS THESE
AREAS AS MID-LEVEL FLOW STRENGTHENS COINCIDENT WITH DIURNAL
DESTABILIZATION AND STORM INITIATION. EXPECT ONE OR MORE WEST-EAST
BANDS OF CONVECTION TO EVOLVE THROUGH THE LATE AFTERNOON WITH
DAMAGING WINDS LIKELY BECOMING THE PRIMARY HAZARD.

...FRONT RANGE...
ISOLATED STRONGER STORMS WILL LIKELY DEVELOP ACROSS THE HIGHER
TERRAIN IN THE PRESENCE OF MODEST INSTABILITY/LAPSE RATES AND
15-20KT NORTHWEST FLOW ALOFT. A CLUSTER OR TWO OF STORMS MAY BE
CAPABLE OF MARGINALLY SEVERE WIND/HAIL INTO THE EARLY EVENING.

...CENTRAL PLAINS...
SECONDARY FRONTAL SURGE WILL SPREAD SOUTHEAST ACROSS ERN NEB/IA AND
NRN IL COINCIDENT WITH MAX HEATING. LIFT ALONG THE ADVANCING
BOUNDARY AND ANTECEDENT LOW LEVEL MOISTURE COULD SPUR A COUPLE OF
STRONGER CELLS THROUGH EARLY EVENING WITH SOME CHANCE OF STRONG
WINDS AND/OR MARGINAL HAIL.

...OREGON...
A COMPACT SHORTWAVE TROUGH AND ASSOCIATED 40-50KT MID-LEVEL WIND MAX
WILL SPREAD NORTHEAST ACROSS OREGON DURING THE DAY. LIFT AND SHEAR
WITH THIS IMPULSE MAY BE SUFFICIENT FOR A FEW HIGH-BASED STORMS AND
PERHAPS A SUPERCELL WITH HAIL AND STRONG TO ISOLATED DAMAGING WINDS
POSSIBLE.

...SOUTHWEST...
RICH BOUNDARY LAYER MOISTURE AND INTENSE HEATING WILL CONTRIBUTE TO
STRONG STORM INITIATION IN A REGIME CHARACTERIZED BY 10-20 EASTERLY
FLOW ABOVE 700MB. THIS SHOULD BE SUFFICIENT FOR STORMS TO SPREAD
WEST WHERE DRIER SUB-CLOUD LAYER WILL SUPPORT STRONG EVAPORATIONAL
COOLING AND DOWNBURST POTENTIAL.

..CARBIN.. 07/12/2014



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