Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 051629
SWODY1
SPC AC 051627

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1127 AM CDT SUN JUL 05 2015

VALID 051630Z - 061200Z

...THERE IS AN ENH RISK OF SVR TSTMS OVER MUCH OF SD INTO SWRN
MN...AND A SMALL PART OF ND...NEB AND IA...

...THERE IS A SLGT RISK OF SVR TSTMS OVER THE NRN PLAINS INTO UPPER
MS VALLEY...

...THERE IS A SLGT RISK OF SVR TSTMS OVER A PART OF THE LOWER MS
VALLEY...

...THERE IS A MRGL RISK OF SVR TSTMS FROM THE NRN AND CNTRL PLAINS
INTO UPPER GREAT LAKES...

...THERE IS A MRGL RISK OF SVR TSTMS FROM THE LOWER MS VALLEY TO MID
AND SERN ATLANTIC COASTS...

...SUMMARY...
SEVERE THUNDERSTORMS WITH LARGE HAIL...DAMAGING WIND...AND POSSIBLY
A TORNADO OR TWO WILL OCCUR TODAY INTO TONIGHT OVER PARTS OF THE
NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY...ESPECIALLY OVER SOUTH
DAKOTA...NORTHERN NEBRASKA...SOUTHWEST MINNESOTA...AND NORTHWEST
IOWA.  ISOLATED SEVERE STORMS YIELDING DAMAGING WINDS WILL BE
POSSIBLE THIS AFTERNOON FROM THE LOWER MISSISSIPPI VALLEY TO
SOUTHEAST ATLANTIC COAST.

...SYNOPSIS...

A DEEP-LAYER CYCLONE OVER NRN MANITOBA WILL CONTINUE EWD ACROSS SRN
PORTIONS OF HUDSON BAY...ENHANCING A BELT OF WLY MID TO UPPER-LEVEL
FLOW OVER THE N-CNTRL CONUS.  EMBEDDED WITHIN THIS HIGH-MOMENTUM AIR
STREAM...A SHORT-WAVE TROUGH PRESENTLY MOVING SEWD INTO THE NRN
INTERMOUNTAIN REGION WILL ACCELERATE ESEWD INTO THE NRN PLAINS WHERE
IT WILL BECOME LOOSELY PHASED WITH A WEAKER...LOWER-LATITUDE IMPULSE
ORIGINATING OVER ERN PARTS OF THE GREAT BASIN.  ELSEWHERE...A
MID-LEVEL TROUGH OVER THE TN VALLEY AND CNTRL GULF COAST STATES WILL
CONTINUE EWD TOWARD THE MID AND SERN ATLANTIC COASTS.

AT THE SURFACE...A COLD FRONT WILL PROGRESS SEWD THROUGH THE RED AND
UPPER MS VALLEYS WHILE FARTHER WEST THE BOUNDARY SURGES SWD FROM THE
NRN INTO CNTRL HIGH PLAINS.  A FRONTAL WAVE ANALYZED OVER WRN SD
THIS MORNING WILL DEVELOP ESEWD ALONG THE FRONT...REACHING SERN SD
BY 12Z/MONDAY.

...NRN PLAINS/UPPER MS VALLEY THIS AFTERNOON INTO TONIGHT...

A SMALL MCS IS PRESENT AS OF MID MORNING INVOF THE SURFACE COLD
FRONT OVER NERN ND...AND IMMEDIATELY DOWNSTREAM FROM A MID-LEVEL
IMPULSE /LIKELY OF CONVECTIVE ORIGIN/ MOVING THROUGH CNTRL ND.
TIME-HEIGHT TRENDS FROM THE BISMARK WSR-88D VAD INDICATE THAT THIS
DISTURBANCE IS ACCOMPANIED BY A BELT OF 40-50 KT MID-LEVEL FLOW
WHICH WHEN COUPLED WITH A WARMING/DESTABILIZING AIR MASS OVER THE
RED RIVER VALLEY SHOULD SUPPORT THE CONTINUATION OF THE MCS AT LEAST
THROUGH NWRN MN THIS AFTERNOON.  DAMAGING OUTFLOW WINDS AND SOME
SEVERE HAIL WITH BE THE PRIMARY HAZARDS ALONG THE MCS TRACK.  FOR
ADDITION NEAR-TERM GUIDANCE...SEE MCD 1303 AND SEVERE THUNDERSTORM
WATCH 390.

OTHER SURFACE-BASED STORMS ARE LIKELY TO DEVELOP THIS AFTERNOON
ALONG THE TRAILING OUTFLOW FROM THE EARLY-DAY MCS AND/OR COLD FRONT
FROM SERN ND THROUGH CNTRL INTO WRN SD AS DEEP-LAYER FORCING FOR
ASCENT INCREASES AHEAD OF THE MID-LEVEL IMPULSES MENTIONED IN THE
SYNOPSIS.  STEEP LOW TO MID-LEVEL LAPSE RATES COUPLED WITH
BOUNDARY-LAYER DEWPOINTS IN THE 60S WILL YIELD MODERATE TO STRONG
INSTABILITY BY AFTERNOON WITHIN THE PRE-FRONTAL WARM SECTOR WHERE
MLCAPE WILL APPROACH 2000-3000+ J/KG.  THIS INSTABILITY WILL ALIGN
WITH STEADILY STRENGTHENING DEEP-LAYER SHEAR TO FOSTER A MIXTURE OF
SUPERCELLS AND BOWING STRUCTURES WITHIN A LARGER-SCALE NE-SW
ORIENTED CONVECTIVE BAND.  INITIAL HAZARDS WILL BE LARGE HAIL AND
PERHAPS A FEW TORNADOES WITH A TRANSITION TO PRIMARILY DAMAGING
WINDS LATE THIS EVENING INTO TONIGHT AS STORMS CONGEAL INTO A
SEWD-MOVING MCS.

...LOWER MS VALLEY THIS AFTERNOON/EVENING...

12Z REGIONAL RAOBS SAMPLED A VERY MOIST AND ALREADY MODERATE TO
STRONGLY UNSTABLE AIR MASS ON THE BACKSIDE OF THE MID-LEVEL TROUGH
MENTIONED ABOVE.  PERSISTENT SWLY LOW-LEVEL FLOW SHOULD ENHANCE
INFLOW OF THIS AIR MASS INTO THE ONGOING STORMS OVER THE
ARKLAMISS...PROMOTING THE GRADUAL INCREASE IN STORM COVERAGE AND
INTENSITY ALONG A GROWING/DEEPENING COLD POOL.  GIVEN THE DEGREE OF
INSTABILITY...A VERTICALLY VEERING WIND PROFILE AND RELATIVELY
STRONG HIGH-LEVEL FLOW...THE SETUP MAY SUPPORT SOME ORGANIZED
DAMAGING WIND POTENTIAL LATER THIS AFTERNOON INTO EVENING.

...SERN STATES THIS AFTERNOON EVENING...

ALTHOUGH THE AIR MASS IS NOT AS UNSTABLE AS THAT OVER THE LOWER MS
VALLEY...AMPLE MOISTURE AND DAYTIME HEATING WILL YIELD POCKETS OF
MODERATE INSTABILITY BY AFTERNOON DOWNSTREAM FROM THE ONGOING STORMS
OVER SWRN GA AND THE FL PNHDL.  A SLIGHT INCREASE IN SWLY MID-LEVEL
FLOW AND FORCING FOR ASCENT/DCVA AHEAD OF THE UPPER TROUGH SHOULD
AID IN THE GRADUAL INTENSIFICATION OF THE GA/FL STORMS AS WELL AS
PROMOTE ADDITIONAL DEVELOPMENT ALONG SEA BREEZE FRONTS AND
PRE-EXISTING OUTFLOW BOUNDARIES.  GIVEN THE CHARACTER OF THE
THERMODYNAMIC ENVIRONMENT...THE POTENTIAL WILL EXIST FOR ISOLATED
DAMAGING DOWNBURST WINDS WITH THE MOST INTENSE STORMS.

..MEAD/MOSIER.. 07/05/2015




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