Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 310536
SWODY1
SPC AC 310534

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1234 AM CDT FRI JUL 31 2015

VALID 311200Z - 011200Z

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PORTIONS OF THE CENTRAL
PLAINS INTO NORTHWEST MO AND SOUTHWEST IA...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS MAINLY NORTHERN AND
CENTRAL INDIANA THROUGH NORTHERN OH...

...SUMMARY...
ISOLATED MARGINALLY SEVERE STORMS WILL BE POSSIBLE ACROSS PARTS OF
THE CENTRAL PLAINS THIS AFTERNOON AND EVENING...AS WELL AS ACROSS
EAST-CENTRAL ILLINOIS THROUGH INDIANA TO NORTHERN OHIO.

...SYNOPSIS...
AN UPPER TROUGH...ANCHORED BY A LARGE CLOSED LOW CENTERED OVER
HUDSON BAY...WILL AMPLIFY ACROSS THE EASTERN U.S. THIS FORECAST
PERIOD WHILE THE CENTER OF AN UPPER RIDGE SHIFTS WESTWARD FROM THE
SOUTHERN HIGH PLAINS INTO THE FOUR CORNERS REGION.  A BELT OF
RELATIVELY STRONG MID/HIGH-LEVEL CYCLONIC FLOW WITHIN THIS AMPLIFIED
LARGE-SCALE PATTERN WILL EXTEND FROM THE UPPER MIDWEST THROUGH THE
GREAT LAKES TO THE NORTHEAST STATES.  A SERIES OF MIDLEVEL IMPULSES
SHOULD TRACK THROUGH THIS CYCLONIC FLOW...WITH A COLD FRONT
ATTENDANT TO ONE OF THESE IMPULSES ADVANCING E/SEWD THROUGH THE
GREAT LAKES INTO THE OH AND MID MS VALLEYS.  THE TRAILING PORTION OF
THIS BOUNDARY SHOULD STALL ACROSS NORTHERN MO WNWWD INTO SOUTHEAST
TO CENTRAL NEB.

...CENTRAL PLAINS TO NORTHWEST MO/SOUTHWEST IA...
POLEWARD MOISTURE RETURN IS EXPECTED TO THE VICINITY OF THE STALLED
FRONT FROM NORTHERN MO TO CENTRAL NEB.  THIS COMBINED WITH DIABATIC
HEATING AND THE EASTERN EXTENT OF STEEP MIDLEVEL LAPSE RATES SHOULD
RESULT IN MODERATELY STRONG INSTABILITY.  WEAK...VERTICALLY VEERING
LOW-LEVEL WINDS WITH THIS REGION TENDING TO RESIDE ON THE SOUTHERN
EXTENT OF STRENGTHENING NWLY FLOW ALOFT WILL RESULT IN EFFECTIVE
BULK SHEAR INCREASING TO 30-40 KT.  ALTHOUGH THERMODYNAMICS AND
KINEMATICS WILL FAVOR STORM ORGANIZATION WITH MULTICELLS AND SOME
SUPERCELL MODES POSSIBLE...MODELS DIFFER ON THE COVERAGE OF STORMS
POTENTIALLY DUE TO THE LACK OF STRONGER LOW-LEVEL CONVERGENCE AND
WEAK FORCING ALOFT.  FOR THESE REASONS...THIS OUTLOOK ISSUANCE WILL
MAINTAIN LOW SEVERE PROBABILITIES FOR WIND AND HAIL.

...NORTHERN OH/NORTHERN AND CENTRAL INDIANA/EAST-CENTRAL IL...
A NARROW MOISTENING BOUNDARY LAYER IS EXPECTED AHEAD OF THE
SOUTHEAST-MOVING COLD FRONT TODAY.  DESPITE THIS FACTOR AND SOME
SURFACE HEATING...WEAK MIDLEVEL LAPSE RATES DUE TO AN INDICATION OF
A WARM LAYER BETWEEN 500-700 MB SHOULD ONLY RESULT IN MARGINAL
INSTABILITY /MUCAPE 500-1000 J PER KG/.  STRENGTHENING NORTHWESTERLY
WINDS WITH HEIGHT WILL LENGTHEN HODOGRAPHS TO SUPPORT STORMS CAPABLE
OF HAIL AND STRONG WIND GUSTS.  THE WEAK INSTABILITY WILL LIMIT THE
COVERAGE OF STRONG TO SEVERE STORMS WITH THE OVERALL THREAT
DIMINISHING THIS EVENING.

...SOUTHEAST STATES...
A STALLED FRONTAL ZONE EXPECTED TO EXTEND FROM THE CAROLINAS SWWD
THROUGH CENTRAL/SRN GA TO SRN AL...SEA BREEZE BOUNDARIES...AND THEIR
VARIOUS INTERSECTIONS WILL BE FOCI FOR SHOWERS AND TSTMS INTO THE
AFTERNOON AND EARLY EVENING.  DESPITE WEAK MIDLEVEL LAPSE RATES...
SOME SURFACE HEATING WITHIN A VERY MOIST ENVIRONMENT /PW VALUES UP
TO 2-2.25 INCHES/ SHOULD RESULT IN A CORRIDOR OF MODERATE
INSTABILITY SOUTH OF THE FRONT...SUPPORTIVE OF TSTM DEVELOPMENT.
VERY WEAK MEAN WINDS AND BULK SHEAR SUGGEST STORMS WILL BE
PULSE-TYPE...WITH A FEW STRONG WIND GUSTS POSSIBLE.  HOWEVER...GIVEN
THE WEAK MIDLEVEL LAPSE RATES AND DEEP SHEAR...LOW SEVERE
PROBABILITIES DO NOT APPEAR WARRANTED AT THIS TIME.

..PETERS/MARSH.. 07/31/2015




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