Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 301621
SWODY1
SPC AC 301619

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1119 AM CDT SAT MAY 30 2015

VALID 301630Z - 311200Z

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

...THERE IS A SLGT RISK OF SVR TSTMS OVER NRN MAINE...

...THERE IS A SLGT RISK OF SVR TSTMS OVER NRN LA...

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

...THERE IS A MRGL RISK OF SVR TSTMS FROM TX TO NEW ENGLAND...

...THERE IS A MRGL RISK OF SVR TSTMS OVER THE NRN ROCKIES INTO NRN
HIGH PLAINS...

...SUMMARY...
SCATTERED THUNDERSTORMS...SOME WITH STRONG TO POSSIBLY SEVERE WINDS
AND HAIL...WILL DEVELOP NEAR AND AHEAD OF A COLD FRONT FROM PARTS OF
THE NORTHEAST AND OHIO VALLEY SOUTHWEST INTO TEXAS. A FEW STRONG TO
POSSIBLY SEVERE STORMS ALSO ARE EXPECTED OVER PARTS OF NEW
MEXICO...AND CENTRAL AND EASTERN MONTANA THIS AFTERNOON AND EVENING.

...SYNOPSIS...

THE PRIMARY BELT OF POLAR WESTERLIES WILL REMAIN CONFINED TO CANADA
IN ASSOCIATION WITH A STRONG SHORT-WAVE TROUGH TRANSLATING FROM
ONTARIO THROUGH QUEBEC.  MEANWHILE...A LOWER-LATITUDE TROUGH WILL
SLOWLY PROGRESS EWD THROUGH THE MS VALLEY WITH THE MOST PROMINENT
EMBEDDED PERTURBATION TRACKING FROM AR INTO THE OH VALLEY.

AT THE SURFACE...A COLD FRONT ASSOCIATED WITH THE CANADIAN IMPULSE
MENTIONED ABOVE WILL ADVANCE SEWD THROUGH THE LOWER GREAT LAKES AND
ST. LAWRENCE VALLEY INTO NRN NEW ENGLAND.  THIS BOUNDARY WILL LINK
WITH A MIGRATORY CYCLONE DEVELOPING FROM THE MID MS VALLEY INTO THE
MID OH VALLEY.  THE TRAILING EXTENSION OF THE COLD FRONT WILL
CONTINUE SEWD THROUGH THE SRN PLAINS AND OZARK PLATEAU INTO THE
LOWER MS VALLEY.

...OH VALLEY THIS AFTERNOON/EVENING...

ANALOGOUS TO FRIDAY OVER THE OZARK PLATEAU REGION...A FAVORABLE
OVERLAP OF ENHANCED TROPOSPHERIC FLOW /IN A NARROW SPATIAL CORRIDOR
AHEAD OF THE VORTICITY MAXIMUM AND SURFACE LOW/ AND A MOIST AND
MODERATELY UNSTABLE AIR MASS WILL MATERIALIZE THIS AFTERNOON OVER
THE SLIGHT RISK AREA.  EXPECT A GRADUAL INCREASE IN STORM COVERAGE
AND INTENSITY THROUGH THE AFTERNOON IN AN ARCING BAND IMMEDIATELY
DOWNSTREAM FROM THE VORTICITY LOBE WHERE DCVA IS MAXIMIZED.
FORECAST HODOGRAPHS EXHIBIT A LARGELY UNIDIRECTIONAL WIND PROFILE
WITH MODEST SHEAR IN THE 0-2-KM LAYER.  AS SUCH...THE STRONGER
STORMS WILL BE CAPABLE OF LOCALLY DAMAGING OUTFLOW WINDS AND/OR A
BRIEF TORNADO INTO THIS EVENING.

FOR ADDITIONAL NEAR-TERM GUIDANCE...SEE MCD 843.

...NRN MAINE LATE THIS AFTERNOON INTO EVENING...

MORE SUBSTANTIAL HEIGHT FALLS WILL OVERSPREAD THE ST. LAWRENCE
VALLEY THIS AFTERNOON DOWNSTREAM FROM THE POTENT SHORT-WAVE TROUGH
MOVING INTO WRN QUEBEC.  AT THE SAME TIME...VERTICAL SHEAR AND
LOW-LEVEL MOISTURE CONTENT WILL INCREASE ALONG AND AHEAD OF THE
SEWD-MOVING COLD FRONT WITH MODEST INSTABILITY DEVELOPING LATER
TODAY DESPITE POOR MID-LEVEL LAPSE RATES.  TSTMS ARE EXPECTED TO
INCREASE IN COVERAGE AND INTENSITY ALONG AND AHEAD OF THE COLD FRONT
THROUGH THE PEAK OF THE DIURNAL HEATING CYCLE WITH THE GREATEST RISK
FOR MAINLY DAMAGING WIND GUSTS REMAINING CONFINED TO THE CONVECTION
FORMING ALONG THE FRONT WHERE THE STRONGEST VERTICAL SHEAR WILL
RESIDE.  ACTIVITY SHOULD WEAKEN BY MID TO LATE EVENING AS THE
BOUNDARY LAYER COOLS AND STABILIZES.

...MID/LOWER RIO GRANDE VALLEY THIS AFTERNOON...

A FORWARD-PROPAGATING MCS IS PRESENT AS OF MID MORNING BETWEEN 6R6
AND DRT WITH A SYSTEM MOTION OF 315/35 KT.  AN INCREASED ELY
LOW-LEVEL WIND COMPONENT ALONG THE OUTFLOW BOUNDARY TRAILING ANOTHER
MCS OVER THE ARKLATEX MAY SERVE TO ENHANCE THE INFLUX OF A
MOIST/MODERATELY UNSTABLE AIR MASS...SUPPORTING THE CONTINUED SEWD
MOVEMENT AND LIKELY INTENSIFICATION OF STORMS TODAY ALONG THE
LEADING EDGE OF THE ACTIVE COLD POOL.  AS SUCH...THE POTENTIAL FOR
AN ORGANIZED DAMAGING WIND EVENT COULD MATERIALIZE BY AFTERNOON OVER
A NARROW CORRIDOR IMMEDIATELY ALONG THE RIO GRANDE.

...ARKLATEX INTO LOWER MS VALLEY THIS AFTERNOON...

THE REMNANTS OF A LONG-LIVED MCS WHICH INITIATED ALONG THE TX-NM
BORDER FRIDAY EVENING ARE ONGOING OVER THE ARKLATEX WITH THE LEADING
EDGE OF THE ASSOCIATED COLD POOL ADVANCING EWD AT AROUND 30 KT.
THIS MCS WILL LIKELY RE-INTENSIFY TODAY AS IT CONTINUES EWD ALONG A
W-E-ORIENTED PRE-FRONTAL TROUGH SITUATED OVER NRN LA.  GIVEN THE
MESOSCALE ENHANCEMENT OF THE GRADIENT FLOW AROUND THE ASSOCIATED MCV
/REF. MID-MORNING FT. WORTH VAD/...THE POTENTIAL WILL EXIST FOR THE
FORWARD ACCELERATION OF THE CONVECTIVE SYSTEM WITH AN ATTENDANT RISK
FOR DAMAGING WINDS INCREASING ACROSS NRN LA.

FOR ADDITIONAL NEAR-TERM GUIDANCE...SEE MCD 842.

...NRN ROCKIES INTO NRN HIGH PLAINS THIS AFTERNOON/EVENING...

MID-LEVEL FLOW WILL STRENGTHEN OVER THE REGION TODAY BETWEEN AN
UPPER LOW OVER BRITISH COLUMBIA AND A BUILDING ANTICYCLONE OVER
BAJA.  AN EMBEDDED LOW-AMPLITUDE DISTURBANCE WILL CONTINUE EWD
THROUGH THE NRN INTER-MOUNTAIN REGION INTO ADJACENT HIGH
PLAINS...ENHANCING FORCING FOR ASCENT AND RESULTANT LEE CYCLONE
DEVELOPMENT.  AND WHILE MOISTURE WILL REMAIN SOMEWHAT
LIMITED...STEEP LOW TO MID-LEVEL LAPSE RATES COUPLED WITH THE
FORCING FOR ASCENT AND STRENGTHENING VERTICAL SHEAR MAY YIELD A FEW
SEVERE STORMS CAPABLE OF MARGINALLY SEVERE HAIL AND/OR LOCALLY
DAMAGING WINDS.

..MEAD/BUNTING.. 05/30/2015



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