Severe Storm Outlook Narrative (AC)
Issued by NWS

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
ACUS01 KWNS 301626
SWODY1
SPC AC 301625

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1125 AM CDT SAT JUL 30 2016

VALID 301630Z - 311200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON AND/OR
TONIGHT ACROSS THE BLACK HILLS REGION...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS SURROUNDING AREAS OF THE
HIGH PLAINS INTO LOWER CENTRAL PLAINS...

...THERE IS A MRGL RISK OF SVR TSTMS THIS AFTERNOON NEAR LAKE
ERIE...

...THERE IS A MRGL RISK OF SVR TSTMS TO THE EAST OF THE ALLEGHENY
MOUNTAINS AND BLUE RIDGE...INTO NORTHERN MID ATLANTIC COASTAL
AREAS...

...SUMMARY...
ISOLATED STRONG TO LOCALLY SEVERE THUNDERSTORMS ARE POSSIBLE FROM
NEAR THE BLACK HILLS INTO THE CENTRAL HIGH PLAINS...ACROSS THE MID
ATLANTIC COAST REGION...AND PERHAPS ACROSS PARTS OF THE LOWER GREAT
LAKES REGION THIS AFTERNOON AND EVENING.  A FEW STRONG STORMS ARE
ALSO POSSIBLE LATE TONIGHT OVER THE CENTRAL PLAINS.

...SYNOPSIS...
WITHIN ONE BELT OF MID-LATITUDE WESTERLIES...A BROAD CLOSED LOW AND
UPPER TROUGH APPEAR LIKELY TO CONTINUE SHIFTING EAST OF THE CANADIAN
ROCKIES...AND ADJACENT INTERNATIONAL BORDER AREA...TOWARD THE
CANADIAN PRAIRIES.  AS THIS OCCURS...MODELS INDICATE SOME
AMPLIFICATION OF SHORT WAVE RIDGING DOWNSTREAM...ACROSS THE NORTHERN
HIGH PLAINS...WITHIN A WEAKER BELT OF WESTERLIES ON THE NORTHERN
PERIPHERY OF GENERALLY FLAT SUBTROPICAL RIDGING ACROSS THE SOUTHERN
TIER STATES.  AT THE SAME TIME...A RESIDUAL SUBTROPICAL HIGH
CENTER...WHICH HAS BEEN OVER THE SOUTHERN GREAT BASIN THE PAST FEW
DAYS...MAY CONTINUE TO REDEVELOP EASTWARD ACROSS PARTS OF THE
SOUTHERN ROCKIES.

DOWNSTREAM OF THE NORTHERN HIGH PLAINS MID/UPPER RIDGING...BROAD
TROUGHING LINGERS...WITH A CONTINUED SLOW EASTWARD PROGRESSION
ACROSS THE OHIO VALLEY.  IN LOWER LEVELS...A DIFFUSE FRONTAL ZONE
ARCS WESTWARD ACROSS THE LOWER OHIO/MIDDLE MISSISSIPPI VALLEYS INTO
THE CENTRAL PLAINS...FROM AN AREA OF LOWER PRESSURE IN THE LAKE ERIE
VICINITY.  EAST OF THE LOW...THE FRONTAL ZONE IS A BIT MORE DISTINCT
ACROSS THE UPPER OHIO VALLEY INTO MID ATLANTIC COAST REGION.

SEASONABLY HIGH MOISTURE CONTENT AIR IS GENERALLY CONFINED TO AREAS
SOUTH/SOUTHEAST OF THE FRONTAL ZONE TO THE EAST OF THE ROCKIES...AND
ACROSS PARTS OF THE LOWER COLORADO VALLEY.  STEEP MID-LEVEL LAPSE
RATES ARE MOSTLY CONFINED TO THE INTERMOUNTAIN WEST/ROCKIES AND
ADJACENT HIGH PLAINS.  BUT...INCREASINGLY WARM ELEVATED MIXED LAYER
AIR...EMERGING FROM THE INTERMOUNTAIN REGION...APPEARS LIKELY TO
EDGE EASTWARD ACROSS THE NORTHERN AND CENTRAL PLAINS THROUGH LATE
TONIGHT...IN RESPONSE TO THE PROGRESSION OF THE WESTERN CANADIAN
IMPULSE.

...NORTH CENTRAL PLAINS...
POTENTIAL FOR INCREASING INHIBITION WITH GRADUAL MID-LEVEL WARMING
AND HEIGHT RISES...COUPLED WITH PERHAPS SOMEWHAT MODEST LOW-LEVEL
MOISTURE...CONTRIBUTE TO UNCERTAINTY WITH REGARD TO CONVECTIVE
POTENTIAL TODAY.

AN AREA OF ENHANCED LOW-LEVEL WARM ADVECTION APPEARS TO HAVE BEEN A
SIGNIFICANT CONTRIBUTOR TO A SUSTAINED CLUSTER OF THUNDERSTORMS NOW
PROGRESSING ACROSS PARTS OF SOUTHEASTERN NEBRASKA INTO NORTHEASTERN
KANSAS.  HOWEVER...ACTIVITY APPEARS TO BE IN THE PROCESS OF
DIMINISHING IN RESPONSE TO WEAKENING FORCING FOR ASCENT...AND IT IS
NOT YET CLEAR WHETHER INHIBITION FOR DOWNSTREAM BOUNDARY LAYER
PARCELS WILL WEAKEN ENOUGH TO ALLOW FOR SUSTAINED NEW STORM
DEVELOPMENT ALONG THE REMNANT COLD POOL.

OTHERWISE...FORCING FOR LARGE-SCALE ASCENT TO SUPPORT THUNDERSTORM
DEVELOPMENT PRIOR TO SOMETIME THIS EVENING OR OVERNIGHT REMAINS
UNCLEAR.  OROGRAPHIC FORCING NEAR THE BLACK HILLS COULD PROVIDE THE
FOCUS/FORCING FOR ISOLATED STORM DEVELOPMENT.  MID-LEVEL INHIBITION
MAY REMAIN WEAK ENOUGH TO ALLOW FOR WIDELY SCATTERED THUNDERSTORMS
TO THE SOUTH AND EAST OF THE BLACK HILLS.  IF THIS OCCURS...SHEAR
BENEATH WEAK TO MODEST /20-30 KT/ NORTHWESTERLY MID-LEVEL FLOW MAY
BE SUFFICIENT FOR SUPERCELLS...IN AN ENVIRONMENT CHARACTERIZED BY
STEEP MID-LEVEL LAPSE RATES...PROVIDING SUPPORT FOR THE RISK OF
LARGE HAIL AND LOCALIZED DAMAGING SURFACE GUSTS.

AT LEAST SOMEWHAT BETTER POTENTIAL FOR THUNDERSTORM DEVELOPMENT
APPEARS TO EXIST LATE THIS EVENING INTO THE OVERNIGHT HOURS.  THIS
MAY BE AIDED BY WARM ADVECTION ASSOCIATED WITH A NOCTURNALLY
STRENGTHENING SOUTHERLY LOW-LEVEL JET...ACROSS PARTS OF
NEBRASKA/KANSAS...AND/OR PERHAPS FORCING WITH A SUBTLE PERTURBATION
ON THE SOUTHERN FRINGE OF THE WESTERLIES...ACROSS THE BLACK HILLS
REGION.

...LOWER GREAT LAKES INTO MID ATLANTIC REGION...
DOWNSTREAM OF LOW AMPLITUDE UPPER TROUGHING...20-30 KT WESTERLY
MID-LEVEL FLOW MAY CONTRIBUTE TO SOME ENHANCEMENT OF THUNDERSTORM
DEVELOPMENT NEAR THE FRONT/LOW IN THE VICINITY OF LAKE ERIE...AND TO
THE EAST OF THE CENTRAL APPALACHIANS.  LOW/MID-LEVEL LAPSE RATES ARE
GENERALLY WEAK...AND SEASONABLY STRONG SURFACE HEATING APPEARS
UNLIKELY.  FURTHERMORE...LOW-LEVEL WIND FIELDS ARE WEAK.
HOWEVER...HEAVY PRECIPITATION LOADING MAY BE ENOUGH TO CONTRIBUTE TO
THE RISK FOR POTENTIALLY DAMAGING DOWNBURSTS IN SUSTAINED
THUNDERSTORM ACTIVITY.  GREATEST POTENTIAL FOR THIS MAY BE NEAR AND
TO THE LEE OF THE BLUE RIDGE LATE THIS AFTERNOON...IN ASSOCIATION
WITH STRONGEST INSOLATION...BUT OVERALL SEVERE WEATHER POTENTIAL
APPEARS LIKELY TO REMAIN MARGINAL IN NATURE.

..KERR/JIRAK.. 07/30/2016

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.