Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 301729
SWODY2
SPC AC 301728

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT SAT MAY 30 2015

VALID 311200Z - 011200Z

...THERE IS A MRGL RISK OF SVR TSTMS FROM SOUTH AND SOUTHEAST TX TO
THE NORTHEAST STATES...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PORTIONS OF MT/WY AND
THE CENTRAL HIGH PLAINS...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PORTIONS OF OREGON...

...SUMMARY...
STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE ACROSS PARTS OF THE
NORTHEAST STATES...APPALACHIANS TO SOUTHEAST AND SOUTHERN TEXAS ON
SUNDAY...IN ADDITION TO PORTIONS OF THE NORTHERN/CENTRAL HIGH PLAINS
AND OREGON.

...NORTHEAST/MID-ATLANTIC STATES...
A COLD FRONT...ATTENDANT TO A PROGRESSIVE UPPER TROUGH DEPARTING
EASTERN CANADA...WILL MOVE EAST OF MAINE AND SWD THROUGH SRN NEW
ENGLAND ON SUNDAY.  A TRAILING PORTION OF THIS BOUNDARY ACROSS ERN
NY TO NWRN PA IS FORECAST TO STALL AS IT ADVANCES INTO THE NRN TIER
OF PA OR PERHAPS CENTRAL PA TO NRN NJ SUNDAY AFTERNOON.
A MIDLEVEL IMPULSE IS EXPECTED TO UNDERGO FURTHER WEAKENING AS IT
MOVES ENEWD FROM THE OH VALLEY INTO A CONFLUENT FLOW REGIME ACROSS
THE NERN STATES...WHILE A WEAKENING FRONTAL WAVE TRACKS ALONG THE
STALLED FRONT THROUGH THE UPPER OH VALLEY AND WRN PA.  THERE REMAINS
LOW CONFIDENCE/UNCERTAINTY IN THE DEGREE OF DESTABILIZATION THAT
WILL OCCUR NEAR THE STALLED FRONT SUNDAY AFTERNOON.  OVERALL
DIABATIC HEATING MAY BE TEMPERED GIVEN THE POTENTIAL FOR ONGOING
SHOWERS/EMBEDDED TSTMS AND ASSOCIATED CLOUDINESS IN VICINITY OF THE
FRONT AT THE START OF DAY 2.  THIS COMBINED WITH WEAK MIDLEVEL LAPSE
RATES SHOULD RESULT IN GENERALLY WEAK INSTABILITY...THOUGH POCKETS
OF MLCAPE UP TO 1000 J/KG MAY BE FOUND IN AREAS OF STRONGER SURFACE
HEATING.  PRIMARILY EAST OF THE SURFACE LOW AND ALONG THE STALLED
FRONTAL SEGMENT...VERTICAL SHEAR WILL BE SUPPORTIVE OF ORGANIZED
STORMS/POTENTIALLY A COUPLE OF SUPERCELLS PENDING AT LEAST MODEST
DIURNAL DESTABILIZATION.  ISOLATED DAMAGING WINDS/MARGINALLY SEVERE
HAIL AND POTENTIALLY A TORNADO RISK WILL EXIST. PORTIONS OF THE
REGION WILL CONTINUE TO BE REEVALUATED FOR A POSSIBLE CATEGORICAL
SLIGHT RISK UPGRADE IN SUBSEQUENT OUTLOOKS...ESPECIALLY IF
DESTABILIZATION IS GREATER THAN CURRENTLY EXPECTED FROM PA INTO NJ.

...SOUTH/EAST TX TO THE TN VALLEY/CENTRAL APPALACHIANS...
A MARGINAL SEVERE RISK IS BEING MAINTAINED FOR THESE REGIONS.  WITH
A MOIST AIR MASS PRECEDING A SOUTHEASTWARD-MOVING COLD FRONT...
DAYTIME HEATING SHOULD CONTRIBUTE TO AN INTENSIFICATION OF TSTMS
INTO THE AFTERNOON.  VERTICAL SHEAR WILL BE WEAK...THOUGH SUFFICIENT
BUOYANCY COULD RESULT IN SOME STRONGER PULSE-TYPE/ MULTICELL STORMS
CAPABLE OF ISOLATED DAMAGING WIND GUSTS/ POSSIBLY SOME HAIL MAINLY
SUNDAY AFTERNOON/EARLY EVENING.

...PORTIONS OF MT/WY TO CENTRAL HIGH PLAINS...
MODELS SUGGEST A COUPLE OF LOW-AMPLITUDE MIDLEVEL IMPULSES WILL MOVE
THROUGH THE NRN EXTENT OF THE WRN RIDGE ACROSS THE NRN ROCKIES TO
NRN HIGH PLAINS AND ALSO SSEWD INTO THE CENTRAL PLAINS WITHIN NWLY
FLOW ALOFT.  FORCING FOR ASCENT WITH THESE IMPULSES AND DIABATIC
WARMING/STEEPENING LAPSE RATES WITHIN A MODESTLY MOIST ENVIRONMENT
SHOULD PROVE FAVORABLE FOR TSTM DEVELOPMENT ACROSS SOUTHWEST/
SOUTH-CENTRAL MT AND ADJACENT PARTS OF WY SUNDAY AFTERNOON.
MODERATE-STRONG EFFECTIVE BULK SHEAR/ADEQUATE BUOYANCY AND A
WELL-MIXED BOUNDARY LAYER MAY ALLOW FOR STRONG/POSSIBLY SEVERE
THUNDERSTORMS CAPABLE OF STRONG DOWNDRAFT WINDS AND HAIL.  THIS
SEVERE RISK REMAINS MARGINAL AT THIS TIME DUE TO LIMITED AMOUNTS OF
INSTABILITY.

FARTHER E/SE...OTHER ISOLATED STORMS SHOULD DEVELOP SUNDAY
AFTERNOON ACROSS PARTS OF EASTERN WY/NORTHEAST CO/NEB PANHANDLE
VICINITY AND SOUTHWEST SD WITH AID OF A SURFACE TROUGH/WEAK UPSLOPE
TRAJECTORIES AND A WEAK MIDLEVEL IMPULSE.  BULK SHEAR WILL BE
SUFFICIENT FOR ORGANIZED STORMS...THOUGH GENERALLY WEAK INSTABILITY
AND WEAK UPPER FORCING LIMIT THE OVERALL COVERAGE OF STRONG TO
SEVERE STORMS.  STORMS SHOULD SPREAD E/SEWD...POSSIBLY EVOLVING INTO
A LOOSELY ORGANIZED MCS SUNDAY NIGHT WITH AID OF A NOCTURNALLY
INCREASING LOW-LEVEL JET.  ISOLATED OCCURRENCES OF SEVERE HAIL/WIND
WILL BE POSSIBLE ACROSS THE REGION PARTICULARLY SUNDAY AFTERNOON AND
EVENING.

...ORE...
A DIFFLUENT MID- TO UPPER-LEVEL FLOW REGIME IS EXPECTED ACROSS
OREGON SUNDAY AFTERNOON/NIGHT WITH THE APPROACH OF A VIGOROUS
PACIFIC SHORTWAVE TROUGH...CURRENTLY LOCATED NEAR 32N/140W PER
SATELLITE IMAGERY.  HEIGHT FALLS WITH THIS SYSTEM AND MODEST
MOISTURE/STEEPENING LAPSE RATES AND MODERATE-STRONG BULK SHEAR
SHOULD RESULT IN SOME STRONG TO SEVERE STORMS PARTICULARLY ACROSS
WESTERN/CENTRAL PORTIONS OF ORE.  ISOLATED HAIL AND STRONG/DAMAGING
WIND GUSTS WILL BE THE PRIMARY THREATS.

..PETERS.. 05/30/2015



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