Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 300515
SWODY2
SPC AC 300513

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1213 AM CDT TUE JUN 30 2015

VALID 011200Z - 021200Z

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF THE
NORTHEASTERN U.S....

...THERE IS A MRGL RISK OF SVR TSTMS FROM THE MID MS VALLEY INTO THE
TN VALLEY...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE NORTHERN HIGH
PLAINS...

...SUMMARY...
ISOLATED SEVERE THUNDERSTORMS ARE EXPECTED WEDNESDAY AFTERNOON FROM
EASTERN PENNSYLVANIA TO VERMONT AND NEW HAMPSHIRE.  SCATTERED
STORMS...A FEW SEVERE...WILL ALSO DEVELOP FROM THE MID MISSISSIPPI
VALLEY INTO THE TENNESSEE VALLEY.  OTHER STORMS...SOME STRONG...WILL
EVOLVE ACROSS THE NORTHERN HIGH PLAINS.

...NERN U.S...

WEAK 12HR HEIGHT FALLS WILL SPREAD ACROSS THE NERN U.S. AHEAD OF
EJECTING SHORT-WAVE TROUGH.  LARGE-SCALE ASCENT IS EXPECTED AHEAD OF
THIS FEATURE WHICH WILL TRANSLATE INTO THE HUDSON VALLEY AND NRN
MIDDLE ATLANTIC REGION BY 18Z...THEN INTO ERN NEW ENGLAND BY SUNSET.
VEERING LOW-LEVEL FLOW ACROSS THE NRN MIDDLE ATLANTIC...NWD INTO THE
HUDSON VALLEY...SHOULD ALLOW STEEPENING LOWER-TROPOSPHERIC LAPSE
RATES SUCH THAT SCT TSTMS WILL READILY EVOLVE AHEAD OF SFC WIND
SHIFT BY EARLY AFTERNOON.  SHEAR PROFILES ARE EXPECTED TO SUPPORT
ORGANIZED UPDRAFTS BUT FORECAST INSTABILITY IS NOT PARTICULARLY
SIGNIFICANT...GENERALLY LESS THAN 1000 J/KG MUCAPE.  EVEN
SO...ROBUST CONVECTION IS EXPECTED TO SPREAD INTO WRN NEW ENGLAND BY
EARLY AFTERNOON AND LOCALLY DAMAGING WINDS APPEAR TO BE THE MAIN
THREAT WITH THIS ACTIVITY.

...MID MS VALLEY TO TN VALLEY...

RIDGE-TOPPING SHORT-WAVE TROUGH THAT DIGS SEWD ACROSS THE PLAINS
WILL LIKELY ENHANCE CONVECTION ACROSS THE MID MO VALLEY LATE DAY1
WHICH SHOULD PROPAGATE INTO THE MID MS VALLEY ALONG NOSE OF VEERED
LLJ.  BOTH THE NAM AND GFS ARE FAIRLY AGGRESSIVE WITH THIS
CONVECTIVE SIGNAL EARLY IN THE PERIOD AND ULTIMATELY ALLOW
THUNDERSTORM CLUSTERS TO SPREAD/DEVELOP INTO THE TN VALLEY AS
DEEP-LAYER FLOW VEERS AND STRENGTHENS AHEAD OF AFOREMENTIONED
DIGGING SHORT WAVE.  AT THIS TIME WILL ONLY INTRODUCE 5 PERCENT
SEVERE PROBS BUT THE POTENTIAL FOR SUBSTANTIAL CONVECTION ASSOCIATED
WITH AN MCS MAY ULTIMATELY WARRANT HIGHER SEVERE PROBS.  SEVERE WIND
GUSTS AND HAIL ARE THE PRIMARY THREATS.

...NRN HIGH PLAINS...

ANOTHER IN A SERIES OF SHORT-WAVE TROUGHS WILL PROGRESS ATOP RIDGE
ACROSS BC/AB/SK THEN DIG SEWD INTO THE NRN PLAINS.  THIS FEATURE IS
FORECAST TO ENHANCE ASCENT ACROSS THE HIGH PLAINS FROM ERN MT INTO
THE BLACK HILLS REGION OF SD DURING THE AFTERNOON FOCUSING VERTICAL
MOTION ALONG A NW-SE CORRIDOR OF WARM ADVECTION.  BOUNDARY-LAYER
LAPSE RATES SHOULD STEEPEN MARKEDLY ALONG WRN FRINGE OF THIS
ZONE...SHARPENING DEMARCATION BETWEEN SOMEWHAT COOLER AIR MASS OVER
THE DAKOTAS.  SHEAR PROFILES FAVOR ORGANIZED DEEP ROTATION AND WILL
INTRODUCE CATEGORY1 SEVERE THREAT FOR HAIL/WIND.

..DARROW.. 06/30/2015



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