SPC AC 081730

   DAY 2 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1230 PM CDT WED APR 08 2015

   VALID 091200Z - 101200Z

   ...THERE IS AN ENH RISK OF SVR TSTMS THURSDAY AFTERNOON AND EVENING
   ACROSS PARTS OF SOUTHERN GREAT LAKES REGION AND LOWER OHIO
   VALLEY...SOUTHWARD THROUGH THE OZARK PLATEAU AND ARKLATEX REGION...

   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE ENH RISK
   AREA...ACROSS THE GREAT LAKES REGION AND OHIO VALLEY...SOUTHWARD
   INTO THE SOUTHEASTERN PLAINS...

   ...THERE IS A MRGL RISK OF SVR TSTMS AS FAR SOUTHEAST AS THE EDWARDS
   PLATEAU AND ADJACENT PORTIONS OF THE RIO GRANDE VALLEY...

   ...SUMMARY...
   SEVERE THUNDERSTORMS ARE LIKELY THURSDAY INTO THURSDAY NIGHT ACROSS
   SOUTHERN PORTIONS OF THE GREAT LAKES REGION...AND MUCH OF THE MIDDLE
   MISSISSIPPI AND OHIO VALLEYS INTO THE SOUTHEASTERN PLAINS.  THIS
   WILL INCLUDE THE RISK FOR DAMAGING WIND GUSTS AND LARGE HAIL.  A
   COUPLE OF STRONG TORNADOES ARE POSSIBLE.

   ...SYNOPSIS...
   A SIGNIFICANT IMPULSE...WITHIN THE SOUTHERN BRANCH OF SPLIT
   WESTERLIES EMERGING FROM THE MID-LATITUDE PACIFIC...IS FORECAST TO
   CONTINUE AN EAST NORTHEASTWARD ACCELERATION OUT OF THE GREAT BASIN
   DURING THIS PERIOD.  THIS FEATURE IS EXPECTED TO REACH THE CENTRAL
   HIGH PLAINS BY 12Z THURSDAY...AND THE UPPER MIDWEST BY THURSDAY
   NIGHT...WHERE/WHEN MODELS SUGGEST THAT IT MAY INCREASINGLY PHASE
   WITH A SIGNIFICANT NORTHERN STREAM IMPULSE.  AS THIS OCCURS...MORE
   SUBSTANTIVE DEEPENING OF AN ASSOCIATED SURFACE CYCLONE...EMERGING
   FROM THE CENTRAL PLAINS...IS EXPECTED TO PROCEED ACROSS AND EAST
   NORTHEAST OF THE GREAT LAKES REGION.

   ALTHOUGH SUBSTANTIVE DEEPENING OF THE LOW IS NOT CURRENTLY FORECAST
   AS IT TRACKS FROM THE MID MISSOURI VALLEY TOWARD LAKE MICHIGAN
   DURING THE DAY THURSDAY...IT STILL IS EXPECTED TO BE AT LEAST
   MODERATELY STRONG WITH LOWEST PRESSURES AT OR BELOW 1000 MB.  A
   TRAILING SURFACE COLD FRONT APPEARS LIKELY TO ADVANCE SOUTHWARD
   THROUGH THE MIDDLE MISSISSIPPI VALLEY AND PORTIONS OF THE OZARK
   PLATEAU AND SOUTHEASTERN PLAINS...WHERE IT WILL GRADUALLY OVERTAKE A
   WELL-DEFINED DRYLINE.  A WARM FRONT EAST OF THE LOW APPEARS LIKELY
   TO ADVANCE NORTHWARD THROUGH THE GREAT LAKES REGION...WHILE COLD AIR
   REMAINS DAMMED TO THE EAST OF MUCH OF THE NORTHERN AND CENTRAL
   APPALACHIANS.

   AIDED BY THE PRESENCE OF MOIST AND POTENTIALLY UNSTABLE AIR IN THE
   WARM SECTOR OF THE CYCLONE...LARGE-SCALE FORCING FOR UPWARD VERTICAL
   MOTION SHOULD BE SUFFICIENT TO SUPPORT WIDESPREAD THUNDERSTORM
   ACTIVITY...FROM THE MISSISSIPPI VALLEY AND SOUTHEASTERN PLAINS INTO
   THE APPALACHIANS...PERHAPS PORTIONS OF THE PIEDMONT TO THE EAST OF
   THE SOUTHERN APPALACHIANS.  IN THE PRESENCE OF MODERATELY
   STRONG...40-50 KT DEEP LAYER MEAN FLOW AND DEEP LAYER SHEAR...A
   NUMBER OF THESE STORMS MAY BECOME SEVERE.  MUCH OF THIS ACTIVITY
   SEEMS LIKELY TO BE FOCUSED ON THE AFOREMENTIONED SURFACE
   BOUNDARIES...PARTICULARLY ALONG THE SOUTHEASTWARD SURGING
   FRONT/DRYLINE ACROSS THE OHIO VALLEY INTO SOUTHEASTERN PLAINS BY
   THURSDAY EVENING.

   ...GREAT LAKES/OHIO VALLEY INTO SOUTHEASTERN PLAINS...
   MODEL OUTPUT IS SUGGESTIVE THAT DEEPER/RICHER BOUNDARY LAYER
   MOISTENING MAY BE CONFINED TO A RELATIVELY NARROW CORRIDOR IN
   ADVANCE OF THE COLD FRONT.  AND CONSIDERABLE CONVECTIVE ACTIVITY MAY
   BE ONGOING IN THE WARM SECTOR ACROSS PARTS OF THE MIDDLE MISSISSIPPI
   AND OHIO VALLEYS AT THE OUTSET OF THE PERIOD.  BY 12Z THURSDAY...IT
   ALSO APPEARS THAT THERE MAY BE CONSIDERABLE STABILIZATION OF THE
   BROAD AREA OF STEEP MID-LEVEL LAPSE RATES NOW PRESENT ACROSS THE
   PLAINS INTO THE VICINITY OF THE APPALACHIANS.  THESE FACTORS...AMONG
   OTHERS...MAY BE LIMITING FACTORS TO A POTENTIALLY MORE SUBSTANTIVE
   SEVERE WEATHER RISK FOR THIS PERIOD.

   STILL...GIVEN THE LARGE-SCALE FORCING AND STRENGTH OF DEEP LAYER
   FLOW/SHEAR...INCLUDING A RATHER BROAD AREA OF 40-50 KT SOUTH
   SOUTHWESTERLY 850 MB FLOW DURING THE DAY...THE ENVIRONMENT WILL BE
   CONDUCIVE TO ORGANIZED CONVECTIVE DEVELOPMENT...INCLUDING
   SUPERCELLS.  AND POCKETS OF STRONGER DESTABILIZATION COULD YIELD
   SCATTERED AREAS WITH POTENTIAL FOR INTENSE SUPERCELLS CAPABLE OF
   PRODUCING A STRONG TORNADO OR TWO...IN ADDITION TO VERY LARGE HAIL. 
   IT IS POSSIBLE THAT ONE OF THESE AREAS COULD DEVELOP NEAR THE WARM
   FRONT...IN THE VICINITY OF THE SURFACE LOW...ACROSS PARTS OF
   NORTHERN ILLINOIS...INCLUDING THE CHICAGO METRO AREA...
   DURING THE MIDDAY AND AFTERNOON HOURS.  ANOTHER COULD DEVELOP NEAR
   THE COLD FRONT/DRY LINE INTERSECTION...ACROSS PARTS OF THE OZARK
   PLATEAU AND ARKLATEX REGION DURING THE LATE AFTERNOON AND EVENING. 
   HOWEVER...TOO MUCH UNCERTAINTY CURRENTLY EXISTS CONCERNING COVERAGE
   AND AREA TO SUPPORT 10 PERCENT SIGNIFICANT SEVERE WEATHER
   PROBABILITIES AT THE PRESENT TIME.

   OTHERWISE...DAMAGING CONVECTIVE SURFACE GUSTS MAY EVENTUALLY BECOME
   THE MOST PROMINENT SEVERE WEATHER THREAT WITH AN EVOLVING SQUALL
   LINE ALONG/AHEAD OF THE COLD FRONT BY THURSDAY EVENING.

   ..KERR.. 04/08/2015

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