Jul 26, 2014 0600 UTC Day 1 Convective Outlook

DAY 1 CONVECTIVE OUTLOOK  

   NWS STORM PREDICTION CENTER NORMAN OK
   1257 AM CDT SAT JUL 26 2014

   VALID 261200Z - 271200Z

   ...THERE IS A MDT RISK OF SVR TSTMS LATE THIS AFTERNOON INTO
   TONIGHT...MAINLY ACROSS MUCH OF CENTRAL ILLINOIS THROUGH CENTRAL AND
   SOUTHERN INDIANA...BUT THIS INCLUDES AT LEAST PARTS OF THE GREATER
   ST. LOUIS...INDIANAPOLIS...LOUISVILLE AND CINCINNATI METROPOLITAN
   AREAS...

   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MODERATE RISK
   AREA ACROSS MUCH OF THE MIDDLE MISSISSIPPI AND LOWER OHIO VALLEYS...

   ...SUMMARY...
   SEVERE STORMS...SOME ACCOMPANIED BY VERY LARGE HAIL...LOCALLY STRONG
   WIND GUSTS AND A COUPLE OF TORNADOES ARE EXPECTED TODAY INTO TONIGHT
   ACROSS PARTS OF THE MIDDLE MISSISSIPPI AND LOWER OHIO VALLEYS.  ONE
   OR MORE ORGANIZED CONVECTIVE CLUSTERS CAPABLE OF GENERATING SWATHS
   OF POTENTIALLY DAMAGING WINDS MAY EVOLVE LATE THIS AFTERNOON AND
   EVENING ACROSS MUCH OF CENTRAL ILLINOIS INTO CENTRAL AND SOUTHERN
   INDIANA...PERHAPS REACHING THE CENTRAL APPALACHIANS BY LATE TONIGHT.

   ...SYNOPSIS...
   WHILE BLOCKING APPEARS LIKELY TO REMAIN PROMINENT WITHIN THE
   WESTERLIES ACROSS THE HIGHER LATITUDES OF NORTH AMERICA...MODELS
   INDICATE UPPER TROUGHING EITHER SIDE OF THE HIGH CENTER OVER
   INTERIOR NORTHERN CANADA WILL BEGIN TO UNDERGO AMPLIFICATION DURING
   THIS PERIOD.  AS THIS OCCURS...SUBTROPICAL RIDGING IS EXPECTED TO
   BUILD NORTHWARD THROUGH MUCH OF THE NORTHERN INTERMOUNTAIN REGION
   AND ROCKIES...AND THE CLOSED LOW...NOW UNDERCUTTING THE CANADIAN
   HIGH...SHOULD DIG SOUTHEASTWARD ACROSS THE CENTRAL CANADIAN/U.S.
   BORDER AREA.

   CONSIDERABLE SPREAD LINGERS WITHIN THE VARIOUS MODEL ENSEMBLE OUTPUT
   CONCERNING THIS LATTER DEVELOPMENT...BUT THE 12Z ECMWF AND 21Z NCEP
   SREF ENSEMBLE MEANS SUGGEST THAT THE REMNANT UPPER LOW/TROUGH
   PROBABLY WILL NOT REACH THE UPPER MIDWEST UNTIL LATE THIS EVENING OR
   OVERNIGHT.  WHILE THE MAIN TRANSITION TO STRENGTHENING AND
   INCREASINGLY CYCLONIC MID-LEVEL FLOW MAY NOT OCCUR UNTIL WELL AFTER
   DARK ACROSS THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY...DEEP
   LAYER SHEAR WILL BE MORE THAN SUFFICIENT FOR ORGANIZED CONVECTIVE
   DEVELOPMENT AS WEAK MID-LEVEL HEIGHT FALLS COMMENCE WITHIN THE
   NORTHWEST FLOW REGIME PRECEDING IT.

   BENEATH A REMNANT PLUME OF VERY WARM AND CAPPING ELEVATED MIXED
   LAYER AIR ALONG THE SOUTHERN EDGE OF THE STRONGER NORTHWEST
   FLOW...LOW-LEVEL MOISTENING SHOULD CONTINUE ACROSS THE LOWER
   MISSOURI/MIDDLE MISSISSIPPI VALLEYS INTO THE OHIO VALLEY.  THIS IS
   EXPECTED TO CONTRIBUTE TO STRONG DESTABILIZATION SUPPORTIVE OF
   INTENSE CONVECTIVE DEVELOPMENT AND THE FOCUS FOR THE PRIMARY SEVERE
   WEATHER POTENTIAL TODAY.

   WEST SOUTHWESTWARD ALONG AN INITIAL SURFACE FRONT ADVANCING
   SOUTHWARD INTO THE CENTRAL PLAINS...SEVERE WEATHER POTENTIAL APPEARS
   LOWER DUE TO STRONGER LINGERING MID-LEVEL INHIBITION AND WEAKER
   SHEAR.  HOWEVER...ISOLATED STRONG/SEVERE STORM DEVELOPMENT MAY NOT
   BE OUT OF THE QUESTION NEAR OR SHORTLY AFTER PEAK HEATING. 
   OTHERWISE...CONDITIONS MAY ALSO BECOME AT LEAST MARGINALLY
   SUFFICIENT FOR STRONG/SEVERE STORM DEVELOPMENT IN RESPONSE TO THE
   EVOLVING UPPER PATTERN...ACROSS PARTS OF THE UPPER GREAT LAKES
   REGION THIS AFTERNOON THROUGH TONIGHT...AND PERHAPS AS FAR EAST AS
   THE LOWER GREAT LAKES/UPPER OHIO VALLEY AND CENTRAL APPALACHIANS BY
   LATE TONIGHT.

   MEANWHILE...MONSOONAL MOISTURE ACROSS THE HIGHER TERRAIN OF THE
   SOUTHERN PLATEAU INTO CENTRAL AND SOUTHERN ROCKIES WILL AGAIN
   SUPPORT CONSIDERABLE THUNDERSTORM ACTIVITY TODAY AND TONIGHT.

   ...MIDDLE MISSISSIPPI INTO LOWER OHIO VALLEYS...
   CONVECTION ALLOWING MODEL GUIDANCE DOES NOT PROVIDE CLARITY FOR THIS
   FORECAST...OFFERING A RATHER BROAD RANGE OF POSSIBLE SOLUTIONS. 
   HOWEVER...A FAIRLY CONSISTENT SIGNAL HAS BEEN EVIDENT IN THE NAM AND
   ECMWF...AMONG OTHER MODEL OUTPUT...SUGGESTING THAT POTENTIAL EXISTS
   FOR THE EVOLUTION OF ONE OR MORE ORGANIZED MESOSCALE CONVECTIVE
   SYSTEMS ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI THROUGH LOWER OHIO
   VALLEYS DURING THIS PERIOD.  GIVEN THE AFOREMENTIONED ENVIRONMENT
   CONDITIONS ANTICIPATED ACROSS THIS REGION BY LATE
   AFTERNOON...CONFIDENCE IS FAIRLY HIGH THAT A SIGNIFICANT SEVERE
   WEATHER EVENT WILL BE REALIZED.

   ALONG/NORTH AND NORTHEAST OF AN AXIS OF STRONG SURFACE HEATING
   ACROSS CENTRAL MISSOURI INTO CENTRAL ILLINOIS...MOISTENING BENEATH
   THE AXIS OF STEEPEST MID-LEVEL LAPSE RATES WILL CONTRIBUTE TO LARGE
   CAPE...BEFORE INHIBITION GRADUALLY ERODES.  PROBABLY AIDED BY
   FORCING ASSOCIATED WITH LOWER/MID TROPOSPHERIC WARM
   ADVECTION...INITIATION OF STORMS MAY OCCUR PRIOR TO 21Z ACROSS PARTS
   OF SOUTHERN IOWA AND NORTHERN MISSOURI.  INITIALLY DISCRETE...A FEW
   SUPERCELLS APPEAR POSSIBLE WITH THE POTENTIAL FOR VERY LARGE
   HAIL...PERHAPS TORNADOES...BEFORE ACTIVITY GRADUALLY CONSOLIDATES
   INTO AN ORGANIZING MESOSCALE CONVECTIVE SYSTEM AND DEVELOPS
   SOUTHEASTWARD ACROSS CENTRAL ILLINOIS AND CENTRAL/SOUTHERN INDIANA
   THROUGH THE EVENING.

   ALTHOUGH MORE UNCERTAIN...AS INITIAL ACTIVITY CONTINUES TO SPREAD
   TOWARD THE CENTRAL APPALACHIANS OVERNIGHT...FORCING ASSOCIATED WITH
   THE DIGGING UPSTREAM IMPULSE MAY SUPPORT RENEWED CONVECTIVE
   DEVELOPMENT ALONG THE TRAILING OUTFLOW BOUNDARY ACROSS THE MIDDLE
   MISSISSIPPI VALLEY.  AT LEAST SOME GUIDANCE SUGGESTS THAT THIS COULD
   EVOLVE INTO ANOTHER SOUTHEASTWARD PROPAGATING MESOSCALE CONVECTIVE
   SYSTEM...IN AN ENVIRONMENT THAT SHOULD REMAIN CONDUCIVE TO THE
   PRODUCTION OF STRONG...POTENTIALLY DAMAGING WIND GUSTS.