SPC AC 120547
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1247 AM CDT FRI JUN 12 2009
VALID 121200Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS TODAY AND TONIGHT FROM PARTS OF
THE CENTRAL PLAINS EASTWARD THROUGH THE SRN MID ATLANTIC STATES....
...SYNOPSIS...
WITHIN THE SOUTHERN BRANCH OF THE PREVAILING SPLIT UPPER FLOW...
MODELS INDICATE TROUGHING WILL PERSIST ACROSS THE PACIFIC COAST INTO
THE GREAT BASIN. A SIGNIFICANT IMPULSE EMBEDDED WITHIN THIS REGIME
IS PROGGED TO LIFT ACROSS SOUTHERN CALIFORNIA AND THE LOWER COLORADO
VALLEY DURING THIS FORECAST PERIOD. AS THIS OCCURS...A DOWNSTREAM
RIDGE IS EXPECTED TO BUILD ALONG AN AXIS FROM A NORTHEAST MEXICAN
SUBTROPICAL HIGH CENTER NORTHWARD THROUGH THE CENTRAL ROCKIES/HIGH
PLAINS REGION. IN RESPONSE...MODERATELY STRONG MID/UPPER FLOW
LIKELY WILL TAKE ON AN INCREASING NORTHWESTERLY COMPONENT ACROSS THE
EAST CENTRAL PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY AND OZARK
PLATEAU. AT THE SAME TIME...MODELS SUGGEST THAT BROADLY CYCLONIC
WESTERLY FLOW WILL PERSIST DOWNSTREAM ACROSS THE LOWER
OHIO/TENNESSEE VALLEYS THROUGH THE MID ATLANTIC COAST...WITH A
WEAKER BUT BROADLY DIFLUENT REGIME ACROSS THE SOUTHEAST...BETWEEN
THE TROUGH AND THE NORTHEASTERN PERIPHERY OF THE SUBTROPICAL RIDGE.
THIS PATTERN WILL MAINTAIN HIGH MOISTURE CONTENT AND VERY WARM TO
HOT CONDITIONS SUPPORTIVE OF MODERATE TO STRONG POTENTIAL
INSTABILITY OVER A BROAD REGION FROM THE CENTRAL/SOUTHERN PLAINS
THROUGH THE MID SOUTH AND MID/SOUTHERN ATLANTIC SEABOARD. AND THIS
IS EXPECTED TO ONCE AGAIN CONTRIBUTE TO CONSIDERABLE VIGOROUS
CONVECTIVE DEVELOPMENT. HIGHEST SEVERE PROBABILITIES...AND THE BEST
CHANCE FOR ONE OR MORE ORGANIZED MESOSCALE CONVECTIVE
SYSTEMS...APPEARS TO EXIST ON THE NORTHEASTERN PERIPHERY OF THE
BUILDING RIDGE...FROM PARTS OF THE EAST CENTRAL PLAINS INTO THE
OZARK PLATEAU.
...CENTRAL PLAINS INTO THE OZARK PLATEAU...
A TIGHTENING LOWER/MID TROPOSPHERIC THERMAL GRADIENT ON THE SOUTHERN
PERIPHERY OF A PERTURBATION CURRENTLY EMERGING FROM THE CENTRAL
ROCKIES MAY BECOME THE FOCUS FOR THE PRIMARY CONVECTIVE DEVELOPMENT
TODAY. THIS APPEARS LIKELY TO SET UP IN THE VICINITY OF THE EASTERN
KANSAS/OKLAHOMA BORDER AREA BY THE 12-18Z TIME FRAME...WHERE ACCESS
TO HIGH MOISTURE CONTENT AIR CHARACTERIZED BY SURFACE DEW POINTS
AROUND 70F AND PRECIPITABLE WATER NEAR TWO INCHES WILL EXIST. IN
THE PRESENCE OF STEEP LAPSE RATES...MIXED LAYER CAPE OF 2000-4000
J/KG IS EXPECTED TO DEVELOP...BENEATH 40-50 KT WEST/NORTHWESTERLY
500 MB FLOW. AIDED BY FORCING ASSOCIATED WITH WARM ADVECTION ALONG
THE BAROCLINIC ZONE... INTENSE CONVECTION IS EXPECTED TO
DEVELOP/CONSOLIDATE AND ORGANIZE INTO A SEVERE MESOSCALE CONVECTIVE
SYSTEM CAPABLE OF PRODUCING VERY LARGE HAIL/HEAVY RAIN. LOW-LEVEL
FLOW FIELDS ARE PROGGED TO REMAIN FAIRLY WEAK...BUT MOMENTUM
ASSOCIATED WITH THE MID-LEVEL FLOW FIELDS SHOULD EVENTUALLY
CONTRIBUTE TO THE FORWARD PROPAGATION OF AN EXPANDING SURFACE COLD
POOL...ACCOMPANIED BY INCREASING DAMAGING WIND POTENTIAL ACROSS
SOUTHERN MISSOURI/NORTHERN ARKANSAS BY THIS AFTERNOON.
...MID SOUTH/NRN GULF STATES INTO THE MID/S ATLANTIC SEABOARD...
MODEST WESTERLY MID-LEVEL FLOW AND MODERATE INSTABILITY ON THE
SOUTHERN FRINGE OF THE WESTERLIES WILL PROVIDE A FAVORABLE
ENVIRONMENT FOR STRONG/SEVERE STORM DEVELOPMENT ACROSS THE REGION
TODAY. MID-LEVEL PERTURBATIONS PROVIDING THE FOCUS FOR ORGANIZED
STORM CLUSTERS ARE STILL UNCLEAR AT THE PRESENT TIME...BUT MID-LEVEL
CAPPING IS EXPECTED TO REMAIN FAIRLY WEAK...AND STORMS COULD BECOME
NUMEROUS BY PEAK AFTERNOON HEATING. IT IS NOT OUT OF THE QUESTION
THAT A SIGNIFICANT MESOSCALE CONVECTIVE SYSTEM INITIATING OVER THE
CENTRAL PLAINS EARLY IN THE DAY COULD PERSIST ...AND CONTINUE EAST
SOUTHEASTWARD THROUGH TENNESSEE AND THE NORTHERN GULF STATES BY LATE
THIS EVENING.
..KERR/GRAMS.. 06/12/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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