SWODY2
SPC AC 121722
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1222 PM CDT SAT MAY 12 2007
VALID 131200Z - 141200Z
..THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE NRN HIGH
PLAINS...
..THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE UPPER MS
VALLEY INTO UPPER GREAT LAKES...
..SYNOPSIS...
SPLIT FLOW LARGE-SCALE PATTERN WILL EXIST OVER N. AMERICA DURING THE
DAY TWO PERIOD WITH THE PRIMARY BELT OF POLAR WESTERLIES FROM THE
WRN STATES EWD THROUGH N-CNTRL TIER TO ERN STATES. SUB-TROPICAL
BRANCH WILL PERSIST FROM MEXICO EWD ACROSS THE GULF OF MEXICO AND S
FL. PRIMARY FEATURE OF INTEREST WILL BE SHORT WAVE TROUGH WHICH
WILL TRANSLATE FROM THE PACIFIC NW EWD INTO THE NRN HIGH PLAINS BY
MONDAY MORNING.
IN THE LOW-LEVELS...LEAD SURFACE LOW ATTENDANT TO WEAKER DOWNSTREAM
IMPULSE WILL DEVELOP ENEWD FROM WRN SD INTO THE UPPER MS VALLEY WITH
SECONDARY/PRIMARY CYCLONE DEVELOPING OVER SERN MT AND FOLLOWING A
SIMILAR TRACK. TRAILING COLD FRONT IS FORECAST TO PUSH SEWD THROUGH
THE NRN ROCKIES AND ADJACENT HIGH PLAINS WHILE LEE TROUGH
STRENGTHENS OVER THE CNTRL HIGH PLAINS.
..NRN HIGH PLAINS...
STEEP LOW/MID-LEVEL LAPSE RATES COUPLED WITH MODEST BOUNDARY LAYER
MOISTURE /DEWPOINTS IN THE UPPER 40S TO LOWER/MID 50S/ ARE EXPECTED
TO CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS SUNDAY AFTERNOON
AHEAD OF FRONT OVER CNTRL/ERN MT WITH MLCAPES OF 1000-1500 J/KG.
INCREASED LARGE-SCALE FORCING FOR ASCENT ASSOCIATED WITH APPROACHING
UPPER TROUGH IN CONJUNCTION WITH FRONTAL CONVERGENCE AND OROGRAPHIC
UPSLOPE WILL COMBINE TO SUPPORT STORM INITIATION BY AFTERNOON OVER
PORTIONS OF CNTRL INTO SWRN MT.
INITIALLY...POTENTIAL FOR A FEW SUPERCELLS WILL BE RELATIVELY HIGH
GIVEN THE PRESENCE OF 50-60 KT EFFECTIVE BULK SHEAR AND THE MODERATE
INSTABILITY. THE MOST INTENSE STORMS WILL BE CAPABLE OF LARGE
HAIL...LOCALLY DAMAGING WINDS AND PERHAPS A FEW TORNADOES.
CONVECTION IS EXPECTED TO GROW UPSCALE INTO AN MCS SUNDAY NIGHT OVER
ERN MT INTO THE WRN DAKOTAS WITH THE PRIMARY SEVERE THREATS BEING
DAMAGING WINDS AND SEVERE HAIL. THIS MAY CONTINUE EWD ACROSS
N-CNTRL SD/S-CNTRL ND INTO MONDAY MORNING.
..UPPER MS VALLEY INTO UPPER GREAT LAKES...
CLUSTERS OF ELEVATED STORMS /SOME CAPABLE OF MARGINALLY SEVERE HAIL/
ARE EXPECTED TO BE ONGOING SUNDAY MORNING OVER PORTIONS OF
MN...FORCED LARGELY BY LOW-LEVEL WAA ALONG SWLY 40-45 KT LLJ. THIS
ACTIVITY SHOULD TEND TO WEAKEN THROUGH THE MORNING AS IT SHIFTS EWD
INTO WI. THE PRIMARY UNCERTAINTY ACROSS THIS REGION IS THE
EVOLUTION OF DIURNAL CONVECTIVE DEVELOPMENT GIVEN THE ANTICIPATED
STRONG CAP ACROSS MODERATELY UNSTABLE AIR MASS /MLCAPES OF 1500-2500
J PER KG/ OVER THE UPPER MS VALLEY.
SURFACE-BASED STORMS ARE EXPECTED TO BECOME INCREASINGLY LIKELY BY
LATE AFTERNOON/EARLY EVENING OVER SERN MANITOBA/SWRN ONTARIO INTO
FAR NRN MN AS FORCING ASSOCIATED WITH A LEAD SHORT WAVE TROUGH AND
LOW-LEVEL WAA ERODE CAP AHEAD OF INITIAL SURFACE LOW. HERE
TOO...INITIAL STORM MODE SHOULD BE SUPERCELLULAR WITH A THREAT OF
LARGE HAIL AND A COUPLE TORNADOES GIVEN STRONG HODOGRAPH CURVATURE
AND 40-50 KT OF EFFECTIVE BULK SHEAR. STORMS SHOULD EVOLVE INTO
CLUSTERS OR AN MCS WITH A DAMAGING WIND/HAIL THREAT SPREADING
EWD/SEWD THROUGH THE ARROWHEAD...NRN WI AND THE UP OF MI SUNDAY
NIGHT.
..GULF COAST STATES...
A MOIST BOUNDARY LAYER /DEWPOINTS IN THE 60S/ COUPLED WITH MODESTLY
COOL MID-LEVEL TEMPERATURES ASSOCIATED WITH SUB-TROPICAL TROUGHING
OVER THE GULF OF MEXICO WILL RESULT IN THE DEVELOPMENT OF MODERATE
INSTABILITY /MLCAPES OF 1500-2500 J PER KG/ ACROSS THE REGION SUNDAY
AFTERNOON. A WEAK LOW-LEVEL FRONTAL BOUNDARY IS EXPECTED TO FOCUS
DIURNAL TSTM DEVELOPMENT WITH SOME POTENTIAL FOR LOCALLY DAMAGING
WINDS AND SEVERE HAIL WITH THE MORE INTENSE STORMS. RELATIVELY WEAK
VERTICAL SHEAR WILL LIMIT A MORE ORGANIZED SEVERE THREAT.
.MEAD.. 05/12/2007
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