SWODY1
SPC AC 180533
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1233 AM CDT FRI MAY 18 2007
VALID 181200Z - 191200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM NERN ND INTO NRN MN...
..SYNOPSIS...
LARGE SCALE UPPER PATTERN WILL REMAIN DOMINATED BY A TROUGH OVER THE
ERN THIRD OF THE COUNTRY AND A RIDGE OVER THE WRN TWO THIRDS.
SHORTWAVE TROUGH NOW MOVING ENEWD THROUGH WRN CANADA WILL CREST TOP
OF UPPER RIDGE AND CONTINUE ESEWD THROUGH S CNTRL CANADA FRIDAY
AFTERNOON. THIS WILL PROVIDE IMPETUS FOR COLD FRONT DRAPED E-W
ACROSS CANADA TO BEGIN TO SHIFT SEWD INTO THE NRN PLAINS AND UPPER
MS VALLEY BY FRIDAY EVENING. IN ADVANCE OF THE FRONT A WEAK SURFACE
LOW IS FORECAST TO DEVELOP EWD INTO THE NRN PLAINS...WITH A TROUGH
OR DRYLINE EXTENDING SSWWD FROM THE LOW THROUGH THE NRN AND CNTRL
HIGH PLAINS. FARTHER WEST...AN UPPER TROUGH OVER THE ERN PACIFIC
WILL MOVE INTO THE PACIFIC NW COASTAL AREA.
..ERN ND THROUGH NRN MN...
PRIMARY MITIGATING FACTORS FOR A MORE ROBUST SEVERE THREAT IN THIS
REGION WILL BE LIMITED LOW LEVEL MOISTURE AND LIKELIHOOD OF A CAP IN
THE WARM SECTOR. THIS EVENING RAOB DATA SHOW AXIS OF SURFACE
DEWPOINTS IN THE LOWER 50S ACROSS THE HIGH PLAINS. THIS MOISTURE
WILL ADVECT NEWD INTO THE UPPER MS VALLEY AS SURFACE LOW DEVELOPS
ACROSS ND AND BOUNDARY LAYER FLOW VEERS TO SWLY. DEWPOINTS MAY DROP
INTO THE UPPER 40S AS MIXING COMMENCES DURING THE DAY. PLUME OF WARM
AIR IN THE 850-700 MB LAYER ASSOCIATED WITH THE EML WILL SPREAD EWD
THROUGH THE WARM SECTOR AND INTO THE UPPER MS VALLEY. THIS ALONG
WITH COOL MID LEVEL TEMPERATURES WILL CONTRIBUTE TO DESTABILIZATION
AND 8+ C/KM 700-500 MB LAPSE RATES WITH MLCAPE AXIS NEAR 1000 J/KG
FROM THE DAKOTAS INTO PARTS OF WRN MN. THE CAP WILL LIKELY LIMIT
SURFACE BASED CONVECTIVE POTENTIAL MUCH OF THE DAY. HOWEVER...A FEW
STORMS WILL BE POSSIBLE NEAR THE DRYLINE AS MIXING WEAKENS THE CAP.
A BETTER CHANCE FOR STORMS MAY EXIST WITHIN ZONE OF STRONGER LIFT
ALONG SWD ADVANCING FRONT AND ON NERN PERIPHERY OF EML FROM PARTS OF
NERN ND INTO NRN MN...ESPECIALLY AS THE LOW LEVEL JET STRENGTHENS
FRIDAY EVENING. THE THERMODYNAMIC ENVIRONMENT WITH SEEP LAPSE RATES
WILL SUPPORT A THREAT FOR ISOLATED LARGE HAIL AND DAMAGING WIND
GUSTS INTO THE EVENING.
..MT...
SURFACE HEATING AND INCREASING UPSLOPE COMPONENT IN POST FRONTAL
REGION MAY RESULT IN A FEW STORMS DEVELOPING OVER THE HIGHER TERRAIN
OF SWRN MT BY LATE AFTERNOON OR EARLY FRIDAY EVENING. SRN EXTENT OF
VERTICAL MOTION ASSOCIATED WITH SHORTWAVE TROUGH NOW APPROACHING THE
PACIFIC NW COAST MAY ALSO GLANCE THE NRN ROCKIES AND INCREASE
THUNDERSTORM POTENTIAL. ACTIVITY WILL SUBSEQUENTLY SPREAD NEWD INTO
THE HIGH PLAINS OF CNTRL MT. PRIMARY MOIST AXIS WILL SHIFT EAST OF
THIS REGION AS SURFACE LOW DEVELOPS OVER THE NRN PLAINS...AND THIS
MAY SERVE AS A LIMITING FACTOR FOR A MORE ROBUST SEVERE THREAT.
HOWEVER...DEEP SHEAR OF 35 TO 40 KT WILL BE SUFFICIENT FOR UPDRAFT
ROTATION. HIGH BASED STORMS CAPABLE OF PRODUCING ISOLATED LARGE HAIL
AND STRONG WIND GUSTS WILL BE THE MAIN THREAT.
..ERN AZ THROUGH NM...
RESIDUAL MOISTURE AND SURFACE HEATING OVER THE HIGHER TERRAIN WILL
LIKELY CONTRIBUTE TO REDEVELOPMENT OF SCATTERED STORMS IN THIS
REGION FRIDAY AFTERNOON. POTENTIAL WILL EXIST FOR ISOLATED HAIL AND
STRONG WIND GUSTS WITH THE STRONGER ACTIVITY...BUT SEVERE COVERAGE
AND STORM ORGANIZATION ARE NOT EXPECTED TO BE SUFFICIENT FOR MORE
THAN LOW SEVERE PROBABILITIES.
.DIAL/CROSBIE.. 05/18/2007
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