SPC AC 280557
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT TUE JUL 28 2009
VALID 281200Z - 291200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL/SOUTHERN
HIGH PLAINS...

...SYNOPSIS...
MEAN LONGWAVE TROUGH WILL REMAIN THE DOMINANT FEATURE OVER THE CONUS
THROUGH THE PERIOD...WITH A WESTWARD EXPANSION OF THE TROUGH OVER
THE NORTHERN/CENTRAL ROCKIES AND A SOUTHWESTWARD SHUNT OF THE UPPER
RIDGE CENTERED OVER THE BAJA VICINITY. ON THE PERIPHERY OF THIS
BROAD LONGWAVE TROUGH...A NUMBER OF SHORTWAVE DISTURBANCES /SOME
CONVECTIVELY ENHANCED/ WILL CYCLONICALLY PIVOT OVER THE ROCKIES...TO
THE ARKLATEX/MID-SOUTH...AND GREAT LAKES REGION. MULTIPLE/SLOW
MOVING REMNANT FRONTAL BOUNDARIES WILL REMAIN FROM THE NORTHEAST TO
THE CENTRAL/SOUTHERN PLAINS...BUT THE MAIN/REINFORCING COLD FRONT IS
EXPECTED TO DEVELOP EAST-SOUTHEASTWARD ACROSS THE WESTERN GREAT
LAKES/MIDWEST/PLAINS.

...CENTRAL/SOUTHERN HIGH PLAINS...
SEVERAL DISTURBANCES WILL SPREAD SOUTHEASTWARD OVER THE
ROCKIES/ADJACENT HIGH PLAINS TODAY/TONIGHT...CHIEFLY A SHORTWAVE
TROUGH CROSSING WY EARLY IN THE OVERNIGHT. TSTMS SHOULD DEVELOP AND
INCREASE IN COVERAGE/INTENSITY RELATIVELY EARLY IN THE
AFTERNOON...INITIALLY OVER THE HIGHER TERRAIN OF SOUTHEAST
WY/EASTERN CO INTO NORTHEAST NM...AND PERHAPS ALONG RESIDUAL OUTFLOW
BOUNDARIES ACROSS THE IMMEDIATELY ADJACENT HIGH PLAINS GIVEN A
MOIST/WEAKLY CAPPED AIRMASS. A SLIGHT SOUTHWESTWARD SHIFT OF
STRONGER MID LEVEL FLOW SHOULD RESULT IN 30-40 KT OF MID LEVEL WINDS
AS FAR SOUTH AS NORTHEAST/EAST CENTRAL NM BY MID/LATE
AFTERNOON...WITH VEERING WIND PROFILES OTHERWISE FAVORABLE FOR
SUPERCELLS/ORGANIZED MULTICELLS. SEVERE HAIL AND PERHAPS A TORNADO
OR TWO WILL BE POSSIBLE THROUGH MID/LATE AFTERNOON. WITH
TIME...UPSCALE GROWTH INTO ONE OR MORE SOUTH-SOUTHEAST
MOVING/ORGANIZED QUASI-LINEAR CONVECTIVE SYSTEMS SEEMS LIKELY BY
EARLY EVENING...WITH POTENTIAL FOR A BROADER DAMAGING WIND THREAT
ACROSS THE SOUTHERN HIGH PLAINS.

...ARKLATEX TO CENTRAL GULF COAST STATES/TN VALLEY...
CONVECTIVELY ENHANCED VORTICITY MAXIMA /OVER THE ARKLATEX EARLY IN
THE OVERNIGHT/ IS EXPECTED TO TRANSITION EAST-NORTHEASTWARD ACROSS
THE MID-SOUTH/CENTRAL GULF COAST STATES/TN VALLEY THROUGH TONIGHT
AMIDST BROADER CYCLONIC LONGWAVE REGIME. AHEAD OF THESE
FEATURES...THE EAST-NORTHEASTWARD DOWNSTREAM ADVECTION OF A
MOISTURE-RICH AIRMASS IS EXPECTED...AS CHARACTERIZED BY AROUND 70F
SURFACE DEWPOINTS AND 15+ G/KG MEAN MIXING RATIOS PER 00Z
SHV/LCH/FWD/JAN OBSERVED RAOBS. FURTHERMORE...00Z NAM/GFS AND PRIOR
12Z ECMWF GUIDANCE ALL SUGGEST THAT ENHANCED LOW LEVEL WIND FIELDS
/40+ KT AROUND 1 KM/ MAY ACCOMPANY THIS SHORTWAVE TROUGH/ATTENDANT
SURFACE LOW. WHILE HIGH MOISTURE CONTENT/AMPLE LOW LEVEL SRH WOULD
SUPPORT THE POSSIBILITY OF ISOLATED TORNADOES/DAMAGING WINDS THROUGH
AROUND SUNSET...POTENTIAL CONVECTIVE FEEDBACK AND UNCERTAINTIES IN
00Z BASED NUMERICAL GUIDANCE LIMITS CONFIDENCE IN SOMEWHAT
HIGHER/MORE FOCUSED TORNADO/SEVERE WIND PROBABILITIES.
REGARDLESS...IF OVERNIGHT TRENDS/EARLY MORNING DATA CONFIRM THE
PRESENCE OF MORE APPRECIABLE LOW LEVEL FLOW FIELDS EARLY IN THE
DAY...AND SUFFICIENT CLOUD BREAKS/DOWNSTREAM HEATING ARE
LIKELY...PORTIONS OF THE REGION COULD WARRANT A CATEGORICAL SLIGHT
RISK.

...MIDWEST...
AMIDST A MODERATELY UNSTABLE AIRMASS AND WEST-SOUTHWESTERLY MOISTURE
INFLUX...SCATTERED TSTMS SHOULD DIURNALLY INCREASE DURING THE
AFTERNOON ALONG THE EAST-SOUTHEASTWARD ADVANCING COLD
FRONT/PREFRONTAL TROUGH. WHILE MAINLY ISOLATED SEVERE WIND/HAIL WILL
BE POSSIBLE WITH THE STRONGEST STORMS THIS AFTERNOON/EARLY EVENING
FROM LOWER MI TO THE OZARKS/MIDDLE MS VALLEY...LESS THAN OPTIMALLY
TIMED LARGE SCALE FORCING FOR ASCENT AND/OR MODEST VERTICAL SHEAR
/GENERALLY 25 KT OR LESS/ SUGGEST POTENTIAL FOR AN
ORGANIZED/APPRECIABLE SEVERE EVENT IS LIMITED.

...NORTHERN INTERMOUNTAIN WEST...
WITH A RELATIVELY MOIST AIRMASS IN PLACE /0.75 TO 1 INCH PWS PER
SPOKANE AND GREAT FALLS 00Z OBSERVED
RAOBS/...AMPLIFYING/SOUTH-SOUTHEASTWARD DIGGING SHORTWAVE TROUGH
FROM THE WESTERN CANADIAN PROVINCES TO THE NORTHERN ROCKIES SHOULD
CONTRIBUTE TO SOME STRONGER/SEVERE TSTMS OVER THE NORTHERN GREAT
DIVIDE VICINITY THIS AFTERNOON/EARLY EVENING.
..GUYER/LEVIT.. 07/28/2009