SPC AC 020559
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT SUN AUG 02 2009
VALID 031200Z - 041200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MIDWEST...
...SYNOPSIS...
THE PREVAILING LONGWAVE PATTERN OVER THE CONUS WILL FLUCTUATE LITTLE
THROUGH MONDAY. MEAN UPPER TROUGH WILL PERSIST OVER MUCH OF THE
NORTH CENTRAL/EASTERN STATES...AS AN UPPER RIDGE REMAINS OVER THE
ROCKIES/SOUTHERN TIER AHEAD OF A QUASI-STATIONARY CLOSED LOW OFF THE
NORTHERN CA COAST.
...MIDWEST INCLUDING PORTIONS OF IA/MO/IL/INDIANA...
STRENGTHENING WEST-NORTHWESTERLY FLOW ALOFT IS EXPECTED OVER THE
UPPER MIDWEST ON MONDAY ON THE PERIPHERY OF THE ONTARIO UPPER
TROUGH. WITHIN THIS REGIME...ONE OR MORE MID LEVEL DISTURBANCES
SHOULD TRAVERSE THE REGION THROUGH THE PERIOD AHEAD OF A MORE
SUBSTANTIAL SHORTWAVE TROUGH DIGGING SOUTHEASTWARD TOWARD THE
NORTHERN MN/LAKE SUPERIOR VICINITY MONDAY NIGHT. AT THE SURFACE...A
COLD FRONT WILL STEADILY ADVANCE SOUTHEASTWARD ACROSS THE REGION
THROUGH MONDAY NIGHT. AIDED BY A PRE-COLD FRONTAL WARM
ADVECTION/MOISTURE TRANSPORT REGIME...IT SEEMS LIKELY THAT SCATTERED
ELEVATED TSTMS WILL BE ONGOING MONDAY MORNING ALONG/AHEAD OF THE
COLD FRONT...POTENTIALLY INCLUDING PORTIONS OF MI/WI/NORTHERN IL AND
IA/NORTHERN MO. THE SPECIFIC EVOLUTION OF THIS EARLY DAY ACTIVITY IS
UNCLEAR...BUT WITH TIME...A PERSISTENT WEST-SOUTHWESTERLY
MOISTURE/INSTABILITY FEED SHOULD CONTRIBUTE A RATHER UNSTABLE
AIRMASS AHEAD OF THE COLD FRONT...ESPECIALLY ACROSS PORTIONS OF
SOUTHERN IA/NORTHERN MO INTO IL. EARLY DAY DEVELOPMENT COULD
POTENTIALLY GROW UPSCALE...BUT OTHERWISE THE DEVELOPMENT OF
SCATTERED STRONG/SEVERE TSTMS WILL BE POSSIBLE ALONG/AHEAD OF THE
COLD FRONT BY MID/LATE AFTERNOON...ALTHOUGH DETAILS OF BACKGROUND
SYNOPTIC SCALE FORCING ARE UNCERTAIN IN THE WAKE OF A POTENTIAL
EARLY DAY LEAD IMPULSE. REGARDLESS...BY EARLY/MID EVENING...THE
RENEWED NOCTURNAL STRENGTHENING OF A WEST-SOUTHWESTERLY LOW LEVEL
JET SHOULD CONTRIBUTE TO INCREASING TSTM COVERAGE AND/OR POTENTIAL
ORGANIZATION OF ONGOING SOUTHEASTWARD MOVING CLUSTERS ACROSS THE
MIDWEST. DAMAGING WINDS/SEVERE HAIL AND PERHAPS A TORNADO WILL BE
POSSIBLE. WHILE SOMEWHAT HIGHER CALIBER SEVERE PROBABILITIES COULD
ULTIMATELY BE WARRANTED FOR PORTIONS OF THE REGION...UNCERTAINTIES
REGARDING IMPACTS OF EARLY DAY TSTMS/PERTURBED NORTHWESTERLY FLOW
AND SUBSEQUENT REDEVELOPMENT LATER IN THE DAY COMPLICATES THE
SPECIFICS AT THIS JUNCTURE.
...WESTERN ORE/FAR NORTHERN CA...
UPPER LOW WILL GENERALLY REMAIN QUASI-STATIONARY OFF THE NORTHERN CA
COAST...WITH POTENTIAL FOR ONE OR MORE MID LEVEL DISTURBANCES TO
OVERSPREAD THE REGION THROUGH THE PERIOD. GIVEN THE PERSISTENCE OF A
MOIST/STEEP LAPSE RATE ENVIRONMENT BENEATH MODERATE SOUTHERLY FLOW
ALOFT...THE STRONGEST STORMS WILL AGAIN BE CAPABLE OF SEVERE
WIND/HAIL MAINLY MONDAY AFTERNOON/EARLY EVENING.
...CAROLINAS/VA AND SOUTHEAST STATES...
BROAD CYCLONIC FLOW...AND PRESENCE OF WEAK FRONT/SURFACE TROUGH
AND/OR ANTICIPATED SEA BREEZE DEVELOPMENT...WILL AGAIN CONTRIBUTE TO
STRONG/SEVERE TSTM POTENTIAL. EXPECTATIONS FOR WEAK VERTICAL SHEAR
ARE SUGGESTIVE OF A MAINLY PULSE/MULTICELLULAR STORM MODE...WITH
BOUTS OF DAMAGING WINDS/PERHAPS SOME HAIL POSSIBLE THROUGH AROUND
SUNSET.
...MT AND ADJACENT NORTHERN HIGH PLAINS...
TSTMS SHOULD DEVELOP MONDAY AFTERNOON/EARLY EVENING ALONG THE
SOUTHWARD ADVANCING COLD FRONT...WITH UPSLOPE TRAJECTORIES
INCREASING INTO THE HIGHER TERRAIN BY LATE IN THE DAY. BENEATH A
STRONG 40+ KT BELT /500 MB/ OF NORTHWESTERLY FLOW ALOFT...SOME OF
THE STRONGER STORMS COULD BE CAPABLE OF ISOLATED SEVERE WIND/HAIL
MONDAY AFTERNOON/EARLY EVENING.
...SOUTHERN AZ...
ON THE IMMEDIATE WESTERN PERIPHERY OF THE ROCKIES UPPER RIDGE...THE
LIKELIHOOD OF INCREASING MOISTURE INTO SOUTHERN AZ ON MONDAY SHOULD
RESULT IN AN UPSWING IN TSTMS...WITH THE POSSIBILITY OF ISOLATED
SEVERE DOWNBURSTS MONDAY AFTERNOON/EARLY EVENING.
..GUYER.. 08/02/2009
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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