SWODY1
SPC AC 101604
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1104 AM CDT WED SEP 10 2008
VALID 101630Z - 111200Z
...THERE IS A SLGT RISK OF SVR TSTMS FOR MUCH OF ARIZONA...
...THERE IS A SLGT RISK OF SVR TSTMS FOR PARTS OF NEB/SD...
...SYNOPSIS...
TROUGH OVER WRN U.S. HAS SPLIT WITH BROAD RIDGE OVER ERN HALF OF
CONUS. NRN PORTION WRN TROUGH DEVELOPS MOVES SEWD FROM WRN MT INTO
NRN WY TONIGHT WITH A CLOSED LOW DEVELOPING. SRN PORTION IN THE
FORM OF A CLOSED LOW NEAR RNO ATTM DROPS SWD TO VICINITY SRN CA
COAST 12Z THU.
IN ADVANCE OF BOTH OF THESE WRN FEATURES LOW LEVEL MOISTURE
CONTINUES TO INCREASE NWD AND WILL PROVIDE INSTABILITY TO SUPPORT
TWO AREAS OF SEVERE THUNDERSTORM POTENTIAL.
...AZ...
LOW LEVEL SLY FLOW CONTINUES TO FEED VERY MOIST AIR UP THE G OF CA
INTO AZ. THERE IS A SHARP GRADIENT TO THE MOISTURE/INSTABILITY
VICINITY OF THE CA/AZ BORDER AND THIS SHOULD MOVE LITTLE AS UPPER
LOW DROPS SWD TOWARDS SRN CA COAST WITH A GRADUAL BACKING OF THE
UPPER FLOW OVER AZ. PRECIPITABLE WATER WILL CONTINUE TO INCREASE
INTO SRN AZ TO AROUND 1.5 INCHES WHICH ALONG WITH MID LEVEL LAPSE
RATES OF 7C/KM COUPLED WITH SURFACE HEATING...WILL RAISE MLCAPES TO
AOA 1500 J/KG IN THE LOWER ELEVATIONS SRN AZ AND 1000 J/KG NRN AZ.
THE OBSERVED 30-35 KTS OF DEEP LAYER SHEAR ON ALL THREE AZ SOUNDINGS
COUPLED WITH THE QUALITY OF THE AIR MASS SUPPORT SCATTERED
STRONG/SEVERE THUNDERSTORMS OVER MUCH OF AZ THIS AFTERNOON. THERE
IS THE POTENTIAL FOR ROTATING STORMS GIVEN THE SHEAR/INSTABILITY
WHICH WILL ENHANCE BOTH THE LARGE HAIL AND DAMAGING DOWNBURST
POTENTIAL. HAVE INCREASED THE THREAT TO A SLIGHT RISK GIVE THESE
PARAMETERS. WHILE ELEVATED STORMS CURRENTLY CENTRAL AZ IN RESPONSE
TO AVAILABLE INSTABILITY...HEATING SHOULD INITIATE SURFACE BASED
STORMS FIRST VICINITY HIGHER TERRAIN BY MID AFTERNOON.
...NEB/SD...
WEAK SURFACE LOW WRN SD WITH LEE TROUGH SWD THRU ERN CO. AS UPPER
SYSTEM APPROACHES FROM THE W...LOW PRESSURE TROUGH WILL SHIFT A
LITTLE E BY THIS AFTERNOON MAINTAINING SLY FLOW OF MOISTURE THRU WRN
NE INTO SD. WHILE STEEP MID LEVEL LAPSE RATES ARE IN PLACE PER 12Z
LBF/RAP SOUNDINGS...EXTENSIVE LOW CLOUDS WILL DELAY THE THREAT FOR
SEVERE THUNDERSTORM DEVELOPMENT UNTIL LATER THIS AFTERNOON.
ONCE THE SURFACE HEATING CAN RAISE TEMPERATURES INTO THE MID/UPR 70S
AND WEAKEN THE CINH...SHEAR AND INSTABILITY WILL BE ADEQUATE FOR
STRONG/SEVERE THUNDERSTORM DEVELOPMENT. THIS SHOULD OCCUR INITIALLY
NEAR TO JUST W OF SURFACE TROUGH WRN NEB INTO SD WHERE HEATING
SHOULD BE STRONGEST. WITH 30-40KT OF DEEP LAYER SHEAR COUPLED WITH
POTENTIALLY MLCAPES AOA 1500 J/KG...SUPERCELLS WILL BE POSSIBLE.
LARGE HAIL AND DAMAGING WINDS WOULD BE MOST LIKELY ASSOCIATED WITH
ANY SUPERCELL THAT FORMS HOWEVER TORNADO POTENTIAL SHOULD BE LIMITED
WITH THE RELATIVELY MARGINALLY KINEMATICS.
...SRN FL...
IKE CONTINUED MOVEMENT AWAY FROM SRN FL HAS JUST ABOUT ENDED THE
THREAT OF ANY ROTATING STORMS ASSOCIATED WITH THE SPIRAL BAND. WILL
CONTINUE A LOW TORNADO PROBABILITY FOR NOW...WITH THAT LIKELY BEING
DROPPED IN THE NEXT OUTLOOK.
..HALES/SMITH.. 09/10/2008
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