Friday, September 10, 2010

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 101950
SWODY1
SPC AC 101949

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0249 PM CDT FRI SEP 10 2010

VALID 102000Z - 111200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF KS...MO...NRN
OK AND FAR SE NEB...

TWO CHANGES HAVE BEEN MADE FOR THE 20Z OUTLOOK. THE FIRST CHANGE IS
TO REMOVE PARTS OF CNTRL SD AND NCNTRL NEB FROM THE 5 PERCENT WIND
AND HAIL PROBABILITIES. A COLD FRONT IS CURRENTLY MOVING INTO ERN SD
AND NE NEB AND CONVECTION IS NOT EXPECTED TO DEVELOP BEHIND THE
FRONT. AHEAD OF THE FRONT...AN AXIS OF INSTABILITY EXTENDS NWD
ACROSS NE NEB...ECNTRL SD INTO SE ND WHERE WSR-88D VWPS SUGGESTS
DEEP LAYER SHEAR PROFILES ARE QUITE STRONG. IN ADDITION...OBJECTIVE
ANALYSIS IS SHOWING A PLUME OF STEEP MID-LEVEL LAPSE RATES EXTENDING
INTO ERN SD FROM THE SOUTHWEST. THIS ENVIRONMENT MAY SUPPORT HAIL
WITH THE MORE INTENSE CELLS NEAR PEAK HEATING. STRONG WIND GUSTS
WILL ALSO BE POSSIBLE IF AN INTENSE SHORT-LINE SEGMENT CAN DEVELOP
ALONG THE FRONT. THE SECOND CHANGE TO THE OUTLOOK IS TO ADD A SMALL
THUNDER AREA IN NCNTRL MT WHERE SCATTERED CONVECTION IS DEVELOPING
ON THE BACKSIDE OF AN EXITING UPPER-LEVEL RIDGE. LAPSE RATES ARE
STEEP WHICH ALONG WITH SFC HEATING COULD BE ENOUGH FOR A FEW
THUNDERSTORMS LATE THIS AFTERNOON.

..BROYLES.. 09/10/2010

.PREV DISCUSSION... /ISSUED 1130 AM CDT FRI SEP 10 2010/

...KS/MO/OK...
A LARGE UPPER TROUGH WILL CONTINUE EAST ACROSS THE NRN/CNTRL PLAINS
THROUGH THE PERIOD. THE PRIMARY OCCLUDED SURFACE LOW ASSOCIATED WITH
THIS SYSTEM WILL TRACK INTO MANITOBA TODAY WHILE A WEAK SECONDARY
AREA OF LOW PRESSURE MOVES EAST ALONG A WARM FRONT SITUATED FROM KS
INTO MO. COOLER AIR IN THE WAKE OF THE GREAT PLAINS TROUGH/LOW WILL
SPREAD SOUTH THROUGH TONIGHT WITH THE COLD FRONT EXPECTED TO LIE
FROM THE UPPER MS VALLEY TO OK BY SATURDAY MORNING.

ABUNDANT MOISTURE /HIGH PW VALUES OF 1.5-2 INCHES/ AND DIURNAL
HEATING WILL CONTRIBUTE TO STRONG WARM SECTOR DESTABILIZATION FROM
OK ACROSS ERN KS AND WRN MO TODAY. SBCAPE IN THESE AREAS SHOULD
EASILY CLIMB TO OVER 2000 J/KG BY LATE AFTERNOON BENEATH
STRONG...BUT GRADUALLY WEAKENING...CAPPING INVERSION. MUCH OF THE
REGION WILL EXPERIENCE ONLY A GLANCING INFLUENCE OF THE STRONGER
HEIGHT FALLS AND DEEP-LAYER ASCENT ASSOCIATED WITH THE TROUGH TO THE
NORTH. IN ADDITION TO AN INCREASE IN WEAK BACKGROUND
ASCENT...STRONGER LIFT FOCUSED NEAR THE WARM FRONT AND SURFACE
LOW...AND EVENTUALLY ON THE COLD FRONT MOVING INTO THE AREA FROM THE
NW...SHOULD PROVE ADEQUATE FOR SURFACE-BASED TSTM DEVELOPMENT.

MID LEVEL SWLY FLOW OF 20-30KT IS FORECAST TO STRENGTHEN BY 10-20KT
THROUGH LATE EVENING. WEAKER EFFECTIVE DEEP-LAYER SHEAR AWAY FROM
THE WARM FRONT AND SURFACE LOW SUGGESTS MARGINALLY ORGANIZED
MULTICELL CONVECTION INITIALLY. HOWEVER...STORMS INITIATING OR
PERSISTING ON THE WARM FRONT AND NEAR THE SURFACE LOW MAY ACQUIRE
SUPERCELL CHARACTER GIVEN LOCALLY ENHANCED LOW LEVEL SHEAR AND
FORCING NEAR THESE FEATURES. DAMAGING WINDS ARE POSSIBLE WITH
INITIAL WARM SECTOR STORMS GIVEN MAGNITUDE OF CAPE AND BOUNDARY
LAYER HEATING WHILE MORE DISCRETE STORMS NEAR THE LOW AND WARM FRONT
COULD POSE A THREAT FOR HAIL AND A COUPLE OF TORNADOES INTO THE
EVENING HOURS.

INCREASING LINEAR FORCING ASSOCIATED WITH THE ADVANCING COLD
FRONT...AS WELL AS STRENGTHENING DEEP-LAYER WLY FLOW IN THE BASE OF
THE GREAT PLAINS UPPER TROUGH ...COULD RESULT IN SQUALL LINE/MCS
EVOLUTION WITH WIND DAMAGE POTENTIAL CONTINUING ACROSS PARTS OF ERN
KS/SWRN MO...AND PERHAPS FAR NRN/NERN OK...INTO LATE TONIGHT/EARLY
SATURDAY.

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