SWODY1
SPC AC 021957
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0257 PM CDT FRI JUL 02 2010
VALID 022000Z - 031200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM MT TO ND...
...THERE IS A SLGT RISK OF SVR TSTMS FROM NERN CO ACROSS THE
ADJACENT CENTRAL/NRN PLAINS...
...MT...
WRN EXTENT OF THE SLIGHT RISK IN SWRN TO CENTRAL MT HAS BEEN SHIFTED
EWD GENERALLY 25-55 MILES TO ACCOUNT FOR THE E/SEWD ADVANCEMENT OF
THE COLD FRONT. EARLY AFTERNOON SURFACE ANALYSIS INDICATED THIS
BOUNDARY EXTENDED SWWD FROM NORTH CENTRAL MT /E OF HVR/ THROUGH SWRN
MT INTO SRN ID AND NWRN NV. OTHERWISE...PREVIOUS OUTLOOK FOR MT
INTO WRN/NRN ND REMAINS ON TRACK WITH STORMS BEGINNING TO DEVELOP
OVER SWRN/SOUTH CENTRAL MT. FARTHER ENE...STRONG CAP PER 18Z GGW
SOUNDING WITH WARMING IN THE 600-750 MB LAYER SINCE 12Z TODAY
SUGGESTS TSTM DEVELOPMENT WILL BE DELAYED UNTIL ACTIVITY SPREADS
INTO THIS REGION FROM THE W/SW WITH THE APPROACH OF THE COLD FRONT.
...UT/CO/MUCH OF WY...
A FEW MIDLEVEL IMPULSES WILL CONTINUE TO TRACK NEWD ACROSS THE FOUR
CORNERS REGION TO WY/NRN HIGH PLAINS...WHILE ADDITIONAL IMPULSES
MOVE NNEWD ALONG W/NW PERIPHERY OF SUB-TROPICAL RIDGE FROM THE SRN
ROCKIES TO CENTRAL HIGH PLAINS TO DAKOTAS. FORCING FOR ASCENT
ATTENDANT TO THESE IMPULSES WILL SUPPORT ADDITIONAL NEWD MOVING
TSTMS PRODUCING ISOLATED STRONG DOWNBURST WINDS GIVEN THE STEEP LOW
LEVEL LAPSE RATE ENVIRONMENT /I.E. DEEP MIXED BOUNDARY LAYER/.
ISOLATED HAIL MAY BE A THREAT WITH THE ACTIVITY FROM ERN UT AND
PARTS OF NRN CO GIVEN DEEP LAYER SHEAR /30 KT/ AND STEEP MIDLEVEL
LAPSE RATES. WEAK INSTABILITY FROM WY SWD INTO ERN UT AND MUCH OF
WRN/CENTRAL CO WILL LIMIT OVERALL SEVERE WEATHER COVERAGE.
..PETERS.. 07/02/2010
.PREV DISCUSSION... /ISSUED 1130 AM CDT FRI JUL 02 2010/
...SYNOPSIS...
BROAD SUB-TROPICAL RIDGE AXIS WILL CONTINUE TO SHIFT EAST ACROSS THE
MS VALLEY AND GREAT LAKES THIS PERIOD WITH 500MB TROUGHS OF MODEST
AMPLITUDE TO THE EAST AND WEST OF THE LARGE UPPER RIDGE AXIS.
MEANWHILE...DEEP ELY FLOW AND ABUNDANT TROPICAL MOISTURE WILL
PERSIST ACROSS THE GULF COAST AND SOUTHERN STATES IN THE WAKE OF
ALEX.
OF PRIMARY INTEREST FOR SEVERE WEATHER TODAY WILL BE THE WRN U.S.
TROUGH AND THE SMALLER SCALE/EMBEDDED LOBES OF VORTICITY ROTATING
THROUGH THIS FEATURE FROM THE INTERIOR NORTHWEST...ACROSS THE NRN
ROCKIES...AND INTO THE CANADIAN PRAIRIES AND ADJACENT NORTHERN
PLAINS. COLD FRONT ASSOCIATED WITH THE LARGER TROUGH IS FORECAST TO
SPREAD GRADUALLY EAST ACROSS MT THROUGH TONIGHT AND WILL ALSO SINK
SEWD FROM THE HIGHER TERRAIN INTO THE NRN HIGH PLAINS...AND EWD INTO
THE WRN DAKOTAS BY DAYBREAK SATURDAY.
...MT TO WRN ND...
SATELLITE IMAGERY LOOP OF PAST 24H DEPICTS A LEAD SHORT WAVE TROUGH
PIVOTING OUT OF THE PACIFIC NORTHWEST TROUGH AND CURRENTLY ENHANCING
LIFT ALONG THE COLD FRONT ENTERING NW MT. DEEP-LAYER SW FLOW OFF THE
HIGHER TERRAIN IS HELPING TO MAINTAIN A BROAD SWATH OF STEEP LAPSE
RATES ACROSS THE ROCKIES AND NORTHERN PLAINS AHEAD OF THE FORCING
ASSOCIATED WITH THE WRN TROUGH AND COLD FRONT. EXPECT AIRMASS WILL
AGAIN BECOME QUITE UNSTABLE OVER MUCH OF CENTRAL AND ERN MT THIS
AFTERNOON WITH LATEST SREF FORECASTING SBCAPE OF 1000-2000
J/KG...ALONG WITH GRADUALLY WEAKENING INHIBITION.
THERE MAY BE A LULL IN SEVERE POTENTIAL IN THE WAKE OF THE ISOLATED
BUT WELL-ORGANIZED MORNING STORM NOW MOVING TOWARD THE CANADIAN
BORDER IN HILL COUNTY MT. DESPITE WHAT APPEARS TO BE A GAP BETWEEN
STRONGER DPVA ASSOCIATED WITH THE TRANSIENT SHORT WAVE TROUGHS OVER
MT THIS AFTERNOON...THERE SHOULD BE SUFFICIENT OROGRAPHIC AND
FRONTAL/OUTFLOW LIFT OVER PORTIONS OF CNTRL... SCNTRL...AND SWRN MT
LATER THIS AFTERNOON FOR ADDITIONAL STORM INITIATION IN THESE AREAS.
LIKE RECENT DAYS...SHEAR ACROSS THE REGION WILL BE SUFFICIENT FOR
STORM UPDRAFT PERSISTENCE AND ORGANIZATION/ROTATION WITH LARGE HAIL
LIKELY. GIVEN STRONG HEATING PRIOR TO INITIATION...DAMAGING
DOWNBURST WINDS WILL ALSO EVOLVE FROM THIS RELATIVELY HIGH-BASED
CONVECTION. WHILE THERE REMAINS UNCERTAINTY REGARDING EVENTUAL
EVOLUTION OF THE AFTERNOON/EARLY EVENING STORMS...THE SCENARIO MAY
NOT BE MUCH DIFFERENT THAN RECENT DAYS WITH AN MCS...OR LARGER-SCALE
TSTM COMPLEX...SPREADING EAST INTO WRN ND THROUGH LATE TONIGHT WITH
A CONTINUING CHANCE FOR SEVERE WIND AND HAIL.
...CO AND ADJACENT PLAINS...
ISOLATED TO SCATTERED STORMS SHOULD AGAIN DEVELOP ACROSS THE HIGHER
TERRAIN AND ON THE EDGE OF FASTER MID LEVEL FLOW FROM WY INTO
CO...AND PERHAPS ALONG THE DRYLINE/THERMAL TROUGH AXIS FROM SD INTO
WRN NE. WHILE INSTABILITY AND EFFECTIVE SHEAR IN THESE AREAS MAY
MARGINALLY SUPPORT HAIL...STRONG DOWNDRAFTS MAY BE A GREATER LOCAL
THREAT FOR DAMAGING WINDS.
STRONG CAP IN PLACE ACROSS THE PLAINS MAY INHIBIT GREATER STORM
COVERAGE. HOWEVER...WATER VAPOR IMAGERY SUGGESTS A WEAK SHORT WAVE
TROUGH MOVING ACROSS CO ATTM THAT COULD AID STORM INITIATION AND
DEVELOPMENT LATER THIS AFTERNOON AS BOUNDARY LAYER UNDERGOES STRONG
HEATING/MIXING NEAR CO/NE BORDER AREA. IF A COUPLE OF STORMS CAN
TAKE ROOT AND DEVELOP EAST INTO GREATER INSTABILITY ACROSS THE
PLAINS...DAMAGING WINDS MAY BE A THREAT WITH THIS CONVECTION AS
DRY/MIXED SUB CLOUD LAYER AID EVAPORATIVE COOLING AND DOWNBURST
POTENTIAL.
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