SPC AC 170541
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1241 AM CDT FRI SEP 17 2004
   
   VALID 171200Z - 181200Z
   
   THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM TRI 20
   SW PSK LYH 65 ENE DAN RDU 35 S CLT 30 S SPA 40 NNW AND 25 SE TYS 35
   NE TYS TRI.
   
   GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 35 E INL 50 S DLH 30
   E RST 10 W IRK 35 WNW SGF 10 W MKO 40 ENE DAL 55 NNE CLL 20 SSE BPT
   ...CONT... 10 W ELP 40 WNW CVS 40 NNE CAO 45 NNW GLD 50 NE ANW 15 NW
   BKX 45 WNW AXN 65 W RRT.
   
   GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 50 ENE CTB 30 W BTM
   25 N BOI 25 SSE CEC.
   
   GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 35 WSW PNS 25 NNE CEW
   20 ENE MGM 35 NNW BHM 50 WSW BNA 35 SW SDF 25 SSE CAK 35 WSW GFL 15
   ESE PWM.
   
   GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 15 S IPL 35 ENE TRM
   15 SW EED 30 SSE IGM 55 WSW SOW 30 NE SAD 35 SSW DMN.
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE SRN
   APPALACHIANS INTO THE SOUTHERN MID ATLANTIC COAST STATES....
   
   IVAN HAS MERGED INTO BELT OF SUBTROPICAL WESTERLIES ACROSS THE
   SOUTHERN TIER STATES...AND STEADY SLOW WEAKENING SHOULD CONTINUE 
   TODAY. MID-LEVEL CIRCULATION...EMBEDDED WITHIN LARGER SCALE SHORT
   WAVE TROUGH...IS PROGGED TO GRADUALLY SHIFT EAST OF THE SOUTHERN
   APPALACHIANS INTO THE SOUTH ATLANTIC COAST STATES.  THIS WILL OCCUR
   MORE OR LESS IN TANDEM WITH EASTWARD PROGRESSION OF EASTERN
   CANADIAN/ST. LAWRENCE VALLEY SHORT WAVE TROUGH...TOWARD THE CANADIAN
    MARITIMES/NORTHERN ATLANTIC COASTAL AREAS.  NORTHERN SYSTEM IS
   EMBEDDED IN THE STRONGER POLAR WESTERLIES...WITHIN WHICH MODELS
   INDICATE SUBSTANTIAL AMPLIFICATION WILL OCCUR UPSTREAM THROUGH THIS
   FORECAST PERIOD.  BY 18/12Z...A LARGE DIGGING UPPER TROUGH IS
   PROGGED ALONG THE NORTHERN/CENTRAL PACIFIC COAST...WITH A SHARPENING
   RIDGE ALONG AN AXIS FROM THE LOWER U.S. PLAINS INTO THE CENTRAL
   CANADIAN PROVINCES.
   
   ...SOUTHEASTERN STATES INTO NORTHERN MID ATLANTIC COASTAL AREAS...
   UNCERTAINTIES EXIST WITH REGARD RATE OF DECAY OF TROPICAL
   SYSTEM...AS WELL AS EXTENT OF CLOUD COVER AND ASSOCIATED
   DESTABILIZATION OF MOIST BOUNDARY LAYER SOUTH OF FRONTAL ZONE
   ASSOCIATED WITH NORTHERN SHORT WAVE TROUGH.  BY LATE
   AFTERNOON...FRONTAL ZONE IS EXPECTED TO EXTEND FROM SOUTHEASTERN NEW
   ENGLAND AND NORTHERN MID ATLANTIC COASTAL AREAS...ALONG THE
   PENNSYLVANIA/MARYLAND BORDER INTO THE CENTRAL APPALACHIANS. 
   ALONG/SOUTH OF THIS BOUNDARY...LOWER/MID 70S DEW POINTS WILL BE
   COMMON...AND SHOULD CONTRIBUTE TO AT LEAST WEAK CONDITIONAL
   INSTABILITY.
   
   IN ADDITION TO CLOUD COVER...WEAK MID-LEVEL LAPSE RATES WILL LIMIT
   CAPE.  HOWEVER...INSTABILITY AND STRONGER FORCING ALONG FRONTAL ZONE
   FROM THE CENTRAL APPALACHIANS INTO THE NORTHERN MID ATLANTIC COAST
   IS EXPECTED TO BE SUFFICIENT TO SUPPORT CONVECTIVE BAND. 
   HOWEVER...PRIMARY SEVERE THREAT IS EXPECTED TO REMAIN CONFINED TO
   AREAS SOUTH/EAST OF FRONTAL ZONE.  ETA PROBABLY WEAKENS REMAINS OF
   IVAN TOO QUICKLY... AND PRESENCE OF DEEP SURFACE LOW/SIGNIFICANT
   AMBIENT VERTICAL VORTICITY NEAR LOW/MID-LEVEL CIRCULATION WILL
   CONTINUE TO SUPPORT RISK OF TORNADOES IN TROPICAL-TYPE BOUNDARY
   LAYER.
   
   BEST CHANCE FOR TORNADOES APPEARS TO BE IN IMMEDIATE LEE OF
   APPALACHIANS...FROM WESTERN NORTH CAROLINA INTO SOUTHWEST VIRGINIA. 
   HOWEVER...BETTER HEATING/SURFACE-BASED DESTABILIZATION IS EXPECTED
   ACROSS THE COASTAL PLAINS OF NORTH CAROLINA INTO EASTERN VIRGINIA
   AND THE DELMARVA BY AFTERNOON...WHERE FLOW/SHEAR WILL BE WEAKER.
   
   ...PLAINS...
   WEAKENING SHORT WAVE TROUGH...EMBEDDED WITHIN INCREASINGLY
   ANTICYCLONIC BROADER SCALE FLOW...MAY CONTINUE TO SUPPORT SCATTERED
   THUNDERSTORM ACTIVITY FROM THE EASTERN DAKOTAS INTO MINNESOTA EARLY
   TODAY. HOWEVER...MID-LEVEL WARMING/WEAK SUBSIDENCE LIKELY WILL
   EVENTUALLY SUPPRESS CONVECTIVE DEVELOPMENT THROUGH MUCH OF THE
   CENTRAL U.S. DURING THE DAYTIME HOURS.
   
   EXCEPTION MAY BE NEAR WEAK THERMAL LOW/SURFACE TROUGH ACROSS THE
   CENTRAL HIGH PLAINS.  STRONG HEATING TO CONVECTIVE TEMPERATURES MAY
   OCCUR ALONG WESTERN FRINGE OF BETTER LOW-LEVEL MOIST TONGUE
   EXTENDING NORTHWESTWARD FROM THE WESTERN GULF OF MEXICO.  AIDED BY 
   WEAK LOW-LEVEL FORCING ASSOCIATED WITH ENHANCED CONVERGENCE/WARM
   ADVECTION...WIDELY SCATTERED THUNDERSTORM ACTIVITY APPEARS POSSIBLE.
    SHEAR PROFILES WILL GENERALLY BE WEAK...BUT FAVORABLE THERMODYNAMIC
   ENVIRONMENT WITH STEEP MID-LEVEL LAPSE RATES AND DEEP MIXED BOUNDARY
   LAYER WILL BE SUPPORTIVE OF MARGINALLY SEVERE HAIL AND ISOLATED
   DOWNBURSTS.
   
   MODEL FORECAST SOUNDINGS SUGGEST SUBSTANTIAL INHIBITION THROUGH MUCH
   OF THE PLAINS OVERNIGHT...BUT FORCING ON NOSE OF NOCTURNALLY
   ENHANCED SOUTHERLY LOW-LEVEL JET MAY SUPPORT SCATTERED CONVECTION
   ACROSS PARTS OF THE MID MISSOURI VALLEY BY DAYBREAK SATURDAY.
   
   ...NORTHWEST STATES...
   SCATTERED...MOSTLY WEAK...THUNDERSTORM ACTIVITY APPEARS POSSIBLE...
   PRIMARILY IN ASSOCIATION WITH STRONGER MID-LEVEL COOLING ASSOCIATED
   WITH DIGGING TROUGH.  THIS FORCING WILL SHIFT ACROSS PACIFIC COASTAL
   AREAS AND THE CASCADES BY LATE TODAY...THEN INTO THE NORTHERN
   INTERMOUNTAIN REGION TONIGHT.
   
   ...SOUTHERN PLATEAU...
   MOISTURE RETURN ON SOUTHERLY FLOW AHEAD OF AMPLIFYING PACIFIC COAST
   TROUGH MAY ALSO SUPPORT SCATTERED THUNDERSTORM ACTIVITY ACROSS PARTS
   OF THE LOWER COLORADO VALLEY BY THIS EVENING... CONTINUING INTO THE
   OVERNIGHT HOURS.
   
   ..KERR/BANACOS.. 09/17/2004
   
   ...NOTICE...
   FOR USERS DECODING THE POINTS PARAGRAPH HEREIN...LATITUDE AND
   LONGITUDE POINTS FOR THE CATEGORICAL AND PROBABILISTIC OUTLOOK
   GRAPHICS ALSO ARE LOCATED IN A SEPARATE PRODUCT UNDER THE WMO
   HEADINGS WUUS01 PTSDY1...WUUS02 PTSDY2...AND WUUS03 PTSDY3.  THE
   INCLUSION OF POINTS IN THIS PRODUCT WILL EVENTUALLY BE DISCONTINUED.
   
   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED FOR 1300Z