Posted by JAC on 4/16/2009, 7:59 am

DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1248 AM CDT THU APR 16 2009 VALID 161200Z - 171200Z ...THERE IS A SLGT RISK OF SVR TSTMS OVER MUCH OF THE SRN THROUGH CNTRL HIGH PLAINS... ...SYNOPSIS... CLOSED UPPER LOW NEAR THE FOUR CORNERS AREA WILL MOVE SLOWLY EAST... REACHING THE CNTRL AND SRN HIGH PLAINS THURSDAY NIGHT. A DRYLINE/LEE TROUGH WILL PERSIST OVER THE HIGH PLAINS IN ADVANCE OF THIS FEATURE. THE DRYLINE WILL MIX ACROSS WRN TX DURING THE DAY THEN RETREAT WWD DURING THE EVENING BEFORE IT IS OVERTAKEN BY A PACIFIC FRONT. ...CNTRL AND SRN HIGH PLAINS... RECENT OBSERVATIONS INDICATE THE RICHER BOUNDARY LAYER MOISTURE WITH DEWPOINTS IN THE LOW 60S IS CONFINED TO SRN TX. ELY LOW LEVEL TRAJECTORIES RESULTING FROM THE CIRCULATION AROUND CP HIGH PRESSURE ANCHORED OVER THE ERN U.S. WILL LIMIT NWD EXTENT OF QUALITY MOISTURE RETURN WITH 60S LIKELY REMAINING ACROSS SOUTH OR SCNTRL TX. MODELS INDICATE AN INCREASE IN ELEVATED/MID LEVEL CONVECTION WILL DEVELOP EARLY THURSDAY OVER PORTIONS OF THE SRN PLAINS AS IMPULSE CURRENTLY MOVING THROUGH NRN MEXICO CONTINUES ENEWD. THIS ACTIVITY MAY BE CAPABLE OF PRODUCING MARGINALLY SEVERE HAIL. IN WAKE OF THE MORNING CONVECTION...ANY LOW CLOUDS WILL LIKELY MIX OUT FROM WRN TX THROUGH THE CNTRL HIGH PLAINS. DIABATIC HEATING BENEATH STEEP MID LEVEL LAPSE RATES WILL CONTRIBUTE TO DESTABILIZATION IN THIS REGION WITH AN AXIS OF MLCAPE RANGING FROM AROUND 1500 J/KG OVER THE TRANSPECOS REGION OF WRN TX TO 500 J/KG FARTHER NORTH INTO ERN CO WHERE MOISTURE WILL BE MORE LIMITED. SURFACE BASED THUNDERSTORMS WILL BECOME INCREASINGLY PROBABLE IN THIS REGION BY MID-LATE AFTERNOON AS THE ATMOSPHERE DESTABILIZES AND CAP WEAKENS. THE LOW LEVEL JET IS FORECAST TO WEAKEN DURING THE DAY AND LOW LEVEL HODOGRAPHS WILL INITIALLY NOT BE PARTICULARLY LARGE THURSDAY AFTERNOON OVER MUCH OF THE HIGH PLAINS. AN EXCEPTION MAY BE OVER PARTS OF ERN CO WHERE STRONGER BACKED FLOW WILL PERSIST NE OF WEAK SURFACE LOW. BULK SHEAR WILL FAVOR SUPERCELL MODES WITH STORMS THAT DEVELOP. LARGE HAIL AND ISOLATED DAMAGING WIND WILL BE THE PRIMARY THREATS. TORNADO THREAT WILL INITIALLY NOT BE PARTICULARLY HIGH OWING TO MORE LIMITED HODOGRAPH SIZE AND FAIRLY LARGE TEMPERATURE/DEWPOINT SPREADS. HOWEVER...A WINDOW OF OPPORTUNITY FOR ISOLATED TORNADOES MAY DEVELOP BY EARLY EVENING AS THE LOW LEVEL JET STRENGTHENS AND THE BOUNDARY LAYER BEGINS TO COOLS...RESULTING IN LOWER SPREADS. THUNDERSTORM COVERAGE IS EXPECTED TO INCREASE...AND STORMS WILL LIKELY GROW UPSCALE INTO AN MCS LATER IN THE EVENING/OVERNIGHT AS THE PACIFIC FRONT AND LEADING EDGE OF COOLER MID-LEVEL TEMPERATURES AND ASCENT ACCOMPANYING THE UPPER TROUGH OVERTAKES THE RETREATING DRYLINE. THREAT FOR MAINLY LARGE HAIL AND ISOLATED DAMAGING WIND WILL LIKELY CONTINUE INTO THE OVERNIGHT. ..DIAL/SMITH.. 04/16/2009 DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1237 AM CDT THU APR 16 2009 VALID 171200Z - 181200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CNTRL/SRN HIGH PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF CNTRL/SCNTRL TX... ...CNTRL HIGH PLAINS TO SCNTRL TX... COMPLEXITIES...REGARDING CONVECTION...WILL BEGIN TO INCREASE EXPONENTIALLY DURING THE DAY2 PERIOD AS SLOW MOVING UPPER LOW MIGRATES ACROSS THE CNTRL/SRN ROCKIES INTO THE PLAINS. LATEST GUIDANCE SUGGESTS DAY1 WILL BE CONVECTIVELY ACTIVE WELL INTO THE OVERNIGHT HOURS...WITH SIGNIFICANT THUNDERSTORM ACTIVITY EXPECTED TO BE ONGOING AT THE BEGINNING OF THE DAY2 PERIOD FROM THE EDWARDS PLATEAU OF TX...NWD INTO WRN OK...ARCING NWWD INTO WRN KS. THIS EARLY MORNING ACTIVITY WILL LIKELY BE ENHANCED BY STRONG LLJ THAT WILL GRADUALLY SHIFT EAST INTO THE ARKLATEX LATER IN THE DAY. ALTHOUGH EARLY MORNING COMPLEX MAY EXHIBIT ORGANIZED SQUALL LINE STRUCTURE...IT/S NOT ENTIRELY CLEAR HOW SEVERE THIS CONVECTION WILL BE AFTER SUNRISE. OF GREATER CONCERN WILL BE CONVECTIVE POSSIBILITIES WITHIN DESTABILIZING ZONE ACROSS PORTIONS OF CNTRL TX...AND PERHAPS IMMEDIATELY AHEAD OF THE UPPER LOW OVER THE HIGH PLAINS. FORECAST MODELS DIFFER A BIT IN THE PROGRESSION OF SQUALL LINE ACROSS TX/OK WITH THE GFS MAINTAINING CONSIDERABLE INTENSITY WITH THIS COMPLEX INTO THE ARKLATEX REGION. AT SOME POINT THE SQUALL LINE SHOULD OUTRUN ITS UPPER SUPPORT AND WEAKEN. LATEST THINKING IS GREATER INSTABILITY WILL HOLD ACROSS CNTRL/SCNTRL TX WHERE A SURGE OF MARITIME TROPICAL AIR SHOULD BE IN PLACE. THIS MAY BE WHERE RENEWED THUNDERSTORMS COULD DEVELOP AS BOUNDARY LAYER WARMS ALONG SRN FRINGE OF STRONGER MID LEVEL FLOW. AT ANY RATE...FORECAST SOUNDINGS FAVOR STORM ROTATION...ESPECIALLY IF MORE DISCRETE UPDRAFTS CAN DEVELOP LATER IN THE DAY. LARGE HAIL...DAMAGING WINDS AND PERHAPS AN ISOLATED TORNADO CAN BE EXPECTED. FARTHER NW...DESPITE MARGINAL LOW LEVEL MOISTURE...STRONG THUNDERSTORMS MAY DEVELOP IN A NARROW CORRIDOR ALONG THE NRN-ERN SEMICIRCLE OF UPPER LOW FROM SERN CO INTO EXTREME WRN OK BY EARLY-MID AFTERNOON. VERY COLD MID LEVEL TEMPERATURES...H5 FROM -20C TO -26C...WILL OVERSPREAD THE SRN HIGH PLAINS BENEATH THE UPPER LOW. THUNDERSTORMS SHOULD EASILY DEVELOP ALONG LOW LEVEL CONVERGENCE ZONE WHERE STRONG HEATING WILL REMOVE INHIBITION QUICKLY. SHEAR PROFILES SUGGEST SUPERCELLS ARE POSSIBLE. PRIMARY SEVERE THREAT WILL BE LARGE HAIL...BUT AN ISOLATED TORNADO CAN NOT BE RULED OUT. ..DARROW.. 04/16/2009