tim66214's blog: "Tim's Blog"

SPC AC 281742 DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK ISSUED BY AFWA OFFUTT AIR FORCE BASE BELLEVUE NE 1242 PM CDT WED MAR 28 2007 VALID 291200Z - 301200Z ...THERE IS A SLGT RISK OF SVR TSTMS CENTRAL PLAINS/SW IA AND NW MO THROUGH S-CNTRL/SW TX... ...SYNOPSIS... MID-UPPER LEVEL CLOSED LOW WILL PARK OVER THE CENTRAL ROCKIES DURING THE PERIOD WITH SEVERAL SMALL PERTURBATIONS FCST TO ORBIT AROUND THE BASE OF THE LOW AND MOVE THROUGH SRN/CNTRL PLAINS STATES. UNCERTAINTY WITH THE PROGGED EWD MIGRATION OF UPPER LOW AND AMOUNT OF ONGOING CONVECTION AT THE BEGINNING OF THE PERIOD IS MAIN CONCERN FOR THE DAY 2 PERIOD. AT SFC...INITIAL CYCLONE OVER NRN PLAINS IS EXPECTED TO OCCLUDE AND WEAKEN...WHILE SECONDARY CYCLOGENESIS OCCURS FARTHER S ALONG COLD FRONT/DRYLINE. THIS LOW SHOULD LIFT NEWD OVER NEB AND DEEPEN...WITH WARM FRONT EXTENDING SEWD ACROSS ERN MO TO MID TN AREA BY 30/00Z. ...CENTRAL/SRN PLAINS...MORNING... MORNING SVR TSTMS SHOULD BE ONGOING AT BEGINNING OF PERIOD MAINLY INVOF WRN FRINGE OF SVR RISK OUTLOOK. PRIND COMPLEX WILL BE MAINLY LINEAR WITH DAMAGING GUSTS AND OCCASIONAL LARGE HAIL POSSIBLE. EXPECT THIS BAND OF CONVECTION TO MOVE EWD THROUGH MORNING INTO PROGRESSIVELY WEAKER INFLOW-LAYER BUOYANCY AND WEAKER VERTICAL SHEAR. CLOUD COVER FROM MORNING COMPLEX MAY BE LIMITING FACTOR FOR AMOUNT OF AFTERNOON INSTABILITY THROUGH CNTRL PLAINS. ...CENTRAL PLAINS TO S-CENTRAL/SW TX...AFTERNOON ONWARD... TSTMS SHOULD DEVELOP ALONG DRYLINE AND COLD FRONT DURING AFTERNOON/EVENING HOURS...WITH SUFFICIENT VERTICAL SHEAR TO SUPPORT BOTH SUPERCELLS AND BOW ECHOES. TWO SUBSTANTIAL CONCERNS ATTM ARE... 1. INSTABILITY -- SPECIFICALLY RELATED TO EXTENT/MAGNITUDE OF DIABATICALLY DRIVEN AFTERNOON HEATING AT SFC...BEHIND INITIAL BAND OF CLOUDS/CONVECTION. DISTANCE IN SPACE AND TIME BETWEEN EARLY ACTIVITY AND POTENTIAL DRYLINE/FRONTAL INITIATION SHOULD DIMINISH WITH NWD EXTENT...RENDERING CORRIDOR OF FAVORABLE BUOYANCY POTENTIALLY WEAKER AND NARROWER WITH NWD EXTENT. POCKETS OF HEATING NEAR AND SE OF NEB SFC LOW MAY SUPPORT ARC OF SUPERCELLS WITH TORNADO POTENTIAL OVER THAT REGION INVOF WARM FRNT WHERE SHEAR VALUES ARE MORE FAVORABLE. 2. CONVECTIVE MODE -- SIGNIFICANT COMPONENT OF MEAN FLOW ALONG COLD FRONT/DRY LINE WILL REMAIN LARGELY PARALLEL...PARTICULARLY FROM N-CENTRAL TX NWD. THIS DOES NOT PRECLUDE DISCRETE SUPERCELLS BUT MAY LIMIT THEIR COVERAGE/DURATION BEFORE MORE LINEAR MODES PREDOMINATE. FARTHER S ACROSS CENTRAL/SW TX...STRONGER CAPPING AND MEAN FLOW SOMEWHAT MORE NORMAL TO DRYLINE MAY SUPPORT MORE DISCRETE MODES. ADDITIONALLY...PRIND LOW-MIDLEVEL LAPSE RATES WILL BE RELATIVELY LARGE OVER CENTRAL/S TX BECAUSE OF STRONGER HEATING AND PROXIMITY TO MEXICAN ELEVATED MIXED-LAYER AIR. POTENTIAL IS LOWER OVER THIS REGION FOR TRAJECTORIES IN THAT LAYER WILL HAVE BEEN AFFECTED BY PRIOR CONVECTIVE OVERTURNING. FURTHER...RELATIVELY RICH SFC MOISTURE IS EXPECTED S OF RED RIVER WITH CLOSER PROXIMITY TO RELATIVELY UNDISTURBED GULF AIR MASS. RESULTANT MLCAPES POTENTIALLY ABOVE 2500 J/KG COMBINED WITH FAVORABLE VERTICAL SHEAR MAY SUPPORT LARGE/DAMAGING HAIL WITH SOME TSTMS. SEVERAL BANDS/CLUSTERS OF TSTMS MAY PERSIST AFTER DARK -- ESPECIALLY OVER TX AND SRN OK...WITH CONTINUING POTENTIAL FOR SVR THROUGH OVERNIGHT HOURS. ..AFWA.. 03/28/2007 CLICK TO GET WUUS02 PTSDY2 PRODUCT