Steering if this fires up (Strong negative-tilt shortwave forecast to come down from the Aleutians)
Posted by JAC on 7/10/2010, 10:38 pm



 DAY 4-8 CONVECTIVE OUTLOOK  
  NWS STORM PREDICTION CENTER NORMAN OK
  0331 AM CDT SAT JUL 10 2010
 
  VALID 131200Z - 181200Z
 
  ...DISCUSSION...
  MEDIUM RANGE MODELS /ECMWF...GFS...GEFS AND ECMWF ENSEMBLE/ MAINTAIN
  REASONABLY GOOD CONTINUITY AND AGREEMENT WITH THE LARGE SCALE
  PATTERN EVOLUTION...ESPECIALLY DURING THE FIRST HALF OF THE DAY 4-8
  PERIOD.  PRIMARY FEATURE OF INTEREST IS THE STRONG UPPER LOW
  IMMEDIATELY SOUTH OF THE ALEUTIANS...WHICH HAS BEEN MOVING STEADILY
  EWD DURING THE LAST 24 HRS.  GUIDANCE INDICATES THIS SYSTEM WILL
  PROGRESS INTO THE WRN CANADIAN PRAIRIES BY THE LATTER PART OF DAY 4
  /JUL 13/ AS A STRONG SHORT WAVE TROUGH BEGINS TO ROTATE SOUTH OF THE
  LOW INTO MT...AND WITH INCREASING UPPER LEVEL DIFLUENCE DEVELOPING
  DOWNSTREAM FROM THE LOW.  THIS SYSTEM IS FORECAST TO CONTINUE EWD
  ACROSS MAN ON DAY 5 /JUL 14/ WITH THE SHORT WAVE TROUGH GRADUALLY
  BECOMING NEGATIVELY TILTED AS IT ACCELERATES ACROSS ND AND NRN MN.
 
  AT THE SURFACE...THE PRIMARY LOW WILL MOVE EWD ACROSS CNTRL CANADA
  WITH AN OCCLUDED/COLD FRONT ARCING SWD FROM THE LOW ACROSS THE NRN
  PLAINS ON DAY 4...AND ACROSS THE UPPER MS VALLEY ON DAY 5.  THERE IS
  SOME DIFFERENCE BETWEEN THE GFS AND ECMWF REGARDING THE INTENSITY OF
  A SECONDARY LOW DEVELOPING OVER SD ON DAY 4 AND THE SUBSEQUENT NWD
  TRANSPORT OF RICHER LOW LEVEL MOISTURE...BUT THE STRENGTH OF THE
  UPPER/LOWER LEVEL JET STRUCTURE SUGGESTS MOISTURE WILL BE
  TRANSPORTED NWD INTO PARTS OF ND AND NRN MN IN ADVANCE OF THE COLD
  FRONT.
 
  SEVERE STORM THREAT IS EXPECTED TO INCREASE OVER PARTS OF THE
  DAKOTAS ON DAY 4 /JUL 13/ AND MAY PERSIST THROUGH THE OVERNIGHT
  HOURS...BEFORE SPREADING EWD ACROSS MN AND PARTS OF WI ON DAY 5 /JUL
  14/.  GUIDANCE INDICATES THE FRONT WILL SURGE EWD ON DAY 5 AS A 100+
  KT UPPER LET STREAK LIFTS NEWD ACROSS THE DAKOTAS...WITH STRONG LOW-
  AND MID-LEVEL VERTICAL SHEAR ACCOMPANYING THE SYSTEM.  GIVEN THE
  STRENGTH OF THE FORECAST WIND FIELDS...DAMAGING WIND GUSTS AND A FEW
  TORNADOES WILL BE THE PRIMARY RISKS.
 
  AFTER DAY 5...THE UPPER SYSTEM LIFTS INTO CANADA AND POTENTIAL FOR A
  REGIONAL SEVERE STORM AREA APPEARS TO DIMINISH.
 
  ..WEISS.. 07/10/2010


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Rolling off the dark continent... - Chris in Tampa, 7/10/2010, 6:45 pm
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