AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE FORT WORTH TX 518 PM CST MON JAN 3 2011
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PREV DISCUSSION... /ISSUED 340 PM CST MON JAN 3 2011/
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BEYOND DAY 7...MEDIUM RANGE GUIDANCE CONTINUES TO ADVERTISE A MASSIVE ARCTIC INTRUSION INTO THE US NEXT WEEK AS AN ANOMALOUSLY STRONG 500MB RIDGE BUILDS OVER NORTHERN ALASKA. BOTH THE GFS AND ECMWF BUILD 500MB HEIGHTS TO NEAR 580DM OVER THIS REGION BY MONDAY. DURING THIS TIME...CROSS POLAR FLOW WILL SET UP ALLOWING EXTREMELY COLD AIR TO BUILD ACROSS NORTHWESTERN CANADA. THE LATEST RUN OF THE ECMWF INDICATES A MASSIVE 1069MB SURFACE ANTICYCLONE OVER WESTERN CANADA ON MONDAY...WHICH IS CONSIDERABLY STRONGER THAN ITS 00Z RUN AND STRONGER THAN THE 12Z GFS WHICH SHOWS A 1063MB HIGH. THE FIRST SHOT OF SIGNIFICANTLY COLDER AIR WILL MOVE INTO TEXAS ON MONDAY BUT THE TRULY ARCTIC AIR WILL REMAIN FARTHER TO THE NORTH AT THAT TIME. WHAT MAKES THIS SETUP SO CONCERNING IS NOT SIMPLY THE MODEL OUTPUT BUT RATHER THE IMPACT THE BLOCKING UPPER RIDGE OVER ALASKA WOULD HAVE. THIS WILL ALLOW THE CROSS POLAR FLOW TO REMAIN IN PLACE FOR SEVERAL DAYS. THE EXTREMELY COLD AND DENSE AIR OVER WESTERN CANADA EARLY NEXT WEEK WILL LIKELY BE ALLOWED TO SLIDE SOUTH OVER MUCH OF THE US BY THE MIDDLE OF NEXT WEEK. RAW MODEL OUTPUT FROM THE ECMWF INDICATES HIGHS ACROSS NORTH TEXAS IN THE 20S BY WED/THU WHICH IS VERY CONCERNING. PROLONGED TEMPERATURES THIS COLD WITH COLDER OVERNIGHT LOWS CAN BEGIN TO HAVE SERIOUS IMPACTS ON SOUTHERN INFRASTRUCTURE SUCH AS PIPES. WHILE THERE IS SOME INDICATION OF POSSIBLE PRECIPITATION AFTER THE COLD AIR HAS ARRIVED...THE MAIN CONCERN AT THIS TIME IS WITH THE TEMPERATURES. THIS SYSTEM BEARS CLOSE WATCHING OVER THE NEXT SEVERAL DAYS.