EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 159 AM EST MON JAN 20 2014 VALID 12Z THU JAN 23 2014 - 12Z MON JAN 27 2014 ...OVERVIEW AND PREFERENCES... AMPLIFIED RIDGE-TROUGH FLOW PATTERN REMAINS ANCHORED OVER NORTH AMERICA THROUGH DAY 7. THE OVERALL FLOW PATTERN ALOFT AND GENERAL AGREEMENT ON THE INTRODUCTION OF 2 ARCTIC SURGES HAS BEEN A MAINSTAY OF THE MEDIUM RANGE FORECAST...AS HAS THE SOURCE REGION FOR THESE COLD AIRMASS INTRUSIONS. THE CURRENT FORECAST MAINTAINS THE SPIRIT OF THIS DAY 3-7 FORECAST WITH VERY GOOD CONTINUITY INTO NEXT WEEKEND. IN THE EAST...THE QUASI-STATIONARY UPPER-LEVEL LOW OVER HUDSON BAY---AND IMPRESSIVE SUB-4800 METER 500MB HEIGHTS WILL BE CENTERED INVOF ST JAMES BAY BY DAY 6 (SUNDAY). IN THE WEST...THE UPPER-LEVEL RIDGE DOES HOLD FIRM...EVEN IF THE RUN-TO-RUN VARIATIONS AND MID-LEVEL SHORTWAVE ENERGY CAN BREACH IT...THE BEST OPPORTUNITY FOR A BREACH WOULD LIKELY COME ALONG ITS EAST FLANKS (WITH ORIGINS IN EASTERN BC/WRN AB)...RATHER THAN FROM A PLACE OVER THE EASTERN PACIFIC OCEAN. IN THE EASTERN PACIFIC...THE BLOCK STARTS AND ENDS NEAR 135W...AND THE FACT THAT A CLOSED HIGH CENTER DEVELOPS NEAR 45W 125W ON DAY 5...WILL NOT HELP IN ESTABLISHING ITS BREAK DOWN ALONG ITS WESTERN FLANKS THROUGH THIS MEDIUM RANGE PERIOD. A QUICK LOOK AT THE 20/00Z DETERMINISTIC GFS MATCHED UP WELL WITH THE PREVIOUS/CURRENT WPC GRAPHICS...WHICH HAVE PREFERRED A BLEND OF THE 19/12Z EC ENSEMBLES AND ITS DETERMINISTIC GUIDANCE. THE PLAINS STATES CONTINUES TO BE THE WILD CARD WITH RESPECT TO TEMPERATURE SWINGS...AND THE SOURCE REGION FOR A TRICKY MID-LEVEL NORTHWEST FLOW THAT WILL SPAWN A SERIES OF WAVES...THAT MIGRATE ALONG THE EASTERN FLANKS OF THE RIDGE AXIS...THEN DOWNSTREAM THROUGH THE MID-MS VALLEY AND OUT TO SEA ALONG THE EAST CENTRAL COAST. THOUGHT A BLEND OF THE 18/12Z ECMWF-19/00Z GFS WILL...GENERALLY DEPICT...THE TIMING OF THE SUBTLE DOWNSLOPE WARMING TO THE LEE OF THE NORTHERN AND NORTH CENTRAL ROCKIES...AND HANDLE THE SOUTHWARD PUSH OF THE CANADIAN SURFACE HIGHS INTO THE SOUTHERN PLAINS. THE RECENT RECORD WARMTH IN PORTIONS OF WYOMING...NORTHEAST COLORADO AND ALONG THE PLATTE RIVER VALLEY...IS INDICATIVE OF THE BIG TEMPERATURES SWINGS THAT WILL BE POSSIBLE AS ONE ARCTIC BOUNDARY DEPARTS AND A FRESH WESTERLY-COMPONENT DOWNSLOPE FLOW REAPPEARS. SOMETHING TO WATCH FOR...BEGINS AND ENDS...WITH THE MID-LEVEL TROUGH THAT CARVES OUT FROM THE MID-MO VALLEY THROUGH THE OZARKS TO THE PIEDMONT. WITH THE GUIDANCE RATHER CLEAR ON THE DEPTH OF THE COLD AIR SETTLING SOUTHWARD...AND A RATHER INTENSE SHORTWAVE DROPPING OUT OF NUNAVUT THAT USHERS IN THE SECOND ARCTIC AIRMASS...DAY 5-6...THE DOWNSTREAM ENVIRONMENT REMAINS FAVORABLE FOR A SERIES OF LOWER QPF...BUT HIGH SLR...PRECIPITATION EVENTS ALONG THE MID-LEVEL BOUNDARY. THE DETERMINISTIC GUIDANCE (ECMWF/GFS) SEEM TO HAVE THE SFC WAVE TRACK ESTABLISHED...BUT ARE POORLY-DETAILED WITH THE TIMING OF THE INDIVIDUAL H85-H7 SHORTWAVE ENERGY EXPECTED TO TRACK THROUGH THE EAST CENTRAL HALF OF THE LOWER 48. ...SENSIBLE WEATHER HIGHLIGHTS... ABOVE NORMAL TEMPERATURES IN THE SOUTHWEST...AND VERY COLD READING IN THE UPPER MIDWEST...AND NORTHEAST. COLD AND BLUSTERY FOR THE GREAT LAKES...WITH LOCAL LAKE-EFFECTS CONDITIONS LIKELY. SHOULD BEGIN TO SEE AN UPTICK IN PRECIPITATION FROM EAST TEXAS TO THE CAROLINAS DURING THE LATTER HALF OF THE FORECAST PERIOD...AS SHORTWAVE ENERGY INCREASES ALONG THE LEADING EDGE OF THE MODIFIED ARCTIC AIRMASS BOUNDARY. VOJTESAK