EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 158 AM EDT MON MAR 16 2015 VALID 12Z THU MAR 19 2015 - 12Z MON MAR 23 2015 NOT MUCH CHANGE FOR THE MEDIUM RANGE FORECAST AS THE 15/12Z ECENS...NAEFS AND GEFS MEANS CONTINUE TO DEPICT THE SPLIT-FLOW PATTERN ACROSS THE LOWER 48---HIGHLIGHTED BY COLD UPPER-LEVEL TROUGH ANCHORED ACROSS SOUTHEAST CANADA AND AN UPPER-LEVEL RIDGE POSITIONED ALONG THE MOUNTAINS OF WESTERN CANADA AND INTERIOR ALASKA. A RELATIVELY 'DRY' NORTHERN STREAM SHOULD FOCUS AN AXIS OF WEST-NORTHWEST FLOW ALOFT BETWEEN WINNIPEG AND BOSTON---WHILE A 'WETTER' SOUTHERN JET AXIS---MIGRATING A SERIES OF MID-LEVEL WAVES BETWEEN PHOENIX AND ATLANTA. EASILY MAINTAINED THE PREVIOUS SET OF WPC SURFACE AND 500MB GRAPHICS USING THE 3 MEANS AND THE DETERMINISTIC 15/12Z ECMWF THROUGH DAY 5 (SATURDAY). THIS WILL KEEP BELOW AVERAGE TEMPERATURES LOCKED IN ACROSS THE NORTHEAST AND UPPER GREAT LAKES---AND BRING A COOLING TREND FOR CALIFORNIA...THE DESERT SOUTHWEST AND GREAT BASIN DURING THE LATTER HALF OF THIS FORECAST PERIOD. A KEY FEATURE OF THE PATTERN---AN ACTIVE SOUTHERN JET STREAM---BRINGS AN INCREASE IN THE FREQUENCY OF MID-LEVEL SHORTWAVES MARCHING ACROSS THE SOUTHERN GREAT BASIN... FOUR CORNERS... RIO GRANDE VALLEY... AND SOUTHERN PLAINS. HIGHEST PRECIPITATION APPEARS TO BE OVER EASTERN TEXAS---LOUISIANA...THE MISSISSIPPI DELTA AND SOUTHEAST. VOJTESAK