THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


EXTENDED FORECAST DISCUSSION




EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
132 AM EDT WED SEP 02 2015

VALID 12Z SAT SEP 05 2015 - 12Z WED SEP 09 2015


THERE WERE INDICATIONS AMONG THE RECENT GLOBAL ENSEMBLE MEANS THAT
THE RELATIVE STABILITY--HENCE, PREDICTABILITY--OF THE FLOW PATTERN
OVER CENTRAL NORTH AMERICA MAY BE DRAWING TO A CLOSE BY THE END OF
THE MEDIUM RANGE. THERE WERE IMPORTANT SYNOPTIC DIFFERENCES
BETWEEN THE 12Z/01 ECENS AND NAEFS MEANS ACROSS ALASKA AND CANADA
THAT LIKELY PORTEND A SHUFFLING OF THE LONGWAVES BY THE MIDDLE OR
END OF NEXT WEEK. MODEL DISPARITY AND VOLATILITY FREQUENTLY ATTEND
SUCH PATTERN CHANGES, SO CONFIDENCE IN THIS FORECAST IS LOWER THAN
OF LATE. USED A BLEND OF THE RECENT ENSEMBLE MEANS TO MITIGATE
THIS UNCERTAINTY, AS WELL AS HONOR CONTINUITY. THE LARGE SWATH OF
PRECIPITATION ASSOCIATED WITH THE TROUGH MOVING ACROSS THE
NORTHERN PLAINS AND SOUTH-CENTRAL CANADA WILL SHRINK AND SINK
SOUTHWARD INTO THE CENTRAL STATES ALONG THE ATTENDANT SURFACE
POLAR FRONT. THIS FAIRLY RAPID TRANSITION WILL BE FACILITATED BY A
KICKER SHORTWAVE COMING INTO THE PACIFIC NORTHWEST EARLY NEXT
WEEK. THE GULF COAST AND SOUTHEAST SHOULD REMAIN SHOWERY, WITH
STABLE HEIGHTS FOR NOW. THE SOUTHWEST MONSOON WILL GET SLOWLY
SQUASHED BY THE STEADY POLAR FLOW ALONG THE WESTERN BORDER WITH
CANADA.


CISCO





Last Updated: 132 AM EDT WED SEP 02 2015