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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1425Z Aug 23, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1025 AM EDT SAT AUG 23 2014

VALID 12Z TUE AUG 26 2014 - 12Z SAT AUG 30 2014

...PATTERN OVERVIEW/PREFERENCES/CONFIDENCE...

THE MEDIUM RANGE PERIOD WILL BEGIN ON DAY 3/TUE WITH A RATHER
AMPLIFIED MID-LEVEL PATTERN AS A BROAD TROF SLIDES THROUGH THE
INTERMOUNTAIN WEST/ROCKIES.  FURTHER DOWNSTREAM A LARGE RIDGE WILL
BUILD FROM THE MS RIVER VALLEY EASTWARD AS THE BERMUDA HIGH
RETROGRADES...ALL WHILE A NEW TROUGH SIMULTANEOUSLY FORMS OVER THE
PACIFIC NORTHWEST.  TWO OF THE BIGGER UNCERTAINTIES TO CONSIDER
THIS PACKAGE ARE HOW MUCH ENERGY SEPARATES FROM THE UPPER TROF
TOWARD THE CENTRAL PLAINS AND THE PROSPECTS FOR TROPICAL
DEVELOPMENT OVER HISPANIOLA. 

THE SOLUTION SPREAD AS A WHOLE IS ABOUT AVERAGE AND TYPICAL FOR
THE EXPECTED PATTERN...WITH THE SPREAD SMALLEST DAYS 3-5
ESPECIALLY IN THE WEST AND CENTRAL BEFORE GROWING IN ALL AREAS
FROM DAY 6 ONWARD.  THE SPREAD IS THE HIGHEST WITH POTENTIAL
TROPICAL DEVELOPMENT OVER HISPANIOLA WITH THE DYNAMICAL GUIDANCE
SHOWING VARIOUS TRAJECTORIES AND INTENSITIES.  GIVEN THESE
ATTRIBUTES OF THE PATTERN ALONG WITH THE SPREAD...A SOLUTION NEAR
THE SLOW SIDE OF THE GUIDANCE IS PREFERRED WITH THE SLOWLY
EJECTING TROUGH ACROSS THE WEST AND THE NEWLY FORMING TROUGH
ACROSS THE PACIFIC NORTHWEST BY THE END OF THE PERIOD.  THE
SOLUTIONS CONFORMING MOST TO THIS PATTERN INCLUDE THE ECMWF AND
ECMWF ENSEMBLE MEAN...WITH SOME ASPECTS OF THE UKMET/CANADIAN ALSO
SUPPORTING AND AGREEING.  THE 00-06Z GFS ARE GENERALLY CONSIDERED
TOO FAST...ALTHOUGH THE 06Z RUN HAS SLOWED AND IS CONSIDERED A
BETTER FIT TO THE PATTERN. 

REGARDING POSSIBLE TROPICAL DEVELOPMENT AFFECTING U.S...CONTINUED
TO FOLLOW THE TRACK SUGGESTED BY YESTERDAY'S MEDIUM RANGE
COORDINATION CALL WITH THE NHC (08/22) UNTIL NEWER AND MORE
RELIABLE GUIDANCE BECOMES AVAILABLE.  THE 00-06Z GUIDANCE SHOWS
HIGH SPREAD...WITH THE 00-06Z GFS SHOWING TRACKS IN OPPOSITE
DIRECTIONS...THE ECMWF/CANADIAN FASTEST TOWARD THE NORTHEAST...AND
UKMET SOMEWHERE IN THE MIDDLE AND NOTICEABLY STRONGER.  THE
ENSEMBLE MEANS ARE SOMEWHERE NEAR THE MIDDLE OF THE ENVELOPE AS
WELL.

...SENSIBLE WEATHER HIGHLIGHTS...

ONE OF THE HIGHLIGHTS DURING THIS PERIOD WILL BE THE COOLER
CONDITIONS AFFECTING A SIGNIFICANT PORTION OF THE NORTHERN
TIER...ESPECIALLY ON DAYS 3/4.  HIGHS ARE EXPECTED TO ONLY REACH
THE 60S WHICH IS APPROXIMATELY 15 TO 20 DEGREES BELOW NORMAL. THIS
STRETCHES FROM THE NORTHERN ROCKIES EASTWARD TO THE UPPER GREAT
LAKES.  MEANWHILE...TEMPERATURES SHOULD APPROACH AND LOCALLY
EXCEED 100 ACROSS PORTIONS OF THE SOUTHERN PLAINS.  THE STRONG
BAROCLINIC ZONE SEPARATING THESE TWO AIR MASSES WILL BE A LIKELY
REGION FOR HEAVY RAINFALL.  THIS RISK FOR HEAVY RAINFALL WILL
EVENTUALLY SHIFT EASTWARD TOWARD THE END OF THE MEDIUM RANGE
PERIOD AND COULD CHANGE IF THE TROPICAL SYSTEM NEARS LAND.

JAMES