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