Prognostic Meteorological Discussion
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000 FXUS02 KWBC 281550 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1149 AM EDT WED JUN 28 2017 VALID 12Z SAT JUL 01 2017 - 12Z WED JUL 05 2017 ***PATTERN OVERVIEW*** THE UPPER-LEVEL SETUP, FEATURING RIDGES OVER THE WEST AND EAST WITH A TROUGH BETWEEN THE TWO OVER THE NORTH-CENTRAL U.S., WILL SHIFT EASTWARD THIS WEEKEND... TRANSITIONING TO A BROAD RIDGE SPANNING THE SOUTHERN HALF OF THE CONUS BY THE MIDDLE OF NEXT WEEK. AN ELONGATED FRONTAL ZONE WITH MULTIPLE WAVES OF LOW PRESSURE ALONG THE BOUNDARY IS EXPECTED ACROSS THE CENTRAL PLAINS TO THE UPPER MIDWEST, AND EXTENDING EASTWARD TO NEW ENGLAND. THE UPPER TROUGH IS FORECAST TO SLOWLY LIFT NORTHEAST INTO CANADA ALONG WITH ITS ACCOMPANYING SURFACE LOW BY SUNDAY NIGHT, WITH QUASI-ZONAL FLOW ACROSS MOST OF THE NATION BEHIND IT. ANOTHER COLD FRONT IS PROGGED TO PASS THROUGH THE PACIFIC NORTHWEST AND NORTHERN ROCKIES EARLY IN THE WEEK IN RESPONSE TO AN UPPER LEVEL TROUGH BUILDING OVER SOUTHWEST CANADA. ***MODEL EVALUATION AND PREFERENCES*** THE MOST CURRENT RUN OF THE MODELS ARE IN FAIRLY DECENT AGREEMENT ON HOW THE SYNOPTIC PATTERN TRANSITIONS BY THE END OF THE FORECAST PERIOD ON WEDNESDAY. THE GFS AND THE CANADIAN SOLUTIONS CONTINUE TO BE FASTER WITH THE TROUGH LIFTING THROUGH THE EASTERN U.S., WHEREAS, THE ECWMF LAGS BEHIND THROUGH ALL PERIODS. BOTH DETERMINISTIC AND THEIR ENSEMBLE MEANS ARE CLUSTERED WELL WITH THE TROUGH OVER THE GULF OF ALASKA/SOUTHWEST CANADA. THE INITIAL FORECAST BLEND UTILIZED A NEAR EQUAL WEIGHTING OF THE GFS, ECMWF, CMC, AND UKMET WITH THE GFS AND ECWMF ENSEMBLE MEANS THROUGH MONDAY. THE WEIGHTING OF THE GFS AND ECWMF ENSEMBLE MEANS WAS HIGHER TO ACCOUNT MESOSCALE DIFFERENCES ON TUESDAY AND WEDNESDAY. ***SENSIBLE WEATHER*** WITH THE BROAD UPPER LEVEL RIDGE OVER THE WESTERN ATLANTIC AND THE TROUGH OVER THE GREAT LAKES REGION, A COLD FRONT WILL BECOME NEARLY STATIONARY FROM THE GREAT LAKES DOWN ACROSS THE MIDWEST AND THE CENTRAL PLAINS. THE BERMUDA HIGH REMAINS PERSISTENT AND KEEPS THE FRONT FROM MAKING SIGNIFICANT EASTWARD PROGRESS. THIS BOUNDARY WILL SERVE AS A FORCING MECHANISM FOR SHOWERS AND THUNDERSTORMS ALONG AND AHEAD OF IT. ANOTHER ROUND OF HEAVY RAIN IS APPEARING MORE LIKELY IN ASSOCIATION WITH A SURGE OF MOISTURE INTERSECTING A WARM FRONT NEAR A SURFACE LOW OVER THE UPPER MIDWEST AND EXTENDING EASTWARD TO THE OHIO VALLEY BY LATER IN THE PERIOD. A SECOND FRONT CROSSING THE NORTHWESTERN U.S. LATER IN THE PERIOD WILL ALSO ENHANCE CONVECTION AHEAD OF IT. SCATTERED AND DIURNALLY DRIVEN CONVECTION IS LIKELY ACROSS MUCH OF THE EASTERN U.S., ESPECIALLY SOUTH OF THE FRONTAL ZONE. HOT AND DRY CONDITIONS WILL PERSIST FOR THE LOWER ELEVATIONS OF THE SOUTHWEST, BUT NOTHING RECORD BREAKING IS CURRENTLY ANTICIPATED. HOT AND HUMID CONDITIONS ARE EXPECTED TO RETURN TO THE EASTERN U.S. WITH WIDESPREAD 90-95 DEGREE HIGHS FOR LOCATIONS EAST OF THE APPALACHIANS. THE COOLEST WEATHER DURING THIS PERIOD SHOULD BE OVER NORTHERN MINNESOTA AND THE UPPER PENINSULA OF MICHIGAN, WHERE SOME AFTERNOON HIGHS COULD REMAIN IN THE 60S. CAMPBELL/HAMRICK $$

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