Prognostic Meteorological Discussion
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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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