Prognostic Meteorological Discussion
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FXUS02 KWBC 290653
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 AM EDT THU JUN 29 2017

VALID 12Z SUN JUL 2 2017 - 12Z THU JUL 6 2017

***PATTERN OVERVIEW***

A BROAD UPPER LEVEL TROUGH AT THE BEGINNING OF THE PERIOD ON
SUNDAY ACROSS THE NORTH CENTRAL U.S. AND LOW AMPLITUDE TROUGH OVER
THE INTERMOUNTAIN WEST IS FORECAST TO EVOLVE INTO A QUASI-ZONAL
PATTERN BY THE MIDDLE OF NEXT WEEK WITH A BROAD UPPER LEVEL RIDGE
OVER THE CENTRAL U.S. BY THURSDAY.  AN ELONGATED FRONTAL ZONE WITH
MULTIPLE WAVES OF LOW PRESSURE ALONG IT 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 MONDAY.
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 DETERMINISTIC MODELS AND THEIR ENSEMBLE MEANS AGREE REASONABLY
WELL ON THE EVOLUTION OF THE SYNOPTIC PATTERN THROUGH EARLY NEXT
WEEK.  BY MONDAY NIGHT, BOTH THE GFS AND ECMWF CONTINUE TO SHOW A
MORE AMPLIFIED MID-LEVEL TROUGH CROSSING THE CENTRAL PLAINS, WITH
THE ECMWF FASTER THAN THE GFS WITH THIS FEATURE.  THE CMC WAS
SLOWER WITH THE UPPER LEVEL TROUGH CROSSING THE PACIFIC NORTHWEST
AND SOUTHWEST CANADA BY MONDAY AND TUESDAY COMPARED TO THE MODEL
CONSENSUS, AND SLOWER WITH ITS SURFACE FRONT.

THE INITIAL FORECAST BLEND UTILIZED A NEAR EQUAL WEIGHTING OF THE
DETERMINISTIC GFS, ECMWF, AND UKMET THROUGH MONDAY, WITH SOME OF
THE EC MEAN ALSO USED.    TOWARDS THE END OF THE FORECAST PERIOD,
GREATER PERCENTAGES OF THE EC AND NAEFS MEANS WERE INCORPORATED TO
ACCOUNT FOR MESOSCALE DIFFERENCES.  THE GEFS WAS SLOWER WITH THE
SHORTWAVE TROUGH CROSSING THE MIDWEST DURING THE TUESDAY TO
THURSDAY TIME PERIOD COMPARED TO THE EC MEAN AND CANADIAN MEAN, SO
A HIGHER PERCENTAGE OF THE EC MEAN WAS USED IN THE BLEND.


***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 NORTHEAST DOWN ACROSS THE OHIO VALLEY
AND WEST TOWARDS THE CENTRAL PLAINS.  THE BERMUDA HIGH REMAINS
PERSISTENT AND KEEPS THE FRONT FROM MAKING SIGNIFICANT
SOUTHEASTWARD 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.  SOME OF THIS MAY OCCUR OVER AREAS THAT HAD
RECENT SIGNIFICANT RAIN, AND SOME INSTANCES OF FLASH FLOODING WILL
BE POSSIBLE DURING THIS TIME, ESPECIALLY THROUGH MONDAY.  A SECOND
FRONT CROSSING THE NORTHWESTERN U.S. EARLY NEXT WEEK 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 WHERE MOISTURE WILL BE PLENTIFUL.

IN TERMS OF TEMPERATURES, EXPECT HOT AND DRY CONDITIONS TO
CONTINUE FOR THE LOWER ELEVATIONS OF THE SOUTHWEST, BUT NOTHING
RECORD BREAKING IS CURRENTLY ANTICIPATED.  HOT AND HUMID
CONDITIONS ARE EXPECTED ACROSS THE EASTERN U.S. WITH WIDESPREAD
88-95 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, AND ALSO NORTHERN
NEW ENGLAND WITH HIGHS IN THE 70S.

HAMRICK

$$




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