Prognostic Meteorological Discussion
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110
FXUS02 KWBC 280612
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
211 AM EDT WED JUN 28 2017

VALID 12Z SAT JUL 1 2017 - 12Z WED JUL 5 2017

***PATTERN OVERVIEW***

A BROAD UPPER LEVEL TROUGH AT THE BEGINNING OF THE PERIOD ON
SATURDAY ACROSS THE NORTH CENTRAL U.S. AND MODEST UPPER LEVEL
RIDGING OVER THE INTERMOUNTAIN WEST AND EAST COAST IS FORECAST TO
SLOWLY TRANSITION EASTWARD THROUGH EARLY NEXT WEEK.  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 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 DETERMINISTIC MODELS AND THEIR ENSEMBLE MEANS AGREE REASONABLY
WELL ON THE EVOLUTION OF THE SYNOPTIC PATTERN THROUGH THIS
WEEKEND.  THE OPERATIONAL GFS HAS TRENDED STRONGER OVER THE PAST 4
RUNS WITH THE UPPER LOW OVER MINNESOTA SATURDAY MORNING, AND THE
ECMWF HAS ALSO TRENDED MORE AMPLIFIED WITH ITS 12Z RUN.  BY
MONDAY, BOTH THE GFS AND ECMWF ARE SHOWING A MORE AMPLIFIED
MID-LEVEL TROUGH CROSSING THE CENTRAL PLAINS, WITH THE ECMWF
TRENDING TO BE THE MOST AMPLIFIED BY DAY 7 (WEDNESDAY) WITH A
GREATER DEPARTURE FROM THE EC MEAN.  THIS IS IN CONTRAST WITH THE
SMALLER DEPARTURE BETWEEN THE GFS AND THE GEFS MEAN FOR THE SAME
FEATURE.

THE INITIAL FORECAST BLEND UTILIZED A NEAR EQUAL WEIGHTING OF THE
DETERMINISTIC GFS, ECMWF, AND UKMET THROUGH SUNDAY.  THE CMC WAS
MORE AMPLIFIED WITH THE UPPER LEVEL TROUGH ACROSS THE GREAT LAKES
REGION COMPARED TO THE MODEL CONSENSUS, BUT SIMILAR WITH ITS
SURFACE PATTERN.  FOR THE MONDAY TO WEDNESDAY TIME PERIOD,
SLIGHTLY MORE GFS WAS USED THAN THE ECMWF, AND GREATER PERCENTAGES
OF THE EC AND GEFS MEAN WERE INCORPORATED TO ACCOUNT MESOSCALE
DIFFERENCES.


***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.

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
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.

HAMRICK

$$





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