Prognostic Meteorological Discussion
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FXUS02 KWBC 271539
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1138 AM EDT TUE JUN 27 2017

VALID 12Z FRI JUN 30 2017 - 12Z TUE JUL 04 2017

***PATTERN OVERVIEW***

THROUGH MUCH OF THE EXTENDED PERIODS A BROAD UPPER-LEVEL RIDGE
WILL RESIDE OVER THE EASTERN STATES. ANOTHER RIDGE LOCATED OVER
THE WEST WILL SLOWLY SHIFT EASTWARD AS A TROUGH DEVELOPS OVER THE
GULF OF ALASKA/NORTH PACIFIC. THIS EASTWARD PROGRESSION WILL CAUSE
THE SANDWICHED TROUGH OVER THE NORTH-CENTRAL U.S. TO LIFT UP AND
OVER THE EASTERN RIDGE.

THIS TRANSLATES TO AN ELONGATED FRONTAL ZONE WITH MULTIPLE WAVES
OF LOW PRESSURE ALONG IT TO BE PRESENT FROM THE SOUTHERN/CENTRAL
PLAINS TO THE UPPER MIDWEST AND EXTENDING EASTWARD TO NEW ENGLAND.
SO AS THE UPPER TROUGH SLOWLY LIFTS INTO CANADA, THE NORTHERN
FLANK OF THE SURFACE FRONT WILL PASS THROUGH THE NEW ENGLAND. A
PACIFIC FRONT WILL MOVE INLAND BY LATE SATURDAY NIGHT/EARLY SUNDAY
MORNING. THIS FRONT WILL PASS THROUGH THE INTERMOUNTAIN WEST AND
INTO THE NORTHERN HIGH PLAINS MONDAY AND TUESDAY AS AN UPPER LEVEL
TROUGH BUILDS OVER SOUTHWEST CANADA.


***MODEL PREFERENCES***

OVERALL, THE DETERMINISTIC MODELS AND THEIR ENSEMBLE MEANS HAVE A
FAIR HANDLING ON THE EVOLUTION OF THE SYNOPTIC PATTERN. HOWEVER,
DAY 4 (SATURDAY) AND BEYOND SEVERAL LOCATIONS HAVE TIMING AND
STRENGTH DIFFERENCES. THE LATEST RUNS OF THE GFS CONTINUE TO BE
MORE AMPLIFIED ACROSS THE CENTRAL U.S., THE CMC IS FASTER AND OUT
OF PHASE, AND ENSEMBLE MEANS RESEMBLE THE GFS AND ECMWF. THE
INITIAL BLEND UTILIZED THE GFS AND ITS ENSEMBLE MEAN AND THE ECWMF
ENSEMBLE MEAN... TRANSITIONING TO MAINLY A BLEND OF THE ENSEMBLE
MEANS BY THE END OF THE FORECAST WHEN UNCERTAINTIES RELATED TO
MESOSCALE DETAILS ARE MORE SIGNIFICANT.


***SENSIBLE WEATHER***

WITH THE EAST COAST RIDGE AND MIDWEST TROUGH, A COLD FRONT WILL
BECOME NEARLY STATIONARY FROM THE GREAT LAKES DOWN ACROSS THE
MIDWEST AND THE CENTRAL PLAINS AS THE BERMUDA HIGH BUILDS AND
KEEPS THE FRONT FROM MAKING SIGNIFICANT EASTWARD PROGRESS. SHOWERS
AND THUNDERSTORMS SHOULD BECOME MORE SCATTERED IN NATURE ACROSS
THE EASTERN HALF OF THE COUNTRY WITH MORE WIDESPREAD COVERAGE
ALONG AND AHEAD OF THIS FRONTAL BOUNDARY. AREAS OF HIGHER RAINFALL
WILL LIKELY SET UP OVER NORTHERN NEW ENGLAND, NEAR SOUTHERN LAKE
MICHIGAN AND ACROSS EASTERN OKLAHOMA/WESTERN ARKANSAS. HOT AND
HUMID CONDITIONS WILL RETURN FOR MOST OF THE EAST COAST REGION
THIS WEEKEND AND INTO THE COMING WEEK.


CAMPBELL

$$





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