Preliminary Forecasts
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FXUS02 KWNH 300527
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
126 AM EDT SAT APR 30 2016

VALID 12Z TUE MAY 03 2016 - 12Z SAT MAY 07 2016

GENERAL FLOW PATTERN
~~~~~~~~~~~~~~~~~~~~
AN AMPLIFIED AND BLOCKY FLOW PATTERN IS EXPECTED THIS PERIOD WITH
INCREASING WESTERN TROUGHING CONSISTING OF A CLOSED LOW MOVING
INTO CA, A ROCKIES RIDGE WHICH MIGRATES INTO THE PLAINS, AND AN
EASTERN TROUGH EVENTUALLY COMPOSED OF A DEEP CYCLONE NEAR THE
COAST OF THE MID-ATLANTIC STATES.


MODEL DISCUSSION/PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE 12Z CANADIAN AND 18Z GFS WERE QUITE DIFFERENT THAN THE
REMAINING GUIDANCE IN BRINGING A LOW/POSSIBLE NOR`EASTER CLOSE TO
NEW ENGLAND EARLY ON, WHICH LEFT THE 12Z GLOBAL ENSEMBLE ENVELOPE.
 HOWEVER, FROM LATE THURSDAY ONWARD, THE 12Z CANADIAN RETURNED TO
THE FOLD.  SINCE ITS 18Z RUN, THE 00Z GFS LOOKS MUCH MORE LIKE THE
REMAINDER OF THE DETERMINISTIC AND ENSEMBLE MEAN GUIDANCE.  THE
12Z ECMWF HAD A STRANGE UPPER LOW IN WY AT THE START OF THE PERIOD
WHICH RETROGRADED OVER THE TOP OF A PROGRESSIVE SOUTHERN STREAM
RIDGE WHICH WAS NOT SUPPORTED BY ITS ENSEMBLE MEAN.  WHILE THE
STRENGTH OF THE RIDGE OVER THE TOP COULD SUPPORT A BUNDLE OF
MID-LEVEL ENERGY UNDER ITS BASE, IT WOULD BE QUASI-STATIONARY DUE
TO THE PROGRESSIVE NATURE OF THE RIDGE MOVING THROUGH THE CANADIAN
PRAIRIE PROVINCES, LIKELY NOT RETROGRESSIVE.

WHEN PRODUCED, THE 500 HPA HEIGHTS/PRESSURES/SURFACE WINDS WERE A
20/30/20/30 BLEND OF THE 12Z CANADIAN/12Z UKMET/18Z GFS/12Z ECMWF
FOR TUESDAY, WHICH WAS SIMPLIFIED TO A 30/30/40 BLEND OF THE 12Z
UKMET/18Z GFS/12Z ECMWF FOR WEDNESDAY, WHICH MORPHED INTO A
MAJORITY BLEND OF THE 12Z UKMET/12Z ECMWF THURSDAY.  FROM FRIDAY
ONWARD, A COMPROMISE OF THE 12Z CANADIAN/12Z ECMWF WITH INCREASING
AMOUNTS OF THE 12Z NAEFS MEAN AND 12Z ECMWF ENSEMBLE MEAN WAS
USED.  THE TEMPERATURES/DEW POINTS/CLOUDS/WEATHER/ RAIN CHANCES
WERE MAINLY A BLEND OF THE 12Z NAEFS MEAN/12Z ECMWF ENSEMBLE MEAN.
 THE DAYS 4-5 QPF WERE A COMPROMISE OF THE 18Z GFS/00Z GFS/12Z
ECMWF WHILE THE DAYS 6-7 QPF WERE A COMPROMISE OF THE 00Z GFS/12Z
ECMWF/12Z CANADIAN SOLUTIONS.


WEATHER HIGHLIGHTS
~~~~~~~~~~~~~~~~~~
THE WEST BECOMES INCREASINGLY WET/UNSETTLED AS A CLOSED LOW
PROGRESSES ACROSS THE REGION.  TEMPERATURES ARE EXPECTED TO BECOME
5-10F BELOW THE MEAN ACROSS PORTIONS OF THE GREAT BASIN AND
SOUTHWEST FRIDAY INTO NEXT SATURDAY.  BEFORE TROUGHING GETS TO THE
WEST, RECORD HIGH MINIMA ARE POSSIBLE ACROSS PORTIONS OF WA
TUESDAY AND WEDNESDAY.  TEMPERATURES ARE EXPECTED TO BE 12-16F
ABOVE THE MEAN ACROSS THE NORTHWEST/NORTHERN ROCKIES FROM TUESDAY
INTO THURSDAY BEFORE RIDGING MOVES OUT INT THE PLAINS.  THE
PLAINS/MISSISSIPPI VALLEY DRY OUT AND WARM UP DUE TO THE INVADING
RIDGE.  MODERATE TO HEAVY PRECIPITATION IS EXPECTED TO SPREAD UP
THE EAST COAST WITH TIME AS A PAIR OF WEAK CYCLONES COMBINE INTO A
STRENGTHENING COASTAL LOW AS A MID-LEVEL CYCLONE DROPS DOWN INTO
THE MID-ATLANTIC STATES.  ONCE THE LOW STARTS SPINNING UP OFFSHORE
THE EAST COAST, PRECIPITATION AND COLD ADVECTION TO ITS WEST ARE
EXPECTED TO KEEP TEMPERATURES 4-8F BELOW NORMAL ALONG PORTIONS OF
THE EASTERN SEABOARD AND GREAT LAKES.

ROTH
$$





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