Prognostic Meteorological Discussion
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FXUS02 KWBC 020530
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
129 AM EDT THU APR 02 2015

VALID 12Z SUN APR 05 2015 - 12Z THU APR 09 2015

...OVERVIEW...

THE PATTERN OVER THE CONUS WILL DEFINITELY RESEMBLE SPRING MORE
THAN WINTER NEXT WEEK. THE UPPER LOW OVER HUDSON BAY THAT HAS
SEEMED TO BE OMNIPRESENT DURING THE WINTER SHOULD LIFT WELL NORTH
AND EASTWARD INTO CANADA DURING THE PERIOD WHICH WILL ALLOW
HEIGHTS TO RISE IN THE EASTERN STATES. FOR THE WEST... UPSTREAM
FLOW OVER ALASKA -- WHICH HAS TAKEN A WHILE TO SORT OUT -- SHOULD
TRANSITION TOWARD A STRONG JET SOUTH OF THE ALEUTIANS WHICH FAVORS
TROUGHING THROUGH THE WESTERN STATES.


...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT...

DETERMINISTIC MODELS CONTINUE TO IMPROVE RELATIVE TO EARLIER RUNS
FROM A FEW DAYS AGO... AND A MODEL CONSENSUS IS A REASONABLE
STARTING POINT THROUGH ABOUT MONDAY. BY THEN... DIFFERENCES ARE
QUITE EVIDENT IN THE GULF OF ALASKA WHERE THE ECMWF AND CANADIAN
ENSEMBLES ARE SLOWER WITH ENERGY THAN THE GEFS MEMBERS. A SIMILAR
PATTERN BECOMES EVIDENT OVER THE PAC NW BY TUE AS A SECOND
SHORTWAVE OR UPPER LOW DIVES INTO THE MEAN TROUGH OFFSHORE. THIS
FEATURE HAS LITTLE PREDICTABILITY AS EVIDENCED BY THE MUCH
DIFFERENT HANDLING OF IT BY THE MODELS IN RECENT RUNS. THIS HAS
LED TO SIGNIFICANT TIMING DIFFERENCES AMONG THE ENSEMBLES
REGARDING HOW QUICKLY TO BRING TROUGHING EASTWARD MIDWEEK. 12Z
ECMWF ENSEMBLES SUFFER FROM TOO MUCH TIMING SPREAD OVER A
RELATIVELY SHORT WAVELENGTH... RESULTING IN A FLATTER ENSEMBLE
MEAN... WHICH IS NOT TOO LIKELY. THE GEFS MEAN WAS MORE
AMPLIFIED... THOUGH IT MAY BE TOO QUICK... SO A BLEND AMONG THOSE
TWO MEANS PLUS THE ECMWF... WHICH MAINTAINED MORE AMPLITUDE AND
ACTED AS A GOOD BALANCE TO THE MEANS... GAVE A GOOD STARTING POINT
FOR NEXT TUE-THU. IN THE EAST... LOCATION OF WAVY SFC FRONT WILL
VARY FROM RUN TO RUN OF THE MODELS... BUT WILL HAVE A GREATER
AFFECT ON FORECASTING TEMPERATURES AS THE GRADIENT WILL BE
EXACERBATED IN TYPICAL SPRING FASHION.


...SENSIBLE WEATHER HIGHLIGHTS...

DESPITE RISING HEIGHTS IN THE THE EAST... SFC BOUNDARY WILL
DICTATE WHO SEES THE SPRING-TIME WARMTH VS WHO RETAINS A BIT MORE
CHILL. FOR NOW... MUCH OF THE GREAT LAKES TO NORTHEAST IS FORECAST
TO STAY ON THE COOL/WETTER SIDE OF THE BOUNDARY... AND PROBABLY
COLD ENOUGH FOR SNOW NEAR THE CANADIAN BORDER. ENSEMBLE RANGE IN
MAX TEMPS FOR REGIONS FROM DC TO BOS EXCEED 40F FROM LOWEST TO
HIGHEST. SUSTAINED WARM SECTOR SOUTHERLY FLOW WILL FAVOR WARM
TEMPERATURES AND A HEAVY RAIN AND CONVECTIVE THREAT FOR THE MID-MS
AND OHIO VALLEYS. WEST WILL STAY RATHER WET BUT LIKELY NOT FARTHER
SOUTH THAN CENTRAL CALIFORNIA... THOUGH SOME ENSEMBLE MEMBERS PUSH
APPRECIABLE PRECIP INTO SOUTHERN CALIFORNIA.


FRACASSO

$$





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