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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1603Z Feb 23, 2015)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1103 AM EST MON FEB 23 2015

VALID 12Z THU FEB 26 2015 - 12Z MON MAR 02 2015

...PATTERN CHANGE FOR THE LOWER 48...

...GENERAL OVERVIEW...

BROAD TROUGHING WILL REMAIN CARVED OUT OVER MUCH OF THE NATION
THROUGH THE END OF THE WORK WEEK...BUT A PATTERN CHANGE IS IN
STORE FOR THE LOWER 48 THIS WEEKEND.  SHORTWAVE ENERGY CROSSING
THE GULF OF ALASKA ON THURSDAY WILL AMPLIFY WHILE DIVING SOUTH
DOWN THE WEST COAST...EVENTUALLY LEADING TO AN ELONGATED MEAN
TROUGH CENTERED OVER THE WESTERN U.S. BY SUNDAY.  DOWNSTREAM...THE
RETURN OF A SOUTHEAST RIDGE WILL RAISE HEIGHTS EAST OF THE
MISSISSIPPI.  

...MODEL EVALUATION AND PREFERENCES...

ALTHOUGH MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH THE MEAN
FLOW OVER THE LOWER 48...THERE IS STILL SOME UNCERTAINTY WITH THE
SMALLER SCALE DETAILS. 

DETERMINISTIC RUNS APPEAR LOCKED INTO A SOLUTION FOR A SURFACE LOW
STREAKING OFF THE SOUTHEAST COAST ON THURSDAY...BUT THE GFS STILL
HINTS AT THE POSSIBILITY OF ANOTHER LOW DEVELOPING ALONG THE
TRAILING COLD FRONT ON FRIDAY.

MODELS ARE STILL STRUGGLING WITH THE EXACT EVOLUTION OF THE TROUGH
DIGGING IN OVER THE WEST THIS WEEKEND...AND THERE IS STILL SOME
UNCERTAINTY DOWNSTREAM WITH HEIGHTS BUILDING IN EAST OF THE
MISSISSIPPI EARLY NEXT WEEK.  DIFFERENCES ARE ESPECIALLY DRASTIC
ON DAY 6...WHEN THE GFS HOLDS A COLD HIGH IN OVER THE MID-ATLANTIC
STATES WHILE THE ECMWF MOVES IT WELL OFFSHORE.

TO ACCOUNT FOR ALL THE DETAIL DIFFERENCES...THE WPC DAY 3-7
FORECAST STARTED WITH A BLEND OF THE 00Z GEFS MEAN/ECMWF ENSEMBLE
MEAN.


...SENSIBLE WEATHER HIGHLIGHTS...

IN THE WEST... DIGGING TROUGHING SHOULD BRING LOWER TEMPERATURES
AND A WIDESPREAD CHANCE OF RAIN/SNOW TO NEARLY THE ENTIRE REGION
BUT FOCUSED FROM THE PAC NW THROUGH THE GREAT BASIN TOWARD THE
FOUR CORNERS. A SFC FRONT EAST OF THE DIVIDE WILL ENHANCE UPSLOPE
PRECIP IN NM/CO/WY. AS THE MEAN LONGWAVE TROUGH LIFTS
NORTHEASTWARD LATE THIS WEEKEND PRECIPITATION SHOULD BLOSSOM OVER
AND THEN EAST OF THE PLAINS. ENSEMBLES HAVE A STRONG SIGNAL FOR
WIDESPREAD RAIN ALONG/AHEAD OF THE SFC FRONT WITH SNOW TO THE
NORTH AND NORTHWEST OF THE BOUNDARY...WHICH WILL PUSH TOWARD THE
OH/TN VALLEYS AND INTO THE MID-ATLANTIC AND NORTHEAST EARLY NEXT
WEEK...HOWEVER...THERE IS STILL A GREAT AMOUNT OF UNCERTAINTY WITH
THE TIMING OF PRECIPITATION SPREADING EASTWARD.  

IN THE EAST... PESKY SYSTEM OFF THE SOUTHEAST COAST ON THURSDAY
WILL EXIT INTO THE ATLANTIC AND ALLOW COLD CANADIAN HIGH PRESSURE
TO SLIDE INTO THE MIDWEST AND OHIO VALLEY ON FRIDAY... SETTING UP
ANOTHER COLD NIGHT. SOME RECORD LOWS AND LOW MAXES ARE POSSIBLE.
THE HIGH WILL LIFT THROUGH NEW ENGLAND AND INTO ATLANTIC CANADA
SETTING UP A RETURN FLOW AND MUCH MILDER AIR -- NEAR TO JUST ABOVE
AVERAGE -- TO STREAM NORTHWARD EARLY NEXT WEEK.


GERHARDT