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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0606Z Jan 22, 2015)
 
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
106 AM EST THU JAN 22 2015

VALID 12Z SUN JAN 25 2015 - 12Z THU JAN 29 2015

THE MODELS AND ENSEMBLES CONTINUE TO SHOW A SLOWLY EVOLVING
LONGWAVE PATTERN FEATURING A HIGH AMPLITUDE RIDGE OVER THE WEST
AND HIGH AMPLITUDE TROUGH IN THE EAST. A PAIR OF EASTERN PACIFIC
TROUGHS MERGE AND WITH THE DEEP LAYER RIDGE DRIFTING INLAND...THE
DOOR IS OPENED FOR HEIGHT FALLS AND MOISTURE TO MOVE ONSHORE INTO
CA AND THE SOUTHWEST.

THE MODELS CONTINUE TO SHOW AN INTENSE CYCLONE DEVELOPING NEAR THE
SOUTHEAST COAST AND MOVING NORTH TOWARDS OR JUST OFFSHORE THE NEW
ENGLAND COAST SATURDAY...AND ACROSS THE CANADIAN MARITIMES SUNDAY.
THE MODELS CLUSTER WITH A CAMP CROSSING EASTERN NEW ENGLAND LED BY
THE 12Z ECMWF/ECMWF ENSEMBLE MEAN AND JOINED BY THE 12-00Z
CANADIAN GLOBAL.  THE GFS AND GEFS MEAN ARE SHADED FURTHER EAST. 

ONCE THIS CYCLONE DEPARTS...ANOTHER DEVELOPS IN THE CANADIAN
PRAIRIES AND MOVES ACROSS THE NORTHERN PLAINS TO UPPER MS VALLEY
BY 12Z SUNDAY
AND MID ATLANTIC MONDAY 26 JAN. THERE REMAINS THE POSSIBILITY OF
SECONDARY CYCLOGENESIS ALONG OR OFF THE MID ATLANTIC COAST WITH
THE NEW CYCLONE TRACKING NORTHEAST OFF THE NEW ENGLAND COAST AND
DOWNSTREAM TO SOUTH OF NOVA SCOTIA 12Z TUE 27 JAN. THERE ARE
TIMING DIFFERENCES WITH THE 12Z OPERATIONAL ECMWF AHEAD OF THE
PACK AS THE SLOWER 18-00Z GFS/CANADIAN GLOBAL CLUSTER BETTER WITH
THE 12Z ECMWF ENSEMBLE MEAN AND 18Z GEFS MEAN.

NEXT WED-THU THE MODELS SHOW A STRONG ANTICYCLONE OVER NORTHWEST
CANADA WITH AN EXTENSIVE RIDGE BUILDING SOUTHEAST TOWARDS THE
NORTHERN PLAINS.
THE 18Z GFS AND 12Z ECMWF SHOWED SFC WAVE DEVELOPMENT IN THE
SOUTHERN PLAINS...BUT THE 00Z GFS RUN MOVED THE WAVE NORTH ABOUT
300 NM 12Z THU 29 JAN...WHILE THE 00Z CANADIAN KEPT THE WAVY FRONT
DOWN IN AR TO NORTHERN TEXAS LIKE THE 18Z GFS DID. 
CONSEQUENTLY...CONFIDENCE IS NOT HIGH IN THE 00Z OPERATIONAL GFS
FCST AS IT PRESERVED A SOUTHERN STREAM WAVE ROTATING AROUND THE
MEAN WESTERN RIDGE WHILE OTHER MODELS SHEARED THE WAVE IN
CONFLUENT FLOW.

WPC SURFACE/500 MB GRAPHICS AND TEMPERATURE/PROBABILITY OF
PRECIPITATION FORECASTS USED A BLEND OF THE 12Z ECENS/18Z GEFS
MEANS. THE 21/12Z DETERMINISTIC ECMWF WAS INCORPORATED THROUGH DAY
5 AND DISCONTINUED AFTERWARD DUE TO CYCLONE TIMING ISSUES IN THE
MID ATLANTIC. 

...SENSIBLE WEATHER HIGHLIGHTS...
THE CYCLONE MOVING UP THE EAST COAST SUNDAY LEADS TO A LARGE
SHIELD OF PRECIPITATION WITH CHALLENGES OF POTENTIAL WINTER
PRECIPITATION ON THE NORTH AND WEST FRINGES OF THE SHIELD IN NEW
YORK/NEW ENGLAND.  THE NEXT CYCLONE LEADS TO A LARGE AREA OF
PRECIPITATION WITH RAIN IN THE WARM SECTOR AND SNOW IN THE COLD
SECTOR ACROSS THE MID-UPPER MS VALLEY TO THE GREAT LAKES AND OH
VALLEY SUN AND CENTRAL APPALACHIANS TO THE MID ATLANTIC AND NY/NEW
ENGLAND MONDAY 26 JAN.     
850-700 MB MOISTURE FLUXES ON THE EAST SIDE OF THE SUBTROPICAL
PACIFIC TROUGH ADVECT MOISTURE INTO SOUTHERN CALIFORNIA AND THE
SOUTHWEST...BRINGING A CHANCE OF SHOWERS THERE EARLY NEXT WEEK.

A VERY MILD PATTERN CONTINUES TO BE FORECAST FOR THE WEST AND THE
PLAINS STATES. TEMPERATURES 10-15 DEGREES ABOVE NORMAL WILL BE
COMMON...PEAKING NEAR 20 DEGREES ABOVE NORMAL IN THE NORTHERN TO
CENTRAL PLAINS AND ROCKIES DAY 3-5...SHIFTING TO THE CENTRAL
PLAINS/CENTRAL ROCKIES AND GREAT BASIN DAY 6...AND CENTRAL TO
SOUTHERN GREAT BASIN DAY 7 THU 29 JAN.  THE COLDEST CONDITIONS
APPEAR TO BE BELOW NORMAL TEMPS IN THE LOWER LAKES/NEW YORK/NEW
ENGLAND ON DAYS 4-7.  BELOW NORMAL TEMPERATURES ARE ALSO FORECAST
IN FLORIDA WITH THE HIGH AMPLITUDE EASTERN TROUGH ALLOWING COLD
FRONTS TO MOVE ACROSS THE STATE.

PETERSEN