Prognostic Meteorological Discussion
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925
FXUS02 KWBC 091600
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1059 AM EST TUE FEB 09 2016

VALID 12Z FRI FEB 12 2016 - 12Z TUE FEB 16 2016

...RECORD COLD FOR PORTIONS OF THE NORTHEAST THIS WEEKEND...

...OVERVIEW...
DEEP TROUGH SWEEPS ACROSS SOUTHEAST CANADA EARLY IN THE
PERIOD---AND WILL USHER IN AN ARCTIC AIRMASS ACROSS THE NORTHEAST
QUARTER OF THE LOWER 48. A `MILDER` TROUGH PATTERN ATTEMPTS TO
ESTABLISH ITSELF OVER THE EASTERN HALF OF THE NORTH AMERICAN
CONTINENT BY DAY 7.

ALONG THE WEST COAST...INTERMOUNTAIN WEST AND EAST PAC---THE
MEDIUM RANGE PATTERN MAINTAINS A PROGRESSIVE SERIES OF MID-LEVEL
WAVES AND SECONDARY WAVE PACKET ENERGY --- DIRECTED ALONG THE
PACIFIC NORTHWEST COAST...NORTHERN DIVIDE AND UPWIND SIDE OF AN
UPPER-LEVEL RIDGE `SEMI-PARKED` OVER WESTERN CANADA --- THEN
DOWNSTREAM INTO THE NORTHERN PLAINS AND GREAT LAKES (A DRY
NORTHWEST FLOW).

...MODEL PREFERENCES...
THE 9/00Z ECENS/GEFS MEANS ALONG WITH SOME OF THE DETAILS EMBEDDED
WITHIN THE 9/00Z DETERMINISTIC ECMWF SEEMED TO SERVE AND SHOULD BE
A GOOD BASELINE FORECAST FOR THE LOWER 48 --- THIS PARTICULAR
MEDIUM RANGE PERIOD. WITH THE LAST TWO DETERMINISTIC RUNS OF THE
GFS (9/00Z & 06Z) SIDING CLOSER TO THE DETERMINISTIC
CANADIAN/ECMWF SOLUTIONS IN THE WEST --- AND IN RATHER GOOD
`CONSENSUS AGREEMENT` THROUGH DAY 5 IN THE EAST AND GULF COAST ---
THOUGHT THE COLD ARCTIC-MODIFIED AIRMASS SPREADING INTO THE
SOUTHEAST AND ACROSS THE EASTERN SEABOARD WOULD/COULD CONCEIVABLY
FORM A DISTINCT MOISTURE BOUNDARY --- THAT MAINTAINS A
SYNOPTIC-SCALE SCENARIO FOR ADDITIONAL SURFACE WAVE DEVELOPMENT
ALONG ITS LEADING EDGE ---DURING THE LATTER HALF THIS FORECAST
PERIOD. THIS SEEMS TO BE A `REPETITIVE THEME` AT DAY6-7 INVOF THE
WESTERN ATLANTIC GULF STREAM CURRENT THIS WINTER SEASON.

...UNCERTAINTY ASSESSMENT...
THE GREATEST VARIANCE BETWEEN ENSEMBLE MEANS AND DETERMINISTIC
SOLUTIONS CONTINUES TO BE IN THE WEST --- THROUGH DAY 5. AND THEN
ALONG THE EAST COAST BEYOND DAY 5 AS THE PACIFIC ENERGY MIGRATES
EASTWARD ACROSS THE CENTRAL PORTION OF THE CONTINENTAL US AND
BEGINS TO `FLUSH OUT` THE PERIPHERY OF THE ARCTIC AIRMASS.

THE DAY 4-5 TRANSITION PERIOD SEEMS TO BE POINT OF CONTENTION ---
WITH THE PACIFIC FLOW ALOFT MIGRATING ATOP A COLD AND STABLE (BUT
EXITING) CANADIAN SURFACE HIGH. THE NATURAL PROGRESSION OF THIS
SCENARIO IS TO `SPLIT` THE UPPER FLOW ---AND ATTEMPT TO TRANSLATE
THE MID-LEVEL ENERGY INTO A SURFACE REFLECTION. THIS IS WHERE THE
9/00Z ECENS/DETERMINISTIC ECMWF TAKES THE PATTERN IN A BETTER
DIRECTION. AND BY DAY 6 ... THERE BECOMES A PROMINENT SURFACE WAVE
OVER THE SOUTHERN GREAT LAKES REGION AND SURFACE TROUGH/FRONT
SPREADING SOUTHWARD INTO THE LOWER MS VALLEY. THE AREA TO MONITOR
--- AND WHERE THERE IS STILL SOME ROOM FOR ADJUSTMENT--- IS ALONG
THE LEADING EDGE OF THE ARCTIC AIRMASS ---IN THE SOUTHEAST AND
INVOF PIEDMONT/OUTER BANKS --- AND WHERE THE BETTER PROSPECTS FOR
DEEPENING SURFACE WAVE DEVELOPMENT HAS POTENTIAL TO BLOOM INTO A
MORE PROMINENT SUB-SYNOPTIC-SCALE ENTITY. THE MEANS TEND TO `WASH
OUT` THE FEATURE AND THE LEADING EDGE OF THE MODIFIED-ARCTIC
BOUNDARY --- AND WHERE I THOUGHT THE WPC DAY6-7 SURFACE GRAPHIC
WOULD ATTEMPT TO DEPICT THE PROJECTED SURFACE WAVE TRACK.
AGAIN...BASED UPON THE ENSEMBLE MEANS AT THOSE TIME SCALES.

...SENSIBLE WEATHER HIGHLIGHTS...
ENTIRE NORTHEAST..MID-ATLANTIC REGION AND SOUTHEAST WILL RECEIVE A
BLAST OF ARCTIC AIR FOR DAYS 3-5 WITH A PEAK DEPTH AROUND 14/12Z
(SUNDAY MORNING). SLOW MODERATION (A WARMING TREND) IS EXPECTED
DAYS 6-7 ... BUT THE THREAT FOR (A WINTRY P-TYPE) PRECIPITATION
EVENT EXPANDS FROM THE GULF COAST NORTHWARD INTO THE NORTHEAST AND
NEW ENGLAND --- ATOP THE RETREATING CANADIAN SURFACE HIGH.

WEST OF THE DIVIDE ---GENERALLY WEST OF 100W LONGITUDE ---NEAR TO
ABOVE NORMAL TEMPERATURES WITH LITTLE PRECIPITATION IN THE
SOUTHWEST QUARTER OF THE NATION. WHAT PRECIPITATION THAT DOES
OCCUR --- WILL CONCENTRATE INVOF WASHINGTON STATE...WESTERN OREGON
AND THE `WINDWARD` NORTHERN THIRD OF THE CONTINENTAL DIVIDE.

VOJTESAK

$$





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