Prognostic Meteorological Discussion
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FXUS02 KWBC 121553
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1052 AM EST FRI FEB 12 2016

VALID 12Z MON FEB 15 2016 - 12Z FRI FEB 19 2016

THE LOWER 48`S MEDIUM RANGE FORECAST WILL BE `IN-TRANSITION` FROM
WEST TO EAST.

...OVERVIEW...
FOR THE WESTERN THIRD OF THE NATION--- HIGH PRESSURE ALOFT AND A
JET-DRIVEN STORM TRACK THAT FAVORS THE ALASKA PANHANDLE AND
SOUTHWEST CANADA ---WILL BE REPLACED BY AN INCREASINGLY STRONGER
SERIES OF --- WARM FRONTS AND PACIFIC COLD FRONTAL
PROGRESSIONS...THAT SHIFT THE STORM TRACK SOUTHWARD OF THE 49TH
PARALLEL BY PERIOD`S END --- TOWARDS NORTH CENTRAL CALIFORNIA AND
THE SIERRA.

THE CENTRAL THIRD OF THE NATION --- A TEMPERATURE TRANSITION ZONE
---WITH A RATHER VARIABLE MIX OF WEST-NORTHWEST FLOW
EVENTS...PACIFIC INFLUENCES FROM THE WEST GRADUALLY REPLACING THE
CONTINENTAL AIRMASS AND INTERIOR CANADIAN INFLUENCES ENTRENCHED
OVER THE NORTHERN PLAINS ---DURING THE EARLY PORTION OF THE
FORECAST PERIOD.

FOR THE EASTERN THIRD OF THE NATION--- COLD/STABLE CANADIAN HIGH
SURFACE PRESSURE AND A NORTHERLY WIND COMPONENT ALOFT (TROUGH) ---
IS REPLACED BY A MILDER... PACIFIC INFLUENCE AND SOUTHWESTERLY
FLOW COMPONENT ALOFT.

...MODEL PREFERENCES...
THE 12/00Z DETERMINISTIC GFS BEST FIT THE GENERAL WEST-TO-EAST
PROGRESSION OF THE SYNOPTIC-SCALE AND WESTERN HEMISPHERIC FLOW
PATTERNS --- FROM GULF OF ALASKA AND SOUTHEAST CANADA. AND THROUGH
DAY 5...SEEMED TO OFFER THE BETTER DETAIL THAT SEEMINGLY EMERGES
FROM THE 12/00Z ENTIRE ENSEMBLE PACKAGE. A GENERIC BLEND OF THE
ECENS...NAEFS AND GEFS MEANS ESSENTIALLY DEPICTS THE LOWER 48`S
500MB FLOW PATTERN TRANSITION FROM `AMPLIFIED TROUGH` IN EASTERN
NORTH AMERICA--- TO A `FLAT` FLOW AND WEST-TO-EAST
`DE-AMPLIFICATION` SEQUENCING OF THE PATTERN FROM 130W TO 80W
LONGITUDE.
THE NATIONAL TEMP/POP AND SURFACE/50MB GRAPHICS EMPHASIZE A
50/30/20 RATIO OF THE ENSEMBLE MEANS (RESPECTIVELY) AFTER 17/12Z
(MID-POINT DAY 5). PRIOR TO THIS BREAK POINT...THE DETERMINISTIC
12/00Z GFS (AT 20%) WAS UTILIZED.

...UNCERTAINTY ASSESSMENT...
OVER THE EAST---
FROM MY PERSPECTIVE...THE QUESTION OF MOISTURE SOURCE AND TIMING
--- CONCERNING THE EAST COAST SYSTEM AND THE STUBBORN `EXIT` OF
THE VERY COLD/DRY CANADIAN SURFACE RIDGE HAS BEEN RESOLVED.
OBVIOUSLY...THE EXIT AND P-TYPE TRANSITION FROM DRY COLD TO MILD
WET FROM SSW-TO-NNE (BETWEEN ATLANTA AND BOSTON) MAINTAINS AN
INDIVIDUAL `AND RELATIVE LEVEL` OF CONFIDENCE FROM `PLACE TO
PLACE`. AND THE 12/00Z DETERMINISTIC GUIDANCE WOULD ADD TO THAT
`UNCERTAINTY`. THAT IS ---IF MY `EXPECTATIONS` --- AT THE
SUB-SYNOPTIC-SCALE PERSPECTIVE WERE TO BE A `PERFECT PROG` OVER
THIS BROAD GEOGRAPHIC REGION. IN ALL HONESTY...NOTHING HAS REALLY
CHANGED FROM 3 OR 4 DAYS AGO AT THESE LARGER TIME SCALE.

TWO POINTS TO MAKE ALONG THIS (MY)PERSPECTIVE ---
1) A SEQUENCE THAT INCLUDES AN OVER-RUNNING SCENARIO ALONG THE
WESTERN AND SOUTHERN FLANKS OF THIS CANADIAN SURFACE RIDGE REMAINS
A VERY KEY PART OF THE LOW-LEVEL ENVIRONMENT (AND FAVORABLE FOR
WINTER WEATHER). THIS HAS NOT CHANGED. ONCE THE UKMET RESOLVED ITS
UNREALISTIC FOUR CORNERS LOW SOLUTION. AND...

2) A SOUTHERN STREAM SYSTEM WILL DEEPEN/INTENSIFY OVER THE GULF
STREAM AND EXITS THE PIEDMONT AND DELMARVA PORTION OF THE
CONTINENT. THIS SYNOPTIC-SCALE DEPICTION HAS NOT CHANGED EITHER.
WHERE THE `ENTANGLEMENT` OF NORTHERN/SOUTHERN STREAMS ATOP THIS
COLD CANADIAN SURFACE RIDGE HAS NOT CHANGED `MUCH`.

WHERE THE DETERMINISTIC GUIDANCE HAS TRENDED OVER THESE PAST 3-4
DAYS ---HAS BEEN TO ---A TRAJECTORY AND DEPTH OF THE SURFACE
CYCLONE IN RELATIONSHIP TO THE MIGRATORY TRACK OF THE SUPPORTING
UPPER-LEVEL DYNAMICS OFF THE EAST CENTRAL COAST. TO LESS OF AN
OFFSHORE-FORCED LOW-LEVEL TRACK AND DEVELOPING SYSTEM (NEAR 40N
LATITUDE) TO ONE THAT IS NEARER TO 45N LATITUDE SYSTEM. IN OTHER
WORDS --- FROM A `SOUTHEAST OF THE 40N/70W BENCHMARK` TRACK---TO
ONE THAT IS `WELL NORTHWEST` OF THIS BENCHMARK. THAT`S
UNDERSTANDABLE---

AND FROM THE LARGER...GEOGRAPHICAL AND OVERALL PERSPECTIVE...THE
12/00Z GFS HAS THE BETTER `LOOK` IN MY OPINION.

OVER THE CENTRAL PORTION OF THE LOWER 48---
THE QUESTION IS MORE OF A WIND SHIFT/TEMPERATURE CHALLENGE --- AND
WHETHER OR NOT THE DETERMINISTIC CANADIAN/ECMWF HAVE THE BETTER
HANDLE WITH THE DOWNSLOPE WESTERLY FLOW TIMING LEE OF THE
CONTINENTAL DIVIDE VERSUS THE GFS AT DAY 4-6. THIS CHALLENGE IS
TIED TO THE ENTIRE DOWNSTREAM PATTERN --- AND THE ACCURACY OF THE
`TRUE` DEPTH OF THE SURFACE CYCLONE INVOF MONTREAL QUEBEC AT
17/12Z. HERE AGAIN...`PERFECT PROG` --- HARDLY IMAGINABLE. BUT
CLEARLY IDENTIFIABLE ACROSS THE MISSOURI VALLEY AS A WEST-TO-EAST
MOVING WARM/STATIONARY BOUNDARY WITH WESTERLY TO ITS WEST AND
NORTHWEST/NORTHERLY COMPONENT TO ITS EAST. BETWEEN 17/12Z AND
18/12Z --- STILL THINK THE GFS `PAINTS` A DECENT PICTURE OF THE
TIMING.

ALONG THE WEST COAST---
THE `SPLIT-FLOW` AND TRANSITION BACK MORE OF THE `EL-NINO` STORM
TRACK WILL BE AN AREA THAT INCORPORATES A LITTLE BIT MORE
`FORECAST PHILOSOPHY` GOING FORWARD (BEYOND DAY 6). IN
COORDINATION WITH THE WPC ALASKA THOUGHT PROCESS --- A COMPROMISE
AND NON-CANADIAN APPROACH IS THE CURRENT THOUGHT. THE SPREAD IS
GREATEST INVOF KODIAK ISLAND AND IS AN AIRSTREAM `SEPARATION`
FORECAST ISSUE BETWEEN 135W-145W INVOF 50N. WITH THE ENSEMBLE
MEANS IN DECENT CONSENSUS AT THE DAY8+ --- TIME FRAME WITH A MEAN
500MB TROUGH BETWEEN 160W AND 170W --- THERE WILL BE AN EXTENDED
PERIOD OF DIFFLUENT SOUTHWESTERLY FLOW ALOFT...THE WILL BE SAGGING
SOUTHWARD IN LATITUDE THROUGH TIME ALONG THE WEST COAST OF NORTH
AMERICA.

...SENSIBLE WEATHER HIGHLIGHTS...
DECENT OVER-RUNNING WINTER P-TYPE EVENT FOR A GOOD PORTION OF THE
EAST FROM THE SOUTHERN APPALACHIAN RIDGE TOPS (ENTIRE APPALACHIAN
TRAIL ACTUALLY) ---  NORTHEASTWARD INTO NEW ENGLAND FOR
MONDAY-TUESDAY AND EXITING THE LOWER 48 (DOWNEAST MAINE) ON
WEDNESDAY WITH A WETTER (ALL LIQUID_PRECIPITATION PATTERN DAY3-4
IN THE NORTHEAST GULF COAST REGION...DOWNWIND OF THE SOUTHEAST
COAST (GA/NRN FL) AND ALONG THE COLD FRONT ACROSS CENTRAL/SOUTH
FLORIDA.

A GRADUAL WARMING TREND ACROSS THE UPPER HALF OF THE MISSOURI
VALLEY AND WESTERN GREAT LAKES AND CONTINUED ABOVE NORMAL
TEMPERATURE-WISE OVER THE SOUTHERN THIRD OF THE PLAINS.

A GRADUAL SOUTHWARD PROGRESSION OF THE `WETTER` PACIFIC MOISTURE
FROM THE WEST COAST OF WASHINGTON...AND LIKELY NOT AS FAST TO
PROGRESS SOUTHWARD AS THE 12/00Z DETERMINISTIC ECMWF WOULD SUGGEST.

VOJTESAK


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