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FXUS10 KWNH 171628
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1127 AM EST FRI NOV 17 2017

VALID NOV 17/1200 UTC THRU NOV 21/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

12Z MODEL ASSESSMENT INCLUDING PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

LARGE STORM SYSTEM OVER THE EASTERN U.S. THIS WEEKEND
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/CMC AND 12Z GFS BLEND.
CONFIDENCE: SLIGHTLY ABOVE AVG TO AVERAGE

GOES-WV MOSAIC DEPICTS A LARGE CYCLONE OVER CENTRAL CANADA WITH A
BROAD POSITIVE TILT TROF EXTENDING BACK TOWARD OFFSHORE CA.  THIS
POSITIVE TILT BASE WILL TRANSLATE FAIRLY QUICKLY ACROSS THE
WESTERN AND CENTRAL US TODAY INTO SAT SUPPORTING A SURFACE WAVE
ACROSS THE CENTRAL GREAT PLAINS THAT LIFTS INTO THE SOUTHERN GREAT
LAKES BY THE SECOND HALF OF SAT AS WELL.  AT THIS POINT SPREAD
BEGINS TO MANIFEST AS THE BASE BEGINS TO AMPLIFY/WIND UP ACROSS
THE OHIO VALLEY INTO THE EASTERN LAKES/SE CANADA/N NEW ENGLAND.
THE 12Z NAM HAS TRENDED UNCHARACTERISTICALLY FLATTER THOUGH IS
ALSO FASTER LIKELY IN THE STRONGER/MORE COMPACT KICKER SHORTWAVE
DESCENDING OUT OF SOUTHERN CANADA LATE SAT/EARLY SUN.  A SECONDARY
SURGE/SHORTWAVE COMES A DAY LATER AND THE THREE SYSTEMS BUILD INTO
THE LARGER SCALE VORTEX OVER QUEBEC BY THE END OF THE FORECAST
PERIOD...BUT THE NAM IS CLEARLY OUTLIER AT THIS POINT.  THE 00Z
UKMET GIVES SOME TIMING SUPPORT TO THE NAM...BUT HOLDS BACK THE
SURFACE LOW A BIT MORE IN LINE WITH THE MODEST CONSENSUS ANCHORED
BY THE ECMWF/ECENS MEAN.  THE 12Z GFS AND THE 06Z RUN BEFORE IT
BREAK FROM THE GEFS MEMBER CLUSTER IN FAVORING AN
UNCHARACTERISTICALLY SLOWER SOLUTION; THE GFS IS A BIT
STRONGER/COMPACT INITIALLY COMING INTO THE GREAT LAKES ALLOWING
FOR A EARLIER DEEPENING HAVING A FAVORABLE NEGATIVE TILT
ORIENTATION WITH THE LARGER SCALE NORTHERN STREAM.  UPSTREAM
KICKER WAVES FOLLOW IN SUBSEQUENT DAYS EXPANDING/BROADENING THE
VORTEX ACROSS QUEBEC BUT FURTHER SOUTH AND WEST THAN OTHER
GUIDANCE/GEFS MEAN.  THIS IS NOT TOO FAR FROM THE EVOLUTION OF THE
00Z ECMWF/CMC UNTIL LATE MONDAY AS THE ECMWF/CMC DO NOT MANIFEST
THE STRONGER KICKER WAVES THAT THEN NAM/GFS RESOLVE...ALLOWING FOR
THE VORTEX/SURFACE LOW TO PRESS EASTWARD TOWARD LABRADOR BY TUES.
 WHILE THE ECMWF/CMC IS PREFERRED OVER THE GFS...THE VARIATION IS
NOT LARGE ENOUGH IN THE ENSEMBLE SUITE TO JUSTIFY THE GFS`S
REMOVAL AT THIS TIME.  AS SUCH WILL SUPPORT A ECMWF/CMC AND GFS
BLEND HEDGING TOWARD THE ECMWF. CONFIDENCE IS STRONG UNTIL SUNDAY
BUT REDUCES ACROSS NEW ENGLAND...AND IS AVERAGE TO SLIGHTLY ABOVE
AVERAGE THROUGH THE ENTIRE FORECAST PERIOD.


NORTHERN PORTION OF TROF APPROACHING PAC NW SUNDAY...TRANSLATES
INTO NORTHERN TIER WITH DEEP SURFACE WAVE JUST NORTH OF US BORDER
WITH FRONT ENTERING NORTHERN PLAINS LATE MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND
CONFIDENCE: AVERAGE

SHORTWAVE OVER GULF OF AK QUICKLY DEFORMS INTO A SHARP ELONGATED
TROF BY LATE SAT/SUN... AN EMBEDDED ENHANCED WAVE IN THE TROF
LIFTS NORTHEAST ALONG THE LEADING TROF INTERFACE SUPPORTING A FAST
MOVING SURFACE WAVE THAT REACHES THE CENTRAL BC COAST LATE SAT
NIGHT INTO SUNDAY MORNING...THIS ALONG WITH STRENGTHENING UPSTREAM
JET STREAK FROM THE NW WILL ALLOW FOR THIS NORTHERN PORTION OF THE
LARGER SCALE TROF TO BEGIN TO DECOUPLE AND ACCELERATE EASTWARD
ACROSS SOUTHERN CANADA MONDAY.  IT IS THE TIMING/MAGNITUDE SPLIT
THAT LEAD TO LARGE MODEL SPREAD FURTHER SOUTH INTO THE NORTHWEST
US...HENCE THE MODEL PREFERENCE SECTIONS WERE SPLIT (SEE SECTION
BELOW FOR MORE DETAILS).

WITHIN THE ENSEMBLE SUITE...THE 00Z UKMET IS A CLEAR OUTLIER
HAVING LESS DECOUPLING WITH THE REMAINING BASE OF THE TROF.  THIS
DELAYS THE EASTWARD PROGRESSION THROUGH THE SOUTHERN CANADIAN
ROCKIES AND ALLOWS FOR A EASY REMOVAL FROM WPC PREFERENCE ATTM.
THE REMAINING GUIDANCE SHOWS SORT OF TYPICAL BIASES: THE 00Z CMC
WHILE A BIT QUICKER IS A BIT COLDER AND RAPID TO WINDING THE
CYCLONE UP/DEEPER SURFACE INFLECTION...IT IS GENERALLY SUPPORTED
BY THE GFS BUT TYPICAL OF THE GFS IT IS A BIT FAST AND NORTH
COMPARATIVELY TO THE ENSEMBLE SUITE.  THE 12Z NAM AND 00Z ECMWF ON
THE OTHER HAND SHOW MORE OF A N-S AMPLIFICATION OF THE WAVE
ALLOWING FOR A SLIGHTLY SOUTHWARD TRACK AND WEAKER SURFACE WAVE.
OVERALL BY DAY 3...THIS IS A MODEST SPREAD/DIFFERENCE LIKELY TO
RESULT IN SOME MIDDLE GROUND COMPROMISE OVER THE NEXT FEW RUNS (AS
THE WAVE ENTERS THE DEEPER DATA NETWORK).   AS SUCH A NON-UKMET
BLEND IS SUPPORTED AT AVERAGE CONFIDENCE.


BASE OF TROUGH APPROACHING THE PAC NW SUNDAY...CONSOLIDATING INTO
WA/OR MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/NAM BLEND
CONFIDENCE: BELOW AVERAGE

4 CYCLE ENSEMBLE SUITE SPAGHETTI ANALYSIS DEPICTS A GROWING LOW
PREDICTABILITY ENVIRONMENT EVOLVING TOWARD THE END OF THE WEEKEND
INTO EARLY NEXT WEEK ACROSS THE PACIFIC NORTHWEST INTO THE
INTERMOUNTAIN WEST...TO THE POINT THAT THE ENSEMBLE MEAN SOLUTIONS
BECOME NEARLY UNUSABLE GIVEN THE INTERNAL VARIATION IN EVOLUTION.
THE DETERMINISTIC GUIDANCE IS LITTLE BETTER.  A MIDDLE-SCALE SHARP
TROF OVER THE GULF OF AK WILL DROP SOUTHEASTWARD LATE SUNDAY.  AT
THIS POINT OUTSIDE FACTORS LEAD TO A VERY LARGE VARIETY OF
OUTCOMES MAINLY IN TIMING OF THE BASE/TAIL END OF THIS TROF.   THE
BASE OF THE TROF BECOMES SEVERED FROM THE NORTHERN STREAM
WAVE...BUT MORE IMPORTANTLY A STRONG SURGE OF COLD (BUT NOT
BRUTALLY COLD) AIR AND THE SUBSEQUENT DEEP GULF OF AK LOW
DEVELOPS.  THE UPSTREAM RIDGING BETWEEN THESE SYSTEM ACTUALLY
GROWS UPSCALE AND OVER WASHES THE LINGERING TAIL END OF THE TROF
(UNDER STRONG SWLY RIDGE PUMPING FROM THE UPSTREAM DEEP CYCLONE).

YET THE SHORTWAVE ENERGY WILL STILL EXIST IN THIS RIDGE AND HAVE
LITTLE LARGER STREAM FLOW TO TRANSLATE IT; AND THEREFORE LEAD TO
THE TREMENDOUS AMOUNT OF VARIATION IN TIMING ENTERING THE
NORTHWEST AND DESCENDING THE EASTERN SIDE OF THE RIDGE INTO THE
CENTRAL PLAINS TUES.  TO COMPLICATE THE SITUATION THE WAVE STILL
WILL BE POTENTIALLY VIGOROUS ENOUGH WHEN BREAKING FROM THE
NORTHERN STREAM TO WIND UP AND BECOME COMPACT AS WELL.  THIS
SCENARIO IS PRESENTED BY THE GFS/CMC/ECMWF AND LESSER SO THE NAM.
THE 00Z UKMET IS AN OUTLIER EVOLUTIONARILY AS IT REMAINS PHASED
WITH THE NORTHERN STREAM ENERGY NEVER TRULY SEVERING ITS
CONNECTION MAKING IT FAST.  THE 00Z ECMWF EVOLUTION IS QUITE
FAVORABLE BUT IS CLEARLY TOO SLOW ALLOWING FOR INCREASED INFLUENCE
FROM THE UPSTREAM WAVE.  THE 00Z CMC APPEARS IDEALLY TIMED WITHIN
THE MIDDLE OF THE GUIDANCE SUITE BUT DUE TO ORIENTATION OF THE
TROF AMPLIFYING PRODUCES A VERY DEEP SURFACE WAVE ALONG THE
FRONTAL ZONE IN LINE WITH THE MODEL`S KNOWN DEEPENING BIAS.  THE
12Z NAM AND GFS BOTH TRENDED FAVORABLY BUT SLOWING...THE GFS
SIGNIFICANTLY SO.  WHILE BOTH DO APPEAR TO SHOW SOME TYPICAL FAST
BIAS COMPARED TO THE CENTRAL ENSEMBLE MEMBERS BUT LOOK QUITE
REASONABLE IN THE EVOLUTION/SHAPE AND TRACK OF THE WAVE AS A
WHOLE.  AS SUCH A 12Z GFS/NAM BLEND IS PREFERRED BUT CONFIDENCE IS
BELOW AVERAGE.

www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

GALLINA

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