Prognostic Meteorological Discussion
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000
FXUS10 KWNH 181610
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1110 AM EST SAT NOV 18 2017

VALID NOV 18/1200 UTC THRU NOV 22/0000 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: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE 12Z NAM HAS SHIFTED SLIGHTLY NORTH TO FURTHER CONSOLIDATE THE
MASS FIELDS TOWARD A COMMON SOLUTION THOUGH THE DEPTH OF THE FULL
LATITUDE CYCLONE.  SOME SMALL DIFFERENCES NEAR THE INNER CORE
ESPECIALLY  MONDAY/TUESDAY SHIFTING INTO CANADA; YET A GENERAL
MODEL BLEND IN THIS CASE WILL SOLIDIFY THIS MINOR VARIATIONS AND
PROVIDE ABOVE AVERAGE CONFIDENCE IN THIS SOLUTION MOVING FORWARD.


NORTHERN PORTION OF TROF TRACKING EASTWARD ACROSS SOUTHERN CANADA
EVENTUALLY AMPLIFYING OVER THE GREAT LAKES TUES INTO WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/00Z CMC BLEND
CONFIDENCE: AVERAGE

GOES-W WV SHOWS TROF IN EASTERN GULF OF AK BEGINNING TO ELONGATE
TOWARD THE SSW AS IT SINKS SW TOWARD PACIFIC NORTHWEST. A SUBTLE
SHORTWAVE LIFTING NORTHEAST AHEAD OF THE MAIN TROF AXIS SPURRING A
SURFACE WAVE THAT REACHES THE CENTRAL BC COAST LATER TODAY INTO
SUN.  THIS ENERGY TRANSLATES ACROSS THE CANADIAN ROCKIES SPURRING
A STRONG LEE CYCLONE WHILE CONCURRENTLY DRAWING THE NORTHERN
POTION OF THE UPPER TROF ALONG WITH IT; EVENTUALLY SEVERING FROM
THE REMAINING TROF ENERGY ACROSS THE NORTHERN US ROCKIES MONDAY.
AS IT DOES SO...THE WAVE STRENGTHENS AND AMPLIFIES ACROSS SOUTHERN
CANADA INTO THE WESTERN GREAT LAKES TUES.   THE 00Z UKMET
CONTINUES TO BE GREATEST PHASED/CONNECTED TO THE BASE OF THE
TROF...AND IN DOING SO LAGS THE MAIN SUITE OF GUIDANCE/ENSEMBLES
ACROSS SOUTHERN CA.  THE 12Z NAM SHOWS A BIT OF KNOWN BIAS WITH A
STRONGER YET VERY CONSOLIDATED INNER CORE OF THE WAVE CROSS INTO
THE GREAT LAKES WHILE THE BULK OF GUIDANCE SHOWS SOME SOUTHWARD
EXTENSION OF THE TROF...MAKING IT A BIT LESS DESIRABLE.  THE 00Z
ECMWF ON THE OTHER SIDE OF THE SPECTRUM...WHILE STRONG WITH THE
SHORTWAVE ENTERING THE WESTERN GREAT LAKES...HAS A STRONG BASE/JET
STREAK CROSSING THE MIDWEST INTO THE OHIO VALLEY BY THE END OF THE
FORECAST PERIOD.  THIS SOUTHWARD EXTENSION IS A BIT MORE DRAMATIC
THAN EVEN THE BULK OF ECENS MEMBERS.  THE 00Z CMC IS QUITE SIMILAR
BUT DOES NOT MANIFEST THE DEEPER TROF THROUGH THE GREAT LAKES.
THE 12Z GFS WHILE INITIALLY FINE THROUGH THE CANADIAN ROCKIES BUT
START TO SHOW SOME TYPICAL FAST SPEED BIAS ALLOWING FOR A SLIGHT
NEGATIVE TILT TROF THROUGH THE GREAT LAKES BY TUES.  WHILE NO
DETERMINISTIC MODEL SEEMS IDEAL TOWARD THE OVERALL ENSEMBLE MEAN
SOLUTIONS...A COMBINATION OF THE 00Z ECMWF AND CMC SEEMS
APPROPRIATE AT AVERAGE CONFIDENCE.


BASE OF TROUGH APPROACHING THE PACIFIC NORTHWEST SUNDAY/SLIDING
SOUTHEAST THROUGH ROCKIES INTO PLAINS TUES FILLING OUT BASE OF
TROF IN GULF WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/NAM AND 00Z ECMWF BLEND
CONFIDENCE: BELOW AVERAGE

THE BASE OF AN ELONGATED TROF WILL BE TRAPPED UNDER STRONG LARGER
SCALE SOUTHWESTERLY PUMPING OF RIDGING LATE SUN/MON WITH THE RAPID
APPROACH OF THE BROAD/CLOSED LOW THAT WILL DOMINATE THE
NORTHEASTERN PACIFIC/GULF OF AK BY EARLY NEXT WEEK.  THIS WILL
LEAVE THE REMAINING ENERGY UNDER WEAK STEERING FLOW BUT ALSO AN
ENVIRONMENT WITH THE POTENTIAL FOR THE SYSTEM TO CONSOLIDATE/WIND
UP INTO A DEEPER CYCLONE.  THIS STRONGER CONSOLIDATED SOLUTION
CONTINUES TO BE PRESENTED BY THE 00Z CMC.  HOWEVER...THE
ECMWF/ECENS MEAN ALONG WITH 12Z AND 00Z/06Z GFS/NAM SOLUTIONS
CONTINUED A SLOWER EASTWARD SHIFT SHOWING GREATER STRETCHING OF
THE WAVE AT THE APEX OF THE BUILDING RIDGE...LEADING TO A SPLIT OF
THE WAVE ENERGY...SOME DOWN THE EASTERN SIDE OF THE TROF TO START
CARVING OUT THE BASE OF THE LARGER SCALE TROF ACROSS THE GULF ON
MONDAY (NAM) OR SOME SLOWER LIFTING NORTH WEST OF THE RIDGE AXIS
INTO BC/ALBERTA BEFORE STARTING THE SLIDE INTO THE ROCKIES/GREAT
PLAINS (ECMWF/GFS).  THE 00Z UKMET IS MUCH TOO PHASED WITH THE
NORTHERN STREAM AND NOT REPRESENTED WELL IN OTHER ENSEMBLE
GUIDANCE SCENARIOS OR WITHIN THE RUN TO RUN TRENDS TO SUPPORT IT.
THE 12Z NAM MAY BE A BIT TOO FAST/GREAT WITH THE STRENGTH OF THE
WAVE LATE TUES BUT ALSO KEEPS WITH SOME CONTINUITY FROM THE PRIOR
RUNS YESTERDAY.

THIS REMAINS A VERY LOW PREDICTABILITY ENVIRONMENT ESPECIALLY IN
TIMING AND THEREFORE CONFIDENCE REMAINS BELOW AVERAGE.  SOMEWHERE
BETWEEN THE 00Z ECMWF AND 12Z GFS SEEMS APPROPRIATE GIVEN THE
OVERALL ENSEMBLE TRENDS/LONGER TERM RELIABILITY IN THESE GUIDANCE
MEMBERS BUT INCLUDE A LOW PERCENTAGE OF THE 12Z NAM FOR CONTINUITY
TO HELP ACCOUNT FOR THE SLIGHTLY FASTER SOLUTIONS IN THE ENSEMBLE
SUITE.


BROAD/DEEP CLOSED DOMINATING THE NORTHEASTERN PACIFIC...SOUTHWEST
FLOW INTO THE PACIFIC NORTHWEST BY LATE TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-GFS BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

AS MENTIONED IN PRIOR TWO SECTIONS...THE INFLUENCE OF THIS
DEVELOPING LARGE SCALE DEEP CYCLONE ALREADY HAS AN IMPACT TO THE
PACIFIC NORTHWEST EVEN BEFORE ITS DIRECT INFLUENCE.  THE STRONG
SOUTHWEST PUMPING OF THE RIDGE MON/TUES WILL USHER IN SMALLER
SHORTWAVE VORT CENTERS FROM THE SUBTROPICAL EASTERN PACIFIC WITH
THE STRONGEST TUESDAY DEVELOPING A SURFACE WAVE BETWEEN 130-140W
BUT ALSO DIRECT ADDITIONAL MOISTURE ALONG THE WARM FRONT SETTING
UP THE NEXT SURGE IN THE ATMOSPHERIC RIVER; HOWEVER THERE REMAINS
A FAIRLY LARGE SPREAD IN TIMING...THE NAM/GFS HAD BEEN LEADING THE
CMC/ECMWF/UKMET ABOUT 6-9HRS FASTER.  HOWEVER THE 12Z NAM HAS
TRENDED MUCH SLOWER THOUGH STILL OUTPACES THE SLOWER NON-NCEP
SOLUTIONS. THE 00Z UKMET MAY PRESS THE WARM FRONTAL TROF A BIT
FURTHER EAST THAN THE OTHER GUIDANCE BUT STILL REMAINS WITHIN THE
REALM OF PROBABILITY GIVEN THE CURRENT ENSEMBLE SPREAD.  THE 12Z
GFS DID NOT MAKE THE SLOWING SHIFT THAT THE NAM DID BUT HAD SLOWED
SLIGHTLY THOUGH STILL REMAINS THE OUTLIER.  AT THIS POINT...THERE
IS LOWER CONFIDENCE DUE TO THE TIMING AND INTERACTION OF THESE
SMALL WAVES ON THE EASTERN SIDE OF THE DEEPER CYCLONE...HOWEVER
WILL FAVOR THE SLOWER GUIDANCE THAT HAS A BIT GREATER
ENSEMBLE/CONTINUITY SUPPORT.  AS SUCH A NON-GFS BLEND IS SUPPORTED
BUT AT SLIGHTLY BELOW AVERAGE CONFIDENCE.


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

GALLINA

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