Prognostic Meteorological Discussion
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FXUS10 KWNH 191844
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
243 PM EDT THU OCT 19 2017

VALID OCT 19/1200 UTC THRU OCT 23/0000 UTC

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

12Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...SHORTWAVE CLIPPING NORTHERN NEW ENGLAND BY THURS EVENING...
...ASSOCIATED COLD FRONT CROSSING THE NORTHEAST BY WEEKS END...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


...ONGOING ATMOSPHERIC RIVER EVENT INTO THE WEST COAST...
...LONGWAVE TROUGH EVOLUTION INTO THE WESTERN U.S. THROUGH FRI...
...EJECTING OUT INTO THE PLAINS ON SAT ALONG WITH COLD FRONT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z UKMET/ECMWF
CONFIDENCE: AVERAGE

THE MODELS ARE IN GOOD AGREEMENT THROUGH FRIDAY WITH THE EVOLUTION
OF THE LONGWAVE TROUGH AND ASSOCIATED COLD FRONT MOVING THROUGH
THE WESTERN U.S. BUT DIFFERENCES GROW OVER THE WEEKEND. THE 12Z
NAM/GFS CONTINUE THEIR IDEA FOR A STRONGER NRN PORTION OF THE
TROUGH AXIS WHICH MOVES INTO SOUTH-CENTRAL CANADA SATURDAY
NIGHT...WHEREAS THE 12Z ECMWF/UKMET/CMC ARE LESS STRONG HERE.

ENSEMBLE SPAGHETTI PLOTS CONTINUE TO SHOW THE NAM/GFS IDEA IS TOO
EXTREME LYING ON THE FAR EDGES OF THE DEEPEST ENSEMBLE MEMBERS
WITH THE 12Z ECMWF/UKMET CLOSEST TO THE MIDDLE OF THE SPREAD. THE
SOUTHERN PORTION OF THE TROUGH REACHING TEXAS/OKLAHOMA IS
SIMILARLY WEAK IN THE 12Z NAM/GFS...AND STRONGER IN THE 12Z
ECMWF/UKMET/CMC WHILE THE 12Z CMC IS FASTEST WITH THE SOUTHERN
STREAM PORTION OF THE UPPER WAVE. ADJUSTMENTS MADE BY THE 12Z
ECMWF TO BE FASTER...AND SLIGHTLY FASTER IN THE 12Z UKMET...NOW
SHOW THE ECMWF/UKMET MUCH CLOSER TO THE MIDDLE OF THE ENSEMBLE
SPREAD. THE PREFERENCE WILL CONTINUE WITH A 12Z ECMWF/UKMET BLEND
THE MOMENT FOR THIS SYSTEM.


...SOUTHERN STREAM UPPER TROUGH REACHING THE SOUTHERN PLAINS FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM...SO A GENERAL
MODEL COMPROMISE WILL BE PREFERRED.


...SHORTWAVE REACHING BRITISH COLUMBIA LATE SAT WITH WARM FRONT...
...NEXT ATMOSPHERIC RIVER ARRIVING OVER THE PACIFIC NORTHWEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NEAR THE 12Z NAM
CONFIDENCE: AVERAGE

DIFFERENCES WITH THIS SYSTEM PERTAIN TO THE AMPLITUDE OF THE
MID-LEVEL WAVE AS IT NEARS THE PACIFIC NORTHWEST. THESE
DIFFERENCES IN THE MID-LEVEL HEIGHTS ARE RELATIVELY MINOR BUT
GREATER IMPACTS ARE SEEN IN THE LOW LEVEL REFLECTION FOR WIND
DIRECTION AND THE MOISTURE AXIS. CURRENTLY THE 12Z NAM APPEARS A
FAVORABLE MIDDLE GROUND WITH THE AMPLITUDE OF THIS
WAVE...SPLITTING THE DIFFERENCE BETWEEN THE MORE AMPLIFIED ECMWF
AND FLATTER 12Z GFS. THERE WAS NO CLEAR CONSENSUS SEEN THE
ENSEMBLE GUIDANCE WITH THIS SYSTEM. 12Z ECMWF/UKMET/CMC
ADJUSTMENTS WERE SMALL BUT IN THE DIRECTION OF THE MIDDLE GROUND
12Z NAM SO THE FINAL PREFERENCE REMAINS UNCHANGED FROM THE
PRELIMINARY.

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

OTTO

$$





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