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FXUS10 KWNH 181849
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EDT WED OCT 18 2017

VALID OCT 18/1200 UTC THRU OCT 22/0000 UTC

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

12Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


...FAST MOVING SHORTWAVE TRACKING ACROSS SRN CANADA
TODAY...CLIPPING NRN NEW ENGLAND THU 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 AHEAD OF
LARGE UPPER TROUGH MOVING INTO THE WEST THROUGH FRI...
...COLD FRONT REACHING THE PLAINS FRI NIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/00Z UKMET BLEND
CONFIDENCE: AVERAGE

THROUGH 00Z/21...SLOWER/FASTER MODELS FROM PREVIOUS CYCLES HAVE
CONVERGED ONTO A COMMON SOLUTION WITH THE LATEST
DETERMINISTIC/ENSEMBLE GUIDANCE SHOWING GOOD AGREEMENT WITH THE
TIMING/AMPLITUDE OF THE UPPER TROUGH AS IT MOVES THROUGH THE
INTERMOUNTAIN WEST. DIFFERENCES APPEAR AS THE SHORTWAVE ADVANCES
BEYOND THE ROCKIES INTO THE NRN PLAINS AND SRN CANADA WITH THE 12Z
GFS ON THE DEEPER SIDE OF THE GUIDANCE. THE LATEST ENSEMBLES SHOW
FAIRLY GOOD RUN TO RUN AGREEMENT IN THE LOW PLOTS ALTHOUGH A
MODERATE AMOUNT OF SPREAD REMAINS IN THE 500 MB 546/564 DAM HEIGHT
LINES THROUGH SATURDAY. CURRENTLY...A BLEND OF THE 12Z ECMWF/00Z
UKMET APPEARS TO BE BEST FITTED TO THE CENTER OF THE ENSEMBLE
MEMBERS WITH THE 12Z NAM MUCH FLATTER/WEAKER THAN IDEAL. THE 12Z
UKMET/CMC APPEAR A BIT FARTHER SOUTH WITH THE VORTICITY MAX TOWARD
THE SRN END OF THE TROUGH AXIS MOVING THROUGH THE PLAINS BY LATE
SATURDAY COMPARED TO THE LATEST AGREEABLE ENSEMBLE MEANS. THE
TIMING OF THE COLD FRONT IS SIMILAR IN THE LATEST DETERMINISTIC
GUIDANCE.


...SRN STREAM UPPER TROUGH REACHING THE SRN PLAINS ON FRI...OUT
AHEAD OF THE UPPER TROUGH REFERENCED IN THE ABOVE SECTION...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: AVERAGE

THE 12Z CMC IS SLIGHTLY FASTER WHILE THE 12Z NAM IS SLIGHTLY
SLOWER THAN THE REMAINING DETERMINISTIC GUIDANCE AS THE UPPER
LEVEL TROUGH REACHES THE PLAINS ON FRI. OVERALL HOWEVER...THE
DIFFERENCES ARE SMALL ENOUGH TO PREFER A GENERAL MODEL COMPROMISE.


...SHORTWAVE REACHING BRITISH COLUMBIA LATE SAT WITH WARM FRONT
AND ATMOSPHERIC RIVER APPROACHING THE PACIFIC NORTHWEST LATE
SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z CMC ADJUSTED WEAKER FROM ITS 00Z RUN WHICH WAS MUCH MORE
AMPLIFIED WITH THE SHORTWAVE APPROACHING BRITISH COLUMBIA COMPARED
TO THE REMAINING DETERMINISTIC/ENSEMBLE GUIDANCE. HOWEVER...THE
12Z CMC REMAINS A BIT DEEPER AND FASTER WITH THE SHORTWAVE
COMPARED TO THE REMAINING 12Z GUIDANCE. GIVEN A LACK OF SUPPORT
FOR THE 12Z CMC...AND GOOD AGREEMENT OTHERWISE...A NON 12Z CMC
BLEND IS PREFERRED.


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

OTTO

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