Prognostic Meteorological Discussion
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FXUS10 KWNH 211845
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 PM EST SUN JAN 21 2018

VALID JAN 21/1200 UTC THRU JAN 25/0000 UTC

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

12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...DEEP LAYER CYCLONE OVER THE FOUR CORNERS REGION TODAY...
...ENERGY/SURFACE LOW CROSSING THE PLAINS ON MONDAY...
...LIFTING ACROSS THE GREAT LAKES AND NORTHEAST THROUGH TUESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE OVERALL IN VERY GOOD AGREEMENT WITH THE DETAILS OF
THE DEEP CLOSED LOW OVER THE FOUR CORNERS REGION WHICH WILL LIFT
NORTHEAST ACROSS THE CENTRAL PLAINS THROUGH MONDAY ALONG WITH A
STRENGTHENING AREA OF LOW PRESSURE. THE SYSTEM WILL CROSS THE MID
MS VALLEY MONDAY NIGHT AND THEN LIFT ACROSS PARTS OF THE GREAT
LAKES AND NORTHEAST THROUGH TUESDAY. THE 12Z NAM IS PERIODICALLY
APPEARING TO BE A TAD TOO DEEP IN THE 500/700 MB LAYER AS THE
SYSTEM APPROACHES AND THEN CROSSES THE MID MS VALLEY...BUT
OTHERWISE THE GUIDANCE IS IN GOOD AGREEMENT WITH THE EVOLUTION OF
THIS SYSTEM THROUGH THE PERIOD. THEREFORE...WILL SUGGEST A GENERAL
MODEL BLEND AT THIS TIME.


...BROAD TROUGH QUICKLY CROSSING THE SOUTHEAST TODAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM CROSSING THE
EASTERN GULF COAST REGION AND SOUTHEAST U.S. THROUGH THIS
AFTERNOON BEFORE THEN DAMPENING OUT/WEAKENING OFFSHORE THE
SOUTHEAST TONIGHT AND MONDAY. A GENERAL MODEL BLEND WILL BE
PREFERRED.


...UPPER TROUGH INITIALLY OFFSHORE BRITISH COLUMBIA...
...ENERGY DIGGING ACROSS THE PLAINS/UPPER MIDWEST BY TUESDAY...
...ARRIVING ACROSS THE OH VALLEY ON WEDNESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS
            NON-GFS CONSENSUS...AFTER 60 HOURS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

AN UPPER TROUGH INITIALLY OFFSHORE BRITISH COLUMBIA TODAY WILL
IMPACT THE PACIFIC NORTHWEST THROUGH TONIGHT AND THEN ADVANCE OUT
ACROSS THE NORTHERN ROCKIES AND HIGH PLAINS THROUGH MONDAY.
THEREAFTER...THE ENERGY SHOULD BEGIN TO DIG SOUTHEAST ACROSS THE
MIDWEST THROUGH TUESDAY IN RESPONSE TO THE UPSTREAM RIDGING OVER
THE GREAT BASIN. THE MODELS ARE IN GOOD AGREEMENT WITH THEIR MASS
FIELD TIMING AND DEPTH THROUGH ABOUT 60 HOURS WITH THIS SYSTEM.
THEREAFTER...THE 12Z GFS SUGGESTS A MORE PROGRESSIVE SOLUTION AND
TENDS TO OUTRUN THE OTHER MODELS AS THE ENERGY ARRIVES ACROSS THE
OH VALLEY. THE LATEST GEFS MEAN AND ECENS MEAN SUGGEST THE
OPERATIONAL GFS IS A TAD TOO PROGRESSIVE...AND SO WILL PREFER A
GENERAL MODEL BLEND THROUGH 60 HOURS AND THEN A NON-GFS CONSENSUS
AFTER 60 HOURS.


...SHORTWAVE IMPACTING THE PACIFIC NORTHWEST ON TUESDAY...
...ATTENDANT SURFACE LOW LIFTING UP OFFSHORE BRITISH COLUMBIA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW A SHORTWAVE ARRIVING ACROSS ESPECIALLY COASTAL
AREAS OF THE PACIFIC NORTHWEST ON TUESDAY WITH THE SYSTEM THEN
DAMPENING OUT AS IT ENCOUNTERS A DEVELOPING RIDGE OVER THE GREAT
BASIN. THIS WILL DRIVE A FOCUS OF STRONGER SOUTH/SOUTHWEST FLOW UP
ALONG THE COASTAL RANGES OUT AHEAD OF A STRONG AREA OF LOW
PRESSURE THAT LIFTS UP OFFSHORE BRITISH COLUMBIA. THE MODELS ARE
IN GOOD AGREEMENT WITH THIS SYSTEM AS IT ARRIVES AND SO A GENERAL
MODEL BLEND WILL BE PREFERRED.


...DEEP UPPER TROUGH OFFSHORE THE WEST COAST BY WEDNESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS ALLOW A DEEP UPPER TROUGH TO EVOLVE OFFSHORE THE WEST
COAST THROUGH TUESDAY AND WEDNESDAY WITH STRONG SOUTHWEST ONSHORE
FLOW SETTING UP SOUTH OF AN APPROACHING AREA OF LOW PRESSURE WHICH
WILL BE APPROACHING COASTAL WA/OR BY LATE WEDNESDAY. THERE ARE
SOME DETAIL DIFFERENCES WITH THE STRENGTH AND POSITION OF THE AXIS
OF HEIGHT FALLS. THE 12Z CMC AND 12Z ECMWF HAVE TRENDED MORE
STRONGLY TOWARD THE 12Z GFS SOLUTION WITH THE EVOLUTION OF THE
HEIGHT FALLS AND THE PLACEMENT OF THE SURFACE LOW PRESSURE TOWARD
THE END OF THE PERIOD. MEANWHILE...THE 12Z NAM AND 12Z UKMET ARE
NOW SOMEWHAT WEAKER THAN THE MODEL CONSENSUS WITH THEIR HEIGHT
FALLS. AT THE SURFACE...THE MODELS HAVE A LOW APPROACHING THE
PACIFIC NORTHWEST AS SHORTWAVE ENERGY ROUNDS THE BASE OF THE MEAN
TROUGH AXIS/CLOSED LOW...AND THE NAM AND UKMET SOLUTIONS ARE A
LITTLE SOUTH OF THE GFS/CMC/ECMWF CLUSTER AND ARE ALSO A LITTLE
WEAKER. THE TRENDS OF THE CMC AND ECMWF PUT THESE MODELS IN
TOLERANCE WITH THE 12Z GEFS MEAN AND 00Z ECENS MEAN TOO WHICH
ALREADY WERE MORE SUPPORTIVE OF THE OPERATIONAL GFS. BASED ON ALL
OF THIS...WILL PREFER A BLEND OF THE GFS AND ECMWF AT THIS TIME.


MODEL TRENDS AT www.wpc.ncep.noaa.gov/html/model2.shtml
500 MB FORECASTS AT www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

ORRISON



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