Prognostic Meteorological Discussion
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000
FXUS10 KWNH 070448
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1147 PM EST TUE DEC 6 2016

VALID DEC 7/0000 UTC THRU DEC 10/1200 UTC

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

00Z NAM/GFS MODEL EVALUATION INCLUDING PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
***850MB TEMPERATURES WERE INITIALIZED 3-4 DEGREES C TOO WARM OVER
THE SOUTHERN APPALACHIANS IN THE NAM AND 2-3 C WARMER IN THE GFS***

CLOSED LOW TRACKING FROM NORTHERN MINNESOTA TO QUEBEC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE DEEP UPPER LEVEL LOW CURRENTLY OVER NORTHERN MINNESOTA IS
FORECAST TO CONTINUE TRACKING TOWARDS THE EAST-NORTHEAST WHILE
BECOMING MORE ELONGATED WITH TIME.  THE COLD FRONT
ASSOCIATED WITH THE SURFACE LOW WILL USHER IN THE COLDEST AIR OF
THE SEASON SO FAR FOR MUCH OF THE EASTERN U.S. BY THE END OF THE
WEEK.

THE 00Z NAM IS CLOSER TO THE MODEL CONSENSUS COMPARED TO ITS
EARLIER RUNS WITH THE TIMING OF THIS UPPER LOW.  THE 12Z CMC IS
SLIGHTLY MORE PROGRESSIVE THAN THE OTHER MODELS.  THE 00Z GFS AND
12Z ECMWF BEST FIT THE PATTERN AND THUS IS RECOMMENDED.


SHORTWAVE TROUGH TRACKING FROM THE INTERMOUNTAIN WEST TO THE EAST
COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~
PREFERENCE: NON-CMC BLEND
CONFIDENCE: AVERAGE

A BROAD UPPER LEVEL TROUGH OVER THE INTERMOUNTAIN WEST AND
NORTHERN ROCKIES AT THE BEGINNING OF THE PERIOD IS FORECAST TO
PROGRESS EASTWARD, WITH THE AXIS OF THE TROUGH REACHING THE EAST
COAST BY FRIDAY.  THIS WILL SERVE TO REINFORCE THE COLD AIR MASS
OVER THE EASTERN HALF OF THE U.S. FOR THE END OF THE WEEK.

THE AMPLIFIED UPSTREAM RIDGING SEEN ON THE 12Z CMC IS AFFECTING
ITS HANDLING OF THIS TROUGH ONCE IT EMERGES OVER THE CENTRAL U.S.,
MAKING IT DEEPER THAN THE MODEL CONSENSUS.  THE OTHER MODEL
SOLUTIONS APPEAR TO HANDLE THIS SIMILARLY, AND THUS A NON-CMC
COMPROMISE IS ADVISED.


SERIES OF STORM SYSTEMS IMPACTING THE WEST COAST BY THE END OF THE
WEEK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~
PREFERENCE: 12Z EC MEAN/18Z GEFS MEAN/12Z UKMET
CONFIDENCE: BELOW AVERAGE

A CLOSED LOW IS FORECAST TO DEVELOP WEST OF THE PACIFIC NORTHWEST
COAST BY THURSDAY EVENING, WITH A 500MB SHORTWAVE TROUGH EXPECTED
TO REACH THE PACIFIC NORTHWEST COAST AROUND FRIDAY EVENING.

NUMEROUS MODEL DIFFERENCES EXIST BY 60 HOURS INTO THE PERIOD
PRIMARILY WITH RESPECT TO LOCATION, WITH THE 00Z GFS/NAM ON THE
FAST SIDE OF THE GUIDANCE, AND THE ECMWF AND TO A LESSER EXTENT
THE UKMET ON THE SLOWER SIDE.  THE CMC APPEARS TO BE FARTHER NORTH
AND MUCH STRONGER WITH THE TRACK OF THE SURFACE LOW, AND THE NAM
THE FARTHEST EAST.  THE LATEST ENSEMBLES ALSO SHOW SIGNIFICANT
SPREAD WITH THIS SYSTEM WHICH REDUCES CONFIDENCE.  THE 12Z UKMET
IS THE CLOSEST DETERMINISTIC MODEL RUN TO THE EC MEAN AND GEFS
MEAN.  GIVEN THE CONTINUING AMOUNT OF MODEL SPREAD FROM BEING
INITIALIZED OVER A DATA SPARSE REGION OF THE NORTH PACIFIC, AN
ENSEMBLE MEAN APPROACH ALONG WITH SOME OF THE 12Z UKMET IS BEST
FOR NOW.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

HAMRICK

$$





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