Prognostic Meteorological Discussion
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FXUS10 KWNH 151641
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1241 PM EDT TUE AUG 15 2017

VALID AUG 15/1200 UTC THRU AUG 19/0000 UTC

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

12Z INITIAL MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

UPPER LEVEL LOW PASSING NORTH OF NEW ENGLAND THROUGH MID-WEEK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z UKMET/00Z ECMWF
CONFIDENCE: ABOVE AVERAGE

A LARGE UPPER LEVEL LOW IS FORECAST TO TRACK EASTWARD FROM HUDSON
BAY TO NEWFOUNDLAND OVER THE NEXT 60 HOURS.  THIS WILL PRODUCE
LOWER 500MB HEIGHTS OVER NEW ENGLAND THROUGH THE MIDDLE OF THE
WEEK, ALONG WITH A SURFACE COLD FRONT CROSSING THE REGION TUESDAY
NIGHT AND INTO EARLY WEDNESDAY.  THE DIFFERENCES ARE RATHER MINOR
WITH THE DETAILS OF THE STRONG UPPER LOW TRACKING EASTWARD.  THE
MAIN DIFFERENCE NOTED WAS THAT THE NAM IS SLIGHTLY MORE AMPLIFIED
AND EVENTUALLY SLOWER WITH THIS FEATURE BY THE END OF THE
SHORT-RANGE FORECAST PERIOD.  THEREFORE, A BLEND OF THE 12Z
GFS/00Z UKMET AND 00Z ECMWF CAN BE RECOMMENDED AT THIS TIME GIVEN
THEIR BETTER CLUSTERING.


LARGE SCALE TROUGH CROSSING THE NORTH-CENTRAL U.S. THROUGH MIDWEEK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A BROAD SYNOPTIC SCALE TROUGH IS FORECAST TO TRACK ACROSS THE
NORTHERN TIER OF THE U.S. WITH MULTIPLE SHORTWAVE IMPULSES
TRAVERSING THE CENTRAL AND NORTHERN PLAINS TO THE UPPER MIDWEST.
AT THE SURFACE, A LOW IS FORECAST TO DEVELOP AND TRACK TOWARDS THE
NORTHEAST ACROSS THE CENTRAL PLAINS AND REACH THE NORTHERN GREAT
LAKES BY THURSDAY NIGHT, WITH A TRAILING COLD FRONT BEHIND IT.
THE MODELS SHOW REASONABLY GOOD AGREEMENT ON THE SYNOPTIC SCALE
WITH THE TROUGH.  THE 12Z NAM BECOMES MORE AMPLIFIED WITH THE
SHORTWAVE TROUGH OVER THE UPPER MIDWEST ON THURSDAY, BUT IS
SIMILAR WITH RESPECT TO TIMING.


BROAD UPPER LEVEL TROUGH OVER THE SOUTHEAST U.S. THROUGH EARLY
THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS PINCH OFF SOME OF THE SHORTWAVE ENERGY ARRIVING OVER
THE WEST WITH THE MAIN UPPER TROUGH AND DROP IT GENERALLY SOUTH
ACROSS THE GREAT BASIN AND INTO THE SOUTHWEST U.S. THROUGH EARLY
THURSDAY.  GIVEN THAT THE AMOUNT OF MODEL SPREAD IS NEGLIGIBLE ON
THE SYNOPTIC SCALE, A GENERAL MODEL COMPROMISE CAN BE PREFERRED AT
THIS TIME.


UPPER TROUGH ARRIVING ACROSS THE PACIFIC NORTHWEST ON FRIDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GEFS/EC MEAN
CONFIDENCE: BELOW AVERAGE

A LARGE UPPER LEVEL LOW OVER THE GULF OF ALASKA TOWARDS THE END OF
THE WEEK WILL BRING THE LEADING EDGE OF 500MB HEIGHT FALLS TOWARDS
THE PACIFIC NORTHWEST BY FRIDAY.  MOST OF THE UPPER LEVEL
TROUGHING WITH THIS FEATURE SHOULD BE NORTH OVER BRITISH COLUMBIA.
 A COLD FRONT IS EXPECTED TO ACCOMPANY THIS TROUGH WHICH SHOULD
EVENTUALLY REACH THE COAST FRIDAY NIGHT.  THE 12Z NAM APPEARS
FASTER THAN THE OTHER MODELS WITH THE ARRIVAL OF THE TROUGH.  THE
ECMWF IS THE SLOWEST AND AMONG THE STRONGER SOLUTIONS.  GIVEN THE
MODEL SPREAD, AN ENSEMBLE MEAN APPROACH SHOULD WORK WELL FOR NOW.


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

Hamrick

$$





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