Prognostic Meteorological Discussion
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000
FXUS10 KWNH 161635
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1234 PM EDT WED AUG 16 2017

VALID AUG 16/1200 UTC THRU AUG 20/0000 UTC

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

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


UPPER LEVEL LOW PASSING NORTH OF NEW ENGLAND THROUGH MID-WEEK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

A LARGE UPPER LEVEL LOW IS FORECAST TO TRACK EASTWARD FROM CENTRAL
QUEBEC TO NEWFOUNDLAND BY THURSDAY NIGHT.  THIS WILL PRODUCE LOWER
500MB HEIGHTS OVER NEW ENGLAND THROUGH EARLY THURSDAY, ALONG WITH
A SURFACE COLD FRONT EXITING THE NEW ENGLAND COAST WEDNESDAY
NIGHT.  THE DIFFERENCES ARE RATHER MINOR WITH THE DETAILS OF THE
STRONG UPPER LOW TRACKING EASTWARD.  THEREFORE, A GENERAL MODEL
BLEND CAN BE USED.


LARGE SCALE TROUGH CROSSING THE NORTH-CENTRAL U.S. THROUGH MIDWEEK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF
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 AND 00Z UKMET BECOME MORE AMPLIFIED
WITH THE SHORTWAVE TROUGH OVER MINNESOTA ON THURSDAY, BUT IS
SIMILAR WITH RESPECT TO TIMING.  THE 00Z CMC IS SLIGHTLY SOUTH OF
THE MODEL CONSENSUS WITH THE TRACK OF THE SURFACE LOW.  THE GFS
AND ECMWF ARE CLOSEST TO THE MEAN SOLUTIONS, AND THUS THESE ARE
SUITABLE CHOICES.


UPPER TROUGH OVER THE SOUTHWEST AND POSSIBLE CLOSED LOW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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
THURSDAY.  BY EARLY SATURDAY, MOST OF THE MODEL GUIDANCE IS
INDICATING A WEAK CLOSED MID LEVEL LOW NEAR SOUTHERN CALIFORNIA.
THE SPREAD IS VERY MINOR HERE, SO A GENERAL MODEL COMPROMISE CAN
BE PREFERRED.


UPPER TROUGH ARRIVING ACROSS THE PACIFIC NORTHWEST BY FRIDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS BRING A PROGRESSIVE UPPER TROUGH ACROSS THE GULF OF
ALASKA AND INTO BRITISH COLUMBIA AND PORTIONS OF THE PACIFIC
NORTHWEST BY FRIDAY. THE MODEL DIFFERENCES ARE RATHER MINOR
THROUGH 60 HOURS, BUT THEREAFTER THE 12Z NAM BECOMES FASTER THAN
THE MODEL CONSENSUS.  A BLEND OF THE 00Z ECMWF AND 12Z GFS SHOULD
HANDLE THIS SYSTEM WELL.


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

HAMRICK

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