Prognostic Meteorological Discussion
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000
FXUS10 KWNH 170654
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EDT THU AUG 17 2017

VALID AUG 17/0000 UTC THRU AUG 20/1200 UTC

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

00Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

LARGE SCALE TROUGH CROSSING THE GREAT LAKES THU AND NORTHEAST FRI
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z GFS AND 12Z 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 CMC AND ECMWF TRENDED STRONGER WITH THE
UPPER LOW OVER THE WESTERN GREAT LAKES, SIMILAR TO WHAT THE NAM
AND UKMET WERE SHOWING.  THERE IS NOW EXCELLENT CLUSTERING WITH
THE TRACK OF THE SURFACE LOW ACROSS THE UPPER MIDWEST AND GREAT
LAKES.  THE GFS AND ECMWF ARE CLOSEST TO THE MEAN SOLUTIONS, AND
THUS THESE ARE SUITABLE CHOICES.

...MID LEVEL TROUGH MOVING OUT OF THE CENTRAL PLAINS TO THE MID MS
VALLEY FRI THROUGH FRI NIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE...A MODEL CONSENSUS
CONFIDENCE...AVERAGE

THE MODELS ARE IN GOOD AGREEMENT IN DEPICTING A 700 MB SHORTWAVE
DEVELOPING IN THE CENTRAL PLAINS THU NIGHT-EARLY FRI.  THE WAVE
MOVES DOWNSTREAM INTO THE MID MS VALLEY FRI NIGHT...AND THEN INTO
THE OH VALLEY AND LOWER MS VALLEY ON SAT AND SAT NIGHT. THERE ARE
TIMING AND EVENTUALLY AMPLITUDE DIFFERENCES WITH THE WAVE.  GIVEN
NORMAL SPREAD OF SOLUTIONS EACH SOLUTION SEEM PLAUSIBLE WITHOUT A
CLEAR OUTLIER SOLUTION.  CONSEQUENTLY...A CONSENSUS OF THE
SOLUTIONS SHOULD ADDRESS TIMING AND AMPLITUDE DIFFERENCES.

....SOUTHWEST US MID LEVEL TROUGH SAT-SUN MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z NAM AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS INDICATE AN AREA OF SHOWERS AND STORMS IN NORTHERN
MEXICO ON DAY 2.  THE 00Z GFS DEVELOPS A FOCUSED 500 MB
CIRCULATION CENTER WITH ABSOLUTE VORTICITY VALUES HIGH CROSSING IN
FAR SOUTHWEST TX TO NEAR THE SOUTHERN BORDER WITH NEW MEXICO. THE
00Z NAM HAS A MAXIMA WITH LOWER MAGNITUDE THAN THE GFS.
WITH THE NAM CLOSER TO THE GEFS MEAN AND OTHER MODEL
FORECASTS...LESS WEIGHTING SHOULD BE PLACE DON THE 00Z GFS UNTIL
OTHER MODELS COME ON BOARD IN DEVELOPING ITS CIRCULATION
INTENSITY.

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

PETERSEN



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