Prognostic Meteorological Discussion
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FXUS10 KWNH 021721
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
120 PM EDT THU JUL 02 2015

VALID JUL 02/1200 UTC THRU JUL 06/0000 UTC

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

12Z NAM/GFS MODEL EVALUATION INCLUDING PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO DEGRADE SHORT RANGE
FORECASTS.


UPPER TROUGH MOVING THROUGH WESTERN CANADA THROUGH SAT/SUN
COLD FRONT DROPPING INTO HIGH PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/00Z ECMWF ENSEMBLE MEAN/GEFS MEAN
CONFIDENCE: AVERAGE

ALL MODELS DEVELOP A STRONG UPPER LOW ACROSS THE NORTHERN CANADIAN
PROVIDENCES...WITH THE SOUTHERN PORTIONS AFFECTING THE NORTHERN
ROCKIES AND HIGH PLAINS BY SAT INTO SUN.  AT THE SURFACE A STRONG
LOW ACROSS CANADA WILL DROP A COLD FRONT INTO A LEE CYCLONE THAT
WILL DROP ALONG THE FLANKS OF THE ROCKIES FROM EASTERN MONTANA ON
SAT TO E COLORADO BY SUN.  STRENGTH  AND TIMING SEEM TO BE THE
MAJOR DIFFERENCES WITH THE MASS FIELDS.  THE 00Z CMC IS STRONG AND
SLOWEST OF THE GLOBAL MODELS.  THE 00Z ECMWF IS MUCH STRONGER THAN
OTHER GUIDANCE THOUGH ARE IN FAIRLY GOOD AGREEMENT WITH THE
PLACEMENT OF THE UPPER LOW  LIKE THE 12Z GFS/NAM AND UKMET. TIMING
ISSUES WITH THE BASE OF THE TROF LEAD TO THE DIFFERENCES IN THE
SPEED OF THE FRONT.  THE 12Z GFS IS THE FASTEST WITH THE FURTHEST
SOUTH LEE-CYCLONE POSITION BY THE END OF DAY 3...THE 00Z ECMWF DUE
TO ITS OVER DEEPENING ALOFT IS THE SLOWEST AND HAS A STRONGER
SURFACE LEE-CYCLONE ACROSS THE BLACK HILLS BY DAY 3 THAN MIDDLE
GROUND GUIDANCE. THE 12Z NAM AND 00Z UKMET SPLIT THE DIFFERENCE
AND ARE SUPPORTED BY THE 00Z ECMWF MEAN AND 00Z GEFS MEAN.  THOUGH
THE MASS FIELDS MAY BE A BIT OUT OF SORT...THE AFFECTS TO SENSIBLE
WEATHER AND QPF DO NOT APPEAR TOO DRAMATIC AT THIS TIME.  A BLEND
OF THE 12Z NAM/00Z UKMET WITH 00Z ECMWF MEAN FITS THIS MIDDLE
GROUND WELL AND IS PREFERRED AT AVERAGE CONFIDENCE.


SURFACE WAVE MOVING EAST FROM KS TO THE MID-ATLANTIC THROUGH SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z GFS AND 00Z ECMWF
CONFIDENCE: AVERAGE

A MID LEVEL SHORTWAVE TROUGH CURRENTLY OVER MID MISSOURI RIVER
VALLEY SHOULD PROGRESS INTO THE LOWER OHIO VALLEY THURS NIGHT AND
THE CENTRAL APPALACHIANS FRI NIGHT.  THERE IS CONTINUED INCREASING
AGREEMENT WITH THE GLOBAL MODELS WITH THE ENSEMBLE RUNS WITH THE
EVOLUTION OF THE THE SHORTWAVE TROF AND SURFACE LOW TRACKING FROM
KANSAS TO THE APPALACHIANS EVENTUALLY TRANSFERRING TO A LEE-LOW
ACROSS THE CAROLINAS BY FRI AND MOVING OFFSHORE BY SAT.  THERE IS
VERY GOOD LATITUDINAL PACKING OF THE LOCATION/TRACK OF THE SURFACE
LOW BUT EASTWARD TIMING IS STILL A BIT DIFFERENT IN THE ENSEMBLE
CLUSTER.  THE 00Z UKMET HAS GOTTEN BETTER BUT REMAINS FAST TO THE
OVERALL SOLUTION. THE 12Z NAM IS A BIT SLOWER LIKELY IN RESPONSE
TO SOME INTERACTION WITH UPSTREAM SHORTWAVE ENERGY THAT APPEARS
TOO STRONG AT THIS TIME (SEE BELOW).  THE 12Z GFS CONTINUES GOOD
AGREEMENT WITH 00Z ECMWF AND ARE GOOD REPRESENTATIONS OF THE MEAN
WITH LOW. AS SUCH A BLEND OF THE 12Z GFS AND 00Z ECMWF WILL BE
PREFERRED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.


SHORTWAVE CLIPPING THE NORTHERN GREAT LAKES FRI/SAT...AND NORTHERN
NEW ENGLAND BY SUN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM/GFS/00Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

FAIRLY GOOD AGREEMENT EXISTS WITH THE SHORTWAVE AND ASSOCIATED LOW
THAT TRAVERSES THE PERIPHERY OF HUDSON AND JAMES BAY CLIPPING THE
WESTERN GREAT LAKES WITH AFFECTS ON LATE FRI INTO SAT.  THE 00Z
CMC BEING A BIT SLOWER THAN THE WELL PACKED CLUSTER OF SURFACE
LOWS IN EASTERN ONTARIO...AND CONTINUES SLOW THROUGH THE REST OF
THE TIME PERIOD.  AS THE SYSTEM PROGRESSES EAST...PHASING WITH
SOUTHERN STREAM ENERGY ALLOWS THE 00Z UKMET TO DIVERGE FROM THE
REST OF THE GROUP...BECOMING FAST AND STRONG ALOFT.  OTHERWISE
GOOD AGREEMENT WITH THE 12Z NAM/GFS ALONG WITH THE 00Z ECMWF
ALLOWS A BLEND OF ALL THREE WITH SLIGHTLY ABOVE AVERAGE
CONFIDENCE.


WEAK SHORTWAVE ENERGY ENTERING BASE OF EASTERN US TROF AS THE
LARGE SCALE TROF LIFTS TOWARD NORTHEAST BY MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 00Z ECMWF/ECMWF ENSEMBLE MEAN/12Z GFS
CONFIDENCE: SLIGHTLY BELOW AVERAGE

WEAK SHORTWAVE ENERGY EXITING THE SOUTHERN CANADIAN ROCKIES INTO
THE BASE 0F THE EASTERN U.S. TROF THROUGH THE WEEKEND.  MODELS
DIFFER IN STRENGTH OF THE WAVE WITH SIGNIFICANT SPREAD IN ENSEMBLE
SOLUTIONS ACROSS THE EASTERN THIRD OF THE U.S BY SUNDAY NIGHT.
THOUGH WITH THE OVERALL TROF FILLING/LIFTING
NORTHEAST...DIFFERENCES ARE REFLECTED BEST BY QPF FIELDS.  THE 12Z
NAM IS THE MOST AGGRESSIVE AND STRONG WITH THE WAVE WITH SOME
SUPPORT FROM THE 00Z UKMET AND 00Z CMC.  THE 00Z ECMWF HAS SOME OF
THIS ENERGY BUT MORE STUNG OUT IN A STRING OF SMALLER VORT CELLS
THAN A MORE CONSOLIDATED LOW.  THE 12Z GFS IS THE SLOWEST AND
WEAKEST BARELY RESOLVING ANY ENERGY WITH THE SHORTWAVE.  GIVEN THE
LARGE SPREAD BY DAY 3...A WEAKER FLATTER SOLUTION IS PREFERRED AT
THIS TIME THOUGH WITH SLIGHTLY BELOW AVERAGE CONFIDENCE...AS SUCH
A BLEND OF THE 00Z ECMWF/12Z GFS AND ECMWF ENSEMBLE MEAN BEST
REPRESENTS THE MIDDLE GROUND AT THIS TIME.


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

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

GALLINA

$$





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