Prognostic Meteorological Discussion
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000
FXUS10 KWNH 021906
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
303 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 MODEL EVALUATION INCLUDING FINAL 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: BLEND OF 12Z OPERATIONAL MODELS
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.  THE 12Z ECMWF HAS WEAKENED A BIT
COMPARED TO ITS 00Z COUNTERPART AND AS SUCH IS A BIT FASTER
BRINGING IT INTO MUCH BETTER AGREEMENT THAN BEFORE.  THE 12Z UKMET
AND 12Z CMC ARE ALSO IN QUITE GOOD CLUSTERING WITH THE UPPER LOW
AND PLACEMENT/ORIENTATIONS OF THE SURFACE LOW AND CONNECTING COLD
FRONT.  THE 12Z NAM/GFS HOLD BACK A BIT MORE ENERGY IN THE BASE OF
THE TROF FOR MORE OF A POSITIVE TILT COMPARED TO THE 12Z
ECMWF/CMC/UKMET.  THIS LEADS TO THE CANADIAN SURFACE LOW TO BE BIT
FURTHER EAST...WITH A TRAILING FRONT WITH A WEAKNESS ALONG THE
US/CANADIAN BOARDER A BIT MORE DISCONNECTED TO THE INVERTED
SURFACE TROF FROM THE LEE-CYCLONE COMPARED TO THE ECMWF/CMC/UKMET.
 THESE SMALL DETAILS...THOUGH IMPORTANT...ARE NOT SIGNIFICANT
ENOUGH TO PREFER ONE SPECIFIC MODEL OVER THE OTHER GIVEN THE
OVERALL BLENDS AGREEMENT WITH THE ENSEMBLE MEANS. THIS LEADS TO
AVERAGE CONFIDENCE IN A 12Z OPERATIONAL MODEL BLEND.


SURFACE WAVE MOVING EAST FROM KS TO THE MID-ATLANTIC THROUGH SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z GFS/ECMWF/UKMET
CONFIDENCE: SLIGHTLY ABOVE 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 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 12Z
ECMWF ALONG WITH THE 12Z GFS CONTINUES GOOD AGREEMENT AND ARE IN
THE MIDDLE OF ENSEMBLE CLUSTER AND AS SUCH REPRESENT THE ENSEMBLE
MEANS QUITE WELL.  THE 12Z UKMET HAS SLOWED A BIT TO ALSO BE IN
VERY GOOD AGREEMENT ENOUGH SO TO ADDED IT TO THE PREFERRED A BLEND
12Z GFS/ECMWF/UKMET.  THE 12Z NAM IS A BIT SLOW ON FRIDAY
DEPARTING FROM THE OTHER WELL CLUSTERED GUIDANCE.  THIS IS LIKELY
IN RESPONSE TO SOME INTERACTION WITH UPSTREAM SHORTWAVE ENERGY
THAT APPEARS TOO STRONG AT THIS TIME (SEE BELOW). MINUS THIS SHORT
TIME FRAME THE 12Z NAM COULD BE USEFUL BUT SHOULD RECEIVE LOW
WEIGHTING IN ANY BLEND.  THE 12Z CMC REMAINS THE SLOWEST MEMBER
AND IS WELL OUTSIDE THE REST OF THE GUIDANCE.


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 BAYS CLIPPING THE
WESTERN GREAT LAKES WITH AFFECTS ON LATE FRI INTO SAT.  THE 12Z
CMC HAS BECOME IN MUCH BETTER AGREEMENT WITH THE LOW BEFORE
BECOMING SLOW INTO SUN...THAT EVENTUALLY LEAD TO ENOUGH
DIFFERENCES ACROSS NEW ENGLAND NOT TO ADD IT TO THE BLEND JUST
YET.  SIMILARLY...THE 12Z UKMET TRENDED MUCH CLOSER TO PREFERRED
BLEND BUT REMAINS WEAK AND FAST IN LINE WITH ITS KNOWN BIAS TO NOT
ADD TO THE BLEND EITHER.  LITTLE CHANGES BETWEEN THE NEW AND OLDER
00Z RUN WITH THE ECMWF ALLOW FOR STRONG AGREEMENT TO CONTINUE WITH
THE 12Z NAM/GFS.  A BLEND OF ALL THREE IS PREFERRED 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: 12Z ECMWF
CONFIDENCE: 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.  THE 12Z
ECMWF/UKMET AND CMC ALL AGREE TO SOME ENERGY BUT MUCH WEAKER.  THE
12Z GFS IS THE SLOWEST AND WEAKEST BARELY RESOLVING ANY ENERGY
WITH THE SHORTWAVE....BECOMING LESS FAVORABLE GIVEN TREND WITHIN
THE MOST RECENT ENSEMBLE RUNS.  THE 12Z ECMWF APPEARS TO BE THE
BEST MIDDLE GROUND OF THE OPERATIONAL MODELS AND 09Z SREF/00Z
ECMWF/06 GEFS MEANS...AND IS PREFERRED AT BELOW AVERAGE CONFIDENCE
GIVEN THE LARGE SPREAD.


...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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