Prognostic Meteorological Discussion
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092
FXUS10 KWNH 220504
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
103 AM EDT SAT JUL 22 2017

VALID JUL 22/0000 UTC THRU JUL 25/1200 UTC

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

00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


...SYSTEM APPROACHING THE PACIFIC NORTHWEST MONDAY/TUESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/GFS BLEND
CONFIDENCE: BELOW AVERAGE

THE MODELS ARE STRUGGLING WITH HOW MUCH...IF ANY...MID-LEVEL
VORTICITY IS SHEARED EASTWARD INTO BRITISH COLUMBIA BY TUE
MORNING. THE 00Z GFS AND ESPECIALLY THE 12Z ECMWF ARE SUGGESTIVE
THAT A SIZABLE PORTION OF THE FEATURE IS PUSHED INTO SWRN CANADA
WHICH ALLOWS THE ENTIRE SHORTWAVE TO BECOME MORE ELONGATED.
ENSEMBLE SPAGHETTI HEIGHTS SUPPORT MORE IN THE WAY OF KEEPING THE
ENERGY COMPACT/TOGETHER LIKE THE 00Z NAM/12Z UKMET/CMC.
HOWEVER...THE 00Z NAM TIMING IS IN THE MIDDLE OF THE DETERMINISTIC
GUIDANCE AND IF ANYTHING...ENSEMBLES SUPPORT A SLOWER PROGRESSION.
THEREFORE A 00Z NAM/GFS BLEND IS RECOMMENDED AT THIS POINT IN
TIME...GIVEN THE 00Z GFS IS A BIT SLOWER THAN THE NAM...BUT
CONFIDENCE IS BELOW AVERAGE GIVEN THE ORIGIN OF THE SYSTEM SOUTH
OF THE ALEUTIANS AND LONGER TIME FRAME BEFORE VERIFICATION.


...UPPER LOW NEAR CALIFORNIA SUNDAY/MONDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE GUIDANCE SHOWS GOOD AGREEMENT WITH THIS FEATURE.


...SYSTEM MOVING THROUGH SOUTH-CENTRAL CANADA LATE MONDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/UKMET BLEND
CONFIDENCE: AVERAGE

THE 00Z NAM IS A BIT FASTER WITH THIS SYSTEM BY MON MORNING...AND
00Z GFS A BIT SLOWER ALOFT...WITH IMPACTS TO THE FRONTAL
PROGRESSION IN THE DAKOTAS MONDAY. A COMPROMISE OF THE 12Z
UKMET/ECMWF IS PREFERRED HERE WITH ABOVE AVERAGE CONFIDENCE GIVEN
THEIR MIDDLE OF THE ROAD PLACEMENT.


...SHORTWAVE MOVING EAST FROM S-CNTRL CANADA TODAY TO THE GREAT
LAKES SUN AND INTO THE NORTHEAST U.S. ON MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF
CONFIDENCE: AVERAGE

BY 00Z/24...THE 00Z NAM ENDS UP A BIT SLOWER WITH THE 850-700 MB
LOW ASSOCIATED WITH THE MID-UPPER LEVEL SHORTWAVE AND DOES NOT
HAVE AS MUCH OF AN EXTENSION TOWARD THE SOUTHEAST AS NOTED IN THE
REMAINING DETERMINISTIC MODELS. THE 00Z GFS IS A BIT WEAKER WITH
THE MID-LEVEL REFLECTION OF THE SHORTWAVE. THE 12Z CMC BECOMES A
BIT SOUTH WITH THIS FEATURE COMPARED TO THE OTHER MODELS...AND THE
12Z UKMET WAS A BIT FASTER/ELONGATED WITH THIS FEATURE BY LATE
MONDAY. THE 12Z ECMWF APPEARED TO BE A DECENT COMPROMISE. FOR
RAINFALL FORECAST PREFERENCES, SEE OUR QPF DISCUSSION (QPFPFD).


...SHORTWAVE MOVING THROUGH THE NORTHERN MID-ATL LATE TODAY/SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE 00Z NAM AND 12Z CMC ARE A BIT STRONGER WITH THIS 850-700 MB
REFLECTION OF THIS SYSTEM BUT THEY OTHERWISE AGREE WITH THE OTHER
DETERMINISTIC MODELS FOR TIMING OF MASS FIELDS INCLUDING A WEAK
SURFACE WAVE. FOR RAINFALL FORECAST PREFERENCES...SEE OUR QPF
DISCUSSION (QPFPFD).


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

OTTO

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