Prognostic Meteorological Discussion
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000
FXUS10 KWNH 240651
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 AM EDT MON JUL 24 2017

VALID JUL 24/0000 UTC THRU JUL 27/1200 UTC

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

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


...SHORTWAVE MOVING ACROSS THE GREAT LAKES/NORTHEAST
TODAY/TUESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 00Z NAM WAS NOTICEABLY STRONGER WITH THE LOW-MID LEVEL
SHORTWAVE CROSSING THE NORTHEAST LATE MONDAY INTO TUESDAY. THE
SURFACE LOW IN THE NAM IS ALSO NORTH AND CLOSER TO THE NEW ENGLAND
COAST COMPARED TO THE LATEST ENSEMBLE SCATTER LOW PLOTS WHICH
TRENDED A BIT OFFSHORE WITH THE 12Z/23 CYCLE. THE 00Z GFS IS
SLIGHTLY WEAKER WITH THE SURFACE LOW BUT ITS POSITION APPEARS
REASONABLE. GIVEN THE 00Z NAM IS UNSUPPORTED WITH ITS
EVOLUTION...A NON 00Z NAM BLEND IS PREFERRED. THE 00Z
ECMWF/UKMET/CMC SHOW ONLY MINOR ADJUSTMENTS FROM THEIR PREVIOUS
12Z CYCLES.


...MID-LEVEL VORTICITY MAX MOVING INTO THE NRN PLAINS
TODAY...CROSSING THE MID-MS VALLEY ON TUE AND EVENTUALLY REACHING
THE SOUTHEAST U.S. ON WED HELPING TO REINFORCE UPPER TROUGHING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: AVERAGE

ONLY MINOR DIFFERENCES EXIST WITH THE DEEPENING UPPER TROUGH OVER
THE SOUTHEAST IN THE LATEST GUIDANCE. HOWEVER...AGREEMENT IS CLOSE
ENOUGH TO SUPPORT A GENERAL MODEL COMPROMISE WITH THIS SYSTEM.


...UPPER LOW NEAR CALIFORNIA THROUGH WED...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z CMC BLEND
CONFIDENCE: ABOVE AVERAGE

ALL OF THE LATEST DETERMINISTIC MODELS HANDLE THIS SYSTEM
SIMILARLY EXCEPT THE 00Z CMC WHICH IS A BIT DEEPER/SOUTH WITH THE
UPPER TROUGH BY WED MORNING.


...SYSTEM MOVING THROUGH SOUTHERN CANADA THROUGH WEDNESDAY...
...SURFACE LOW FORECAST TO INTO THE UPPER MIDWEST BY THU MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/UKMET BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

CONFIDENCE IS LOWER THAN USUAL BUT THE 00Z GFS/NAM APPEAR TO BE
CATCHING ONTO TRENDS WITH A VORTICITY MAX SWINGING AROUND THE SWRN
U.S. RIDGE INTO THE PLAINS. WHILE THE 00Z NAM BECOMES QUITE DEEP
AND IS NOT SUPPORTED IN THE GEFS/EC/CMC ENSEMBLE MEMBERS REGARDING
ITS UPPER TROUGH BY WED/THU...THE 00Z GFS SEEM LIKE A MORE
TEMPERED AND PLAUSIBLE VERSION OF THE NAM. GIVEN INFLUENCES OF
THIS FEATURE ORIGINATE OVER THE SOUTHWEST U.S. TODAY...IT IS
UNCLEAR HOW STRONG THIS SMALL SCALE FEATURE WILL BE AND JUST HOW
IT WILL INTERACT WITH THE BASE OF THE UPPER TROUGH MOVING ACROSS
SRN CANADA. THE TIMING OF THE 00Z GFS AND 12Z ECMWF APPEAR
REASONABLE WITH THE CANADIAN TROUGH THROUGH 00Z/27 BUT THE 12Z/00Z
UKMET LOOK FASTER WITH THIS FEATURE.

THE 00Z ECMWF/UKMET SHOWED SOME TRENDS IN THE DIRECTION OF THE
NAM/GFS BUT PREFER TO STAY CLOSER TO A GFS/UKMET BLEND FOR NOW
WHICH SEEMS TO BE NEARER TO THE MIDDLE OF THE LATEST DETERMINISTIC
GUIDANCE.


...UPPER TROUGH MOVING INTO BRITISH COLUMBIA ON WEDNESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


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

OTTO

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