Prognostic Meteorological Discussion
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FXUS10 KWNH 210658
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT MON AUG 21 2017

VALID AUG 21/0000 UTC THRU AUG 24/1200 UTC

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

...AN EVALUATION OF THE 00Z MODEL GUIDANCE ALONG WITH
PREFERENCES/FORECAST CONFIDENCE...

...DEEP UPPER TROUGH AMPLIFYING ACROSS THE GREAT
LAKES/NORTHEASTERN U.S. BY TUESDAY/WEDNESDAY...
...ATTENDANT SURFACE CYCLONE AND PROGRESSIVE COLD FRONT...

PREFERENCE: BLEND OF THE NAM/GEFS MEAN/ECMWF
FORECAST CONFIDENCE: AVERAGE

OVERALL...WITH RESPECT TO THE LARGER SCALE FEATURES...THE MODELS
ARE IN FAIRLY GOOD AGREEMENT THROUGH MUCH OF THE PERIOD.  BY EARLY
THU HOWEVER...THE 00Z GFS IS LESS AMPLIFIED WITH THE UPPER TROUGH
ACROSS THE OH VALLEY/MID ATLANTIC...WHILE MAINTAINING A STRONGER
RIDGE ALOFT ACROSS FL AND THE EASTERN GULF.  ACROSS THE EASTERN
U.S. THE GEFS MEAN SUPPORTS A SOLUTION CLOSER TO THE NAM AND
ECWMF.

THERE ARE FURTHER DIFFERENCES TO THE NORTH WITH A SHORTWAVE THAT
IS FORECAST TO SLIDE OUT CENTRAL CANADA INTO THE TROUGH AXIS OVER
THE GREAT LAKES EARLY THU.  CURRENTLY THE ECMWF AND CANADIAN
GLOBAL ARE SLOWER AND MORE AMPIFIED WITH THIS FEATURE THAN THE NAM
AND GFS.  THE 12Z EC ENSMEAN IS SIMILAR TO THE NAM AND
GFS...HOWEVER THE GFS DID TREND SLOWER WITH THIS RUN AND THEREFORE
THE SLOWER SOLUTIONS SHOULD NOT BE RULED OUT.

...TUTT CELL SLIDING WESTWARD ACROSS THE GULF OF MX...

PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: AVERAGE

OVERALL THE LATEST GUIDANCE REMAIN IN GENERALLY GOOD
AGREEMENT...SHOWING THIS SYSTEM MOVING WEST ACROSS THE NORTHERN
GULF BEFORE REACHING THE WESTERN GULF COAST ON TUE.

...POTENT IMPULSE LIFTING OUT OF THE SOUTHERN ROCKIES TOWARD THE
CENTRAL HIGH PLAINS...

PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: AVERAGE

OVERALL...THE MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE TIMING
OF THIS SYSTEM AS IT CONTINUES TO THE LIFT TO THE NORTHEAST TOWARD
THE CENTRAL PLAINS WHERE BY LATE TUE IT IS FORECAST TO CAPTURED BY
AN AMPLIFYING UPPER TROUGH.

...NEARLY QUASI-STATIONARY UPPER LOW LINGERING ACROSS
SOUTHERN/CENTRAL CA...

PREFERENCE: A NON-CMC MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

OVERALL THE MODELS REMAIN IN FAIRLY GOOD AGREEMENT.  THE CANADIAN
GLOBAL REMAINS THE ONLY SIGNIFICANT OUTLIER.  AS THE LOW
TRANSITIONS TO AN OPEN WAVE BY LATE WED...THE CANADIAN TAKES THE
SYSTEM FURTHER TO THE EAST THAN THE OTHER MODELS.

...AMPLIFIED FLOW REACHING THE PACIFIC NORTHWEST/BRITISH COLUMBIA
COAST BY MID-WEEK...

FINAL PREFERENCE: BLEND OF THE 00Z ECMWF/GFS
FORECAST CONFIDENCE: AVERAGE

WITH RESPECT TO THE UPPER TROUGH AXIS MOVING ACROSS WESTERN CAN
AND THE PACIFIC NW EARLY THU...THE 00Z NAM AND UKMET ARE NOW ON
THE EASTERN EDGE OF THE GUIDANCE ENVELOPE.  BOTH SHOW FLAT
UPSTREAM FLOW OVER THE GULF OF AK/NORTHEASTERN PACIFIC AND IN TURN
PUSH THE UPPER TROUGH FURTHER EAST THAN MOST OF THE GUIDANCE BY
EARLY THU.  THE 00Z GFS AND ECMWF ARE FURTHER TO THE WEST AND HAVE
THE SUPPORT OF THEIR SPECTIVE ENSEMBLE MEANS.  THE 00Z CANADIAN
GLOBAL HAS SHIFTED EAST FROM ITS PREVIOUS RUN AND IS ALSO IN GOOD
AGREEMENT WITH THE THE GFS AND ECMWF.

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

PEREIRA

$$





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