Prognostic Meteorological Discussion
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FXUS10 KWNH 221856
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 PM EDT FRI SEP 22 2017

VALID SEP 22/1200 UTC THRU SEP 26/0000 UTC

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

12Z MODEL FINAL EVALUATION INCLUDING PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...WESTERN CONUS TROUGH AMPLIFICATION AND MOVEMENT THROUGH
MONDAY...
...SURFACE LOW CYCLOGENESIS AND FRONTAL TROF ACROSS THE GREAT
PLAINS THROUGH MONDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/ECMWF BLEND
CONFIDENCE: ABOVE AVERAGE

19Z UPDATE: COMPARISON OF THE 12Z AND 00Z UKMET HIGHLIGHTS THE TWO
KEY PIECES OF ENERGY TO TRACK WITH THE EVOLUTION OF THE TROUGH.
THE MAIN 500MB VORT LOBE AT 25/00Z IS SHIFTED WEST TO SOUTHERN
UTAH WHICH IS IN LINE WITH THE REST OF THE DETERMINISTIC GUIDANCE.
HOWEVER, ADVECTION OF THE NORTHERN LOW/VORT LOBE CHANGED, WAS
SHIFTED EAST ACROSS MONTANA. THE PRESENCE AND MOVEMENT OF BOTH OF
THESE PIECES OF ENERGY WILL DETERMINE WHERE THE LOW LEVEL FORCING
IS FOR PRECIPITATION UP THE GREAT PLAINS. THAT SAID, THERE IS
REMARKABLE AGREEMENT TO THE POSITION OF RAINFALL THIS WEEKEND
THROUGH MONDAY WITH A GENERAL EASTWARD MOVEMENT DEPICTED IN ALL
DETERMINISTIC GUIDANCE. WILL PREFER A 12Z GFS/ECMWF BLEND DUE TO
THEIR PARTICULARLY TIGHT AGREEMENT.

GOOD AGREEMENT ON POSITION AND STRENGTH OF THIS ANOMALOUSLY DEEP
TROUGH AMONG DETERMINISTIC GUIDANCE INTO SUNDAY. VARIABILITY IN
MOVEMENT OF THE TROUGH BECOMES APPARENT BY THE 25/00Z WITH THE 00Z
UKMET EJECTING NORTH AND EAST SOONER AND THE 00Z CMC REMAINING
DEEPER AS COMPARED TO 00Z ECMWF AND 12Z GFS/NAM. WILL MONITOR THE
12Z CMC AND UKMET FOR TRENDS TO THE CONSENSUS OF THE REST...BUT AS
OF NOW WILL MAINTAIN A GFS/NAM/ECMWF BLEND.


...POST-TROPICAL CYCLONE JOSE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/UKMET/CMC/ECMWF
CONFIDENCE: REFERENCE NHC PRODUCTS

19Z UPDATE: THE 12Z GFS IS THE ONLY DETERMINISTIC MODEL TO STAND
OUT WITH A FARTHER EAST TRACK AFTER 23/12Z AS THE SYSTEM WEAKENS
FURTHER.

GREAT AGREEMENT AMONG DETERMINISTIC GUIDANCE IN POST-TROPICAL JOSE
REMAINING NEARLY STATIONARY INTO SATURDAY MORNING BEFORE SHIFTING
SOUTH THROUGH THE DAY SATURDAY...BRINGING AN END TO RAIN ACROSS SE
MA SATURDAY. UNCERTAINTY OF CENTER POSITION INCREASES SATURDAY
WITH THE 00Z ECMWF THE FARTHEST EAST. THE 12Z NAM AND 00Z
UKMET/CMC ARE CLOSEST TO THE 15Z ADVISORY POSITIONS THROUGH 48HR
BY WHICH TIME THE REMNANT LOW IS RATHER WEAK.


...WEAK UPPER LEVEL TROUGH OVER THE SOUTHEAST THROUGH MONDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/ECMWF BLEND
CONFIDENCE: ABOVE AVERAGE

19Z UPDATE: THE 12Z CMC AND UKMET ARE STILL FARTHER EAST WITH THE
RIDGE MOVING INTO THE NORTHEASTERN CONUS SUNDAY. THE 12Z NAM IS
FARTHER WEST SO THE 12Z ECMWF/GFS IS PREFERRED.

GOOD AGREEMENT AMONG DETERMINISTIC MODELS ON THE ELONGATED TROF
OVER THE SOUTHEAST CONUS AND RIDGE OVER THE MIDWEST TO THE
MID-SOUTH STATES THROUGH SATURDAY. THE 00Z CMC IS FARTHER EAST
WITH THE RIDGE BY SUNDAY MORNING SO WILL RECOMMEND A NON-CMC BLEND.

...HURRICANE MARIA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/ECMWF BLEND
CONFIDENCE: REFERENCE NHC PRODUCTS

19Z UPDATE: THE 12Z CMC MANAGED TO BE EVEN FASTER COMPARED TO THE
15Z NHC ADVISORY. A BLEND OF THE 12Z ECMWF AND GFS PROVIDES A GOOD
APPROXIMATION TO THE 15Z NHC ADVISORY.

THE 12Z NAM CONTINUES TO BE SLOWEST AND FARTHEST EAST WHILE THE
00Z UKMET/CMC CONTINUE TO BE THE FASTEST COMPARED TO THE 15Z NHC
ADVISORY. A BLEND OF THE 12Z GFS/00Z ECMWF IS CLOSEST TO THE NHC
TRACK FORECAST.


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

JACKSON

$$





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