Prognostic Meteorological Discussion
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000
FXUS10 KWNH 220645
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 AM EDT FRI SEP 22 2017

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

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

00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...WESTERN CONUS TROUGH AMPLIFICATION AND MOVEMENT THROUGH MON...
...SURFACE LOW CYCLOGENESIS AND FRONTAL TROF ACROSS THE GREAT
PLAINS THROUGH SATURDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/GFS/ECMWF BLEND
CONFIDENCE: ABOVE AVERAGE

BOTH THE 00Z GFS AND NAM ARE FAIRLY STEADFAST IN THEIR SOLUTIONS
OVER THE LAST 2-3 CYCLES.  THE 00Z NAM LOOKS TO BE A BLEND BETWEEN
THE 00Z GFS AND THE 12Z ECMWF WHILE THE 12Z UKMET IS MORE SIMILAR
TO THE 00Z GFS OVERALL.  THE ONLY SIGNIFICANT DEPARTURE IS IN THE
LATITUDE OF THE COMMA HEAD/DEFORMATION ZONE ACROSS THE CENTRAL
ROCKIES INTO THE NORTHERN HIGH PLAINS.   THIS IS RELATED SOLELY TO
THE PERSISTENCE OF THE 12Z ECMWF TO CLOSE OFF THE UPPER LOW IN N
AZ RATHER THAN SLIGHTLY FURTHER NORTH IN UT...THE BULK OF ECENS
MEMBERS ARE NORTH OF THE OPERATIONAL; THOUGH TO BE FAIR MORE GEFS
MEMBERS ARE SOUTH OF THE OPERATIONAL GFS.   WHILE SUBTLE DETAILS
ARE IMPORTANT THE AGREEMENT EVEN THROUGH THE END OF DAY 3 IS
REMARKABLE FOR SUCH A VAST SYSTEM WITH INTERNAL SHORTWAVES WHICH
MANIFESTS ITS WAY TO THE SURFACE PATTERN AS WELL.

WHILE THE DIFFERENCE IS NOT DRAMATICALLY DIFFERENT IN
EVOLUTION/TIMING...THE 12Z CMC IS A DISTINCT OUTLIER FAVORING A
DEEPER UPPER LOW WITH GREATER CONNECTION WITHIN THE DEFORMATION
ZONE CONNECTING THE MAIN UPPER LOW AS IT SHEDS A MAJORITY OF
SHORTWAVE ENERGY NORTH ON SUNDAY TO STRENGTHENING THE NORTHERN
STREAM BY MONDAY.   ALL CONSIDERED...A NON-CMC BLEND IS PREFERRED
AT ABOVE AVERAGE CONFIDENCE.

07Z UPDATE: THE 00Z UKMET CONTINUES TO MATCH WELL TO THE GFS/NAM
INITIALLY BUT TOWARD SUNDAY IT INTENSIFIES THE DEFORMATION ZONE
ACROSS MT INSTEAD OF SHIFTING THE ENERGY TOWARD THE EXITING
NORTHERN STREAM SHORTWAVE THAT WILL CROSS THE CANADIAN
PROVIDENCES...EVENTUALLY THIS STRONGER FEATURE THEN CONSOLIDATES
AND DROPS SOUTH AS THE DOMINANT FEATURE OVER THE MAIN CLOSED
LOW...WELL OUT OF PHASE WITH CURRENT THINKING/ENSEMBLE SUPPORT.
THE 00Z CMC REMAINS A BIT TOO AGGRESSIVE ACROSS THE NORTHERN
ROCKIES/HIGH PLAINS OF MT TOWARD MONDAY TO SUPPORT ITS INCLUSION.
IT IS NOT ALL BAD NEWS THOUGH...THE 00Z ECMWF SHOWED A SLIGHT
NORTHWARD SHIFT TOWARD THE 12Z ECENS MEAN AND THE 00Z GFS/NAM.
AS SUCH WILL SUPPORT A 00Z NAM/GFS/ECMWF BLEND AT ABOVE AVERAGE
CONFIDENCE.


...TROPICAL STORM JOSE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS
CONFIDENCE: REFERENCE NHC PRODUCTS

LIKELY DUE TO A SLOWER MARIA AND STRONGER RIDGING BUILDING NORTH
OF JOSE THE 00Z NAM BEGINS TO BECOME UNGLUED FROM AN OTHERWISE
STRONG CLUSTERING OF THE GLOBAL GUIDANCE.  THE 12Z NAM SLOWLY
DROPS THE REMAINS OF JOSE SOUTH ALONG 70W.   THE ONLY OTHER MAJOR
DEPARTURE WAS THE 12Z UKMET RETAINING A VERY STRONG REPRESENTATION
OF JOSE PARTICULARLY IN THE MID-LEVELS WHERE THERE DOES NOT SEEM
TO BE MUCH DISSIPATION AND PERHAPS EVEN OCCASIONAL
STRENGTHENING...WHICH DOES NOT MATCH WITH CURRENT PREFERENCE.  AS
SUCH A BLEND OF THE 12Z ECMWF/CMC AND THE 00Z GFS WILL LIKELY
REPRESENT THE BEST PROXY OF THE 03Z OFFICIAL NHC FORECAST.

07Z UPDATE: THE 00Z UKMET SHIFTED TO MATCH THE NAM NEARLY
IDENTICALLY BUT IS NO LONGER INDICATING A DEEP WAVE.  THAT TREND
REMAINS WITH THE 00Z ECMWF WHICH DEPICTS A SLOWER WEAKENING AND
FURTHEST EAST SOLUTION BY THE END OF THE FORECAST PERIOD...THOUGH
FAIRLY CLOSE TO THE NHC FORECAST.  THE 00Z CMC IS THE QUICKEST TO
WEAKEN THE LOW AND IS FAIRLY CLOSE TO THE 00Z GFS.  AT THIS POINT
THE 00Z GFS LOOKS MOST SIMILAR TO THE OFFICIAL FORECAST.


...WEAK UPPER LEVEL TROUGH OVER THE SOUTHEAST THROUGH MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

ELONGATED TROF OVER THE SOUTH INTO THE SOUTHERN
MID-ATLANTIC/CAROLINAS WILL CONTINUE TO SHIFT/RETROGRADE BECOMING
ORIENTED INTO A REX BLOCK PATTERN BY LATE SAT/EARLY SUN.  WHILE
THERE REMAIN MINOR DIFFERENCES IN THE PRECISE
ORIENTATION/INTERACTION WITH INTERNAL VORTICITY CENTERS WITHIN THE
LARGER TROF...A GENERAL MODEL BLEND SHOULD SUFFICE AT ABOVE
AVERAGE CONFIDENCE.

07Z UPDATE: SMALL DIFFERENCES REMAIN: THE UKMET IS A BIT STRONGER
WITH THE REMAINING RIDGING OVER E KY BY THE END OF THE FORECAST
PERIOD AND THE CMC IS A SHADE DEEPER BUT OVERALL DOES NOT APPEAR
TO BE TOO NEGATIVE FOR REMOVAL IN THE BLEND. AS SUCH A GENERAL
MODEL BLEND REMAINS PREFERRED.


...HURRICANE MARIA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/GFS BLEND
CONFIDENCE: REFERENCE NHC PRODUCTS

THE 00Z NAM CONTINUES TO LAG AND BE A EAST OUTLIER WITH RESPECT TO
THE OFFICIAL NHC 03Z FORECAST AS WELL AS THE MAIN GLOBAL GUIDANCE
MEMBERS EVEN EARLY IN THE FORECAST PERIOD.  THE REMAINING GUIDANCE
IS A GOOD PROXY TO THE OFFICIAL FORECAST UNTIL ABOUT 06Z SUNDAY
WHEN THE 12Z UKMET BEGINS TO BREAK FROM THE CONSENSUS FASTER AND
EVENTUALLY FURTHER WEST.  THIS IS FOLLOWED BY THE 12Z CMC AROUND
12 HOURS LATER ON SUNDAY WHICH BECOMES FURTHER OUT TO THE WEST BUT
ALSO OUTPACES THE UKMET.  AS SUCH THE 12Z ECMWF/00Z GFS CONTINUE
TO BE BEST PROXY TO THE OFFICIAL FORECAST AND WOULD LIKELY DO BEST
TO POPULATE ANY GRIDS.

07Z UPDATE: THE 00Z UKMET/CMC CONTINUE TO BREAK AWAY ABOUT THE
SAME TIME ON SUNDAY MOVING FURTHER EAST AND SLIGHTLY FASTER THAN
THE GFS.  THE 00Z ECMWF CONTINUES TO BE MATCHED WELL IN
TIMING/SPACE WITH THE OFFICIAL FORECAST AND GFS TO KEEP INITIAL
PREFERENCE FOR BEST PROXY OF THE OFFICIAL NHC FORECAST.


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

GALLINA

$$





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