Prognostic Meteorological Discussion
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FXUS10 KWNH 171904
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 PM EST TUE JAN 17 2017

VALID JAN 17/1200 UTC THRU JAN 21/0000 UTC

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

...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL
PREFERENCES/FORECAST CONFIDENCE...


...TRIO OF SHORTWAVES MOVING THROUGH THE OH VALLEY/MID-ATLANTIC...
...SURFACE LOW FORMING OFF THE NJ COAST BY 18/1200Z...

FINAL PREFERENCE: A NON-12Z CMC MODEL COMPROMISE
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

WATER VAPOR IMAGERY THIS AFTERNOON SHOWED A PAIR OF LEAD
SHORTWAVES CROSSING THE LOWER GREAT LAKES. BOTH OF THESE IMPULSES
SHOULD GRADUALLY FLATTEN/SHEAR AS THEY EXIT THE NEW ENGLAND COAST
EARLY WEDNESDAY MORNING. ON ITS HEELS...A MORE DEFINED SYSTEM
CURRENTLY CROSSING THE MIDDLE MS VALLEY WILL SLIDE THROUGH THE
UPPER OH VALLEY BY 18/1200Z WITH THE GUIDANCE IN MUCH BETTER
AGREEMENT THAN THE EARLIER ISSUANCE. THE 12Z ECMWF/UKMET TRENDED
TOWARD THE 12Z NAM/GFS WHICH NOW LEAVES THE 12Z CMC AS A SLOWER
OUTLIER. GIVEN THIS...WILL SHIFT THE PREFERENCE TO A NON-12Z CMC
MODEL COMPROMISE.


...BROAD UPPER LOW EJECTING OUT OF THE SOUTHERN HIGH PLAINS...
...EVENTUAL NEGATIVELY-TILTED TROUGH/WEAK SURFACE WAVE ACROSS THE
MIDDLE MS VALLEY...

FINAL PREFERENCE: A NON-12Z NAM/09Z SREF MEAN BLEND
FORECAST CONFIDENCE: ABOVE AVERAGE

CURRENTLY...A BROAD POSITIVELY-TILTED UPPER TROUGH IS POSITIONED
OVER WESTERN MX AND EXTENDING UP INTO THE FOUR CORNERS REGION. A
SERIES OF EMBEDDED SHORTWAVES WILL LIFT NORTHEASTWARD AS THE
LONGWAVE TROUGH MIGRATES SLOWLY TOWARD THE EAST. DIFFERENCES ARE
MINIMAL THROUGH 19/0000Z BEFORE SOME DIVERGENCE IN THE SOLUTIONS
IS NOTED THEREAFTER. ON THURSDAY...THE 12Z NAM BECOMES NOTABLY
FASTER WHICH SOMEWHAT MIMICS THE 09Z SREF MEAN. THE OVERALL SPREAD
IS NOT TERRIBLY LARGE THROUGH THE REMAINDER OF THE WORK WEEK.
CONSEQUENTLY...A NON-12Z NAM/09Z SREF MEAN WILL BE THE
RECOMMENDATION HERE.


...SERIES OF PERTURBATIONS MOVING INTO THE PACIFIC
NORTHWEST/BRITISH COLUMBIA EARLY ON...
...LONGWAVE TROUGH DIGGING INTO THE SOUTHWESTERN U.S. BY EARLY
THURSDAY...

FINAL PREFERENCE: INITIAL SYSTEM: BLEND OF 12Z
GFS/ECMWF...LONGWAVE TROUGH: MODEL COMPROMISE BETWEEN THE 12Z
GFS/ECMWF/UKMET
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

MULTIPLE PERTURBATIONS WITHIN AN ACTIVE PATTERN ACROSS THE EASTERN
PACIFIC WILL PUSH THROUGH THE PACIFIC NORTHWEST/BRITISH COLUMBIA
THE NEXT 24 HOURS OR SO. ONE PARTICULAR WAVE SHOULD BE RATHER
INTENSE AS NOTED IN THE 12Z GFS/ECMWF AS WELL AS THE 06Z
GFS-PARALLEL WITH MORE OF A NEGATIVE TILT TO THEIR SHORTWAVES.
THIS PARTICULAR SYSTEM IS CURRENTLY IN THE VICINITY OF 50N/160W
CROSSING SOUTH OF THE ALEUTIANS. GIVEN THE INTENSE NATURE OF THIS
SHORTWAVE AS NOTED ON WATER VAPOR IMAGERY...WILL LEAN IN THE
DIRECTION OF STRONGER HERE AND FAVOR A 12Z GFS/ECMWF MODEL BLEND.

REGARDING THE LONGWAVE TROUGH DIGGING INTO CA AND EVENTUALLY INTO
THE FOUR CORNERS REGION ON THURSDAY/FRIDAY...MODELS ARE IN DECENT
AGREEMENT EXCEPT FOR THE 12Z/00Z CMC WHICH WERE A HAIR FASTER. BY
20/0000Z...THE 12Z NAM BECOMES QUICKER AND AWAY FROM THE STRONGER
CONSENSUS FORMED BY THE 12Z GFS/ECMWF/UKMET. THIS IS IN REMARKABLE
CONTRAST FROM A FEW RUNS AGO WHERE THE ECMWF SUITE WAS DECIDEDLY
FASTER LEADING TO A LARGE AMOUNT OF SPREAD. OVERALL...WILL SUGGEST
SOME FORM OF MODEL COMPROMISE BETWEEN THE 12Z GFS/ECMWF/UKMET.


...SECONDARY HEIGHT FALLS REACHING THE WEST COAST BY
FRIDAY/INAUGURATION DAY...

FINAL PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

ON THE HEELS OF THE INITIAL LONGWAVE TROUGH PUSHING THROUGH THE
SOUTHWESTERN U.S...AN EVEN STRONGER UPPER TROUGH BEGINS TO
APPROACH THE WEST COAST BY FRIDAY. ON THE LARGE SCALE...THERE ARE
NOT A WHOLE LOT OF DISCERNIBLE DIFFERENCES. EVEN COMPARING THE
SPAGHETTI PLOTS OVER THE LAST FEW MODEL CYCLES DOES NOT SHOW ANY
MAJOR DIFFERENCES OCCURRING. AS SUCH...A GENERAL MODEL COMPROMISE
IS WARRANTED.


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

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

RUBIN-OSTER

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