Prognostic Meteorological Discussion
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FXUS10 KWNH 171701
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1200 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 NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...


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

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: AVERAGE

WATER VAPOR IMAGERY THIS MORNING 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 SOME TIMING DIFFERENCES NOTED IN THE
GUIDANCE. ON THE QUICKER SIDE ARE THE 12Z NAM/GFS AS WELL AS THE
06Z GEFS/09Z SREF MEANS. ENSEMBLE SPAGHETTI PLOTS HAVE SHOWN A
GENERAL DICHOTOMY BETWEEN THE GFS/ECMWF CAMPS WITH THE LATTER
CONTINUING TO SHOW SUPPORT FOR A SLOWER FORECAST. AT THIS
POINT...WILL SPLIT THE DIFFERENCE BETWEEN THE TWO CAMPS UNTIL
FUTURE GUIDANCE ARRIVES. THE PREFERENCE IS A BLEND OF THE 12Z
GFS/00Z ECMWF.


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

PRELIMINARY 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...

PRELIMINARY PREFERENCE: INITIAL SYSTEM: BLEND OF 12Z GFS/00Z
UKMET...LONGWAVE TROUGH: MODEL COMPROMISE BETWEEN THE 12Z GFS AND
00Z 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/00Z UKMET WITH MORE OF A NEGATIVE
TILT TO THEIR SHORTWAVES. ADDITIONALLY...THE 12Z GFS IS QUICKER
THAN THE 00Z ECMWF/ECMWF ENSEMBLE MEAN WHICH WAS ALSO A THEME
FURTHER DOWNSTREAM WITH THE OH VALLEY SYSTEM. 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/00Z UKMET 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 00Z CMC WHICH WAS A HAIR FASTER. BY
20/0000Z...THE 12Z NAM BECOMES QUICKER AND AWAY FROM THE STRONGER
CONSENSUS FORMED BY THE 12Z GFS AND 00Z 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 AND 00Z ECMWF/UKMET.


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

PRELIMINARY 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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