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FXUS10 KWNH 261718
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1218 PM EST SUN FEB 26 2017

VALID FEB 26/1200 UTC THRU MAR 02/0000 UTC

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

12Z NAM/GFS EVALUATION INCLUDING PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

FAST MOVING MID-LEVEL SHORTWAVE TRACKING THROUGH THE NWRN GREAT
  LAKES TONIGHT INTO ONTARIO BY MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


SHORTWAVE SWINGING THROUGH THE SOUTHWEST TODAY AND REACHING THE
  SRN PLAINS LATE TONIGHT BEFORE HEADING INTO CONFLUENT FLOW
  ACROSS THE CENTRAL U.S. LATE MON INTO TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE

RUN TO RUN CHANGES IN THE MODELS HAVE BEEN RATHER SMALL SINCE
YESTERDAY. WHILE MINOR DIFFERENCES REMAIN WITH THE EVOLUTION OF
MID-LEVEL SHORTWAVE ENERGY ACROSS THE PLAINS TONIGHT AND INTO THE
OHIO VALLEY FOR MON...THE BIGGER DIFFERENCES ARE WITH
PRECIPITATION AND MESOSCALE BOUNDARIES DRIVEN BY CONVECTIVE
PRECIPITATION EARLY MON MORNING ACROSS THE LOWER MS VALLEY. GIVEN
THIS...USERS WILL BE REFERRED TO THE QPFPFD FOR INFORMATION
REGARDING PRECIPITATION WHILE A GENERAL MODEL COMPROMISE WILL BE
PREFERRED IN THIS DISCUSSION FOR MODEL MASS FIELDS.


NEXT SHORTWAVE DROPPING SOUTH OFF OF THE NWRN U.S. COAST TODAY
  AND EXITING INTO THE N-CNTRL U.S. TUE MORNING
MERGING ENERGY FROM COASTAL BRITISH COLUMBIA AND REMNANT OFFSHORE
  OFFSHORE UPPER LOW INTO NWRN MEXICO BY TUE MORNING
STRENGTHENING SURFACE LOW INTO THE GREAT LAKES TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/12Z GFS BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

A SOMEWHAT COMPLEX EVOLUTION OF 3 SHORTWAVES INTO THE WRN U.S.
THROUGH TUE MAKES FOR A SENSITIVE EVOLUTION FROM THE ROCKIES INTO
THE PLAINS. A LEADING SHORTWAVE IS CURRENTLY OFF OF THE PACIFIC
NORTHWEST COAST AND IS EXPECTED TO DEAMPLIFY INTO SOUTH DAKOTA BY
TUE MORNING. MEANWHILE...SHORTWAVE ENERGY DROPPING SOUTH ALONG THE
BRITISH COLUMBIA COAST ON MON WILL LIKELY INTERACT TO SOME DEGREE
WITH A REMNANT CLOSED LOW...TURNED SHEARED VORTICITY MAX...INTO
NWRN MEXICO BY EARLY TUE...RESULTING IN A LARGE...NEUTRALLY
ORIENTED TROUGH AXIS EXTENDING FROM THE NRN PLAINS TO THE SRN
ROCKIES BY TUE NIGHT.

THE BIGGEST DIFFERENCES THROUGH TUE ARE WITH THE SHORTWAVE
APPROACHING NWRN MEXICO EARLY TUE...WITH THE 00Z CMC SLOWER AND
00Z UKMET A BIT QUICKER THAN THE CONSENSUS. THE RESULT IN THE 00Z
CMC IS A LESS AMPLIFIED TROUGH OVER THE WEST LATE. FARTHER
NORTH...THERE ARE TIMING DIFFERENCES WITH THE 12Z GFS AT THE
LEADING EDGE OF THE ENSEMBLE CONSENSUS AND IS FASTEST WITH THE
TIMING OF THE RESULTING COLD FRONT MOVING ACROSS THE MIDDLE MS
VALLEY TUE NIGHT. CONCERNING THE SURFACE LOW...THE MIDDLE OF THE
ENSEMBLE SCATTER LOW PLOTS SUPPORTS A POSITION BETWEEN THE 12Z GFS
AND 00Z ECMWF UNTIL ABOUT 00Z/01 AT WHICH POINT THE BEGINS TO LIFT
FARTHER NORTH INTO SERN CANADA WHILE A VAST MAJORITY OF ENSEMBLES
ARE SOUTH. THE ENSEMBLES ALSO SHOW THE 00Z ECMWF A BIT SLOW WITH
THE FRONT AND THE 00Z ECMWF MEAN A BIT FASTER BUT STILL SLOWER
THAN THE 12Z GFS COLD FRONTAL TIMING.

THE END RESULT IS A BLEND OF COLD FRONTAL TIMING BETWEEN THE 12Z
GFS AND 00Z ECMWF THROUGHOUT THE SHORT RANGE...OR THROUGH 00Z/02.
HOWEVER WITH THE SURFACE LOW...A 12Z GFS...00Z ECMWF...00Z UKMET
BLEND WILL WORK THROUGH ABOUT 00Z/01 WITH A 00Z ECMWF/UKMET BLEND
WORKING FROM 00Z/01 TO 00Z/02.


LOW AMPLITUDE SHORTWAVE CLIPPING THE NRN ROCKIES WED MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS...00Z ECMWF...00Z UKMET BLEND
CONFIDENCE: AVERAGE

THE ENSEMBLE SPAGHETTI PLOTS SUPPORT THIS FEATURE STAYING A LOW
AMPLITUDE WAVE BUT THERE ARE MINOR TIMING DIFFERENCES WITH THE 12Z
NAM ON THE FASTER EDGE OF THE LATEST GUIDANCE. AT THIS POINT IN
TIME...WILL FAVOR SOMEWHERE NEAR THE MIDDLE OF THE SPREAD GIVEN
POSSIBLE UPSTREAM DIFFERENCES IN FUTURE CYCLES AFFECTING THE
POSITION OF THIS WAVE. THE MIDDLE IS BEST REPRESENTED BY A
GFS/ECMWF/UKMET BLEND. WITHIN THIS 3-MODEL COMBO...THE FASTER 12Z
GFS AND SLOWER 00Z UKMET REPRESENT THE ENDS OF THE SPREAD WITH THE
00Z ECMWF SOMEWHERE IN THE MIDDLE...BUT A BIT LESS DEFINED.

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

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

OTTO


$$





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