642
FXUS10 KWNH 281714
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1214 PM EST TUE JAN 28 2020
VALID JAN 28/1200 UTC THRU FEB 01/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...SPLIT FLOW TROUGH CROSSING THE GREAT PLAINS TODAY AND REACHING
THE SOUTHEAST WEDNESDAY NIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THE LATEST NUMERICAL GUIDANCE REMAINS IN DECENT AGREEMENT WITH THE
EVOLUTION OF A SHORTWAVE WHICH WAS OVER THE SOUTHERN PLAINS AT 12Z
TODAY/TUESDAY. AS THE WAVE TRACKS EAST, THE 12Z NAM SLOWS COMPARED
TO THE REMAINING MODEL CONSENSUS AND THE 00Z UKMET ALSO SLOWS
LIKELY DUE TO DIFFERENCES IN THE HANDLING OF THE NORTHERN STREAM
COMPONENT DISCUSSED BELOW. A 12Z GFS/00Z ECMWF BLEND LOOKS GOOD
FOR THIS SYSTEM WITH THE 00Z CMC SERVING AS A SECONDARY PREFERENCE.
...SPLIT FLOW TROUGH IN NORTHERN STREAM FROM THE UPPER MIDWEST TO
THE MID-ATLANTIC THURSDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z UKMET BLEND
CONFIDENCE: AVERAGE
THE NORTHERN COMPONENT OF AN ELONGATED MID-LEVEL TROUGH TRACKING
ACROSS THE UPPER MIDWEST ON WEDNESDAY NOW SHOWS FAIRLY GOOD
AGREEMENT OUTSIDE OF THE 00Z UKMET. THE 00Z UKMET IS MORE
AMPLIFIED THAN THE REMAINING CONSENSUS REGARDING THE 500 MB
VORTICITY MAX MOVING ACROSS THE OHIO VALLEY WEDNESDAY NIGHT. THERE
ARE MINOR LATITUDE DIFFERENCES OUTSIDE OF THE 00Z UKMET WITH THE
SHORTWAVE AS IT REACHES THE EAST COAST LATE THURSDAY AND AN
ACCOMPANYING SURFACE LOW IN THE WESTERN ATLANTIC. HOWEVER, A NON
00Z UKMET BLEND APPEARS REASONABLE GIVEN THE DIFFERENCES ARE
RELATIVELY SMALL.
...MID-LEVEL TROUGH OVER THE PACIFIC NORTHWEST TODAY AND
AMPLIFYING INTO THE DESERT SOUTHWEST WEDNESDAY, REACHING THE
SOUTHERN PLAINS THURSDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF BLEND
CONFIDENCE: AVERAGE
ENSEMBLE GUIDANCE SHOWS THE 12Z NAM AND 00Z CMC AS SLOWER/MORE
AMPLIFIED THAN THE CONSENSUS AS THE TROUGH AXIS REACHES THE
SOUTHERN PLAINS. MEANWHILE, THE 00Z UKMET BECOMES MUCH FASTER WITH
THE TROUGH BY 12Z/31. THE ENSEMBLE MEANS ARE IN THE MIDDLE ALONG
WITH THE AGREEABLE 12Z GFS/00Z ECMWF.
...MID-LEVEL TROUGH ENTERING BRITISH COLUMBIA ON WEDNESDAY AND
AMPLIFYING SOUTHWARD INTO THE GREAT PLAINS BY FRIDAY MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF OR 06Z GEFS/00Z ECENS MEANS
CONFIDENCE: BELOW AVERAGE
A HIGH DEGREE OF UNCERTAINTY EXISTS WITH HOW THE SOUTHERN END OF A
SHORTWAVE TROUGH EVOLVES ONCE IT CROSSES THROUGH A RIDGE CENTERED
OVER SOUTHWESTERN CANADA AND THE NORTHWESTERN U.S. RUN TO RUN
CONSISTENCY HAS BEEN POOR AND ENSEMBLE SPREAD IS LARGE. HOWEVER,
540 DAM ENSEMBLE SPAGHETTI PLOTS AT 500 MB SEEM TO SUGGEST THE 00Z
UKMET/CMC ARE ON THE FAR SOUTHERN END, IF NOT OUTLIERS, WITH THEIR
TROUGHING OVER THE UPPER MIDWEST BY 00Z/01. GIVEN THE 12Z NAM
APPEARS TOO SLOW WITH THE SYSTEM REFERENCED ABOVE INTO THE
SOUTHERN PLAINS BY 12Z/31, IT WILL NOT BE INCLUDED AS PART OF THE
PREFERENCE. THIS LEAVES THE 12Z GFS AND 00Z ECMWF WHICH ARE
DIFFERENT BUT A BLEND BETWEEN THE TWO IDEAS IS RECOMMENDED AT THIS
TIME, OR NEAR THE GEFS/ECENS MEANS.
...LEADING EDGE OF LONGWAVE TROUGH, OFFSHORE OF THE WEST COAST OF
CANADA FRIDAY EVENING AND DOWNSTREAM ATMOSPHERIC RIVER INTO THE
PACIFIC NORTHWEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/00Z ECMWF BLEND
CONFIDENCE: AVERAGE
AFTER THE PASSAGE OF A SHORTWAVE AND ACCOMPANYING COLD FRONT INTO
BRITISH COLUMBIA ON THE 30TH, INITIALLY ZONAL FLOW INTO WESTERN
CANADA WILL BEGIN TO AMPLIFY AS RIDGING INCREASES AHEAD OF AN
UPSTREAM SHORTWAVE NEAR 40N 145W BY 00Z/01. ENSEMBLE MEANS AND THE
REMAINING DETERMINISTIC CONSENSUS SUGGEST THAT THE 12Z GFS IS TOO
QUICK WITH THE SHORTWAVE, LOCATED AT THE LEADING EDGE OF A
LONGWAVE TROUGH BETWEEN 12Z/31 AND 00Z/01. A BLEND OF THE 12Z NAM
AND 00Z ECMWF IS CLOSEST TO THE RELATIVELY AGREEABLE ENSEMBLE
MEAN'S POSITION WITH THE SHORTWAVE AND DOWNSTREAM ATMOSPHERIC
RIVER INTO THE PACIFIC NORTHWEST.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
OTTO
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