821
FXUS10 KWNH 121635
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1134 AM EST SUN JAN 12 2020
VALID JAN 12/1200 UTC THRU JAN 16/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..LARGE SCALE PATTERN ACROSS THE CONUS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-GFS BLEND
CONFIDENCE: AVERAGE
A BROAD LARGE SCALE TROUGH IS EXPECTED TO DEVELOP OVER THE CONUS
THROUGH THE NEXT FEW DAYS AS A RESULT OF A CLOSED, SLOWLY MOVING
LOW SETTLES ACROSS INTERIOR WESTERN CANADA. A STRONG IMPULSE
RIDING THE PERIPHERY OF THIS FEATURE LIFTS THROUGH THE CENTRAL US
AND GREAT LAKES REGION MONDAY/TUESDAY FOLLOWED BY A COUPLE
DIFFERENT SHORTWAVES MID WEEK (ANOTHER CENTRAL US SHORTWAVE AND
THEN A PACIFIC NORTHWEST LOW).
THE LARGEST AND MOST SIGNIFICANT MODEL DIFFERENCES ARE
ATTRIBUTABLE TO THE POLAR VORTEX OVER WESTERN CANADA AND ITS
PROGRESSION (OR LACK OF) EASTWARD IN THE INCREASINGLY SHEARING,
ZONAL FLOW BY THE END OF THE FORECAST PERIOD. THE GFS HAS
CONSISTENTLY BEEN SHEARING THE VORTEX TOO QUICKLY EASTWARD AHEAD
OF ALL THE OTHER AVAILABLE GLOBAL DETERMINISTIC GUIDANCE. ITS 12Z
SOLUTION REMAINS WAY AHEAD OF EVEN THE GEFS MEAN, WHICH IS ALSO
CONSIDERABLY FASTER THAN THE NON-NCEP GUIDANCE AND THE 12Z NAM AS
WELL.
ACROSS THE PACIFIC NW TOWARD MID-WEEK, A STRONGER BUT ALSO MORE
AMPLIFIED WAVE CROSSES THE ALASKAN PENINSULA AND UPPER ALEUTIANS
LATE MONDAY INTO TUESDAY, A RELATIVELY FLAT DOWNSTREAM 'RIDGE' OR
LACK THEREOF, ALLOWS FOR GREATER BUCKLING OF THE FLOW THAT THE
LEAD PORTION OF THE WAVE SUPPORT STRONG CYCLOGENESIS BY LATE
TUESDAY INTO WED NEARING 130W. MOST OF THE GUIDANCE NOW HAS
CONVERGED ON THIS IDEA INCLUDING THE CMC. THE GFS IS A BIT FASTER
BUT HAS TRENDED TOWARD THE CONSENSUS. A BLEND OF THE NAM/ECMWF
AND GFS SEEMS APPROPRIATE BUT HEDGING TOWARD THE ECMWF/NAM GIVEN
THE GFS MAY BE SHOWING FAST BIAS. UNCERTAINTY, IS OBVIOUSLY HIGH
GIVEN THE PROGRESSIVE FLOW, BUT THE AGREEMENT EVEN AT 84HRS IS
HIGH ENOUGH TO HAVE AVERAGE CONFIDENCE IN A NAM/ECMWF WEIGHTED
BLEND.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
TAYLOR
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