Prognostic Meteorological Discussion
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000
FXUS10 KWNH 111643
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1142 AM EST MON DEC 11 2017

VALID DEC 11/1200 UTC THRU DEC 15/0000 UTC

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

12Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...LEAD SHORTWAVE OVER THE WESTERN GREAT LAKES TODAY...
...PRIMARY SHORTWAVE OVER NRN ONTARIO DIGGING INTO GREAT LAKES AND
NORTHEAST TUE-WED WITH DEVELOPING CYCLONE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

MODEL SOLUTIONS ARE GENERALLY QUITE SIMILAR IN THEIR DEPICTION OF
THE MASS FIELDS WITH THIS EVOLVING SYSTEM OVER THE NORTHEASTERN
QUADRANT OF THE CONUS OVER THE NEXT FEW DAYS. THE INTENSITY AND
POSITION OF THE SURFACE LOW THROUGH 13/12Z IS EXTREMELY CLOSE FOR
BOTH THE OPERATIONAL MODELS AND THE GEFS AND ECMWF ENSEMBLE MEANS.
THEREFORE...A GENERAL MODEL BLEND IS PREFERRED WITH RELATIVELY
HIGH CONFIDENCE. FOR DETAIL DIFFERENCES: ENSEMBLE SENSITIVITY
ANALYSIS SHOWS THAT THE LARGEST PORTION OF VARIANCE WITH THE SEA
LEVEL PRESSURE FIELDS IS EXPLAINED BY TIMING DIFFERENCES AS THE
SURFACE LOW OCCLUDES AND TRACKS THROUGH INTERIOR NEW ENGLAND. AND
THIS VARIANCE IS WELL CORRELATED WITH THE HEIGHT FIELDS ASSOCIATED
WITH THE UPSTREAM WAVES: HIGHER HEIGHTS WITH THE WAVES TODAY TEND
TO CORRELATE WITH SLIGHTLY SLOWER SOLUTIONS.


...STRONG SHORTWAVE IN NERN PACIFIC NEAR 45N/135W TODAY ROUNDING
THE WESTERN RIDGE THROUGH TUESDAY...
...DIGGING INTO CENTRAL US TUESDAY NIGHT AND WEDNESDAY...
...SECONDARY SHORTWAVE EMBEDDED IN NWLY FLOW DIGGING INTO NRN
PLAINS AND GREAT LAKES LATE WED INTO THU...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z GFS / 00Z ECMWF / 00Z CMC
CONFIDENCE: AVERAGE

WITH THE LEAD SHORTWAVE CURRENTLY OVER THE NE PACIFIC OCEAN...THE
00Z UKMET APPEARS TO BE STRONGEST WITH THE DOWNSTREAM RIDGE OVER
WRN NOAM AND THUS PUSHES THE SHORTWAVE FURTHER NORTH THROUGH THE
CANADIAN ROCKIES. MEANWHILE...THE 12Z NAM SHOWS THE SHORTWAVE
ROUNDING THE RIDGE AT A SLIGHTLY LOWER LATITUDE THAN OTHER
MODELS...AND BREAKS THROUGH THE NORTHERN PERIPHERY OF THE RIDGE
FASTER...LEADING TO SOME TIMING DIFFERENCES DOWNSTREAM. THESE ARE
THE LARGEST DIFFERENCES INITIALLY...AND THEREFORE NEITHER THE
UKMET OR NAM ARE INCLUDED IN THE PREFERENCE. ADDITIONALLY...THESE
TWO MODELS SHOW A STRONGER AND MORE AMPLIFIED SECONDARY
WAVE...WHICH SEEMS LESS LIKELY GIVEN THE CLOSE PROXIMITY TO THE
INITIAL WAVE (WHICH SHOULD BE QUITE STRONG ITSELF). PREFER A BLEND
OF THE 12Z GFS...00Z ECMWF AND 00Z CMC WHICH KEEP A FLATTER
SECONDARY WAVE AND PROVIDE AN INTERMEDIATE SOLUTION WITH THE
PRIMARY WAVE IN HOW IT ROUNDS THE WESTERN RIDGE.


...UPPER LEVEL LOW LINGERING NEAR THE NRN GULF OF CALIFORNIA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS / 12Z NAM / 00Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 00Z UKMET AND 00Z CMC CONSOLIDATE AN UPPER LEVEL LOW FURTHER
EAST IN THE VICINITY OF THE GULF OF CALIFORNIA THAN THE OTHER
MODELS AND ENSEMBLE MEANS...AND THUS EVENTUALLY SHOW DIFFERENT
INTERACTIONS WITH THE GRADUALLY EXPANDING TROUGH OVER THE CENTRAL
CONUS. THE VORTICITY FIELDS ALOFT ARE STILL VERY DISPERSED IN THIS
REGION...AND THUS THE UKMET AND CMC SOLUTIONS CANNOT BE TOTALLY
DISCOUNTED AS UNREASONABLE POSSIBILITIES. HOWEVER...GOES
HIGH-DENSITY WINDS IN THE 500-350MB LAYER AND LATEST WATER VAPOR
LOOPS SHOW THE DOMINANT MID-UPPER LEVEL CIRCULATION CURRENTLY
FURTHER WEST SO THE PREFERENCE IS TO REMAIN CLOSE TO A SOLUTION
THAT SHOWS A SIMILAR POSITION.


MODEL TRENDS AT www.wpc.ncep.noaa.gov/html/model2.shtml
500 MB FORECASTS AT www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

LAMERS

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