Prognostic Meteorological Discussion
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000
FXUS10 KWNH 221901
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST MON DEC 22 2014

VALID DEC 22/1200 UTC THRU DEC 26/0000 UTC

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

==============================================
12Z MODEL EVALUATION AND PREFERENCES
==============================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==============================================

UPPER MIDWEST AND GREAT LAKES THROUGH TUE NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z NAM/GFS/ECMWF
CONFIDENCE: AVERAGE

A MODERATELY DEVELOPED CYCLONE WILL SWING INTO THE UPPER MIDWEST
AND WESTERN GREAT LAKES THROUGH TUESDAY EVENING...AND THEN MAY
BECOME SHEARED OR DE-AMPLIFY AS IT MOVES NORTHEAST. MODELS SHOW
GOOD AGREEMENT AT THE SURFACE AND IN THE LOW LEVELS THROUGH 24/12Z
WHEN THE SYSTEM BEGINS TO LOSE DEFINITION. A MID LEVEL
PERTURBATION IS BETTER DEFINED IN THE NAM/GFS/ECMWF AS IT LIFTS
INTO ONTARIO WEDNESDAY. THE GFS IS ON THE QUICK SIDE...BUT THESE
DIFFERENCES SHOULD HAVE LITTLE IMPACT ON FORECASTS OVER THE
U.S...ESPECIALLY RELATIVE TO THE NEXT CYCLONE MOVING UP FROM THE
SOUTH AND DISCUSSED IN THE NEXT SECTION.


CYCLOGENESIS OVER THE TENNESSEE AND OHIO VALLEYS WEDNESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z ECMWF AND 00Z ECMWF...SUPPORT FROM 00Z
GFS AND 06Z GEFS MEAN
CONFIDENCE: SLIGHTLY BELOW AVERAGE

WESTERN U.S. SOUNDINGS SAMPLED A 170 KNOT 250 MB JET DIGGING INTO
THE BASE OF A CENTRAL U.S. TROUGH. AS IT ROUNDS THE BASE THIS
ENERGY WILL SPUR CYCLOGENESIS. THE MODELS SHOW A LARGE AMOUNT OF
SPREAD WITH RESPECT TO THE TRACK AND SPEED OF THE RESULTING
CYCLONE. THE SPREAD IS PERHAPS BEST VIEWED IN THE SURFACE
PREDICTIONS VALID AT 25/00Z...IN WHICH THE LOW CENTER RANGES FROM
LAKE HURON IN THE CANADIAN MODEL TO FORT WAYNE INDIANA IN THE
ECMWF TO DAYTON OHIO IN THE NAM.

TRENDS HAVE BEEN DIFFICULT TO IDENTIFY GIVEN THE AMOUNT OF RUN TO
RUN VARIABILITY. THE 00Z GFS AND ECMWF PRODUCED SOME OF THE SLOWER
SOLUTIONS IN DEVELOPING AND LIFTING THIS SYSTEM NORTHWARD. THEY
WERE SUPPORTED BY A SLOWING TREND IN THE 06Z GEFS MEAN. DURING THE
12Z CYCLE THE GFS REVERSED THIS TREND...AS THE OPERATIONAL RUN AND
PARALLEL RUN BECAME FASTER SOLUTIONS...CLOSER TO THE CANADIAN. THE
ECMWF UNDERWENT RELATIVELY LITTLE CHANGE...WITH THE 12Z RUN
TRACKING THE LOW ABOUT 75 MILES NORTH AND WEST OF THE 00Z RUN.

GIVEN THE STRENGTH OF THE DIGGING JET WE PREFER SLIGHTLY SLOWER
SOLUTIONS AND THOSE WHICH INTRODUCE A CLOSED MID LEVEL CIRCULATION
AT LEAST BRIEFLY DURING THE PEAK MATURITY OF THE LOW LEVEL CYCLONE
AS IT LIFTS TOWARD MICHIGAN AND THE EASTERN GREAT LAKES. THIS
LEADS US TO FAVOR THE SOLUTIONS LIKE THE 00Z GFS AND 00Z AND 12Z
ECMWF. THIS IS SUPPORTED SOMEWHAT BY THE 12Z UKMET...WHICH TRACKS
AT THE SAME LATITUDE AS THE ECMWF...BUT WHICH IS QUICKER TO THE
EAST GIVEN A LACK OF DEPTH ALOFT. WE ALSO NOTE THAT THE 12Z GEFS
MEAN IS SLOWER THAN THE OPERATIONAL GFS. ALL OF THIS GIVES US
ROUGHLY AVERAGE CONFIDENCE IN RECOMMENDING A BLEND OF THE RECENT
ECMWF RUNS...BUT MODEL SPREAD IS UNUSUALLY LARGE FOR A 60 HOUR
FORECAST IN THE MIDDLE OF THE CONTINENT.


NEXT PACIFIC TROUGH INTO THE WESTERN U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z NAM/ECMWF
CONFIDENCE: AVERAGE

THE NEXT TROUGH INTO THE WESTERN U.S. IS OF MODERATE DEPTH AND
MEDIUM WAVELENGTH...AND SHOULD BE HANDLED FAIRLY WELL BY THE
MODELS. SPAGHETTI PLOTS OF THE 552 DECAMETER HEIGHT
CONTOUR...VIEWED OVER SEVERAL MODEL CYCLES...SHOW A STEADY
CONVERGENCE OF THE LESSER AMPLIFIED GEFS MEMBERS TOWARD THE DEEPER
ECMWF ENSEMBLE MEMBERS. THE CANADIAN ENSEMBLE MEMBERS GENERALLY
LEND MORE SUPPORT TO THE ECMWF. THE 12Z ECMWF IS VERY SIMILAR TO
THE 00Z ECMWF AND ECMWF ENSEMBLE MEAN...MAKING IT A GOOD CHOICE AS
A BASELINE FOR THE FORECAST. THE GFS IS TRENDING TOWARD THE
ECMWF...BUT THE 12Z RUN APPEARED SLIGHTLY FAST. AT LEAST THIS DID
IMPROVE UPON THE GFS SOLUTION OVER THE NORTHERN PLAINS ON DAY
3...WHEREAS EARLIER RUNS WERE TOO SLOW TO BRING COLD AIR
SOUTHWARD. THE NAM...HOWEVER...FORMS A BETTER PAIR WITH THE ECMWF
AS THE TWO ARE SLIGHTLY CLOSER IN TERMS OF DEPTH AND TIMING OF THE
MID LEVEL WAVE.


WEAK FRONTAL LOW MOVING UP THE EAST COAST THROUGH TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE OPERATIONAL MODELS...EXCLUDING THE NAM
CONFIDENCE: AVERAGE

THIS SYSTEM IS BEST DEFINED NEAR THE SURFACE...WITH A WEAK COASTAL
LOW STARTING NEAR THE OUTER BANKS OF NORTH CAROLINA AS OF THIS
AFTERNOON AND LIFTING TOWARD SOUTHERN NEW ENGLAND BY TUESDAY
EVENING BEFORE DISSIPATING. SHORT RANGE FORECASTS FROM THE RAP
VALID 23/06 SUPPORT THE GLOBAL MODELS OVER THE NAM. THE NAM WAS
FARTHER NORTH AND INDICATED A SHARPER LOWER TO MIDDLE LEVEL WAVE
ACCOMPANYING THE SURFACE SYSTEM.

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

BURKE
$$





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