Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11
000
FXUS10 KWNH 260450
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1149 PM EST THU DEC 25 2014

VALID DEC 26/0000 UTC THRU DEC 29/1200 UTC

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

...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS OF THE 00Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...INITIAL SHORTWAVE LIFTING FROM THE CENTRAL PLAINS TO THE UPPER
MIDWEST...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

WATER VAPOR IMAGERY SHOWED A BROAD UPPER TROF SINKING TOWARD THE
FOUR CORNERS REGION WITH SEVERAL BATCHES OF VORTICITY SEEN
CIRCULATING ABOUT THE REGION. THE NORTHERN MOST IMPULSE CURRENTLY
SPREADING LIGHT/MODERATE SNOW ACROSS AREAS OF NORTHEASTERN
CO/SOUTHEASTERN WY/NE PANHANDLE WILL SHIFT ITS FOCUS NORTHEASTWARD
IN TIME. MODELS ARE UNANIMOUS IN FLATTENING OUT THE SHORTWAVE AS
IT PROGRESSES THROUGH MN/WI ON FRIDAY AFTERNOON BEFORE MOVING INTO
SOUTHERN ONTARIO BY NIGHTFALL. THE SOLID AGREEMENT WARRANTS A
GENERAL MODEL COMPROMISE.


...FULL-LATITUDE TROF SLIDING EASTWARD ACROSS THE CONUS THIS
WEEKEND...
...PROGRESSIVE COLD FRONT/WAVE OF LOW PRESSURE CROSSING THE GREAT
LAKES...

PRELIMINARY PREFERENCE: THROUGH 28/1200Z...BLEND OF THE 00Z
GFS-PARALLEL/12Z ECMWF...THEREAFTER: BLEND OF THE 12Z ECMWF WITH
THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS
FORECAST CONFIDENCE: AVERAGE

AS THE LEAD MID-LEVEL ENERGY MOVES TOWARD THE UPPER MIDWEST BY
FRIDAY EVENING...THE AFOREMENTIONED TROF ACROSS THE SOUTHWESTERN
U.S. WILL GRADUALLY ADVANCE EASTWARD. THE CORE OF LOWER HEIGHTS
ARE FORECAST TO BE LOCATED OVER THE FOUR CORNERS REGION ON
26/1800Z. MODELS SUGGEST THE LEADING EDGE OF THE HEIGHT FALLS WILL
LIFT NORTHEASTWARD TOWARD THE MIDDLE MS VALLEY/GREAT LAKES REGION
ON SATURDAY. THERE IS SOME ENSEMBLE SPREAD WITH THE RESULTANT AREA
OF LOW PRESSURE MOVING THROUGH THE GREAT LAKES MIDDAY SATURDAY.
THE BEST CLUSTERING IS WITH THE FASTER SOLUTION FEATURING THE 00Z
NAM/GFS/GFS-PARALLEL AND 12Z UKMET. THE 12Z ECMWF IS SLOWER BUT
ALSO HAS THE BETTER ENSEMBLE SUPPORT VIA THE ENSEMBLE SURFACE LOW
PLOTS WHICH DEPICT VERY LITTLE CHANGE IN THE PAST COUPLE RUNS.
PLAN ON SPLITTING THE DIFFERENCE BETWEEN THE TWO.

WHILE THE INITIAL WAVE MOVES THROUGH THE GREAT LAKES...THE
REMAINING PORTION OF THE UPPER TROF IS FORECAST TO EJECT EASTWARD
CROSSING THE RIO GRANDE BY SUNDAY MORNING. THE 12Z CMC/UKMET LOOK
DECIDEDLY SLOW...PARTICULARLY EVIDENT ON THE 564-DM SPAGHETTI
PLOT. LATER IN THE PERIOD...THERE ARE SOME TIMING DIFFERENCES
BETWEEN THE 0OZ GFS/GFS-PARALLEL AND 12Z ECMWF WITH THE 00Z GFS
BEING THE QUICKEST SOLUTION WHILE THE 12Z ECMWF UNDERGOES A BIT
MORE AMPLIFICATION. THROUGH DAY 2/SUNDAY MORNING...A COMBINATION
OF THE 00Z GFS-PARALLEL/12Z ECMWF APPEARS REASONABLE BUT WILL
BEGIN TO INCORPORATE THE MORE STABLE ENSEMBLE MEANS INTO THE MIX
ON DAY 3. THAT IS...A BLEND OF THE 12Z ECMWF WITH THE 18Z GEFS/12Z
ECMWF ENSEMBLE MEANS.


...STRONG SHORTWAVE REACHING THE PACIFIC NORTHWEST BY LATE
SATURDAY...
...SURGE OF ARCTIC AIR INTO THE WEST...

PRELIMINARY PREFERENCE: MODEL COMPROMISE BETWEEN THE 00Z NAM/GFS
AND 12Z ECMWF
FORECAST CONFIDENCE: AVERAGE

MODELS SHOW A STOUT UPPER RIDGE SETTING UP ACROSS THE EASTERN
PACIFIC AT THE START OF THE PERIOD. BY SATURDAY...A PRONOUNCED
SHORTWAVE IS FORECAST TO DIG SOUTHWARD FROM THE GULF OF AK
CARRYING STRONG HEIGHT FALLS INTO THE STATE OF WA BY SATURDAY
EVENING. AS THE SYSTEM PROPAGATES SOUTH AND EAST...THE 12Z
CMC/UKMET ARE EAST OF THE MODEL CONSENSUS...PARTICULARLY THE 12Z
UKMET WHICH BECOMES MORE OUTLYING WITH ITS FASTER SOLUTION. WHILE
THERE ARE DIFFERENCES BETWEEN THE 00Z NAM/GFS AND 12Z ECMWF...A
COMPROMISE BETWEEN THESE SEEMS REASONABLE GIVEN THEY CONFORM MOST
TO THE ENSEMBLE MEANS. WILL RECOMMEND SUCH A COMPROMISE AND AWAIT
ADDITIONAL 00Z GUIDANCE FOR POTENTIAL TWEAKS TO THE SOLUTION.



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

RUBIN-OSTER

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.