Prognostic Meteorological Discussion
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FXUS10 KWNH 191845
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 PM EST FRI DEC 19 2014

VALID DEC 19/1200 UTC THRU DEC 23/0000 UTC

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

...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...MULTIPLE SHORTWAVES EXITING THE NORTHEASTERN U.S...

FINAL PREFERENCE: NON-12Z UKMET SOLUTION
FORECAST CONFIDENCE: ABOVE AVERAGE

WATER VAPOR IMAGERY SHOWED THREE DISTINCT FEATURES CURRENTLY
AFFECTING THE NORTHEASTERN U.S. A POSITIVELY-TILTED CLOSED LOW
OVER NOVA SCOTIA SHOULD CONTINUE TO LIFT AWAY FROM THE CONUS WHILE
A WEAKER SHORTWAVE TO ITS SOUTH SLIDES WELL EAST OF THE DELMARVA.
BOTH SYSTEMS APPEAR WELL RESOLVED AND ARE ALSO OF NO FURTHER
CONSEQUENCE OF THE STATES. LASTLY...A COMPACT CLOSED LOW PINCHED
UNDERNEATH A CLOSED UPPER HIGH SOUTH OF HUDSON BAY WILL SPIN IN
PLACE FOR ROUGHLY THE NEXT 12 TO 18 HOURS. THE DETERMINISTIC
MODELS HAVE COME INTO BETTER AGREEMENT THAN PREVIOUS WITH THE 12Z
ECMWF/CMC SLIDING WESTWARD MORE IN ALIGNMENT WITH THE 12Z
NAM/GFS/GFS-PARALLEL. THIS LEAVES THE 12Z UKMET AS A FAR WESTERN
OUTLIER. WITH THAT SAID...A NON-12Z UKMET SOLUTION IS RECOMMENDED.
THE MERGING OF THE SOLUTIONS RAISES THE CONFIDENCE TO ABOVE
AVERAGE.


...SPLIT FLOW INITIALLY OVER THE CENTRAL U.S...
...WAVE OF LOW PRESSURE CROSSING THE NORTHERN GULF OF MX...

FINAL PREFERENCE: SOUTHERN STREAM: NON-12Z CMC SOLUTION...NORTHERN
STREAM: NON-09Z SREF MEAN SOLUTION
FORECAST CONFIDENCE: AVERAGE

A WAVY/LOW-AMPLITUDE UPPER PATTERN WILL BE IN PLACE AT THE START
OF THE PERIOD. THE NORTHERN BRANCH OF THE JET IS FORECAST TO BE
SLOWER MOVING AS IT ENCOUNTERS THE BLOCKING RIDGE DOWNSTREAM. TO
THE SOUTH...A PROGRESSIVE AXIS OF HEIGHT FALLS WILL MIGRATE FROM
THE SOUTHERN PLAINS/LOWER MS VALLEY TOWARD THE LOWER MID-ATLANTIC.
AT THE SURFACE...A BRIEF AREA OF LOW PRESSURE WILL DEVELOP ACROSS
THE NORTHWESTERN GULF OF MX BEFORE WEAKENING ON ITS PROGRESSION
TOWARD THE EAST. MULTI-CYCLE TRENDS VIA THE ENSEMBLE LOW PLOT
SHOWS A LARGE SHIFT TOWARD THE WEAKER DIRECTION. IT SEEMS LIKE THE
DETERMINISTIC MODELS ALL AGREE WITH THIS TREND. THE WEAK SURFACE
WAVE IS FORECAST TO LIFT AWAY FROM THE SOUTHEASTERN U.S. COAST BY
21/0600Z WITH THE 12Z CMC BEING WEST OF THE CONSENSUS. THE
PREFERENCE WITH THE SOUTHERN STREAM WILL BE A NON-12Z CMC
SOLUTION. REGARDING THE NORTHERN STREAM...THE 09Z SREF MEAN
APPEARS TO BE A SLOWER OUTLIER BEING ON THE WESTERN SIDE OF THE
CONSENSUS. GIVEN THIS ASSESSMENT...A NON-09Z SREF MEAN WILL BE
UTILIZED FOR THE NORTHERN STREAM.


...SHORTWAVE MIGRATING FROM THE PACIFIC NORTHWEST TO THE NORTHERN
PLAINS THROUGH 21/0000Z...

FINAL PREFERENCE: NON-12Z NAM MODEL COMPROMISE
FORECAST CONFIDENCE: AVERAGE

A PRONOUNCED AREA OF HEIGHT FALLS WILL MOVE THROUGH THE PACIFIC
NORTHWEST TODAY BEFORE REACHING THE NORTHERN HIGH PLAINS BY MIDDAY
SATURDAY. THE 12Z NAM RESIDES NORTH OF THE STRONGER CONSENSUS THE
VORTICITY CENTERS MOVES INTO THE DAKOTAS ON 21/0600Z.
OVERALL...THERE ARE PLENTY OF DETAIL DIFFERENCES WITH THE OTHER
GUIDANCE BUT FEEL SOME SORT OF COMPROMISE WILL WORK AMONG THE
OTHER SOLUTIONS EXCLUDING THE 12Z NAM.


...DEEP UPPER TROF ANCHORING THE CENTRAL U.S. BY LATE SUNDAY...
...AREAS OF LOW PRESSURE ACROSS THE UPPER MIDWEST AND EASTERN
SEABOARD...RESPECTIVELY...

FINAL PREFERENCE: BLEND OF THE 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: BELOW AVERAGE

BY LATE IN THE WEEKEND AND INTO NEXT WEEK...THE FLOW BECOMES MUCH
MORE AMPLIFIED IN NATURE. A SERIES OF SHORTWAVES WILL TRACK ABOVE
AN EASTERN PACIFIC RIDGE INTO THE ROCKY MOUNTAIN REGION WHICH WILL
CARVE OUT A PRONOUNCED CENTRAL U.S. TROF. THERE ARE A MYRIAD OF
SOLUTIONS OUT THERE WITH THE 12Z CMC BEING MUCH MORE PROGRESSIVE
WHILE THE 12Z NAM/GFS/UKMET ARE STRONGER ALOFT. THE TREND IN THE
540-DM SPAGHETTI PLOTS IS TO BE A LITTLE SLOWER WHICH RULES OUT
THE QUICKER 12Z CMC SOLUTION. THE 12Z ECMWF CONTINUES TO OFFER A
MORE MIDDLE GROUND SOLUTION WHICH IS NOT AS DEEP AS THE NCEP
GUIDANCE AND IS SLOWER THAN THE 12Z CMC. ONLY LIMITED CHANGES WERE
NOTED IN THE LATEST ECMWF WHICH BODES A LITTLE MORE CONFIDENCE IN
ITS SOLUTION. WILL MAINTAIN THE PREVIOUS PREFERENCE WHILE
INCORPORATING THE 12Z ECMWF.


...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

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