Prognostic Meteorological Discussion
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FXUS10 KWNH 280459
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1158 PM EST SAT DEC 27 2014

VALID DEC 28/0000 UTC THRU DEC 31/1200 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 WITH THE 00Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...BROAD UPPER TROF REACHING THE APPALACHIANS BY SUNDAY EVENING...
...SURFACE WAVE CROSSING THE CAROLINAS EARLY NEXT WEEK...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF
FORECAST CONFIDENCE: AVERAGE

AN UPPER TROF CURRENTLY EXTENDING FROM THE LOWER GREAT LAKES DOWN
TO NORTHERN MX WILL SLIDE EASTWARD IN TWO PARTS. THE NORTHERN MOST
SHORTWAVE SHOULD EXIT INTO NEW ENGLAND AND FAR EASTERN CANADA WITH
NO REAL MODEL DIFFERENCES EVIDENT. THE LARGER UNCERTAINTY IS WITH
THE SOUTHERN FEATURE AS IT LIFTS THROUGH THE MID-ATLANTIC ON
MONDAY MORNING. THERE ARE SUBTLE DIFFERENCES ONLY 24 HOURS INTO
THE FORECAST WITH THE 00Z NAM/GFS AHEAD OF THE OTHER MODELS WHILE
THE 12Z ECMWF HAS AGREEMENT WITH THE 18Z GEFS/21Z SREF/12Z ECMWF
ENSEMBLE MEANS. THESE VARIATIONS CARRY AS THE SYSTEM SHEARS ON ITS
APPROACH TOWARD THE MID-ATLANTIC REGION. THE BROAD SOUTHWESTERLY
FLOW ALOFT WILL ALLOW THE FRONTAL ZONE TO HANG OUT BRIEFLY WITH A
WAVE OF LOW PRESSURE RIDING ALONG THE BOUNDARY. THE TWO BIGGEST
OUTLIERS WITH THIS SURFACE LOW ARE THE 00Z NAM/12Z CMC. THE LATTER
CARRIES A MORE AGGRESSIVE AREA OF LOW PRESSURE FARTHER OFFSHORE
MONDAY EVENING WHILE THE FORMER TAKES THE WAVE OFF OF THE VA CAPES
BRINGING WINTRY PRECIPITATION TO THE MID-ATLANTIC. EVEN THE 12Z
UKMET SEEMS TO BE TOO AGGRESSIVE WITH THE SYSTEM AS IT DEPARTS
OFFSHORE. THIS LEAVES THE 00Z GFS/12Z ECMWF AS A CONSERVATIVE
SOLUTION SO WILL LEAN THAT DIRECTION HERE.


...SHORTWAVE DIGGING THROUGH THE PACIFIC NORTHWEST AND INTO THE
CENTRAL ROCKIES...

PRELIMINARY PREFERENCE: A NON-12Z CMC MODEL COMPROMISE
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

WATER VAPOR IMAGERY SHOWS A WELL DEFINED SHORTWAVE CURRENTLY
MOVING THROUGH THE STATE OF WA. MODELS SHOW THE SYSTEM SLIDING
SOUTH AND EAST REACHING THE CENTRAL ROCKIES BY SUNDAY EVENING. THE
VORTICITY GETS STRETCHED OUT AS THE SHORTWAVE CROSSES THE GREAT
PLAINS WITH MODELS BEGINNING TO SHOW MORE SPREAD AT THIS TIME. THE
12Z CMC STANDS OUT AS A QUICK SOLUTION BY 29/1200Z WHILE OTHER
MODELS ARE MUDDLED TOGETHER TOWARD THE WEST. WILL FAVOR A NON-12Z
CMC MODEL COMPROMISE GIVEN THIS ASSESSMENT.


...ANOMALOUS CLOSED LOW OVER CA ON TUESDAY/WEDNESDAY...
...ARCTIC BOUNDARY PLUNGING INTO THE SOUTHWESTERN CONUS...

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

ON THE WINGS OF THE INITIAL SHORTWAVE CROSSING THE PACIFIC
NORTHWEST WILL BE A STRONG LOBE OF VORTICITY DROPPING DOWN FROM
THE YUKON TERRITORY. THE MODELS VARY WITH THE TIMING OF THIS
POSITIVELY-TILTED TROF AS IT DROPS DOWN ALONG THE WESTERN U.S. THE
00Z NAM/12Z CMC ARE SLOWER WITH THE EVOLUTION RELATIVE TO THE
BETTER CLUSTERED 00Z GFS/GFS-PARALLEL AND 12Z ECMWF/UKMET. BY
MID-WEEK...THE 12Z UKMET ENDS UP A HAIR WEST OF THE 00Z
GFS/GFS-PARALLEL AND 12Z ECMWF SOLUTIONS AS THE SYSTEM SPINS OVER
SOUTHERN CA. THE WPC RECOMMENDATION IS A COMPROMISE BETWEEN THE
00Z GFS/GFS-PARALLEL AND 12Z ECMWF.


...SYSTEM SLIDING EASTWARD ACROSS THE LOWER MO VALLEY BY EARLY
TUESDAY...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF
FORECAST CONFIDENCE: AVERAGE

A STRONG LOBE OF SHORTWAVE ENERGY EMERGING OUT OF THE CENTRAL
ROCKIES MIDDAY MONDAY WILL EVENTUALLY MAKE IT TO THE LOWER MO
VALLEY BY THE FOLLOWING MORNING. THE ENSEMBLE MEANS SEEM TO BE
WELL ALIGNED AND STABLE GIVEN THEIR AGREEMENT WHICH MAKES THE 12Z
CMC/UKMET LOOK TOO FAST. MEANWHILE...AS WAS THE CASE
YESTERDAY...THE 00Z NAM COMES IN MORE AGGRESSIVE WITH HOW
AMPLIFIED THE WAVE IS AS IT CROSSES THE MID-ATLANTIC ON 31/0000Z.
CHOOSE TO STAY CLOSER TO THE ENSEMBLE MEANS GIVEN THEIR SIMILARITY
WITH THE 00Z GFS/12Z ECMWF SUPPORTING THESE SOLUTIONS.


...PROGRESSIVE UPPER TROF CROSSING THE GREAT LAKES BY 31/0600Z...

PRELIMINARY PREFERENCE: BLEND OF THE 18Z GEFS/12Z ECMWF ENSEMBLE
MEANS
FORECAST CONFIDENCE: BELOW AVERAGE

A FAST-FLOWING NORTHERN STREAM WILL FEATURE A SERIES OF MID-LEVEL
IMPULSES WHICH WILL MOVE FROM THE UPPER MIDWEST TOWARD THE GREAT
LAKES REGION NEXT WEEK. THERE IS A LOT OF VARIABILITY IN THE
SOLUTIONS SO THIS APPEARS TO BE A GOOD TIME TO UTILIZE THE
ENSEMBLE MEANS. WILL REASSESS THE SITUATION AS ADDITIONAL 00Z
GUIDANCE ARRIVES.



...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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