Prognostic Meteorological Discussion
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000
FXUS10 KWNH 280644
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
143 AM EST SUN DEC 28 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 MODEL GUIDANCE ALONG WITH FINAL
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...

FINAL PREFERENCE: BLEND OF THE 00Z GFS/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 00Z ECMWF HAS AGREEMENT WITH THE 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 UP BRIEFLY WITH A WAVE OF LOW
PRESSURE RIDING ALONG THE BOUNDARY. THE BIGGEST OUTLIER WITH THIS
SURFACE LOW CONTINUES TO BE THE 00Z NAM WHICH CARRIES A SURFACE
LOW MUCH CLOSER TO THE VA CAPES ON TUESDAY. SUCH A SOLUTION IS
ALSO NOTABLY SLOWER. THE 00Z CMC/UKMET HAVE MADE POSITIVE CHANGES
IN THEIR RECENT CYCLES BUT FEEL CONTINUITY WOULD BE BEST SUITED
HERE WITH A 00Z GFS/ECMWF BLEND RECOMMENDED.


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

FINAL PREFERENCE: A NON-00Z CMC/UKMET 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
00Z CMC/UKMET STAND OUT AS BEING QUICKER SOLUTIONS BY 29/1200Z
WHILE OTHER MODELS ARE MUDDLED TOGETHER TOWARD THE WEST. WILL
FAVOR A NON-00Z CMC/UKMET MODEL COMPROMISE GIVEN THIS ASSESSMENT.


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

FINAL PREFERENCE: BLEND OF THE 00Z GFS/GFS-PARALLEL/ECMWF
FORECAST CONFIDENCE: SLIGHTLY 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. IN
ADDITION TO THE VARIATIONS IN TIMING...SOME OF THE MODELS HAVE
EXHIBITED LARGE JUMPS BETWEEN THEIR RUNS. FOR INSTANCE...THE 00Z
CMC HAS SHIFTED TO BEING ONE OF THE QUICKEST SOLUTIONS AFTER BEING
THE SLOWEST IN THE PREVIOUS MODEL CYCLE. THE CLUSTERING DOES NOT
LOOK AS GOOD AS PREVIOUSLY BUT THE 00Z GFS/GFS-PARALLEL/ECMWF ARE
IN STILL IN THE BALLPARK WITH THE 00Z GEFS/12Z ECMWF ENSEMBLE
MEANS. WILL LOWER THE CONFIDENCE IN THE PREFERENCE GIVEN THE
MODELS ARE STILL SHIFTING ABOUT WITH THE POSITION OF THE CLOSED
LOW ACROSS SOUTHERN CA. HOWEVER...THE PREFERENCE WILL REMAIN THE
SAME.


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

FINAL PREFERENCE: NON-00Z NAM MODEL COMPROMISE
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 WITH THIS SYSTEM AND A NUMBER OF THE
DETERMINISTIC MODELS HAVE TRENDED IN THEIR DIRECTION. THE BIGGEST
OUTLIER CONTINUES TO BE THE 00Z NAM WHICH REMAINS MORE AGGRESSIVE
WITH HOW AMPLIFIED THE WAVE BECOMES WHILE CROSSING THE
MID-ATLANTIC ON 31/0000Z. CHOOSE TO STAY AWAY FROM THIS MORE
DEVELOPED SOLUTION AND FAVOR A NON-00Z NAM MODEL COMPROMISE.


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

FINAL PREFERENCE: BLEND OF THE 00Z 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.



...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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