Prognostic Meteorological Discussion
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FXUS10 KWNH 300445
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1144 PM EST THU JAN 29 2015

VALID JAN 30/0000 UTC THRU FEB 02/1200 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.


...UPPER TROF BECOMING NEGATIVELY-TILTED OVER NEW ENGLAND ON
FRIDAY EVENING...
...STRENGTHENING COASTAL LOW...

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

CURRENT WATER VAPOR IMAGERY SHOWED A DEEP UPPER TROF DIGGING
THROUGH THE GREAT LAKES AND OH VALLEY REGION. THE MULTITUDE OF
SHORTWAVES WILL EVENTUALLY BECOME ABSORBED BY A STRONGER BAND OF
VORTICITY DIVING DOWN FROM THE UPPER GREAT LAKES. THE EVOLVING
SYSTEM IS FORECAST TO BECOME NEGATIVELY-TILTED IN NATURE AS IT
MOVES OFF THE NJ COAST FRIDAY EVENING. A DEEPENING SURFACE LOW OFF
THE MA COAST HAS SHOWN A TREND TOWARD THE MORE OFFSHORE DIRECTION
BASED ON THE PAST TWO ENSEMBLE SCATTER LOW PLOTS. MOST
NOTABLY...THE 12Z GEFS MEMBERS MOVED AWAY FROM THE ME COAST TOWARD
THE CONSENSUS FORMED BY THE 12Z ECMWF ENSEMBLE MEMBERS. BY
31/1200Z...THE ENSEMBLE LOWS DO SHOW SOME SPREAD WITH THE
GEFS/ECMWF ENSEMBLE MEMBERS BEING ON THE SOUTHWESTERN FLANK OF THE
CLUSTERING. WOULD PREFER TO STAY ON THIS SIDE OF THE SPREAD GIVEN
THE STRONG CLOSED LOW IN PLACE OVERHEAD. THIS WOULD RULE OUT THE
MORE OUTLYING 12Z CMC. THE RECOMMENDATION HERE IS A NON-12Z CMC
MODEL COMPROMISE.


...SLOW-MOVING UPPER LOW REACHING WESTERN MX BY LATE IN THE
WEEKEND...

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

INITIALLY...A BROAD UPPER TROF WILL LIFT FROM 30N/120W TOWARD THE
DESERT SOUTHWEST WHERE IT IS EXPECTED TO INTERACT WITH A STREAM OF
VORTICITY DIPPING DOWN FROM NORTHERN CA. THIS EVENTUAL MERGER
PROCESS WILL LEAD TO THE DEVELOPMENT OF A CLOSED UPPER LOW ACROSS
FAR WESTERN MX AND BACK TOWARD BAJA CA. THROUGH 01/0000Z...THE 21Z
SREF/18Z GEFS/12Z ECMWF ENSEMBLE MEANS ARE FAIRLY CONSISTENT WITH
ONE ANOTHER WHILE THE 00Z NAM IS A TAD FASTER AND THE 12Z
CMC/UKMET ARE SLOWER IN NATURE. THIS IS PARTICULARLY THE CASE WITH
THE 12Z UKMET AS IT IS FAR ENOUGH WEST TO ALLOW NORTHERN STREAM
ENERGY TO DIP DOWN INTO THE SOUTHERN HIGH PLAINS. TOWARD THE END
OF THE PERIOD...THE 12Z UKMET ENDS ON THE FAR WESTERN END OF THE
FORECAST SPREAD WHILE THE 00Z NAM BECOMES QUICKER CARRYING THE
CLOSED LOW TOWARD CENTRAL MX. THE ENSEMBLE MEANS SIT IN THE MIDDLE
WHICH WILL BE FAVORED. THIS SOLUTION LEANS ON THE SLOWER SIDE
WHICH IS BETTER GIVEN THE SYSTEM FEATURES A SLOW-MOVING CLOSED
LOW. THE 00Z GFS/12Z ECMWF BEST SUPPORT THESE MEANS SO WILL
RECOMMEND THESE DETERMINISTIC MODELS.


...MID-LEVEL HEIGHT FALLS REACHING THE NORTHERN PLAINS BY
01/1200Z...
...SURFACE LOW CROSSING THE MID-ATLANTIC LATE IN THE PERIOD...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS WITH THE 21Z SREF/12Z
ECMWF ENSEMBLE MEANS
FORECAST CONFIDENCE: BELOW AVERAGE

A BAND OF HEIGHT FALLS DIPPING DOWN INTO THE NORTHERN/CENTRAL
PLAINS ON SUNDAY MORNING WILL PLAY A KEY ROLE IN THE FORECAST
GIVEN THE THREAT FOR WINTRY PRECIPITATION FROM THE CENTER OF THE
CONUS EASTWARD TO THE MID-ATLANTIC. AS WAS THE CASE
YESTERDAY...THE QUICKER AND MORE AMPLIFIED 12Z UKMET SUPPORTS
SURFACE LOW DEVELOPMENT THAT IS MORE DEFINED AND NORTH OF THE
MODEL ENVELOPE. THIS RESULTS IN A NORTHWARD DISPLACED
PRECIPITATION AXIS ON DAY 2. AS TIME MOVES FORWARD...TIMING
DIFFERENCES PREVAIL WITH THE 12Z UKMET CONTINUING TO BE QUICKER
RESULTING IN THE SURFACE WAVE BEING OFFSHORE OF SOUTHERN NEW
ENGLAND BY 02/1200Z. MEANWHILE...THE 00Z NAM/12Z CMC BEING SLOWER
RESULT IN TIMING ISSUES. THE MODELS DO CONTINUE TO WAFFLE AS
EVIDENT BY THE 00Z GFS WHICH SHIFTED ITS LOW TRACK BY A COUPLE
HUNDRED MILES ON MONDAY MORNING. THE 21Z SREF/12Z ECMWF ENSEMBLE
MEANS PRESENT THE BEST MIDDLE GROUND SOLUTION RIGHT NOW BUT WILL
INCORPORATE THE NORTHWARD SHIFTING 00Z GFS INTO THE MIX IF THIS
INDEED A TREND IN THE NORTHERN DIRECTION. THE SOLUTION PRESENTED
HERE DOES CONSIST OF BELOW AVERAGE CONFIDENCE HOWEVER.


...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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