Prognostic Meteorological Discussion
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000
FXUS10 KWNH 270445
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1145 PM EST MON JAN 26 2015

VALID JAN 27/0000 UTC THRU JAN 30/1200 UTC

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

00Z NAM/GFS MODEL EVALUATION WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


EVOLVING COASTAL STORM ALONG THE NORTHERN MID ATLANTIC/NORTHEAST
MON-WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z EC MEAN OR A 2/3 00Z NAM...1/3 12Z ECMWF COMPROMISE
CONFIDENCE: AVERAGE

THE 12Z ECMWF CONTINUES TO BE TOWARD THE EDGE OF THE ENSEMBLE
SCATTER LOW PLOTS CONSISTING OF 12Z ECMWF/GEFS/CMC MEMBERS. OVER
ITS PAST 3 RUNS...THE DETERMINISTIC ECMWF HAS BEEN TRENDING IN THE
DIRECTION OF THE CENTROID OF ENSEMBLE MEMBERS WHICH IS BEST
REPRESENTED BY THE 12Z EC MEAN OR A BLEND OF THE 00Z NAM AND 12Z
ECMWF. THE 00Z GFS...12Z UKMET...12Z CMC APPEAR TO BE SLIGHTLY
FASTER THAN THE 18Z GEFS AND 21Z SREF MEANS...SO WILL STICK WITH
THE SLOWER EDGE OF THE GUIDANCE. THIS PREFERENCE IS SUPPORTED BY
SHORT TERM FORECASTS MADE UP OF A CONSENSUS OF HI-RES MODEL
GUIDANCE. TOWARD THE SLOWER CAMP ALSO ALIGNS CONCEPTUALLY GIVEN
THE ORIENTATION OF THE SYSTEM ALOFT (NEGATIVE TILT) AND A
SIGNIFICANT UPSTREAM RIDGE NOSING INTO THE CANADIAN MARITIMES.

AS IS ALWAYS THE CASE WITH THESE BIG STORMS...EVEN SMALL DETAIL
DIFFERENCES RESULT IN LARGE IMPACT DIFFERENCES...ESPECIALLY WITH
PRECIPITATION. PREFERENCES LISTED HERE REFLECT MODEL POSITION AND
MASS FIELDS...BUT REFER TO WPC WINTER WEATHER AND QPF DESK
PRODUCTS FOR INFORMATION ON LIQUID EQUIVALENTS/SNOW.


WEAKENING CLOSED LOW MOVING INTO CALIFORNIA EARLY TUE
REMNANT SHORTWAVE PASSING THROUGH THE CENTRAL PLAINS WED AND THE
  OH VALLEY ON THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS...12Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE MODELS HAVE CONVERGED TOWARD ONE ANOTHER THROUGH THU
MORNING...12Z/29...WITH SOME DIVERGENCE AFTERWARD. BEYOND
12Z/29...THE UKMET STRAYS FROM THE PACK WHEN A STRONGER UPPER
TROUGH DIGS THROUGH THE GREAT LAKES...A SOLUTION ON THE EDGE OF
THE ENSEMBLE GUIDANCE. THE 12Z CMC IS SLOWER AND THE NAM IS WEAKER
WITH ENERGY DROPPING SOUTH THROUGH THE UPPER MISSISSIPPI VALLEY
AND IN TURN...WINDS UP FASTER WITH THE VORTICITY MAX MOVING
THROUGH THE OHIO VALLEY. THEREFORE A GFS/ECMWF BLEND IS PREFERRED
WITH THIS SYSTEM AND THE BEGINNING OF POTENTIAL SECONDARY LOW
DEVELOPMENT NEAR THE NEW ENGLAND COAST 12Z/30.


MID-LEVEL SHORTWAVE MOVING INTO BRITISH COLUMBIA EARLY TUE
SUBSEQUENT MOVEMENT INTO THE N-CENTRAL U.S./GREAT LAKES THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS...12Z ECMWF BLEND
CONFIDENCE: AVERAGE

SIMILAR TO THE ABOVE MENTIONED SYSTEM...THE GFS/ECMWF/UKMET SHOW
GOOD AGREEMENT UNTIL LATE THU...AT WHICH POINT THE 12Z UKMET
BECOMES MORE AMPLIFIED WITH AN UPPER TROUGH AMPLIFYING ACROSS THE
UPPER GREAT LAKES. THE GFS/ECMWF SHOW GOOD AGREEMENT WITH SUPPORT
FROM THE ENSEMBLE MEANS...THOUGH THE GFS IS SLIGHTLY FASTER THAN
THE ECMWF.


UPPER TROUGH MOVING INTO THE SOUTHWEST TOWARD THE END OF THE WEEK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS...12Z ECMWF...12Z UKMET BLEND
CONFIDENCE: AVERAGE

THERE IS RELATIVELY MINOR SPREAD IN A SOMEWHAT BROAD UPPER TROUGH
MAKING ITS WAY TOWARD THE WEST COAST. TRENDS SHOW NO REAL PUSH ONE
WAY OR ANOTHER...AND THE MIDDLE OF THE LATEST ENSEMBLE SPAGHETTI
HEIGHTS SUPPORTS A BLEND OF THE GFS/ECMWF/UKMET.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

OTTO

$$




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