Prognostic Meteorological Discussion
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FXUS10 KWNH 271643
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1140 AM EST THU NOV 27 2014

VALID NOV 27/1200 UTC THRU DEC 01/0000 UTC

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

==================================================
12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES
==================================================
THE NAM INITIALIZED WITH 500 MB HEIGHTS ROUGHLY
10 TO 20 METERS TOO LOW/COLD ACROSS MUCH OF THE
WESTERN U.S.
==================================================

BROAD TROUGH / JET AFFECTING THE NORTHERN AND EASTERN U.S.
WITH ASSOCIATED ARCTIC FRONT AND MODEST GULF RETURN FLOW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 00Z ECMWF/UKMET/CANADIAN

MODEL TRENDS AND PATTERN RECOGNITION SUGGEST THAT THROUGH SATURDAY
FLOW SHOULD AMPLIFY IN BOTH THE NORTHERN AND SOUTHERN STREAMS
ACROSS THE EASTERN PACIFIC AND WESTERN NORTH AMERICA. THE NCEP
GUIDANCE...GFS/NAM...ARE NOT AMPLIFYING THE PATTERN AS SHARPLY AS
WOULD BE PREFERRED WHEN VIEWING THEIR MID AND UPPER LEVEL
SOLUTIONS. DIFFERENCES BETWEEN THE OPERATIONAL MODELS ARE LESS
PRONOUNCED IN THE LOWER LEVELS UNTIL DAY 3...SATURDAY NIGHT AND
SUNDAY...WHEN THE NAM/GFS ARE CONSIDERABLY FASTER WITH THE ARCTIC
FRONT SWEEPING THROUGH THE CENTRAL/EASTERN U.S. WHILE THESE MODELS
ARE THOUGHT TO BE TOO FAST BASED UPON THE UPPER PATTERN...IT IS
COMMON LEAN ON FASTER SOLUTIONS WHEN ARCTIC AIR IS
INVOLVED...ESPECIALLY OVER THE PLAINS. FOR THIS REASON...WE
RECOMMEND BLENDING THE ECMWF...AND ITS APPROPRIATELY AMPLIFIED
UPPER PATTERN...WITH THE UKMET AND CANADIAN...WHICH REPRESENT A
NICE MIDDLE GROUND IN THE LOW LEVELS. THE UKMET IS INCLUDED
HERE...ALTHOUGH IT PROBABLY DOES LEAVE TOO MUCH MID LEVEL
TROUGHING BACK OVER THE PACIFIC NORTHWEST ON DAY 3.


SHORTWAVE APPROACHING CALIFORNIA SAT NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 00Z ECMWF/UKMET/CANADIAN

THE GLOBAL MODELS ARE QUITE SIMILAR OFFSHORE OF CALIFORNIA IN THE
SHORT TERM. THEY ALL BRING A LOW AMPLITUDE SHORTWAVE TROUGH OUT
AHEAD OF THE DEEP LOW THAT WILL FORM SOME 800 MILES WEST OF
CALIFORNIA. THE GFS DISSIPATES THE STRENGTH OF THE LEAD SHORTWAVE
RATHER ABRUPTLY AS IT COMES ONSHORE SATURDAY NIGHT. MORE GENERALLY
THE GFS MOVES OUT OF PHASE WITH THE OTHER MODELS...IN PART DUE TO
A QUICKER/LESS AMPLIFIED SOLUTION FOR THE DEEP LOW...AND LESSER
GRADIENTS IN PLACE OVER THE PACIFIC NORTHWEST. GIVEN THAT THESE
DIFFERENCES RESULT IN SOME SIGNIFICANT PRECIPITATION
DIFFERENCES...WE PREFER THE ECMWF/UKMET/CANADIAN...WHICH ARE MORE
IN LINE WITH PREVIOUS FORECASTS AND WITH THE OVERALL CONSENSUS. WE
WERE MORE QUICK TO DISCOUNT THE NAM...AS IT QUICKLY MOVES OUT OF
PHASE WITH CONSENSUS REGARDING EACH INDIVIDUAL SHORTWAVE IN THE
EASTERN PACIFIC.


UPPER LEVEL TROUGH MOVING THROUGH NORTHERN MEXICO
TROUGH MOVING THROUGH AND LIFTING OUT OF THE EAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: ANY OF THE OPERATIONAL MODELS

THE GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE CONSOLIDATING
NEGATIVELY TILTED TROUGH MOVING THROUGH THE NORTHEAST AND GOOD
AGREEMENT WITH THE SHORTWAVE MOVING THROUGH NORTHERN MEXICO.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

BURKE
$$




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