Prognostic Meteorological Discussion
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000
FXUS10 KWNH 271934
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
233 PM 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 MODEL EVALUATION AND PREFERENCES
===============================================
THE NAM INITIALIZED WITH 500 MB HEIGHTS ROUGHLY
10 TO 20 METERS TOO LOW/COLD ACROSS MUCH OF THE
WESTERN U.S.
===============================================

...CORRECTED THE TIME STAMPS ON MODEL PREFERENCES...
...THE 12Z UKMET WAS UNAVAILABLE...
...THE 12Z CANADIAN WAS AVAILABLE ONLINE...

BROAD TROUGH / JET AFFECTING THE NORTHERN AND EASTERN U.S.
WITH ASSOCIATED ARCTIC FRONT AND MODEST GULF RETURN FLOW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z ECMWF/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. IN THE
NORTHERN STREAM THIS MEANS A TROUGH SHARPENING OVER THE PACIFIC
NORTHWEST AND THEN EXPANDING EASTWARD. AN ARCTIC COLD FRONT WILL
ACCOMPANY THE TROUGH. THE MODELS AGREE TO THESE SIMPLE
CONCEPTS...BUT VARY IN AMPLITUDE AND TIMING. GENERALLY...THE ECMWF
HAS BEEN A LITTLE SLOWER THAN CONSENSUS...BUT THE 12Z RUN TRENDED
SLIGHTLY FASTER. THIS PLACES ALL THE MODELS IN GOOD AGREEMENT
THROUGH DAY 2...AFTER WHICH THE NAM BECOMES DEEPER ALOFT AND THE
GFS RACES OUT AHEAD OF THE PACK. THE UKMET IS A LITTLE WEAK WITH
THE ARCTIC FRONT...WHEREAS THE ECMWF DEPICTS WHAT SEEMS LIKE A
MORE REALISTIC SURGE THROUGH THE HIGH PLAINS ON WESTERN KANSAS
SUNDAY. THE NAM ALSO DEPICTS THIS SURGE...BUT IS LESS PREFERRED
ALOFT. OVERALL...THE ECMWF/CANADIAN CONTINUE TO BEST REPRESENT THE
CONSENSUS AND THE TRENDS...KEEPING WITH THE OVERNIGHT PREFERENCE.


SHORTWAVE APPROACHING CALIFORNIA SAT NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z ECMWF/CANADIAN WITH 00Z UKMET

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 QUICKER 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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