Prognostic Meteorological Discussion
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000
FXUS10 KWNH 281659
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1258 PM EDT FRI APR 28 2017

VALID APR 28/1200 UTC THRU MAY 02/0000 UTC

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

12Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...COLD FRONT CLEARING THE NORTHEAST EARLY FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

ONLY VERY MODEST MASS FIELD SPREAD IS NOTED WITH THIS SYSTEM. A
GENERAL MODEL BLEND SHOULD SUFFICE.


...UPPER LOW OVER SOUTHERN ALBERTA MOVING SLOWLY EAST ACROSS
SASKATCHEWAN BY SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

ONLY MINOR TIMING/DEPTH DIFFERENCES WITHIN THE MODELS WERE NOTED
WITH THIS SYSTEM AS IT SLOWLY MOVES EAST INTO SASKATCHEWAN BY
SAT...BUT THE MODELS AGREE IN DAMPENING THE ENERGY OUT BY SUN. NO
SIGNIFICANT TRENDS WERE NOTED IN THE 12Z NAM/GFS COMPARED TO
PREVIOUS RUNS...UNTIL PERHAPS MUCH LATER IN THE FORECAST PERIOD AS
THE ENERGY IS SHEARING EAST ACROSS NRN ONTARIO. A GENERAL MODEL
BLEND IS PREFERRED.


...INITIAL TROUGH/HEIGHT FALLS OVER THE HIGH PLAINS TODAY WITH
WEAKENING SURFACE LOW TRACKING EAST FROM KANSAS THIS MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z CMC BLEND
CONFIDENCE: ABOVE AVERAGE

THE 00Z CMC STANDS OUT WITH A MUCH STRONGER SURFACE LOW...RELATIVE
TO THE OTHER MODELS...THROUGH 00Z INTO THE KS/MO BORDER TONIGHT.
THE 00Z CMC IS ALREADY 3-4 MB STRONGER WITH THE SURFACE LOW
COMPARED TO 15Z OBSERVATIONS AND IS LIKELY OVER DEVELOPED WITH
THIS FEATURE GIVEN ITS STRONGER MID-LEVEL REFLECTION. THIS FEATURE
BECOMES INDISTINGUISHABLE BEYOND ABOUT 06Z TONIGHT. THE REMAINING
DETERMINISTIC/ENSEMBLE GUIDANCE SHOWS SIMILARLY WITH THIS FEATURE.


...AMPLIFYING TROUGH OVER THE INTERMOUNTAIN WEST...
...CLOSED LOW DEVELOPMENT OVER THE FOUR CORNERS REGION FRI/SAT...
...SYSTEM EJECTING ACROSS THE PLAINS/MIDWEST THROUGH SUN/MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NEAR THE 00Z ECMWF BEAN
CONFIDENCE: AVERAGE

THE ECMWF/CMC HAVE BEEN MORE CONSISTENT WITH THE TIMING OF THE
UPPER LOW AS IT REACHES THE PLAINS SUN MORNING BUT THE 00Z
ECMWF/CMC ARE SOUTH OF THE REMAINING GUIDANCE. THE GFS HAS BEEN
SOMEWHAT INCONSISTENT FROM RUN TO RUN AND THE 12Z GFS HAS ADJUSTED
NORTH...AND LIES ON THE NRN EDGE OF THE LATEST ENSEMBLE SPREAD.
TRENDS IN THE ENSEMBLES HAVE SHOWN A SLOWER SHIFT TOWARD THE SOUTH
ON SUN ACROSS THE CNTRL PLAINS WITH THE 500 MB LOW BUT THE 00Z
ECMWF APPEARS TO BE ON THE SRN EDGE OF THE LATEST ENSEMBLE
GUIDANCE.

THERE IS GROWING CONVERGENCE ON THE TIMING OF THE CLOSED LOW
EJECTING OUT THROUGH THE PLAINS INTO THE UPPER MIDWEST WITH EACH
ENSEMBLE CYCLE BUT THE ECMWF MEAN APPEARS TO BE THE MOST
CONSISTENT AND REPRESENTS THE BEST CLUSTERING OF THE LATEST
ECMWF/GEFS/CMC MEMBERS. THE 00Z ECMWF MEAN LIES BETWEEN THE
SOMEWHAT SLOWER 00Z ECMWF AND THE FARTHER NORTH 12Z GFS POSITION.


...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC
NORTHWEST SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE 00Z UKMET REMAINS SLIGHTLY SLOWER WITH THE PROGRESSION OF THE
UPPER TROUGH AND SURFACE LOW TROUGH SWRN CANADA BUT DIFFERENCES
ARE MINOR HERE AND ALMOST NON-EXISTENT ACROSS THE PACIFIC
NORTHWEST.


WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/

OTTO

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