Prognostic Meteorological Discussion
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000
FXUS10 KWNH 240643
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
242 AM EDT WED MAY 24 2017

VALID MAY 24/0000 UTC THRU MAY 27/1200 UTC

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

00Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...CLOSED UPPER LOW OVER THE UPPER MIDWEST DIGGING ACROSS THE
MIDDLE/LOWER MS VALLEY LATE WED...MOVING TO THE EAST COAST
THU...EXITING NEW ENGLAND FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 0Z GFS/NAM/ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

OVERALL MODELS ARE IN PRETTY GOOD AGREEMENT WITH THE EVOLUTION OF
THIS SYSTEM AS IT PUSHES ACROSS THE EASTERN PORTION OF THE
COUNTRY. THE 12Z GEM APPEARS A BIT DEEPER THAN THE CONSENSUS WITH
THE SURFACE AND MID LEVEL LOW OVER THE MID ATLANTIC BY 0Z FRIDAY
AND APPEARS TO REPRESENT A LESS LIKELY OUTCOME. ALSO NOTE THAT THE
12Z UKMET BECOMES A BIT STRONGER WITH THE MID LEVEL LOW BY 12Z
FRIDAY...RESULTING IN A SLIGHTLY SLOWER NORTHEASTWARD PROGRESSION
OF THE SYSTEM. FOR NOW PREFER TO STICK CLOSER TO A BLEND OF THE 0Z
GFS/NAM AND 12Z ECMWF...WHICH ALL SEEM TO REPRESENT PLAUSIBLE
SOLUTIONS AND ARE GENERALLY PRETTY CLOSE TO EACH OTHER.

FINAL UPDATE: THE 0Z GEM AND UKMET STILL HANDLE THE DEEP LAYERED
LOW MOVING UP THE EAST COAST A BIT DIFFERENTLY THAN THE
GFS/NAM/ECMWF CLUSTER.


...UPPER TROUGH MOVING ACROSS THE NORTHWEST THROUGH MID WEEK...
...DEVELOPING LONGWAVE TROUGH OVER THE WEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE

A CLOSED DEEP LAYER LOW WILL MOVE ACROSS ALBERTA TODAY AND INTO
SASKATCHEWAN THURSDAY...WITH THIS SYSTEM HELPING TO CARVE OUT A
LONGWAVE TROUGH OVER OVER THE WEST THROUGH THE WEEK. THIS PROCESS
WILL BE AIDED BY SHORTWAVE ENERGY DIVING SOUTHEAST ALONG THE
PERIPHERY OF THE CLOSED LOW INTO THE PACIFIC NORTHWEST AND
INTERMOUNTAIN WEST INTO FRIDAY. THIS ENERGY WILL EJECT EASTWARD
TOWARDS THE WESTERN PLAINS BY EARLY SATURDAY...WITH SURFACE LOW
DEVELOPMENT POSSIBLE OVER THE SOUTHERN/CENTRAL PLAINS BY 12Z
SATURDAY.

MODELS ARE GENERALLY IN PRETTY CLOSE AGREEMENT WITH THE CLOSED LOW
AS IT MOVES ACROSS SOUTHERN CANADA...HOWEVER BEGIN TO SEE SOME
DIFFERENCES DEVELOP AS EARLY AS 12Z THURSDAY WITH THE SHORTWAVE
ENERGY DROPPING SOUTH INTO THE PACIFIC NORTHWEST. THESE
DIFFERENCES PERSIST...SO THAT BY 12Z SATURDAY THE LOCATION AND
DEPTH OF THE TROUGH AXIS OVER THE INTERMOUNTAIN WEST/ROCKIES
DIFFERS BETWEEN MODEL SOLUTIONS...WHICH IN TURN IMPACTS THE
LATITUDE AND STRENGTH OF THE DEVELOPING PLAINS SURFACE LOW.

THE 0Z GFS ENDS UP A BIT QUICKER AND STRONGER WITH THE ENERGY AS
IT MOVES INTO WY/CO BY 0Z SAT...WITH THE 12Z ECMWF SLOWER AND MORE
STRUNG OUT. THUS THE MID LEVEL FLOW ENDS UP A BIT MORE AMPLIFIED
IN THE GFS COMPARED TO THE ECMWF. NOTHING REALLY STANDS OUT IN
MODEL TRENDS OR THE ENSEMBLE DATA TO PREFER ONE SOLUTION OVER
ANOTHER AT THIS POINT. THE NAM/UKMET/GEFS ARE CLOSER TO THE GFS
SOLUTION AND THE GEM/EC MEAN CLOSER TO THE ECMWF. THUS FOR NOW
WOULD PREFER TO JUST GO DOWN THE MIDDLE AND STAY PRETTY CLOSE TO A
GENERAL MODEL BLEND THROUGH 12Z SATURDAY.

FINAL UPDATE: SOME MODEL DIFFERENCES STILL EXIST...WITH THE 0Z
ECMWF/GEM GENERALLY SIDING A BIT CLOSER TO THE ECMWF SOLUTION.
OVERALL DIFFERENCES ARE NOT TOO SIGNIFICANT THROUGH 12Z
SATURDAY...AND GIVEN LACK OF A CLEAR TREND...WILL CONTINUE
RECOMMENDING A GENERAL MODEL BLEND.

...SUBTLE SHORTWAVE ENERGY AND POSSIBLE SURFACE LOW MOVING EAST
FROM THE MS VALLEY INTO THE OH VALLEY FRIDAY INTO SATURDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON NAM BLEND
CONFIDENCE: AVERAGE

MODELS ALL SHOW SOME WEAK SHORTWAVE ENERGY MOVING EAST IN ZONAL
FLOW ACROSS THE OH VALLEY SOMETIME FRIDAY INTO SATURDAY...WITH A
POSSIBLE SURFACE LOW REFLECTION AS WELL. THE 0Z NAM APPEARS TO BE
SUFFERING FROM SOME CONVECTIVE FEEDBACK ISSUES RESULTING IN A
FURTHER NORTH LOW BY 0Z SATURDAY. THE 12Z GEM ALSO APPEARS TOO FAR
NORTH. THE GFS HAS CONSISTENTLY BEEN QUICKER AND GENERALLY WEAKER
THAN THE OTHER GUIDANCE WITH THIS FEATURE. THIS MAY IN PART BE DUE
TO A SLIGHTLY STRONGER SHORTWAVE MOVING ACROSS THE DAKOTAS AT 0Z
FRI HELPING KICK THE SOUTEHRN WAVE EAST QUICKER. WHILE NOT
IMPOSSIBLE...WILL LEAN AGAINST THIS FOR NOW SINCE ALL THE OTHER
DETERMINISTIC GUIDANCE ARE AGAINST IT. THE ECMWF/UKMET ARE THE TWO
PIECES OF GUIDANCE THAT APPEAR TO FIT MORE IN THE CENTER OF THE
MODEL SPREAD WITH REGARDS TO BOTH THE TIMING AND LATITUDE OF THE
WAVE/LOW.

FINAL UPDATE: THE ECMWF/UKMET/GEM DID SPEED UP A BIT WITH THIS
WAVE/LOW...ALTHOUGH ARE STILL SLOWER THAN THE GFS. HOWEVER THE GFS
NO LONGER APPEARS TO BE AS BIG OF AN OUTLIER AND CAN THUS INCLUDE
IT BACK INTO OUR PREFERENCES. WOULD LEAN TOWARDS THE FURTHER SOUTH
ECMWF SOLUTION...BUT THE UKMET/GEM EVOLUTIONS ARE STILL PLAUSIBLE
(ALTHOUGH SOME CONVECTIVE FEEDBACK MAY BE PUSHING UKMET/GEM QPF
FIELDS TOO FAR NORTH). THUS A NON NAM BLEND SHOULD BE OKAY.

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

CHENARD

$$





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