Prognostic Meteorological Discussion
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000
FXUS10 KWNH 271841
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
240 PM EDT MON MAR 27 2017

VALID MAR 27/1200 UTC THRU MAR 31/0000 UTC

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

12Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/CMC AND ECMWF
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...WEAKENING UPPER LOW CROSSING INTO NORTHEAST THROUGH THIS
EVENING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN VERY GOOD AGREEMENT WITH THIS SYSTEM AT THIS
TIME. A GENERAL MODEL COMPROMISE WILL BE PREFERRED.


...NORTHERN STREAM TROUGH CROSSING THE UPPER MIDWEST THROUGH MON...
...ENERGY CROSSING SOUTHEAST CANADA THROUGH TUES/WED...
...UPPER TROUGH OVER THE CNTRL PLAINS WEAKENING INTO THE OH
VALLEY/NORTHEAST MON NIGHT/TUES...
...POSSIBLE SHORTWAVE PHASING OVER NEW ENGLAND BY WED...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PREFERENCE: NON-NAM CONSENSUS...THROUGH 60 HOURS
            BLEND OF THE 12Z GFS AND 12Z UKMET...AFTER 60 HOURS
CONFIDENCE: ABOVE AVERAGE...BECOMING AVERAGE BEYOND 60 HOURS

A NORTHERN STREAM TROUGH EXITING THE NORTHERN PLAINS WILL CROSS
THE UPPER MIDWEST THIS AFTERNOON AND EVENING AND THEN MOVE
DOWNSTREAM ACROSS SOUTHEAST CANADA WHERE IT WILL BEGIN TO AMPLIFY.
MEANWHILE...A SOUTHERN STREAM CLOSED LOW AND ASSOCIATED UPPER
TROUGH APPROACHING THE MID MS VALLEY WILL GRADUALLY WEAKEN THROUGH
THE PERIOD AS IT APPROACHES THE OH VALLEY AND THEN MOVES INTO THE
NORTHEAST. THIS WILL ALLOW SURFACE LOW PRESSURE TO ALSO LIFT
NORTHEAST ACROSS THE AREA.

THE NORTHERN STREAM ENERGY BY TUES AND WED IS EXPECTED TO BECOME
DOMINANT AND THERE IS EXPECTED TO BE A DEEP LAYER LOW CENTER
EVOLVING NEAR NOVA SCOTIA BY EARLY THURS. PREVIOUS MODEL CYCLES
HAD HINTED AT SOME POTENTIAL FOR PHASING NORTHERN AND SOUTHERN
STREAM SHORTWAVES NEAR ENGLAND...WITH PREVIOUS GFS RUNS IN
PARTICULAR DOING THIS...BUT COLLECTIVELY THE MODELS HAVE NOW COME
INTO AGREEMENT ON LITTLE TO NO PHASING AS THE SOUTHERN ENERGY
DAMPENS OUT AND THE SURFACE LOW TRACKS A LITTLE FARTHER SOUTH AND
EAST BEFORE GETTING CAUGHT BY THE STRONGER NORTHERN STREAM ENERGY.

THE 12Z ECMWF CONTINED A TREND THAT HAS SHOWN UP IN RECENT RUNS OF
BECOMING TOO FAST TO EJECT THE WEAKENING TROUGH EASTWARD.  GIVEN
THE CONTINUITY SHOWN BY THE NAM AND THE GFS...WILL CONTINUE TO
RECOMMEND A GENERAL MODEL COMPROMISE EARLY AND THEN SHIFT TOWARDS
A 12Z GFS/UKMET BLEND BY DAY 3.


...WEAKER NORTHERN STREAM TROUGH OVER THE NORTHWEST MON/TUES...
...STRONG CLOSED LOW EVOLUTION INTO THE SOUTHWEST MON/TUES...
...EJECTING INTO THE CNTRL/SOUTHERN PLAINS WED/THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF
CONFIDENCE: AVERAGE

TODAY THROUGH TUES...THE MODELS ARE IN VERY GOOD AGREEMENT WITH
THE DEVELOPMENT OF A RATHER STRONG UPPER TROUGH AND ASSOCIATED
CLOSED LOW THAT WILL DROP DOWN THROUGH THE SOUTHWEST AND INTO THE
FOUR CORNERS REGION. THE HEIGHT FALLS WILL BE ENCROACHING ON THE
SOUTHERN HIGH PLAINS BY WED AND THEN THE LOWER MS VALLEY ON THURS
ALONG WITH A WELL-DEFINED LOW PRESSURE CENTER. MEANWHILE...THE
MODELS SHOW A WEAKER NORTHERN STREAM COMPONENT OF THE ORIGINAL
TROUGH CROSSING THE NORTHWEST U.S. AND EJECTING OUT INTO THE
NORTHERN HIGH PLAINS BY TUES AND WED.

THE 12Z RUN OF THE NAM SPED UP COMPARED WITH ITS PREVIOUS RUNS AND
WAS IN BETTER AGREEMENT WITH OTHER MODELS RELATIVE TO ITS
LONGITUDINAL PLACEMENT.  EVEN SO...WITH HELD MORE ENERGY ON THE
SOUTH END OF THE CLOSED LOW WHICH RESULTED IN A MORE OBLONG SHAPE
WHICH EXTENDS SOUTH OF OTHER MODELS ACROSS TX.  THE 12Z GFS AT THE
SURFACE AND ALOFT WAS NOT QUITE AS DEEP AS IT WAS WITH THE MID
LEVEL CLOSED LOW AND THE ASSOCIATED SURFACE FEATURES AS IT WAS IN
EARLIER RUNS.  ACCOUNTING FOR SOME OF THE MODEL SPREAD AND THE
SMALLER SCALE DETAILS...THE 00Z ECMWF STILL APPEARS TO BE A VIABLE
OPTION AND IT REMAINED CLOSE TO THE MODEL CONSENSUS.


...COLD FRONT WEAKENING INTO BRITISH COLUMBIA ON TUES...
...ONSHORE FLOW INTO THE PACIFIC NORTHWEST THROUGH TUES NIGHT...
...LOW PRESSURE ENTERING BRITISH COLUMBIA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF
CONFIDENCE: AVERAGE

RELATIVELY MODEST SPREAD IS NOTED WITH THIS NEXT SYSTEM...BUT
GENERALLY THE STRONGER MODEL CLUSTERING RESIDES WITH THE 12Z UKMET
AND 12Z ECMWF. GIVEN FAIRLY GOOD RUN TO RUN CONTINUITY WITH THE
NAM...IT STILL FALLS ON THE SOMEWHAT FASTER SIDE OF THE ENVELOPE
OF SOLNS.  ON THE OTHER SIDE OF THE COIN...THE 00Z CMC APPEARS A
TAD TOO SLOW. WILL TO FAVOR A BLEND OF THE UKMET/ECMWF SOLUTIONS.


...SHORTWAVE/SURFACE LOW NEAR THE PACIFIC NORTHWEST BY WED...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM AND 12Z GEFS MEAN
CONFIDENCE: BELOW AVERAGE

THE 12Z GFS CONTINUED ITS TREND TOWARDS A MORE AMPLIFIED SOLUTION
WITH A MID LEVEL SHORTWAVE AND THE ATTNEDANT SURFACE LOW.  IT AND
THE 12Z CANADIAN FORM A CLOSED MID LEVEL LOW BY THE END OF DAY 3.
THE 12Z UKMET AND 12Z NAM SPLIT THE DIFFERENCE...WITH THE NAM
SOMEWHAT STRONGER COMPARED TO THE UKMET. GIVEN THAT THE LATEST
GEFS MEAN AND EC ENSEMBLE MEAN STILL FAVOR A SLOWER SOLN...WE WILL
CONTINUE TO GIVE THE NOD TO THE 12Z NAM AND THE MOST RECENT GEFS
MEAN. CONFIDENCE IS LIMITED.


...VIGOROUS TROUGH DIGGING INTO THE WEST ON THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS AGREE IN DIGGING A STRONG UPPER TROUGH INTO THE WESTERN
U.S. ON THURS. THE MODELS ARE ACTUALLY WELL CLUSTERED WITH TIMING
AND DEPTH THROUGH EARLY THURS WITH EXCEPTION TO THE 12Z UKMET
WHICH IS STRONGER.  A NON-UKMET CONSENSUS WILL BE PREFERRED AT
THIS TIME.


www.wpc.ncep.noaa.gov/html/model2.shtml...

www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

BANN

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