Prognostic Meteorological Discussion
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FXUS10 KWNH 221644
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1244 PM EDT SAT APR 22 2017

VALID APR 22/1200 UTC THRU APR 26/0000 UTC

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

12Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE INTERVALS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

TROF SWEEPING THROUGH NORTHEAST TODAY/CAPE COD AND CANADIAN
MARITIME LOW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE 12Z NAM HAS TRENDED A BIT SLOWER THAN THE 06Z RUN AND MATCHES
THE TIGHT CLUSTERING WITH THE TROF AND DEVELOPING SURFACE LOW OFF
CAPE COD THROUGH  TONIGHT WITH ONLY SMALLER DEPARTURES OF THE NAM
WELL EAST OF NOVA SCOTIA BY 00Z MON.  AS SUCH A GENERAL MODEL
BLEND CAN BE SUPPORTED AT ABOVE AVERAGE CONFIDENCE.


DEEP CYCLONE IN THE SOUTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z NAM REMAINS ON THE NORTHERN SIDE OF THE GUIDANCE WITH THE
CLOSED UPPER LOW CENTER PREFERRING A SHALLOWER OVERALL TROF
ALLOWING FOR THE SURFACE LOW TO LIFT ASHORE ACROSS THE CAROLINAS
TOWARD THE END OF THE PERIOD.  WHILE THIS APPEARS A LARGE
DEPARTURE FROM THE OTHERWISE MUCH TIGHTER CLUSTER CENTERED NEAR
THE 12Z GFS AND 00Z UKMET/ECMWF (INCLUDING THE GEFS/ECENS
MEANS)...THERE IS SOME PAUSE TO COMPLETELY REJECT IT OUTRIGHT
GIVEN THIS HAS BEEN A TREND OF THE NAM THROUGHOUT THE WINTER
(FURTHER NORTH) THAT HAS VERIFIED A BIT BETTER THAN THE GFS/ECMWF.
 ADDITIONALLY WITH THE 12Z GFS DID TREND THIS DIRECTION TOO BUT
DID NOT SHIFT AS FAR AS THE NAM ONLY MATCHING THE 00Z ECMWF BETTER
OVERALL.  STILL IT BARES WATCHING AND INCLUSION WITHIN THE BLEND
AS A WHOLE FOR THE NAM.

THE 00Z CMC ON THE OTHER HAND GIVEN THE PATTERN AND LIKELIHOOD FOR
A MORE PROGRESSIVE SHORTWAVE OUT OF THE FL STRAITS PRECEDING
IT...IS LESS FAVORED BEING QUITE SLOW ROUNDING THE CURVE THROUGH
THE SOUTHEAST TUESDAY... AS SUCH WILL REJECT IT AND SUPPORT A
GENERAL.  CONFIDENCE IS SLIGHTLY ABOVE AVERAGE IN THIS BLEND GIVEN
THE POINT ABOUT THE NAM AND STILL SOME MODEST SPREAD IN ENSEMBLES
ON TUESDAY INTO WED MAINLY IN TIMING.


DEEP CANADIAN UPPER LOW CLIPPING THE NORTHERN TIER WITH A
FLATTENING SURFACE FRONT TONIGHT...GLANCING BLOW TO N MAINE EARLY
MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

MASS FIELDS SHOW REMARKABLY STRONG AGREEMENT WITH TIMING/STRENGTH
AND PLACEMENT OF THE UPPER LOW SWINGING THROUGH S HUDSON BAY/JAMES
BAY WITH INFLUENCES TO WEAK SURFACE BOUNDARIES ACROSS NE ND/N MN
TONIGHT BEFORE RETURNING AS A WEAK WARM FRONT (SEE SECTION BELOW)
ON MON...AS WELL AS CLIPPING N NH/N ME BY MIDDAY MON.  EVEN WITH
THE STRONG MASS AGREEMENTS THERE REMAINS SOME DISCREPANCY IN THE
QPF/SNOWFALL.  SO PLEASE REFER TO THE QPFPFD AND QPFHSD
DISCUSSIONS AS WELL AS GRAPHICAL PRODUCTS ON THE WEB FOR THOSE
PREFERENCES.


SHORTWAVE CROSSING N CA AND CENTRAL ROCKIES EARLY MONDAY SPURRING
LEE SFC LOW THAT MARCHES FROM MT/N WY TOWARD MN MON TO LATE TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

SHORTWAVE AND ASSOCIATED SURFACE WAVE LIFTING ACROSS PACIFIC
NORTHWEST TODAY REMAINS IN STRONG AGREEMENT BEFORE IT RAPIDLY
WEAKENS THROUGH THE RIDGE AND INTO THE CONFLUENT FLOW OF SOUTH
CENTRAL CANADIAN ON THE UPSTREAM SIDE OF THE DOMINANT DEEP
CANADIAN UPPER LOW.  STILL THE FEATURE IS THERE TO PROVIDE SOME
INFLUENCES TO THE MAIN HEIGHT FALLS APPROACHING OUT N CA AND
INTERMOUNTAIN WEST LATE SUNDAY.  THIS SHORTWAVE APPEARS FAIRLY
WELL HANDLED IN THE GUIDANCE EVEN THOUGH IT IS SMALL AND THERE IS
FAIRLY COMPLEX INTERACTION WITH SMALLER FEATURES IN THE TROF
CROSSING THROUGH THE LARGER SCALE RIDGING OVER THE ROCKIES.  THIS
LEADS TO SOME MODERATE DIFFERENCES LOCALLY BUT AT THE SYNOPTIC TO
MESO-ALPHA SCALE SEEM FAIRLY AGREEABLE ESPECIALLY WITH THE
PLACEMENT/STRENGTH AND TRACK OF THE SURFACE WAVE FROM W MT 12Z SUN
THRU  N WY TO CENTRAL SD BY 12Z MON.  AS THE SHORTWAVE EJECTS OUT
OF THE WY ROCKIES...THE WEAK INFLUENCE OF THE SHORTWAVE IN CANADA
ALLOWS FOR WEAK NEGATIVE TILT TO MAINTAIN THE SURFACE WAVE INTO
MN/NW WI BY EARLY TUESDAY.  THE 00Z UKMET IS A BIT NORTH AND WEST
OF THE CLUSTER AND A BIT DEEPER...WHILE THE CMC IS FLATTER AND
FURTHER SOUTH.  THE 12Z NAM HAS TRENDED TOWARD BETTER AGREEMENT
WITH THE TIGHTER/CENTRALIZED GFS/ECMWF SOLUTIONS.  OVERALL THE
SPREAD IS MINOR TO SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE
CONFIDENCE...HOWEVER WOULD FAVOR A GFS/ECMWF HIGHER WEIGHTING
GIVEN CONTINUITY AND CENTRAL POSITION THROUGHOUT THE DEPTH OF THE
SYSTEM.


BINARY INTERACTION OF STALLED UPPER LOW OFF VANCOUVER ISLAND AND
FAST MOVING PACIFIC SHORTWAVE THAT ENTERS THE PACIFIC NORTHWEST
MIDDAY MONDAY LEADING TO BROAD BUT DEEP TROF EXITING THE NORTHERN
ROCKIES TUESDAY EVENING WITH DEEP SURFACE LOW NEAR OK PANHANDLE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/UKMET AND 06Z GFS BLEND
CONFIDENCE: AVERAGE

INITIAL SETUP DENOTES ELONGATED UPPER LEVEL TROF ON WV EXTENDING
TOWARD VANCOUVER ISLAND...AS THE EASTERN PORTION OF THE TROF
BREAKS AWAY TO THE NORTHEAST (SEE SECTION ABOVE) THE CENTRAL
PORTION OF THE TROF CLOSES OFF AND SLOWLY SHIFTS EAST SUNDAY JUST
SOUTH OF 50N.  BY LATE SUN INTO EARLY MON A STRONG SHORTWAVE
ACCELERATES EAST UNDERCUTTING THE UPPER LOW SPURRING A SURFACE
CYCLONE TO IMPACT THE OPENING TO THE COLUMBIA RIVER MONDAY.   THE
12Z GFS LAGS THE OTHERWISE TIGHT CLUSTERING WHILE THE 00Z UKMET IS
A BIT NORTH...BUT OVERALL THIS APPEARS MINOR AND A GENERAL MODEL
BLEND IS SUFFICIENT THROUGH 25/00Z.

AFTERWARD...THE UNDERCUTTING SHORTWAVE CONTINUES TO RAPIDLY CROSS
THROUGH THE GREAT BASIN AND WY ROCKIES AND EVENTUALLY INTO THE
GREAT PLAINS SPURRING A LARGE BUT MODESTLY DEEP SURFACE LOW ACROSS
E CO/SW KS/OK PANHANDLE BY THE END OF THE FORECAST PERIOD.
HOWEVER...GIVEN PROXIMITY TO THE FORMER CLOSED LOW...THE BINARY
INTERACTION IS STRONG ENOUGH TO DRAW THE REMAINING UPPER LOW
ENERGY/SHORTWAVE SOUTHEAST INTO THE GREAT BASIN/SNAKE RIVER PLAIN
BY LATE TUESDAY....LEADING TO A LARGE AMPLIFYING BUT BROAD TROF
STRETCHING FROM THE INTERMOUNTAIN WEST TO THE CENTRAL PLAINS.
GIVEN THE SMALLER SCALE NATURE OF THE INTERACTION AND DEPENDENCE
ON TIMING THERE IS FAIRLY LARGE SPREAD IN OPERATIONAL GUIDANCE.

THE 12Z NAM CONTINUES TO BE VERY ROBUST WITH THE UPPER LOW
SHORTWAVE AND SUPPORTS A DEEP TROF ACROSS THE INTERMOUNTAIN WEST
AS FAR SOUTH AS THE FOUR CORNERS WITH A MILDER/FLATTER SWLY FLOW
REGIME ACROSS THE CENTRAL PLAINS TO UPPER MS RIVER VALLEY BY THE
END OF THE FORECAST PERIOD.  THE 12Z GFS...TRENDED A BIT FASTER
WITH THE LEAD WAVE (A TYPICAL NEGATIVE BIAS) ALLOWING FOR A MORE
LIMITED BINARY INTERACTION AND SLOWER SOUTHEASTWARD PROGRESSION OF
THE REMAINING UPPER LOW FEATURE...BREAKING FROM ITS BETTER
CONTINUITY AND CLOSER SPACED APPROACH...AS NOTED IN THE 06Z GFS
AND GEFS MEAN.  THE 00Z ECMWF IS QUITE THE OPPOSITE OF THE 12Z
NAM...FAVORING THE LEAD WAVE AND NEARLY WEAKENING THE UPPER LOW
CROSSING THE ROCKIES BUT ALSO IS A BIT MORE MODERATE IN TIMING
THAN THE FASTER GFS INTO THE MID-MO RIVER.  WHILE NOT EVOLVING THE
SAME AS THE ECWMF THE 00Z UKMET IS FAVORABLE TO THE ECMWF AND THE
06Z GFS.  AS SUCH WILL FAVOR THE 00Z ECMWF/UKMET AND INCLUDE SOME
06Z GFS.  GIVEN THE MOVING PARTS/INFLUENCE OF BINARY INTERACTION
CONFIDENCE IS ONLY AVERAGE IN THIS BLEND.


APPROACH OF NEXT SHORTWAVE/CLOSED LOW NEARING VANCOUVER ISLAND
LATE TUES INTO WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE PARADE OF SHORTWAVES CONTINUES INTO TUESDAY AS MORE ENERGY
CROSSES THROUGH THE WEAK GLOBAL MEAN RIDGE AROUND 140 AND SLIDES
UNDER THE BLOCKING HIGH IN NORTHERN BC.  THE CLEAR OUTLIER IS THE
00Z UKMET FAVORS PUMPING THE RIDGE IN ADVANCE OF THE NEXT
SHORTWAVE CLEARLY AWAY FROM NEARLY ALL ENSEMBLE GUIDANCE MEMBERS.
THE 00Z ECMWF IS UNCHARACTERISTICALLY FAST WITH ITS FEATURE AND
CLOSES OFF THE 540 DM LINE BY 00Z WED...THIS MATCHES THE MEAN
ECENS LOCATION BUT GIVEN THE EAST-WEST SPREAD REMAINING THERE IS
SOME LACK OF CONFIDENCE OVERALL.  THE 12Z GFS WHILE NOT AS FAR
EAST IS QUITE STRONG THOUGH NOT FULLY CLOSED AT 540...AND APPEARS
TO BE VACILLATING BETWEEN FASTER AND SLOWER/DEEPER SOLUTIONS OVER
THE LAST FEW ITERATIONS.  THE 00Z CMC AND 12Z NAM ARE MUCH SLOWER
AND SUPPORT A FURTHER NORTH SOLUTION.  GIVEN THE OVERALL ENSEMBLE
SPREAD AND CREDENCE TO THE HIGHER PERFORMING GUIDANCE WILL PREFER
A 12Z GFS/00Z ECMWF BLEND TO BEST REPRESENT THE ENSEMBLE
SOLUTIONS.  CONFIDENCE IS SLIGHTLY BELOW AVERAGE GIVEN SAID
SPREAD.


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

GALLINA

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