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049
FXUS10 KWNH 151625
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1124 AM EST MON JAN 15 2018

VALID JAN 15/1200 UTC THRU JAN 19/0000 UTC

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

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

CLOSED LOW OVER UPPER MIDWEST WITH SURFACE LOW IN LOWER CENTRAL
GREAT LAKES TODAY/TOMORROW...UNFOLDS INTO POSITIVE TILT TROF OVER
OH/TN VALLEYS WED WITH DEVELOPING COASTAL LOW BY NEW ENGLAND WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM AND 00Z ECMWF/UKMET BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE


THE LARGE CLOSED LOW OVER THE WESTERN GREAT LAKES WITH
UNDERCUTTING JET STREAK THROUGH THE MID-MS VALLEY WILL BEGIN TO
UNFOLD INTO A SHARPER POSITIVE TILT TROF BY WED AND STRETCH FROM
THE NORTH ATLANTIC TO ARKANSAS.  HERE MODEL GUIDANCE IS QUITE
AGREEABLE...THE DIFFERENCE ARISES IN WHERE THE ELONGATION OF THE
TROF WANTS TO RECONSOLIDATE/SEVER; WITH A KEY BEING AN ARCTIC S/W
CURRENTLY ENTERING THE TOP OF THE WESTERN RIDE IN THE YUKON.  THE
NCEP GUIDANCE HAS BEEN MORE PROGRESSIVE WITH THIS WAVE EVENTUALLY
LEADING TO A SHARPENING OF THE TROF AND KICKING OF THE WAVE INTO
THE NORTHWEST ATLANTIC.  IN THE PROCESS DEVELOPING A SURFACE WAVE
THAT SKIRTS BY NEW ENGLAND WED INTO THURS.   HOWEVER...THE 12Z NAM
AND GFS BOTH DEPICT A SLIGHT SLOWING OF THIS WAVE ALLOWING FOR
GREATER AMPLIFICATION SOUTH OF JAMES BAY BY 00Z THURS.  THIS
DELAYS THE SURFACE LOW AND TRANSLATION OF THE TROF OFFSHORE.
HOWEVER BOTH ARE STILL MUCH FASTER THAN THE REMAINING NON-NCEP
SUITE.  ALL THREE DEPICT A MUCH SLOWER SOUTHERN STREAM OF THE TROF
THROUGH THE TN VALLEY INTO THE MID-ATLANTIC/CAROLINAS; IN DOING SO
THE VORTICITY STRIP IS ABLE TO CURL/CONSOLIDATE.  THE 00Z CMC GOES
TO THE EXTREME AND BECOMES SYMMETRIC AND DEVELOPS A SECONDARY
SURFACE WAVE THAT RAPIDLY DEEPENS OFF THE MID-ATLANTIC COAST BY
THURSDAY.  THE 00Z ECMWF/ECENS MEAN HAD TRENDED AWAY FROM THIS
SCENARIO UNFOLDING AND WHILE STILL MUCH MORE CONSOLIDATED THAN THE
GFS... THERE IS SOME SHADES OF THE NAM MIDDAY THURS TO HAVE SOME
INDICATION THAT GUIDANCE IS HONING IN ON A COMMON SOLUTION.  THE
00Z UKMET BUILDS CREDENCE TO THIS EVOLUTION...AS A MIDDLE GROUND
TO THE NAM/ECMWF.   AS SUCH A BLEND OF THE 00Z UKMET/ECMWF AND 12Z
NAM IS PREFERRED YET THE RUN TO RUN VARIANCE AND MODEL SPREAD
PROVIDE LOWER THAN AVERAGE CONFIDENCE.


DEEP LAYERED CYCLONE OFF PACIFIC NORTHWEST LIFTS NORTH ALONG
CANADIAN COAST WITH SLOW EASTWARD PUSH OF FRONTAL ZONE INTO THE
WEST EARLY TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

GOES-W WV LOOP SHOWS A BROAD UPPER LOW WITH SPOKES OF OUTER EDGE
S/W VORT CENTERS NEARING THE PACIFIC NW COAST.  THIS DEEP CYCLONE
IS WELL HANDLED BY THE GUIDANCE WHICH SHOWS GOOD SIMILARITY IN
TIMING/PLACEMENT OF THE MAIN FEATURES INCLUDING THE SURFACE
LOW/TRIPLE POINT AND COLD FRONT. THE 12Z NAM JOINED THE 00Z UKMET
SUPPORTING A SLIGHTLY ENHANCED/STRONGER TRIPLE POINT DEVELOPING
ALONG 130W AND LIFTING NORTH...WHILE DEEPER IT CONTINUES TO MATCH
THE TIMING/PLACEMENT IN THE INFLECTION OF THE 12Z GFS/00Z
ECMWF/CMC TO KEEP WITHIN ANY BLEND.   THE MODEL SPREAD INCREASES
AS THE INNER CORE/MAIN ENERGY LIFT AWAY INTO TUES AND THE TAIL END
OF UPPER LOW BEGINS TO SHARPEN INTO A NEGATIVE TILT TROF CROSSING
THE COLUMBIA BASIN INTO SW CANADA...PLEASE SEE SECTION BELOW FOR
FURTHER DETAILS ABOUT ITS INFLUENCE/EVOLUTION THEREAFTER.
OTHERWISE A GENERAL MODEL BLEND CAN BE SUPPORTED AT ABOVE AVERAGE
CONFIDENCE FOR THE DEEP LAYERED LOW AND THE FRONTAL ZONE ENTERING
THE US TUES.


TAIL END OF WESTERN LOW CROSSES US/CANADIAN ROCKIES WED BEFORE
SLIDING THROUGH THE NORTHERN PLAINS/GREAT LAKES THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS AND 00Z ECMWF/UKMET BLEND
CONFIDENCE: AVERAGE

THE SHARPENING TAIL END OF THE DEEP CYCLONE LIFTING OFF THE
CANADIAN COAST WILL REACH THE MEAN RIDGE AXIS OVER THE SOUTHERN
CANADIAN/N US ROCKIES BY EARLY WED...WITH A BULK OF THE VORTICITY
AT THE BASE OF THE TROF TO HELP BREAK DOWN THIS RIDGE.  IN DOING
SO THE WAVE REMAINS CONSOLIDATED AS IT BOWLS THROUGH THE NORTHERN
PLAINS INTO THE GREAT LAKES BY THURSDAY.  THE 00Z CMC IS LEAST
ALIGNED WITHIN THE GUIDANCE SUITE WITH RESPECT TO THE
CONSOLIDATION OF THE VORT CENTER AS IT HITS THE RIDGE...AND AS
SUCH REMAINS MORE STRUNG OUT AND SLIDES THROUGH MUCH FURTHER NORTH
AND IN PIECES; OPPOSED TO THE TRENDS IN THE GUIDANCE.  THE NAM
WHICH HAD PARTNERED WITH THE CMC BUT THE 12Z NAM TRENDED AWAY
`BASE-LOADING` THE TROF AND SO THE WAVE EJECTS MORE CONSOLIDATED.
HOWEVER THE 12Z NAM ALSO REMAINED FURTHER NORTH EMERGING OVER THE
RIDGE INTO CENTRAL CANADA AND NORTH OF THE MAIN CLUSTERING.   THE
12Z GFS CONTINUED ITS TREND OF EJECTING FASTER OUT OF THE
WEST...THIS ALLOWED IT TO KEEP PACE AND GENERAL SHAPE WITH THE 00Z
ECMWF THOUGH REMAINS SLIGHTLY WEAKER/SLOWER THAN THE FASTER UKMET.
 OVERALL A BLEND OF THE 12Z GFS AND 00Z ECMWF ALONG WITH A LOWER
WEIGHTED 00Z UKMET SEEMS APPROPRIATE IN TIMING/STRENGTH AND
LATITUDINAL PLACEMENT TO HAVE AVERAGE CONFIDENCE IN THIS BLEND.


SUBTLE PACIFIC JET/SHORTWAVE ENERGY SLIPS UNDER MEAN RIDGE IN
ROCKIES ON TUES/WED BEFORE AMPLIFYING ACROSS TX/N OLD MEXICO THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM AND 00Z CMC/ECMWF BLEND
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE

AS THE TAIL END OF THE WESTERN LOW CROSSES THE CANADIAN
ROCKIES...KICKER SPEED MAX/SHORTWAVES EMERGE FROM THE PACIFIC FLOW
AND BEGIN TO SLIDE UNDER THE MEAN RIDGE THAT WAS ANCHORED THROUGH
THE CORE OF THE NORTHERN AND NORTH CENTRAL US ROCKIES.  WITH THE
EXIT OF THE MEAN POSITIVE TILT TROF DOWNSTREAM...WEAK S/W RIDGING
ALLOWS FOR THIS S/W ENERGY TO AMPLIFY ALONG THE SOUTHERN ROCKIES
INTO TX AND NORTHERN COAHUILA BY EARLY THURS.  THE 00Z UKMET IS A
BIT STRONGER/TIGHT WITH THE CORE INITIALLY AND EJECTS NEARLY 6-12
HRS EARLIER AND RACES THROUGH TO THE GULF STATES AND AWAY FROM THE
ENSEMBLE SUITE AND OVERALL TREND TOWARD THE BROAD TROF IN IN TX BY
00Z FRI.  THE 00Z ECMWF IS OVERALL LEAST CONSOLIDATED AND BROADER
WITH DIGGING FURTHEST SOUTH AND DRAWING TROPICAL MOISTURE FROM THE
PACIFIC AND CARIBBEAN NORTH LATER IN THE PERIOD (THOUGH WITH
SLIGHTLY WEAKER FLOW). THE 12Z NAM/00Z CMC ARE CENTRAL IN BOTH
STRENGTH/CONSOLIDATION AND LOCATION OF THE INNER CORE OF THE
BROADER TROF.  THE 12Z GFS SAW MARKED CHANGES FROM THE 06Z
RUN...LEADING TO A SHIFT TOWARD THE UKMET EVOLUTION.  THIS IS
LIKELY TO LESS SOUTHWARD INJECTION OF S/W ENERGY AS THE NORTHERN
STREAM IS MUCH FASTER (SEE SECTION ABOVE)...AS SUCH THE REMAINING
WEAK ENERGY IS MORE PROGRESSIVE IN MODEST FLOW COUNTER TO THE
TREND IN THE NAM/CMC/ECMWF.  GIVEN THE LARGE SHIFT WILL EXCLUDE
THE GFS/UKMET AT THIS TIME BUT LACK OF CONFIDENCE MAY ALLOW FOR
SOME INCLUSION IF THE CMC/ECMWF TREND THIS WAY AS WELL.   SO AT
THIS POINT A 12Z NAM AND 00Z CMC/ECMWF BLEND IS PREFERRED BUT AT
AVERAGE TO SLIGHTLY BELOW AVERAGE CONFIDENCE.


NEXT DEEP LAYERED PACIFIC CYCLONE NEARING SW CANADA WITH FRONTAL
ZONE ENTERING NORTHWEST TO CENTRAL CA LATE WED AND THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE HIGHLY AMPLIFIED PATTERN CONTINUES BY WED INTO THURSDAY AS
ANOTHER BROAD DEEP LOW TRACKS NORTHEAST...THERE REMAINS (AS
EXPECTED) INTERNAL TIMING DIFFERENCES IN THE TIMING OF THE
OCCLUSION AND THE EVOLUTION TO THE MAIN INNER CORE OF THE UPPER
LOW ITSELF.  THE 00Z ECMWF IS SLOWER AND LOADS A STRONGER S/W ON
THE SOUTH AND EASTERN SIDE AS IT ADVANCES TOWARD SW CANADA LEADING
TO A SLIGHT EASTWARD WOBBLE OF THE INNER CORE AND SURFACE LOW MORE
THAN THE OTHER MAIN GLOBAL GUIDANCE MEMBERS.  THE 12Z GFS IS AS
EXPECTED A BIT FASTER TO OCCLUDE AND THAT MATURITY KEEPS THE INNER
CORE WEST-MOST OF THE REMAINING GUIDANCE.  THE 12Z NAM AND 00Z
UKMET/CMC SPLIT THESE DIFFERENCES.   THE ORIENTATION/STRENGTH AND
TIMING OF THE JET CORE AND ITS INTERFACE WITH THE MOISTURE STREAM
INTO THE PACIFIC NORTHWEST AHEAD OF THE FRONTAL ZONE LOOK
REMARKABLY AGREEABLE THROUGH THE END OF THE DAY 3 PERIOD (00Z
FRIDAY) TO SUPPORT A GENERAL MODEL BLEND.  THE CONFIDENCE IS HIGH
BUT GIVEN THE VARIATIONS IN THE OCCLUSION THE OVERALL CONFIDENCE
IS ONLY SLIGHTLY ABOVE AVERAGE AS THE BLEND OF THESE MASS/INNER
CORE DIFFERENCE WILL LIKELY NOT VERIFY BUT SLOWLY ADJUST TOWARD A
COMMON SOLUTION AS THE SYSTEM APPROACHES.


PREVIOUS MODEL TRENDS AT www.wpc.ncep.noaa.gov/html/model2.shtml
PREVIOUS 500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml


$$





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