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FXUS10 KWNH 270443
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1143 PM EST SUN FEB 26 2017

VALID FEB 27/0000 UTC THRU MAR 02/1200 UTC

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

12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SHORTWAVE SWINGING THROUGH THE SOUTHWEST TODAY AND REACHING THE
SRN PLAINS LATE TONIGHT BEFORE HEADING INTO CONFLUENT FLOW ACROSS
THE CENTRAL U.S. LATE MON INTO TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE

RUN TO RUN VARIATION CONTINUES TO TAPER OFF AS THE WEAK SHORTWAVE
SHEARS INTO CONFLUENT FLOW OVER THE EASTERN US LATER TODAY...WITH
FAIRLY STRONG MASS FIELD AGREEMENT SUPPORTING A GENERAL MODEL
BLEND AT HIGH CONFIDENCE.  WHILE THE MASS AGREES THERE REMAINS
SOME MODEST SPREAD IN QPF DRIVEN IN THE MESOSCALE AND CONVECTIVE
INTERACTIONS THUS PLEASE REFER TO THE LATEST QPFPFD FOR THESE QPF
DIFFERENCES.


LARGE SCALE TROF DEVELOPING OVER THE WEST WITH CONFLUENCE OF THREE
SHORTWAVES. EJECTS INTO THE PLAINS TUES THROUGH LATE WED BEFORE
TRACKING INTO THE GREAT LAKES/NORTHEAST BY THURS WITH ASSOCIATED A
BROAD AREA OF SURFACE PRESSURE FALLS THAT WILL TRACK INTO THE
GREAT LAKES WED WITH TRAILING COLD FRONT INTO THE MS RIVER VALLEY
AND THROUGH THE SOUTHEAST BY MIDDAY THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/12Z ECMWF BLEND UNTIL 01/18Z
            00Z NAM AFTERWARD
CONFIDENCE: SLIGHTLY BELOW AVERAGE

COMPLEX EVOLUTION AS THREE DISTINCT SHORTWAVE FEATURES INTERACT
AND SUPPORT UPSCALE GROWTH TOWARD A GLOBAL MEAN TROF THAT WILL
DOMINATE THE WESTERN 2/3RD OF THE US EARLY THIS WEEK AND TRANSLATE
INTO THE EASTERN THIRD BY THURSDAY.  THIS INTERACTION AND
SUBSEQUENT EVOLUTION OF THE MEAN TROF IS QUITE SENSITIVE TO TIMING
DIFFERENCES LEADING TO MODERATE SPREAD PARTICULARLY IN THE LOWER
PORTIONS OF THE ATMOSPHERE ESPECIALLY WITH FRONTAL TIMING AND
QPF/CONVECTION PLACEMENT.

GOES WV MOSAIC DEPICTS THE FIRST FAIRLY BROAD AND CONCENTRIC
SHORTWAVE ENTERING THE PACIFIC NORTHWEST AS IT TRANSLATES INTO THE
NORTHERN ROCKIES THERE WILL BE SOME PHASING WITH THE LINGERING
SHORTWAVE ENERGY OFF THE SW CA COAST AROUND 30N130W ATTM  AS IT IS
REACHES THE SOUTHWEST BY TUES AND TAKES UP THE BASE OF THE
MERIDIONALLY EXPANDING LONGWAVE TROF.   THE THIRD PIECE IS
UPSTREAM NORTHERN STREAM SHORTWAVE FEATURE THAT WILL SHORTEN IN
DISTANCE TO THE FIRST NORTHERN WAVE SUPPORTING DAMPENING AND
EVENTUAL EJECTION OF THE WAVE INTO THE NORTHERN PLAINS TUESDAY
INTO WED.  THE MEAN WAVE AND BROAD SWLY FLOW WILL SPUR LEE
CYCLOGENESIS IN E CO EARLY TUES MORNING THAT WILL SHIFT INTO THE W
GREAT LAKES WITH THE LEADING WAVE/HEIGHT FALLS WITH SURFACE FRONT
EXTENDING BACK TO THE SOUTHERN HIGH PLAINS IN ANTICIPATION OF THE
EJECTION OF THE MEAN WAVE AS IT SWINGS NEUTRAL INTO THE PLAINS
EARLY WED.

THE MODELS SHOW MODEST SPREAD AND EVOLUTION DIFFERENCES AFTER
TUESDAY NIGHT...AS THE 00Z GFS CONTINUES TO BREAK FAST FROM THE
SPREAD IN A TYPICAL BUT GENERALLY NEGATIVE BIAS.  THIS FAST BIAS
OF THE GFS AND GEFS MEMBERS WILL COMPOUND THROUGHOUT THE REMAINDER
OF THE FORECAST PERIOD LEADING TO NEARLY ALL REMAINING SHORTWAVE
FEATURES PROGRESSING TOO FAST TO THE REMAINING GUIDANCE.  THE LEAD
SHORTWAVE IS GENERALLY EXPECTED TO WEAKEN AND STALL AS THE
SOUTHERN SHORTWAVE LIFTS OUT...BECOMING THE FULCRUM OR PIVOT FOR
THE MEAN TROF TO SWING/CONSOLIDATE AROUND AMPLIFYING AND DEEPENING
THE TRAILING SURFACE WAVE ACROSS THE GREAT LAKES INTO THE
NORTHEAST BY THURS.  THE GFS BEING FAST...HAS THE PIVOT
DEVELOPMENT OCCUR WELL EAST AND LATER IN THE PROCESS OVER NE NEW
ENGLAND/SE CANADA LATE THURS.

ON THE OTHER SIDE OF THE SPECTRUM THE 12Z ECMWF IS SLOW TO EJECT
THE LEAD SHORTWAVE WHICH AS IT WEAKENS STALLS ACROSS THE UP OF MI
ALLOWING FOR A STRONGER/DEEPER AMPLIFICATION OF SOUTHERN SHORTWAVE
AND SURFACE LOW LATE WED INTO THURS ACROSS THE EASTERN GREAT
LAKES... MORE SO (AND WEST) OF ANY OTHER SOLUTION.  THOUGH THIS
DOES FEED INTO THE TYPICAL EC NEGATIVE BIAS OF SLOWER/WOUND UP
SOLUTIONS...THE REMAINING GUIDANCE/ENSEMBLE MEMBERS ARE CLOSER TO
THIS SOLUTION IN TIMING/EVOLUTION MAKING THE ECMWF POTENTIALLY
USEFUL UNTIL ABOUT 01/18 OR 02/00Z. 12Z UKMET IS A SHADE MORE
ELONGATED AND UNCHARACTERISTICALLY FLAT THROUGH THE EASTERN
LAKES/NEW ENGLAND BY LATE WED INTO THURS WITH A NORTHERN SURFACE
SOLUTION TRACK.  THE 12Z CMC IS A LITTLE FASTER TOWARD THE GFS
SOLUTION INITIALLY SLIGHTLY OUTPACING THE NAM/UKMET/ECMWF THROUGH
THE GREAT LAKES; HOWEVER... THE ORIENTATION OF THE FRONT/SURFACE
TROF LOOKS QUITE FAVORABLE TO CURRENT EXPECTATIONS PARTICULARLY AS
THE UKMET MAY LOOK A BIT TOO SLOW WITH THE COLD FRONT TRAVERSING
THE SOUTH.  THIS LEAVES THE 00Z NAM WHICH TRACKS ALONG WITH THE
12Z ECMWF UNTIL LATE WED WHICH THE NAM BECOMES MORE SENSIBLE WITH
LESS AMPLIFICATION IN THE FAIRLY PROGRESSIVE EASTWARD MOVEMENT OF
THE OVERALL PATTERN.  ALL IN ALL...THIS MAKES THE 00Z NAM SEEMS TO
BE THE BEST/MIDDLE GROUND AND MOST PREFERABLE SOLUTION AT THIS
POINT BUT TO ENCOMPASS SOME OF THE MODEL SPREAD...WPC PREFERENCE
WILL INCORPORATE THE 12Z ECMWF PRIOR TO 01/18Z AND 00Z NAM
AFTERWARD.  CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE GIVEN ALL
THE MOVING PARTS/INTERACTIONS THAT ARE TIME/SPACING SENSITIVE AND
LIKELY TO VARY RUN TO RUN UNTIL THE PIECES ARE WELL SENSED AND
ASSIMILATED.


LOW AMPLITUDE SHORTWAVE CLIPPING THE NRN ROCKIES WED MORNING INTO
NORTHERN PLAINS BY THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/UKMET/CMC BLEND
CONFIDENCE: AVERAGE

A DEEP UPPER LOW CRASHES INTO THE AK PANHANDLE/NW BC LATE TUESDAY
AND SHEDS SOME SHORTWAVE ENERGY INTO THE NORTHERN STREAM AS A LOW
AMPLITUDE WAVE THAT CLIPS THE NORTHERN ROCKIES/NW MT INTO THE
DAKOTAS BY EARLY THURS.  DOWNSTREAM EVOLUTION DICTATES OBVIOUS
DIFFERENCES AS THE 00Z GFS HAS A BIT MORE SPACING AND THEREFORE
SPEEDS THIS WAVE UP WITH SOME AMPLIFICATION WITH LITTLE TO NO
SUPPORT WITH EXCEPTION TO ITS GEFS MEMBERS.   THE 00Z NAM ALSO
SHOWS SOME DEEPER AMPLIFICATION TO THE WAVE THAN THE
ECMWF/UKMET/CMC BUT LIKE PRIOR NAM RUNS IS A BIT FASTER EVEN WITH
SIMILAR SPACING AS PRESENTED BY THE NON-NCEP SOLUTIONS.  THIS ALSO
MAKES THE 00Z NAM GENERALLY FURTHER NORTH AND EAST OF THE
REMAINING GUIDANCE/ENSEMBLE MEMBERS.  AS SUCH WILL PREFER A BLEND
OF THE 12Z ECMWF/UKMET/CMC AT AVERAGE CONFIDENCE.

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

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

GALLINA


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