Prognostic Meteorological Discussion
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FXUS10 KWNH 260434
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1233 AM EDT TUE SEP 26 2017

VALID SEP 26/0000 UTC THRU SEP 29/1200 UTC

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

00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...HURRICANE MARIA...
~~~~~~~~~~~~~~~~~~~~~~~~~
PROXY PREFERENCE: 00Z GFS/12Z CMC
CONFIDENCE: REFER NHC TO LATEST FORECAST

THE 12Z ECMWF/UKMET CONTINUE TO BE A BIT DEEPER AND TO THE LEFT OF
THE OFFICIAL 03Z NHC FORECAST BOTH EVENTUALLY BECOME MUCH FURTHER
WEST OF THE FORECAST AS THE CYCLONE IS RAPIDLY USHERED EASTWARD
AFTER 54HRS.  THIS IS MORE IN LINE WITH THE 00Z NAM/GFS AND CMC.
THE 00Z NAM IS STILL A BIT RIGHT AND SOUTH OF TRACK THROUGH THE
FORECAST.  WHILE THE 00Z GFS AND 12Z CMC EVENTUALLY OUTPACE THE
03Z FORECAST AT 84HRS...IT IS EVER SO SLIGHT AND THEIR COMBINATION
PRIOR TO 72HRS MATCHES VERY WELL OVERALL TO SUGGEST THIS BLEND AS
BEST NHC 03Z FORECAST PROXY.


...MID-LEVEL LOW OVER NORTHERN HIGH PLAINS ACCELERATES TO QUEBEC
BY LATE WED WITH SURFACE LOW AND ATTENDANT COLD FRONT SLIDING
THROUGH NEW ENGLAND THROUGH THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

IMPRESSIVE COMPACT CLOSED LOW CURRENTLY OVER EASTERN MT WILL LIFT
NORTHEAST AND SPUR SURFACE CYCLOGENESIS OVER WI/WESTERN GREAT
LAKES THIS MORNING THAT WILL DEEPEN/OCCLUDE AND TRANSLATE RAPIDLY
INTO QUEBEC BY WED NIGHT.  BY THURSDAY A NEW TRIPLE POINT LOW WILL
FORM ACROSS S QUEBEC/NEW BRUNSWICK WITH A TRAILING COLD FRONT
ACROSS NEW ENGLAND.  THE 00Z NAM TRENDED TOWARD THE GROWING STRONG
CONSENSUS WITH THE EVOLUTION OF THE ENTIRE SYSTEM.  MASS FIELDS
ARE QUITE AGREEABLE TO SUPPORT A GENERAL MODEL BLEND AT ABOVE
AVERAGE CONFIDENCE.


...NORTHERN STREAM SHORTWAVE DIVING INTO THE GREAT LAKES BY FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND
CONFIDENCE: ABOVE AVERAGE

SHORTWAVE ENERGY EMERGES FROM THE NORTHERN CANADIAN ROCKIES OVER
THE MEAN RIDGE TODAY INTO WED AND BEGINS TO DESCEND AND AMPLIFY IN
THE WAKE OF THE EXITING TROUGH AS MENTIONED ABOVE BY THURS AS IT
APPROACHES THE UPPER MIDWEST.  OVERALL GUIDANCE SHOWS REMARKABLE
AGREEMENT IN BOTH PLACEMENT/DEPTH OF THE WAVE.  THE ONLY OUTLIER
APPEARS TO BE THE 12Z UKMET WHICH OVERALL IS A BIT BROADER IN
LENGTH AND EVER SO SLIGHTLY FASTER THAN THE REMAINING GUIDANCE.
THIS ALSO WILL GENERATE A SURFACE REFLECTION (WHILE IN THE SAME
LOCATION AS THE EVER SO SLIGHTLY FASTER 00Z GFS/NAM
SOLUTIONS)...IT IS NEARLY 4MB DEEPER THAN THE REMAINING GUIDANCE.
AS SUCH A NON-UKMET BLEND IS SUGGESTED AT ABOVE AVERAGE
CONFIDENCE.


...CLOSED LOW PINCHING OFF OVER THE DESERT SOUTHWEST ON WED AND
SLIPPING NORTH INTO A REX FORMATION BY FRI OVER INTERMOUNTAIN
WEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

GOES-WV MOSAIC DEPICTS SHORTWAVE DESCENDING ACROSS GREAT BASIN
WITH STRONG UPSTREAM JET STREAK STARTING TO ROUND THE TOP OF THE
NORTHWEST US RIDGE...THESE FEATURES WILL ALLOW FOR A NEW UPPER LOW
TO PINCH OFF IN THE DESERT SOUTHWEST BY WED.  THE ORIENTATION OF
THE DEVELOPMENT WILL ALSO SUPPORT THE AMPLIFICATION OF THE NW US
RIDGE TO DEVELOP AND SHIFT EASTWARD OVER THE NORTHERN US ROCKIES
BY THURS.  WHILE THE REX FORMATION SETS UP THE SHORTWAVE AT THE
BASE OF THE CLOSE LOW WILL LIFT NORTHWARD TOWARD UT/CO.  THE MAIN
DIFFERENCE IN EVOLUTION IS WHICH FEATURE IS DOMINANT WITHIN THE
REX BY FRI; THE 00Z NAM/GFS BOTH FAVOR A STRONGER TIGHTER CLOSED
LOW/SHORTWAVE WHILE THE NON-NCEP GUIDANCE SUGGESTS A STRONGER
RIDGE...AS SUCH THE ECMWF/CMC AND UKMET ALL GENERALLY FLATTEN THE
SHORTWAVE E-W ACROSS THE CENTRAL ROCKIES BY FRIDAY WITH THE UKMET
GOING TO THE GREATEST EXTREME.  IT IS DIFFICULT TO DETERMINE WHICH
FEATURE WILL DOMINATE BUT THE UKMET FINAL SOLUTION BY FRIDAY SEEMS
MOST UNLIKELY WITH THE ENSEMBLE SUITE... AS SUCH A NON-UKMET BLEND
IS SUGGESTED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.


...DEEP WEST COAST TROF ENTERING PACIFIC NORTHWEST LATE THURS INTO
FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

12Z SPAGHETTI ANALYSIS DEPICT A STRONGER MORE AMPLIFIED WAVE
THROUGHOUT MUCH OF THE GUIDANCE/ENSEMBLE SUITE COMPARED TO 00Z AND
YESTERDAYS ANALYSES.  THE 00Z GFS IS LEANING A BIT FORWARD ALOFT
BUT DOES NOT SEEM TO BE A NEGATIVE TO THE TIMING/PLACEMENT OF THE
FRONTAL ZONE AND ASSOCIATED MOISTURE FEED MATCHING WELL WITH THE
12Z ECMWF AND CMC.  THE 12Z CMC IS A BIT WEAKER/FURTHER SOUTH WITH
THE CENTER OF THE WAVE BUT MUCH LIKE THE GFS DOES NOT SEEM TO BE
TOO NEGATIVE TO THE EVOLUTION (PARTICULARLY AT SUCH A LONGER TIME
SCALE -- DAY 3).  THE 00Z NAM SHOWS GOOD SIMILARITY TO THE
ENSEMBLES AND 12Z ECMWF TO FURTHER INCREASES CONFIDENCE IN THE
DEEPER/AMPLIFIED SHIFT AT 12Z.  THE CLEAR OUTLIER IS THE SLOW AND
FLATTER 12Z UKMET AND WHILE NOT WAY OUT OF PHASE FOR A STRONGER
SIGNAL IN THE BLEND...WILL SUGGEST A NON-UKMET BLEND AT SLIGHTLY
ABOVE AVERAGE CONFIDENCE.



...SHEARED ELEMENTS OF PILAR LIFTING THROUGH CENTRAL MX...
...ENERGY ARRIVING ACROSS THE TX BIG BEND/RIO GRANDE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

GOES-WV LOOP DEPICTS VERY SHEARED REMNANTS OF TD PILAR LIFTING
NORTH THROUGH EASTERN PACIFIC MOISTURE FEED TOWARD SW TX ATTM.
THE GUIDANCE HAS BEEN CONSOLIDATING IN TIMING OF THE
MAIN/STRONGEST MID-LEVEL WAVE APPROACHING DEL RIO LATER TODAY.
UPSTREAM DEEPENING/CLOSING UPPER LOW AS WELL AS CONVECTIVE
FEEDBACK/ENHANCEMENT OF THE WAVE (DUE TO HIGH
MOISTURE/INSTABILITY...LATENT HEAT RELEASE MCV ENHANCEMENT) KEEPS
MASS FIELDS QUITE SIMILAR.  THE 00Z NAM SHOWS MUCH STRONGER WAVES
LIFTING NORTH BUT THIS IS LIKELY DUE TO THE MODEL`S GREATER GRID
RESOLUTION TO RESOLVE THESE FEATURES BUT HAS GENERALLY SLOWED
COMPARED TO PRIOR RUNS AS THE SYSTEM HAS HUNG ON JUST OFF THE
EASTERN MX COAST AND ONLY LAGS THE UKMET EVER SO SLIGHTLY. THE 12Z
ECMWF IS NOW THE QUICKEST LIFTING THE WAVE NORTH BUT IS ON TRACK
WITH THE 00Z GFS/12Z CMC AND THEN THE UKMET/NAM.  OVERALL THE
SPACING/TIMING IS MODEST TO SUPPORT A GENERAL MODEL BLEND AT
SLIGHTLY ABOVE AVERAGE CONFIDENCE.


...MID LEVEL WEAKNESS OVER EASTERN GULF...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z ECMWF BLEND
CONFIDENCE: AVERAGE

GOES-EAST WV DEPICTS AN ILL-DEFINED UPPER TROF OVER THE NORTHEAST
GULF OF MEXICO THAT WILL BE ENHANCED BY WEAK VORT ENERGY SHED FROM
MARIA TOWARD N FL BY EARLY THURSDAY...FURTHER STRENGTHENING THE
FEATURE THOUGH LITTLE MOTION IS EXPECTED STAYING GENERALLY BETWEEN
90W AND WESTERN FLORIDA.  STRONGER AND MORE SOUTHEASTWARD GUIDANCE
WITH RESPECT TO MARIA (IE UKMET/ECMWF SHED MORE ENERGY THAN SAY
GFS/NAM...IN DOING SO THE ORIENTATION/CENTER OF THE BINARY BETWEEN
THE TWO WEAK SYSTEMS LEADS TO THE LARGER SPREAD OVERALL.  THE 12Z
UKMET IS VERY STRONG AND MUCH FURTHER EAST OVER CENTRAL FL TOWARD
FRI.  THE 12Z CMC AND 00Z NAM ARE MUCH BROADER WITH A REDUCED
RADIUS OF DEFORMATION GENERATING A BROADER SYSTEM.  THE 00Z GFS
AND 12Z ECMWF ARE COMPROMISES TO THE MORE EXTREMES WITH THE ECMWF
CLOSER TO THE UKMET AND THE GFS CLOSER TO THE CMC...STILL BOTH
RESULT IN SIMILAR SOUTHWESTERLY FLOW AND MOISTURE STREAMING FROM
THE WESTERN CARIBBEAN.  AS SUCH WILL FAVOR A 00Z GFS/12Z ECMWF
BLEND.  WEAK SYSTEMS LIKE THIS ARE PRONE TO MODEST RUN TO RUN
VARIATION FOR SMALLER SCALE INTERNAL THOUGH SENSIBLY IMPORTANT
DETAILS LEADING TO LOW CONFIDENCE AT THE STORM/MESOSCALE  BUT THE
LARGE SCALE ORIENTATION/ENVIRONMENT SEEMS FAIRLY CONSISTENT AND SO
IS HIGHER CONFIDENCE IN A SYNOPTIC SENSE.  AS SUCH OVERALL
CONFIDENCE IS AVERAGE.


www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

GALLINA

$$





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