Prognostic Meteorological Discussion
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FXUS10 KWNH 251838
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
237 PM EDT MON SEP 25 2017

VALID SEP 25/1200 UTC THRU SEP 29/0000 UTC

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

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

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

THE LATEST NHC TRACK FORECAST OVERALL IS RATHER CLOSE TO THE 12Z
GFS SOLUTION. AFTER ABOUT 48 HOURS...THE 12Z ECMWF AND 12Z UKMET
ARE SLOWER WITH MARIA AND ALSO A BIT LEFT OF THE NHC TRACK AS BOTH
OF THESE MODELS AGAIN INSIST ON MAINTAINING A SOMEWHAT STRONGER
MID LEVEL RIDGE NORTH OF MARIA FOR LONGER BEFORE EVENTUALLY AN
UPSTREAM TROUGH ERODES THE RIDGE AND ALLOWS FOR RECURVATURE. THE
12Z CMC TENDS TO BE OCCASIONALLY A BIT FASTER THAN THE NHC
TRACK...WITH THE 12Z NAM AGAIN INSISTING ON A TRACK FARTHER TO THE
RIGHT AND FASTER WITH A RECURVATURE THAN ANY OTHER MODEL.


...UPPER TROUGH LIFTING ACROSS THE DAKOTAS BY TONIGHT...
...HEIGHT FALLS THEN EXITING THROUGH SOUTHEAST CANADA WED...
...CLIPPING NORTHERN NEW ENGLAND BY THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE IMPRESSIVE COMPACT CLOSED LOW OVER CENTRAL WY PER LATEST
NON-OPERATIONAL GOES-16 WV SUITE WILL CONTINUE TO LIFT NORTHEAST
FOSTERING HEIGHT FALLS AND SURFACE LOW DEVELOPMENT ACROSS NORTHERN
WI BY TUES MORNING THAT QUICKLY DEEPENS ACROSS ONTARIO AND
OCCLUDING THROUGH QUEBEC ON WED WHICH WILL ALLOW A DRAPING COLD
FRONT TO QUICKLY CROSS THE GREAT LAKES AND MOVE INTO THE NORTHEAST
THROUGH THURS. ACROSS THE NORTHEAST BY THURS MORNING. THE 12Z NAM
IS THE MOST PROGRESSIVE SOLUTION...WITH THE GLOBAL MODELS ARE
CLUSTERED A TAD SLOWER AND SHOWING GENERALLY GOOD AGREEMENT WITH
THEIR TIMING AND DEPTH. THERE ARE SOME MODEST LATITUDINAL
DIFFERENCES WITH THE GLOBAL MODELS REGARDING THE LOW TRACK...BUT
AT THIS TIME THE NAM IS THE OVERALL OUTLIER AND SO WILL PREFER A
NON-NAM CONSENSUS.


...NORTHERN STREAM SHORTWAVE OVER THE UPPER MIDWEST BY THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

SHORTWAVE ENERGY EMERGES FROM THE NORTHERN CANADIAN ROCKIES OVER
THE MEAN RIDGE TUES 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. THIS WILL DRIVE A NEW COLD FRONT
SOUTHEAST FROM CENTRAL CANADA THAT WILL APPROACH THE GREAT LAKES
REGION BY LATE THURS. THE 12Z UKMET IS THE MOST PROGRESSIVE
SOLUTION WITH THIS ENERGY...WITH THE 12Z NAM AND 12Z CMC SOLUTIONS
THE SLOWEST. OVERALL THERE IS ONLY VERY MINOR SPREAD REGARDING
DEPTH OF THE TROUGH. THE 12Z GFS AND 12Z ECMWF BOTH MORE CLOSELY
MATCH THE MODEL CONSENSUS AND GIVEN THEIR STRONG MASS FIELD
CLUSTERING...A BLEND OF THESE TWO SOLUTIONS WILL BE PREFERRED.


...CLOSED LOW PINCHING OFF OVER THE DESERT SOUTHWEST ON WED...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM CONSENSUS
CONFIDENCE: ABOVE AVERAGE

THE MODELS CONTINUE TO SHOW MUCH STRONGER AGREEMENT IN EVOLUTION
AND TIMING OF THE SHORTWAVE ENTERING THE WESTERN U.S. BY LATE
TODAY...AND DESCENDING ACROSS THE GREAT BASIN BEFORE THEN
FOSTERING A PINCHED OFF CLOSED LOW OVER THE LOWER CO RIVER VALLEY
BY WED. THE 12Z NAM IS A BIT FASTER TO EJECT THE ENERGY BACK OFF
TO THE EAST TOWARD THE CENTRAL ROCKIES BY THE END OF THE
PERIOD...WITH ALL OF THE GLOBAL MODELS CLUSTERED FARTHER WEST AND
SLOWER. WILL PREFER A NON-NAM CONSENSUS.


...SHEARED ELEMENTS OF PILAR LIFTING THROUGH CENTRAL MX...
...ENERGY ARRIVING ACROSS THE TX BIG BEND/RIO GRANDE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MID LEVEL ENERGY ASSOCIATED WITH T.D. PILAR JUST OFF THE
SOUTHWEST COAST OF MEXICO WILL BEGIN TO SHEAR OFF TO THE
NORTH-NORTHEAST OVER THE NEXT COUPLE OF DAYS AND BECOME EMBEDDED
WITHIN DEEP LAYER SOUTHERLY FLOW ASSOCIATED WITH A DEEP
TROUGH/CLOSED LOW DIGGING ACROSS THE SOUTHWEST U.S. AND EXTENDING
WELL SOUTH DOWN ACROSS THE BAJA PENINSULA. THE 12Z NAM APPEARS TO
HAVE SOME STRONG CONVECTIVE FEEDBACK ASSOCIATED WITH THIS ENERGY
AS IT ARRIVES TOWARD THE TX BIG BEND AREA AND ADJACENT AREAS OF
THE MIDDLE RIO GRANDE VALLEY. THE REMAINING MODELS SHOW MODEST
SPREAD WITH THE VORT ENERGY DETAILS...AND SO AT THIS POINT A
NON-NAM CONSENSUS WILL BE PREFERRED.


...WEAK MID LEVEL LOW CENTER NEAR THE CENTRAL GULF COAST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS TAKE A WEAK MID LEVEL LOW CENTER NEAR THE CENTRAL GULF
COAST AND VERY SLOWLY RETROGRADE IT WEST OVER THE NEXT COUPLED OF
DAYS WHILE IT CONTINUES TO WEAKEN. THE MODELS SHOW GOOD AGREEMENT
WITH THIS FEATURE AND SO A GENERAL MODEL BLEND WILL BE PREFERRED.


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

ORRISON

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