Prognostic Meteorological Discussion
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173
FXUS10 KWNH 190439
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 AM EDT THU OCT 19 2017

VALID OCT 19/0000 UTC THRU OCT 22/1200 UTC

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

00Z MODEL EVALUATION ALONG WITH MODEL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...SHORTWAVE CLIPPING NORTHERN NEW ENGLAND BY THURS EVENING...
...ASSOCIATED COLD FRONT CROSSING THE NORTHEAST BY WEEKS END...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN VERY GOOD AGREEMENT WITH THE MASS FIELD DETAILS
OF THIS SYSTEM. THUS A GENERAL MODEL COMPROMISE WILL BE PREFERRED.


...ONGOING ATMOSPHERIC RIVER EVENT INTO THE WEST COAST...
...LONGWAVE TROUGH EVOLUTION INTO THE WESTERN U.S. THROUGH FRI...
...EJECTING OUT INTO THE PLAINS ON SAT ALONG WITH COLD FRONT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE...THROUGH 48 HOURS
            12Z ECMWF...AFTER 48 HOURS
CONFIDENCE: AVERAGE

THE MODELS ARE IN GOOD AGREEMENT THROUGH ABOUT 48 HOURS WITH THE
EVOLUTION OF THE LONGWAVE TROUGH AND ASSOCIATED COLD FRONT MOVING
THROUGH THE WESTERN U.S. THEREAFTER THE MODEL ALL AGREE IN
SHIFTING THE TROUGH OUT ACROSS THE PLAINS...BUT THERE ARE SOME
DIFFERENCES WITH RESPECT TO THE LEVEL OF ENERGY DIGGING INTO THE
BASE OF THE TROUGH AND ATTEMPTS FOR STREAM SEPARATION. THE 12Z CMC
AND TO AN EXTENT THE 12Z UKMET ALLOW MORE ENERGY TO DIG TOWARD THE
BASE OF THE TROUGH...AND AT LEAST ATTEMPT TO CLOSE OFF A MID LEVEL
LOW CENTER IN VICINITY OF THE CENTRAL OR SOUTHERN PLAINS BY SUN.
THE 00Z NAM/GFS AND 12Z ECMWF ALL SUGGEST MORE OF AN ELONGATED N/S
TROUGH AXIS WITH LITTLE IN THE WAY OF SOUTHERN STREAM SEPARATION
OR ATTEMPTS TO CLOSE OFF A NEW LOW CENTER. THE GFS DOES APPEAR TO
BE A TAD TOO DEEP WITH ITS CLOSED LOW FEATURE BY SUN OVER SOUTHERN
CANADA WHICH ALSO RESULTS IN A STRONGER AND MORE WRAPPED UP
SURFACE LOW. WILL PREFER A GENERAL MODEL COMPROMISE THROUGH 48
HOURS...FOLLOWED BY A PREFERENCE TOWARD THE ECMWF THEREAFTER.


...SOUTHERN STREAM UPPER TROUGH REACHING THE SOUTHERN PLAINS FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

A SOUTHERN STREAM SHORTWAVE TROUGH CROSSING THE SOUTHWEST THROUGH
THURS WILL EJECT EAST OUT ACROSS THE SOUTHERN PLAINS BY FRI OUT
AHEAD OF THE STRONG LONGWAVE TROUGH MOVING INTO THE WESTERN U.S.
THIS PERIOD. THE MODELS ARE IN GOOD AGREEMENT WITH THIS
SYSTEM...SO A GENERAL MODEL COMPROMISE WILL BE PREFERRED.


...SHORTWAVE REACHING BRITISH COLUMBIA LATE SAT WITH WARM FRONT...
...NEXT ATMOSPHERIC RIVER ARRIVING OVER THE PACIFIC NORTHWEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS ARE IN VERY GOOD AGREEMENT IN BRINGING A STRONG WARM
FRONT AND AN ASSOCIATED SHORTWAVE INTO THE PACIFIC NORTHWEST BY
LATE SAT...ALONG WITH THE ARRIVAL OF THE NEXT ATMOSPHERIC RIVER
EVENT ACROSS THE REGION. THE WARM FRONT WILL QUICKLY LIFT
NORTHEAST ACROSS THE PACIFIC NORTHWEST BY EARLY SUN WHICH WILL BE
FOLLOWED BY A STRONG DEEP LAYER ONSHORE FLOW PATTERN WITH ENHANCED
RAINFALL POTENTIAL. THE 12Z CMC IS A BIT QUICKER WITH THE LEAD
SHORTWAVE IMPULSE AND WARM FRONT BY LATE SAT...AND OVERALL IS A
BIT OUT OF TOLERANCE COMPARED TO THE OTHERWISE WELL CLUSTERED
GLOBAL MODELS AND INCLUDING THE NAM. WILL PREFER A NON-CMC
CONSENSUS AS A RESULT.


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

ORRISON

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