Prognostic Meteorological Discussion
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FXUS10 KWNH 230639
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MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 AM EDT MON OCT 23 2017

VALID OCT 23/0000 UTC THRU OCT 26/1200 UTC

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

00Z MODEL EVALUATION...WITH LATEST MODEL PREFERENCES/CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...SOUTHERN STREAM LOWER MS VALLEY CLOSED LOW...
...SURFACE COLD FRONT SWEEPING ACROSS THE MS/TN VALLEYS...
...NORTHERN STREAM TROUGH AMPLIFICATION OVER CENTRAL/EASTERN U.S...
...DEEP PHASED CYCLONE OVER THE GREAT LAKES REGION BY TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM CONSENSUS...WEIGHTED TOWARD THE 00Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A SOUTHERN STREAM CLOSED LOW THAT HAS DEVELOPED OVER THE LOWER MS
VALLEY IS EXPECTED TO ADVANCE EAST-NORTHEASTWARD OVER THE NEXT 12
HOURS WHILE ELONGATING AND ACQUIRING A NEGATIVE TILT AS IT CROSSES
THE TN VALLEY. THIS ENERGY ALONG WITH A DEVELOPING SURFACE LOW
CENTER WILL LIFT NORTH UP ACROSS THE OH VALLEY AND INTO THE GREAT
LAKES REGION ON MONDAY AS IT GETS CAUGHT UP AND GRADUALLY ABSORBED
BY A STRONG NORTHERN STREAM TROUGH THAT WILL AMPLIFY SOUTHEAST
ACROSS THE MIDWEST. THIS NORTHERN STREAM ENERGY IS ALREADY QUICKLY
EJECTING ACROSS THE NORTHWEST U.S. AND THE LATEST MODELS ARE IN
GOOD AGREEMENT IN THE DETAILS OF THIS SHARP AMPLIFICATION. THIS
WILL LEAD TO A STRONG PHASED CYCLONE OVER THE GREAT LAKES BY
TUESDAY AND A DEEP LONGWAVE TROUGH MOVING INTO THE EASTERN U.S.
TUESDAY AND WEDNESDAY. A COLD FRONT WILL CROSS THE TN/OH VALLEYS
MONDAY AND SWEEP TOWARD THE EASTERN SEABOARD ON TUESDAY BEFORE
THEN MOVING OFFSHORE. THE MODELS HAVE COME INTO MUCH BETTER
AGREEMENT WITH THE DETAILS OF THE PHASING OF NORTHERN AND SOUTHERN
STREAM ENERGY AND THE DEEPENING SURFACE LOW CENTER...HOWEVER THE
00Z NAM APPEARS TO BE STILL A TAD TOO WEAK WITH THE LOW CENTER
OVER THE GREAT LAKES MONDAY AND TUESDAY. THE REMAINING MODELS ARE
RATHER WELL CLUSTERED WITH THE EVOLUTION OF THIS SYSTEM AND ITS
EXIT INTO ONTARIO THROUGH WEDNESDAY ALTHOUGH THERE IS SOME MODEST
SPREAD WITH THE STRENGTH OF THE LOW CENTER AS IT EXITS NORTHEAST
FROM THE GREAT LAKES. THE ECMWF HAS BEEN AMONG THE MOST CONSISTENT
OF MODELS WITH THIS SYSTEM OVER THE LAST COUPLE OF DAYS...AND SO
THE PREFERENCE WILL BE A NON-NAM CONSENSUS WEIGHTED TOWARD THE
ECMWF.


...SHORTWAVE DIGGING TOWARD THE NORTHERN PLAINS TUES NIGHT/WED...
...ASSOCIATED SURFACE LOW OVER SOUTHERN CANADA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z GFS/UKMET/ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A NORTHERN STREAM SHORTWAVE WILL BE QUICK TO DROP SOUTHEAST ACROSS
SOUTHERN CANADA AND TOWARD THE NORTHERN PLAINS AND UPPER MS VALLEY
TUESDAY NIGHT AND WEDNESDAY ALONG WITH A SURFACE WAVE. THE 00Z NAM
AND 00Z CMC ARE A LITTLE SLOWER THAN THE 00Z GFS/UKMET AND ECMWF.
THE GFS/UKMET AND ECMWF ARE BETTER CLUSTERED AND HAVE EXCELLENT
ENSEMBLE SUPPORT...AND SO A GFS/UKMET/ECMWF BLEND WILL BE
PREFERRED.


...SHORTWAVE TROUGH APPROACHING THE PACIFIC NORTHWEST BY WED...
...AMPLIFYING OUT ACROSS CENTRAL/NORTHERN PLAINS BY THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z GFS/ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

A NORTHERN STREAM SHORTWAVE OVER THE GULF OF AK ON TUESDAY IS
FORECAST BY THE MODELS TO DROP IN ACROSS THE PACIFIC NORTHWEST BY
WEDNESDAY WHICH VERY QUICKLY EJECTS OUT ACROSS THE CENTRAL AND
NORTHERN PLAINS BY THURSDAY WHILE ALSO AMPLIFYING. THIS WILL LEAD
TO A STRENGTHENING LOW CENTER WHICH INITIALLY COMES IN ACROSS
BRITISH COLUMBIA BY TUESDAY NIGHT AND THEN REDEVELOPS OVER
SOUTHERN ALBERTA BEFORE THEN DROPPING SOUTHEAST ACROSS THE
NORTHERN PLAINS AND UPPER MIDWEST BY LATER WEDNESDAY AND THURSDAY.
THE MODELS ARE IN GOOD AGREEMENT AS THE SYSTEM ARRIVES IN ACROSS
BRITISH COLUMBIA...BUT 00Z NAM BECOMES A NORTHERLY OUTLIER WITH
THE TRACK OF THE LOW CENTER ACROSS SOUTHERN CANADA THEREAFTER AND
LIKELY IS TOO STRONG AS WELL. THE GLOBAL MODELS ARE ALL CLUSTERED
FARTHER SOUTH OVER THE NORTHERN PLAINS AND EVENTUALLY THE UPPER
MIDWEST BUT HAVE SOME TIMING DIFFERENCES...WITH THE 00Z GFS THE
FASTEST...AND THE 00Z CMC/ECMWF SOLUTIONS THE SLOWEST. THE 00Z
UKMET TENDS TO BE FASTER LIKE THE GFS BUT IS FARTHEST SOUTH WITH
ITS LOW TRACK. THERE ARE A FAIR NUMBER OF 12Z EURO ENSEMBLE
MEMBERS THAT ARE FASTER THAN THE OPERATIONAL ECMWF AND SUPPORT A
TIMING THAT IS ESSENCE MIDWAY BETWEEN THE GFS AND ECMWF. THE BULK
OF THE 00Z GEFS MEMBERS ARE ALSO A BIT SLOWER AND WEST OF THE
OPERATIONAL GFS BY THE END OF THE PERIOD. THUS...BASED ON THE
LATEST TRENDS AND AVAILABLE ENSEMBLE GUIDANCE...A BLEND OF THE GFS
AND ECMWF WILL STILL BE PREFERRED. CONFIDENCE THOUGH IS A BIT LOW
CONSIDERING THE SPREAD IN THE DETERMINISTIC GUIDANCE.


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

ORRISON

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