Prognostic Meteorological Discussion
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000
FXUS10 KWNH 221839
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT WED MAR 22 2017

VALID MAR 22/1200 UTC THRU MAR 26/0000 UTC

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

...PLEASE NOTE THAT THE NAM WAS UPGRADED TO A NEW VERSION 21/12Z
CYCLE...


12Z MODEL EVALUATION WITH FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT
RANGE FORECASTS.


...UPPER TROUGH LEAVING NEW ENGLAND TODAY AND ASSOCIATED COLD FRONT
  MOVING THROUGH THE SOUTHEAST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


...NRN STREAM SHORTWAVE TRACKING ACROSS S-CNTRL CANADA TODAY/THU...
...CLOSED LOW DIVING THROUGH SERN CANADA BY SAT MORNING...
...COLD FRONT CLIPPING THE DAKOTAS THU...GREAT LAKES ON FRI...AND
  INTO THE NRN MID-ATLANTIC ON SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z UKMET COMPROMISE
CONFIDENCE: AVERAGE

THE MODELS SHOW SIMILAR TO ONE ANOTHER WITH THIS SYSTEM(S) UNTIL
SAT WHERE SOME DIFFERENCES ARISE WITH THE STRENGTH OF HIGH
PRESSURE OVER JAMES BAY IN SERN CANADA. THERE HAVE BEEN SOME
TRENDS IN THE DETERMINISTIC AND ENSEMBLE GUIDANCE TO BACK UP THE
SURFACE COLD FRONT ACROSS THE NRN MID-ATLANTIC REGION SAT
EVENING...BUT THE 12Z UKMET IS ON THE WEAKER SIDE THE HIGH
PRESSURE AND HAS THE COLD FRONT FARTHEST NORTH. HOWEVER...ENSEMBLE
SPAGHETTI PLOTS SHOW THE MIDDLE GROUND NEAR THE 12Z NAM...12Z GFS
AND 12Z CMC WHICH IS A BIT FARTHER SOUTH THAN THE 00Z ECMWF MEAN
AND WELL SOUTH OF THE 12Z UKMET. THE 12Z ECMWF ADJUSTED SOUTH WITH
THE FRONT SAT EVENING COMPARED TO ITS 12Z RUN BUT IS INCLUDED IN
THE BLEND AS IT HAS MORE SUPPORT COMPARED TO THE 12Z UKMET.


...STRONG UPPER TROUGH ADVANCING FROM THE SOUTHWEST ON THU INTO
  THE SRN/CNTRL PLAINS FOR FRI AND MS VALLEY FOR SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z NAM COMPROMISE
CONFIDENCE: AVERAGE

THERE HAS BEEN CONVERGENCE IN THE DETERMINISTIC RUNS REGARDING THE
TIMING OF THE CLOSED LOW AS IT MOVES THROUGH THE PLAINS INTO THE
MS VALLEY COMPARED TO MODEL CYCLES FROM YESTERDAY...BUT ENSEMBLES
CONTINUE TO SHOW TWO DIFFERENT PICTURES. THE ECMWF MEMBERS ARE
FASTER WHILE THE GEFS ARE SLOWER. THE DETERMINISTIC ECMWF HAS BEEN
SWITCHING BETWEEN FASTER AND SLOWER SINCE ITS 00Z/21 RUN BUT THE
CURRENT 12Z ECMWF MADE A SMALL NUDGE TOWARD THE 12Z GFS.
MEANWHILE...THE 12Z UKMET NUDGED TOWARD THE 00Z ECMWF AND THE 12Z
CMC ADJUSTED FASTER TOWARD THE CONSENSUS LEAVING ONLY THE 12Z NAM
ON THE EDGE OF THE DETERMINISTIC GUIDANCE WITH A FASTER
PROGRESSION. A NON 12Z NAM BLEND REPRESENTS THE MIDDLE GROUND OF
THE ENSEMBLE SPREAD THAT IS PREFERRED. THIS IDEA IS CONSISTENT
WITH THE UPSTREAM KICKER DESCRIBED IN THE LAST SECTION OF THIS
DISCUSSION.



...NRN STREAM UPPER TROUGH/COLD FRONT REACHING THE NORTHWEST
  THU-FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THERE ARE ONLY MINOR TIMING DIFFERENCES WITH THIS SYSTEM AND ITS
ASSOCIATED COLD FRONT...THUS A GENERAL MODEL COMPROMISE IS
PREFERRED TO SMOOTH OUT THESE SMALLER SCALE DIFFERENCES.


...SRN STREAM COMPONENT OF LARGER UPPER LEVEL TROUGH OVER THE WEST
  ON SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z NAM COMPROMISE
CONFIDENCE: ABOVE AVERAGE

SIMILAR TO THE THIRD SECTION OF THIS DISCUSSION...THE ECMWF
ENSEMBLE MEMBERS ARE ON THE FASTER SIDE WHILE THE 00Z GEFS ARE
SLOWER. THE 06Z GEFS SPED UP FROM THE 00Z GEFS...AND THE 12Z
GFS/GEFS IS FASTER THAN BOTH 00/06Z GEFS BUT MORE IN LINE WITH THE
CENTER OF THE ENSEMBLE SPREAD. THE PREFERENCE IS TO STAY NEAR THE
MIDDLE OR NEAR THE 12Z GFS...12Z ECMWF AND 12Z UKMET. THE 12Z CMC
JOINTED THE CAMP ONLY LEAVING THE 12Z NAM AS A SLOWER...LOW
PROBABILITY SOLUTION.


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

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

OTTO

$$




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