Prognostic Meteorological Discussion
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FXUS10 KWNH 221701
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
101 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 NAM/GFS EVALUATION WITH PRELIMINARY 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: 12Z NAM...12Z GFS...00Z ECMWF 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 00Z CMC REMAINS ON THE STRONGER SIDE WITH THE
HIGH PRESSURE AND HAS THE COLD FRONT FARTHEST SOUTH.
HOWEVER...ENSEMBLE SPAGHETTI PLOTS SHOW THE MIDDLE GROUND NEAR THE
00Z CMC AND 00Z UKMET WHICH IS A BIT FARTHER SOUTH THAN THE 00Z
ECMWF MEAN...AND CURRENTLY LIES NEAR THE 00Z ECMWF AND THE 12Z NAM
AND 12Z GFS. THE PREFERENCE IS TO STAY NEAR THE MIDDLE OF THE
LATEST ENSEMBLE SPREAD GIVEN TRENDS...WHICH IS NEAR THE 12Z
NAM/GFS AND 00Z ECMWF.


...STRONG UPPER TROUGH ADVANCING FROM THE SOUTHWEST ON THU INTO
  THE SRN/CNTRL PLAINS FOR FRI AND MS VALLEY FOR SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS...00Z ECMWF...00Z UKMET 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 GFS...00Z ECMWF AND 00Z UKMET REPRESENT A MIDDLE
GROUND IN THE ENSEMBLE SPREAD THAT IS PREFERRED. THIS 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: 12Z GFS...00Z ECMWF...00Z UKMET 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
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...00Z ECMWF AND 00Z UKMET.


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

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

OTTO

$$





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