Prognostic Meteorological Discussion
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FXUS10 KWNH 231709
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
108 PM EDT THU MAR 23 2017

VALID MAR 23/1200 UTC THRU MAR 27/0000 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...INCLUDING PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...NORTHERN STREAM SHORTWAVE CROSSING SOUTH-CENTRAL CANADA TODAY...
...CLOSED LOW DIVING THROUGH SOUTHEAST CANADA BY SAT MORNING...
...COLD FRONT ADVANCING DOWN ACROSS THE GREAT LAKES/NORTHEAST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

LARGEST DIFFERENCES DEVELOP ON SUN WITH THE MID-LEVEL TROUGH OVER
SRN CANADA AND HOW THAT RELATES TO THE POSITION OF THE SURFACE
BOUNDARY ACROSS THE NRN-MID ATLANTIC REGION. THE PRESENCE OF A
STRONGER SHORTWAVE EMANATING FROM THE BRITISH COLUMBIA/ALBERTA
BORDER THIS MORNING REACHING NEW ENGLAND SAT NIGHT ALLOWS FOR A
DEEPER AND FARTHER SOUTH LOWER HEIGHTS ACROSS NRN NEW ENGLAND AND
A FARTHER SOUTH SURFACE BOUNDARY. MULTI-CYCLE TRENDS IN THE
ENSEMBLES HAVE BEEN TOO THE NORTH ALONG WITH THE DETERMINISTIC
ECMWF...BUT BOTH LAG THE LARGER CLUSTERING TO THE NORTH. A FRONTAL
POSITION NEAR THE 12Z GFS HAS MORE ENSEMBLE SUPPORT AND LIES NORTH
OF THE ECMWF FOR SUN.


...STRONG UPPER TROUGH CROSSING THE SOUTHWEST/FOUR CORNERS TODAY...
...CLOSED LOW EVOLUTION OVER THE CENTRAL PLAINS FRI...
...ENERGY CROSSING THE MID MS/OH VALLEYS THROUGH SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

AT 500 MB...THERE HAS BEEN A NOTABLE TREND IN THE GEFS ENSEMBLES
TO ADJUST FASTER COMPARED TO SLOWER EARLIER CYCLES...SO MUCH SO
THAT THEY HAVE PASSED THE ECMWF ENSEMBLES WHICH HAVE BEEN TRENDING
SLOWER VALID LATE FRI. WHILE DIFFERENCES ARE RELATIVELY MINOR
THROUGH ABOUT 00Z/26...THE 12Z NAM/GFS PULL AWAY FASTER THAN THE
00Z ECMWF/UKMET/CMC FOR SUN WITH THE 500 MB AND SURFACE COLD
FRONT. THE 00Z UKMET BECOMES AN OUTLIER JUST AFTER 00Z/27. THE
INFLUENCE FROM AN UPSTREAM KICKER TROUGH MAY BE THE DECIDING
FACTOR IN THE TIMING OF THE DOWNSTREAM FEATURE. GIVEN TRENDS IN
THE GEFS BUT STEADY CONSISTENCY IN THE ECMWF...CONFIDENCE IS
LOWERED. GOING IN THE MIDDLE IS THE BEST APPROACH AT THIS
TIME...REPRESENTED BY A 50/50 BLEND OF THE 12Z GFS AND 00Z ECMWF.


...NORTHERN STREAM TROUGH/COLD FRONT REACHING THE NORTHWEST
THURS/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.


...SOUTHERN STREAM COMPONENT OF UPPER LEVEL TROUGH OVER THE WEST
ON SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z NAM/GFS HAVE TRENDED QUICKER WITH THE TIMING OF THE UPPER
TROUGH MOVING THROUGH THE FOUR CORNERS REGION SAT EVENING...AND
ARE CURRENTLY FASTER THAN THE 00Z ECMWF/UKMET/CMC. SIMILAR TO THE
2ND SYSTEM DESCRIBED IN THIS DISCUSSION...TRENDS IN THE GEFS HAVE
BEEN FASTER BUT THE ECMWF MEAN HAS BEEN INCONSISTENT. WHILE THE
PREFERENCE IS TO GO IN THE MIDDLE OF THE SLOWER AND FASTER...WOULD
NOT BE SURPRISED TO SEE LATER ARRIVING MODEL GUIDANCE TO JUMP
ABOARD THE FASTER TRENDS SEEN IN THE 12Z NAM AND 12Z GFS.


...UPPER TROUGH REACHING THE WEST COAST SUN EVENING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.


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

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

OTTO

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