002
FXUS10 KWNH 200634
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
233 AM EDT MON APR 20 2020
VALID APR 20/0000 UTC THRU APR 23/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..SURFACE LOW TRACKING OFF THE MID ATLANTIC COAST
THEN
SOUTHEAST OF NOVA SCOTIA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~
PREFERENCE: 18Z GFS/00Z ECMWF/12Z ECMWF ENSEMBLE MEAN BLEND
CONFIDENCE: AVERAGE
THE 00Z GFS IS FASTER THAN THE BULK OF THE GUIDANCE LIFTING THE
SHORT WAVE OVER THE SOUTHEAST THIS MORNING OFF THE MID ATLANTIC
COAST, THEN SOUTHEAST OF NOVA SCOTIA BY 21/12Z. AS A RESULT, IT IS
MUCH FASTER WITH THE SURFACE LOW THAT DEVELOPS AFTER LEAVING THE
MID ATLANTIC COAST. THE 19/18Z GFS, WHILE ALSO FASTER THAN THE
CONSENSUS, WAS CLOSER TO THE 00Z ECMWF/12Z ECMWF ENSEMBLE MEAN,
WHICH FOR A FAIRLY TIGHT CLUSTER WITH THE LOW.
THE 12Z UKMET REMAINS SLOWER/LEFT WITH THE SURFACE TRACK, AS ITS
SHORT WAVE IS SLOWER AND A BIT DEEPER THAN THE CONSENSUS (AND THE
00Z CMC). BASED ON THE ABOVE, AN 19/18Z GFS/00Z ECWMF/12Z ECMWF
ENSEMBLE MEAN IS PREFERRED. HOWEVER, GIVEN THE SPREAD IN THE TRACK
OF THE SURFACE LOW, ESPECIALLY AFTER 21/00Z, FORECAST CONFIDENCE
IS AVERAGE.
...DEVELOPING LONG WAVE TROUGH TAKING ON A NEGATIVE TILT OVER NEW
ENGLAND...
..SURFACE LOWS OVER QUEBEC/MAINE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/00Z ECMWF/00Z UKMET BLEND
CONFIDENCE: AVERAGE
SHORT WAVE ENERGY DIVING OUT OF CENTRAL CANADA IN THE FAST MID
LEVEL FLOW DROPS TO THE BASE OF A DEVELOPING LONG WAVE TROUGH OVER
THE UPPER GREAT LAKES BY 21/12Z. THE 00Z GFS/NAM ARE CLOSE TO THE
CONSENSUS THROUGH THIS TIME, BUT AS THE LONG WAVE TROUGH TAKES ON
A NEGATIVE TILT, THE 00Z NAM SLOWS THE FORWARD SPEED OF THE
TROUGH, BECOMING SLOWER THAN THE CONSENSUS AFTER 22/12Z.
THE 00Z GFS REMAINS CLOSE TO THE CONSENSUS THROUGH THE NEGATIVE
TILT. ITS DEPICTION OF THE PRIMARY LOW OVER QUEBEC AND AN
INCIPIENT SECONDARY SURFACE LOW FORMATION OVER SOUTHERN ME/COAST
WATER IS CLOSE TO THE 00Z ECMWF/00Z UKMET BLEND, FORMING A FAIRLY
TIGHT CLUSTER. IN CONTRAST, THE 12Z CMC BECOMES SLOWER AND WEAKER
WITH THE PRIMARY SURFACE LOW.
THOUGH MUCH OF THE GUIDANCE IS CLOSE WITH THE EVOLUTION OF THE
LONG WAVE TROUGH, THERE IS SOME SPREAD CONCERNING THE
PLACEMENT/STRENGTH OF THE SURFACE LOWS ASSOCIATED WITH IT. BASED
ON THE ABOVE, A 00Z GFS/00Z ECMWF/12Z ECMWF ENSEMBLE MEAN COMPRISE
THE PREFERRED BLEND. HOWEVER, DUE TO THE SPREAD IN THE SURFACE LOW
DETAILS, FORECAST CONFIDENCE IS AVERAGE.
..MID LEVEL TROUGH TRACKING FROM CA TO THE MID MS VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
THE 00Z NAM/GFS ARE CLOSE TO THE CONSENSUS TAKING THE SHORT WAVE
ENERGY FROM SOUTHERN NV ACROSS THE CENTRAL AND SOUTHERN ROCKIES
THROUGH 22/12Z. AFTER THAT TIME, THE 00Z NAM BECOMES DEEPER/SLOWER
WITH THE ELONGATING TROUGH, THOUGH NOT NEARLY AS DEEP AND SLOW
WITH SURFACE LOW AS THE 00Z UKMET.
THE 00Z GFS REMAINS CLOSE TO THE 00Z ECMWF WITH THE TROUGH
POSITION AS IT APPROACHES THE MID MS VALLEY, WITH THE 00Z CMC
STILL A BIT FLATTER AND WEAKER WITH TROUGH. THE 00Z GFS/00Z ECMWF
BLEND HAS GENERAL SUPPORT OF THE ENSEMBLE MEANS, SO THIS BLEND IS
PREFERRED. SINCE THERE IS SOME MODEL SPREAD CONCERNING HOW THE
PIECES OF SHORT WAVE ENERGY COALESCE IN THE MID LEVEL TROUGH,
FORECAST CONFIDENCE IS SLIGHTLY BELOW AVERAGE.
...SURFACE LOW TRACKING FROM WESTERN CANADA INTO THE NORTHERN
PLAINS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THE 00Z NAM/GFS ARE CLOSE TO THE CONSENSUS TAKING THE SURFACE LOW
OUT OF ALBERTA AND TRACKING IT ACROSS THE NORTHERN PLAINS TOWARD
THE END OF THE PERIOD. THOUGH THERE ARE SOME SUBTLE DIFFERENCES IN
THE TIMING OF THE SHORT WAVE ENERGY SUPPORTING THE SURFACE LOW IN
THE VERY FAST MID LEVEL FLOW, THERE IS ENOUGH CLUSTERING FOR A
GENERAL MODEL BLEND WITH THIS FEATURE.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
HAYES
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