315
FXUS10 KWNH 250440
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 AM EDT SAT APR 25 2020
VALID APR 25/0000 UTC THRU APR 28/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z PRELIMINARY EVALUATION WITH NAM/GFS MODEL PREFERENCES AND
FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SHORTWAVE AND ASSOCIATED DEVELOPING LOW PRESSURE MOVING FROM THE
MIDWEST THROUGH THE NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: ECMWF/ECENS/UKMET/NAM THROUGH D2, ECMWF/ECENS D3.
CONFIDENCE: SLIGHTLY BELOW AVERAGE
A SHORTWAVE MOVING THROUGH THE BROAD CYCLONIC FLOW ACROSS THE EAST
WILL DIG ACROSS THE TN VALLEY SATURDAY BEFORE INTERACTING WITH
SEVERAL OTHER IMPULSES TO AMPLIFY ACROSS THE
MID-ATLANTIC/NORTHEAST. THE LEAD SHORTWAVE IS LIKELY TO WEAKEN AS
A SECONDARY ENERGY DIGS INTO THE MEAN TROUGH AND BECOMES DOMINANT.
THIS WILL CAUSE THE SURFACE LOW ACROSS THE OH VALLEY TO TRANSFER
TOWARDS THE TIDEWATER OF VA AS NEW CYCLOGENESIS, WHICH WILL THEN
LIFT E/NE THROUGH MONDAY INTO THE GULF OF MAINE. THROUGH 48 HOURS,
THE MASS FIELDS, WITH THE EXCEPTION OF THE CMC, ARE IN GENERALLY
GOOD AGREEMENT. HOWEVER, IN THE 48-72 HOURS TIME FRAME, THE NAM
BECOMES MUCH DEEPER WITH THE CLOSED LOW AND DEGREE OF NEGATIVE
TILT FROM ONTARIO INTO MAINE. THE GFS/ECMWF AND ITS ENSEMBLES ARE
IN GENERALLY GOOD AGREEMENT IN THE UPPER TROUGH MONDAY/MONDAY
NIGHT AS IT CLOSES OFF EAST OF MASSACHUSETTS, BUT TIMING AND
INTENSITY DIFFERENCES OF THE COUPLED JET STRUCTURE LEAD TO
SIGNIFICANT PLACEMENT DISCREPANCY WITH THE SURFACE LOW. THE GFS IS
A BIT SLOWER AND WEST OF THE ECMWF, WHICH IS SLOWER THAN THE CMC.
THE GFS IS ALSO WARMER WITH ITS THERMAL STRUCTURE, WHICH SEEMS
UNLIKELY IN THE PRESENCE OF COLD CANADIAN HIGH PRESSURE TO THE
NORTH. THE ECMWF BEING IN THE MIDDLE, ALONG WITH ITS GOOD ENSEMBLE
SUPPORT, LENDS CREDENCE TO THIS SOLUTION, AND A HEAVY WEIGHT OF
ECMWF/ECENS IS PREFERRED IN THE BLEND. THE UKMET AND NAM ARE ALSO
USABLE, ESPECIALLY THROUGH 60 HOURS, BUT SHOULD HAVE LESS WEIGHT
ON D3.
TROUGH AXIS AFFECTING THE NORTHWEST INTO THE UPPER MIDWEST THROUGH
MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE
A LONG WAVE TROUGH AXIS ANCHORED ALONG THE GULF OF ALASKA WILL
HELP TO PIVOT MID-LEVEL ENERGY EAST INTO THE WEST COAST OF CANADA.
THIS FAIRLY WEAK TROUGH AXIS WILL TRAVERSE THE CANADIAN ROCKIES
THROUGH SUNDAY, MOVING INTO MANITOBA AND ONTARIO BY MONDAY. THE
IMPACT OF THIS TROUGH AXIS WILL BE MINIMAL ACROSS THE NORTHERN
ROCKIES AND PLAINS UNTIL IT INTERACTS WITH A BIT MORE MOISTURE,
EVENTUALLY BECOMING NEGATIVITY TILTED (STRONG FORCING FOR ASCENT)
ACROSS THE UPPER MIDWEST AND GREAT LAKES REGION. THE MODELS ARE
IN FAIRLY DECENT AGREEMENT, THOUGH THERE ARE SOME TIMING AND
AMPLITUDE DIFFERENCES. THESE VARIABILITIES ARE STILL WITHIN THE
MODEL GUIDANCE CLUSTERING WITH ONLY MODEST IMPACTS TO QPF/THERMAL
DIFFERENCE OVERALL.
SHORTWAVE ENERGY AFFECTING THE PACIFIC NORTHWEST ON MONDAY INTO
THE PLAINS BY TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z GEFS/12Z EC/ECENS
CONFIDENCE: AVERAGE
A SECOND PACIFIC SHORTWAVE WILL TRANSLATE ALONG THE BASE OF THE
CONSOLIDATING CLOSED LOW OVER THE GULF OF AK. THIS WAVE IS DRAWN
MORE NORTHWARD WITH ONLY THE BASE RAPIDLY SWINGING MORE NEGATIVE
THROUGH VANCOUVER ISLAND LATE SUNDAY INTO EARLY MONDAY. THE
TRAILING COLD FRONT AND MOISTURE PLUME PRESS ACROSS THE COASTAL
RANGE AND INTO THE NORTHERN US ROCKIES. THE TIMING AND AMPLITUDE
REPRESENTED BY THE MODELS DO VARY WITH THE GFS A BIT TOO FAST AND
THE UKMET ENTIRELY TOO SLOW BASED ON THE SPAGHETTI PLOTS. THE 00Z
NAM ALSO REMAINS A FAIRLY DRY OUTLIER AT THIS POINT AS WELL. AS
THE SYSTEM CONTINUES TO TRACK EAST, THE MASS FIELD DIFFERENCE
REMAIN CONSISTENT AND DO NOT DIVERGE GREATLY. HOWEVER, IT IS
APPARENT BY THE END OF DAY 3 (LATE MONDAY) THAT THE 00Z NAM IS
MORE PROGRESSIVE WITH THE ENERGY INTERACTING WITH THE TROUGH OFF
THE EAST COAST. IN ADDITION, THE 12Z UKMET WAS TOO SLOW AND THE
CMC TOO INCONSISTENT WITH ITS AMPLITUDE. BASED ON QPF ALONE,
THERE ARE SOME WILD DIFFERENCES THAT ARE NOT AS TIED TO THE
TYPICAL MASS FIELD STRUCTURE BUT RATHER THE IMPULSES THAT RIDE
WITHIN THE MID-LEVELS. REGARDLESS, BASED ON THE MASS FIELDS ALONE,
FELT BETTER CONSENSUS AMONG THE 00Z GFS, 12Z EC AND THEIR
RESPECTIVE ENSEMBLE MEANS.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
PAGANO/WEISS
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