507
FXUS10 KWNH 190444
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1243 AM EDT SUN APR 19 2020
VALID APR 19/0000 UTC THRU APR 22/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..TRACK OF THE SOUTHERN STREAM SHORT WAVE
...SURFACE LOW TRACKING ACROSS THE DEEP SOUTH TO THE MID ATLANTIC
COAST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 21/00Z, 00Z GFS/12Z
NAM/12Z CMC THEREAFTER
CONFIDENCE: AVERAGE
THE 00Z NAM/GFS ARE CLOSE TO THE CONSENSUS TAKING SHORT WAVE
ENERGY FROM NM ACROSS THE ARKLATEX TO THE DEEP SOUTH THROUGH
20/00Z. IN FACT, MUCH OF THE 00Z/12Z GUIDANCE IS CLOSE WITH THIS
FEATURE AND SURFACE LOW DEVELOPMENT ALONG THE MID ATLANTIC COAST
THROUGH 20/12Z. THE SURFACE LOW TRACKS ARE ABOUT THE SAME, SO THE
MAIN DIFFERENCES BETWEEN THE MODELS REMAINS THE PLACEMENT OF THE
AXIS OF HIGHEST RAINFALL, WHICH HAS MORE TO DO WITH MESOSCALE
INTERACTIONS AND THE OVERLAY OF THE INSTABILITY AND MID LEVEL
LIFT.
THE 12Z ECMWF/UKMET BECOME SLOWER AND LEFT OF THE CONSENSUS WITH
THE SURFACE LOW AFTER 21/00Z, LIKELY DUE TO THE SLOWER SHORT WAVE
ENERGY IN THE DEVELOPING TROUGH. BECAUSE OF THIS, THESE MODELS
WERE LEFT OUT OF THE PREFERRED BLEND BEYOND THAT TIME. BECAUSE OF
THE DIFFERENCES WITH THE QPF PLACEMENT AND THE TRACK OF THE
SURFACE LOW OFF THE COAST, FORECAST CONFIDENCE REMAINS AVERAGE.
...SHORT WAVE ENERGY TRACKING ACROSS CENTRAL CANADA INTO THE UPPER
GREAT LAKES...
..DEVELOPING LONG WAVE TROUGH HEADED FOR NEW ENGLAND
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODE BLEND THROUGH 21/12Z, 00Z GFS/12Z ECMWF
AFTER THAT
CONFIDENCE: SLIGHTLY ABOVE AVERAGE THROUGH 21/12Z, SLIGHTLY BELOW
AVERAGE AFTER THAT
THE 00Z GFS/NAM ARE CLOSE TO THE CONSENSUS TRACKING SHORT WAVE
ENERGY IN THE VERY FAST MID LEVEL FLOW FROM MANITOBA ACROSS THE
UPPER GREAT LAKES THROUGH 21/12Z. BEYOND THAT TIME, THE 00Z NAM
BECOMES SLOWER WITH THE DEVELOPING LONG WAVE TROUGH (WHICH TAKES
ON A NEGATIVE TILT) APPROACHING NORTHERN NEW ENGLAND. THE 12Z
UKMET/CMC APPEAR TO HAVE THE SAME ISSUE, WHILE THE 00Z GFS/12Z
ECMWF ARE CLOSER WITH THE LONG WAVE TROUGH AND THE SURFACE LOW
THAT STARTS DEEPENING OVER QUEBEC TOWARD THE END OF THE PERIOD.
SINCE THE GFS/ECMWF HAVE THE SUPPORT OF THEIR ENSEMBLE MEANS,
THESE SOLUTIONS COMPRISE THE PREFERRED BLEND. HOWEVER, DUE TO THE
SPREAD CONCERNING THE EVOLUTION OF THE DEVELOPING LONG WAVE
TROUGH, FORECAST CONFIDENCE DROPS TO SLIGHTLY BELOW AVERAGE TOWARD
THE END OF THE PERIOD.
...DEVELOPING LONG WAVE TROUGH OVER THE SOUTHWEST AND ROCKIES
MON/TUE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/12Z ECMWF/12Z UKMET BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
THE 00Z NAM/GFS ARE CLOSE TO THE MODEL CONSENSUS DROPPING A
POSITIVELY TILTED LONG WAVE TROUGH FROM THE PACIFIC NORTHWEST
ACROSS THE NORTHERN ROCKIES BEFORE 20/00Z. IN THE WAKE OF THIS
SHORT WAVE, MID LEVEL RIDGING DEVELOPS FROM CENTRAL CA INTO THE
PACIFIC NORTHWEST, PEAKING BEFORE 20/12Z BEFORE ERODING AHEAD OF
THE NEXT SHORT WAVE IN THE FLOW.
THE COLLAPSING MID LEVEL RIDGE IS RESULTING IN SOME MODEL
INSTABILITY CONCERNING HOW QUICKLY THE NEXT SHORT WAVE CROSSES THE
CA COAST BEFORE CLOSING OFF IN THE MID LEVELS OVER SOUTHERN NV BY
21/00Z. THE TIMING ISSUES SUGGEST THAT THE 00Z GFS MAY BE TOO
QUICK TO OPEN UP THE MID LEVEL CLOSED LOW INTO A LONG WAVE TROUGH
CROSSING THE SOUTHERN ROCKIES BY 22/12Z. IN CONTRAST, THE 00Z
NAM/12Z ECMWF/12Z UKMET INDICATED A SLOWER MOVEMENT, WHICH TRACKS
BETTER WITH A MID LEVEL CLOSED LOW OPENING UP AND MOVING EAST.
HOWEVER, THE DETAILS OF HOW THESE MODELS GET TO THE FINAL
SOLUTIONS MAY YET STILL CHANGE, CONSIDERING HOW MUCH SPREAD THERE
IS IN THE EVOLUTION OF THE CLOSED MID LEVEL SYSTEM. DUE TO THAT
SPREAD, FORECAST CONFIDENCE IS SLIGHTLY BELOW AVERAGE.
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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