798
FXUS10 KWNH 180451
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1245 AM EDT SAT APR 18 2020
VALID APR 18/0000 UTC THRU APR 21/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z NAM/GFS EVALUATION WITH INITIAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...SHORT WAVE ENERGY TRACKING FROM THE MID MS VALLEY INTO SOUTHERN
NEW ENGLAND...
...SURFACE LOW PRESSURE CROSSING THE OHIO VALLEY INTO THE NORTHERN
MID ATLANTIC...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THE 00Z NAM/GFS ARE CLOSE TO THE CONSENSUS TAKING SHORT WAVE
ENERGY FROM IA/MO ACROSS THE OH VALLEY INTO SOUTHERN NEW ENGLAND
BY THIS EVENING. THE SHORT WAVE AIDS IN SPINNING UP SURFACE LOW
PRESSURE ON A FRONTAL BOUNDARY EXTENDING ACROSS THE SOUTHERN OH
VALLEY, WHICH TRACKS TO THE SOUTHERN NEW ENGLAND COAST. THE
SURFACE LOW DEEPENS OFF THE NEW ENGLAND COAST AFTER 20/12Z, AND
THE 12Z ECMWF/CMC BECOME A BIT SLOWER THAN THE CONSENSUS ONCE THIS
OCCURS.
THE DIFFERENCES ARE GREATEST ONCE THE SURFACE LOW IS WELL OFF THE
COAST, SO THE SENSIBLE WEATHER WITH THE SYSTEM IS OFFSHORE. BASED
ON THIS, A GENERAL MODEL BLEND IS PREFERRED, WITH SLIGHTLY ABOVE
AVERAGE CONFIDENCE, INFLUENCED BY DIFFERENCES LATE IN THE PERIOD.
..SHORT WAVE ENERGY IN THE SOUTHERN STREAM
...SURFACE LOW TRACKING FROM THE SOUTHERN PLAINS TO THE MID
ATLANTIC COAST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z ECMWF BLEND THROUGH 20/12Z, 00Z GFS/12Z
GEFS/12Z ECMWF MEAN THEREAFTER
CONFIDENCE: AVERAGE
THE 00Z NAM/GFS ARE CLOSE TO THE CONSENSUS TAKING THE SHORT WAVE
ENERGY IN THE SOUTHERN STREAM FROM AZ/NM INTO THE SOUTHERN PLAINS
BY 20/00Z. AFTER THIS TIME, THE 00Z NAM BECOMES FLATTER AND FASTER
WITH THE MID LEVEL WAVE, WHICH RESULTS IN A SLIGHTLY NORTHWARD
DISPLACEMENT OF THE SURFACE LOW TRACK THAT FORMS OVER THE SOUTHERN
PLAINS.
THE 00Z GFS HAS BEEN THE MOST CONSISTENT WITH THE TRACK OF THE
SHORT WAVE AND DEVELOPING SURFACE LOW OVER THE PAST THREE MODEL
CYCLES. IT IS CLOSELY MIRRORED BY THE 12Z ECMWF THROUGH ABOUT
20/00Z. HOWEVER, THE 12Z ECMWF BECOMES FLATTER AND SLOWER WITH THE
MID LEVEL SHORT WAVE, WHICH RESULTS IN THE SURFACE LOW LAGGING THE
CONSENSUS. BECAUSE OF THIS, THE 12Z ECMWF IS DROPPED FROM THE
PREFERENCE AFTER 20/12Z, AND THE MODEL PREFERENCE BECOMES THE MORE
CONSISTENT 00Z GFS, WHICH HAS THE SUPPORT OF THE 12Z GEFS AND 12Z
ECMWF ENSEMBLE.
GIVEN THE AMOUNT OF SPREAD IN THE GUIDANCE, ESPECIALLY WITH THE
TRACK OF THE SURFACE LOW, FORECAST CONFIDENCE IS AVERAGE.
...SHORT WAVE ENERGY IN THE NORTHERN STREAM FROM MANITOBA INTO THE
UPPER GREAT LAKES...
...ATTENDANT COLD FRONT CROSSING THE NORTHERN PLAINS INTO THE
UPPER GREAT LAKES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
WHILE THERE IS GENERALLY GOOD MODEL AGREEMENT WITH THE SHORT WAVE
IN THE VERY FAST MID LEVEL FLOW TRACKING FROM CENTRAL MANITOBA
INTO THE UPPER GREAT LAKES BETWEEN 20/12Z AND 21/12Z, THE 00Z NAM
BECOMES SLOWER THAN THE CONSENSUS WITH THE CLOSED LOW THAT FORMS
OVER EASTERN ONTARIO BY THE END OF THE PERIOD.
THERE IS ALSO FAIRLY GOOD MODEL AGREEMENT WITH TIMING OF THE
SURFACE COLD FRONT THAT CROSSES THE NORTHERN PLAINS INTO THE GREAT
LAKES. DESPITE SOME TIMING ISSUES IN THE SIX HOUR FORECAST PERIODS
WITH THE FRONT, THERE IS ENOUGH MODEL CLUSTERING TO FAVOR A
GENERAL MODEL BLEND WITH SLIGHTLY ABOVE AVERAGE FORECAST
CONFIDENCE.
..SHORT WAVE OVER THE PACIFIC NORTHWEST INTO SUN
..SHORT WAVE APPROACHING THE CENTRAL CA COAST LATE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
THE 00Z GFS/NAM ARE CLOSE TO THE CONSENSUS WITH THE SHORT WAVE
THAT DROPS SOUTH FROM WESTERN BRITISH COLUMBIA ACROSS THE PACIFIC
NORTHWEST THROUGH 19/12Z. AFTER THAT TIME, THE 00Z NAM BECOMES
FASTER AND FLATTER WITH THE INITIAL SHORT WAVE AS IT KICKS OUT
OVER THE NORTHERN ROCKIES. THE 00Z GFS REMAINS CLOSER TO THE
CONSENSUS BY EJECTING THE INITIAL SHORT WAVE MORE SLOWLY ACROSS
THE GREAT BASIN.
THE NEXT SHORT WAVE IN THE FLOW TRACKS TOWARD THE CENTRAL CA COAST
AFTER 20/12Z. THERE IS QUITE A BIT OF MODEL SPREAD CONCERNING THE
TIMING OF THIS SHORT WAVE, AS IT UNDERCUTS MID LEVEL RIDGING
ACROSS THE PACIFIC NORTHWEST. THOUGH THERE IS A LOOSE CONSENSUS
TAKING THE MID LEVEL SYSTEM OVER NV/AZ BY THE END OF THE PERIOD,
EACH SOLUTION TAKES A SLIGHTLY DIFFERENT ROUTE GETTING THERE. AT
THIS POINT, A 00Z GFS/12Z ECMWF BLEND IS PREFERRED, AS THESE
MODELS HAVE THE SUPPORT OF THEIR ENSEMBLE MEANS. HOWEVER, SINCE IT
IS UNCLEAR HOW THE SECOND SHORT WAVE EVOLVES OVER THE SOUTHWEST
LATE IN THE PERIOD, 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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