559
FXUS10 KWNH 221709
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
108 PM EDT FRI MAY 22 2020
VALID MAY 22/1200 UTC THRU MAY 26/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z NAM/GFS EVALUATION INCLUDING PRELIMINARY PREFERENCES AND
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...CUT-OFF LOW IMPACTING THE OH VALLEY AND NORTHERN MID-ATLANTIC
INTO SUNDAY MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
ONLY MINOR TIMING DIFFERENCES EXIST WITH THIS SYSTEM WITH THE 00Z
UKMET SLOWEST AND 12Z GFS FASTEST. THE DIFFERENCES ARE GREATEST
AFTER THE SYSTEM MOVES OFFSHORE OF THE EAST COAST AND SO A GENERAL
MODEL BLEND SHOULD SUFFICE FOR THIS SYSTEM.
..DEEP UPPER TROUGH/CLOSED LOW RELOADING OVER THE WESTERN U.S
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/00Z ECMWF BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
THE 12Z NAM AND 12Z GFS STAND OUT EARLY IN THE PERIOD (SATURDAY
EVENING) WITH A FASTER PROGRESSION WITH A MID-LEVEL CLOSED LOW
TRACKING ACROSS THE GREAT BASIN. BY SUNDAY MORNING THE 12Z GFS
PULLS AWAY FROM ALL OF THE GUIDANCE WITH A FASTER PROGRESSION
TOWARD THE NORTHERN PLAINS. MEANWHILE, ADDITIONAL ENERGY WILL BE
DIVING INTO THE WESTERN U.S., HELPING TO AMPLIFY A LONGWAVE TROUGH
AXIS THROUGH MONDAY.
WHILE TRENDS HAVE BEEN SLOWER OVER THE PAST 24-48 HOURS WITH THE
MEAN TROUGH AXIS TRANSLATING EASTWARD, THE 12Z GFS REMAINS FASTER
TO TAKE THE SYSTEM EAST, WHILE THE 00Z UKMET IS SLOWEST. THE 12Z
NAM HAS SOME SIMILARITIES TO THE 00Z UKMET BY LATE MONDAY BUT WHEN
BLENDED WITH THE FASTER 00Z ECMWF, A FAVORABLE BLEND IS REACHED.
THE LATEST ENSEMBLE MEAN'S POSITION FOR THE TROUGH AXIS IS A
LITTLE SLOWER THAN THE 00Z ECMWF BUT AHEAD OF THE 12Z NAM. GIVEN
TRENDS IN THE ENSEMBLE GUIDANCE, PREFER TO BE SLIGHTLY SLOWER THAN
THE MEANS, ESPECIALLY WHEN CONSIDERING THE POTENTIAL CUTOFF NATURE
OF THIS SYSTEM MOVING FORWARD.
...SHORTWAVE LIFTING NORTHEAST TOWARD THE GREAT LAKES THROUGH
SATURDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM, 00Z ECMWF, 00Z CMC BLEND
CONFIDENCE: ABOVE AVERAGE
GENERALLY THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM, BUT
THE 12Z GFS IS SLIGHTLY QUICKER AND THE 00Z UKMET IS NOTABLY
SLOWER. PREFER THE MIDDLE GROUND AT THIS TIME WHICH IS NEAR THE
12Z NAM, 00Z ECMWF AND 00Z CMC.
...ZONAL FLOW INTO PACIFIC NORTHWEST WITH EMBEDDED WEAK
SHORTWAVES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-12Z GFS BLEND
CONFIDENCE: AVERAGE
THERE ARE SOME MINOR DIFFERENCES WITHIN A REGION OF ZONAL FLOW
SANDWICHED BETWEEN A LARGE CLOSED LOW CENTERED OVER THE ALUETIANS
AND BROAD RIDGING IN THE EASTERN PACIFIC. LOW AMPLITUDE SHORTWAVES
ARE FORECAST WITHIN THE ZONAL FLOW WITH IMPACTS MAINLY TO BRITISH
COLUMBIA. HOWEVER, A SLIGHTLY MORE DEFINED SHORTWAVE IS EXPECTED
TO NEAR VANCOUVER ISLAND EARLY NEXT WEEK, ASSOCIATED WITH COLD
FRONT A THE SURFACE WHICH WILL EDGE NEARER TO THE COAST.
THE NAM/GFS HAVE BEEN TRENDING STRONGER WITH THIS WAVE SINCE
YESTERDAY BUT THE 12Z GFS STANDS OUT WITH LOWER HEIGHTS INTO THE
PACIFIC NORTHWEST WHICH IS AGAINST THE REMAINING MODEL CONSENSUS.
A NON-12Z GFS BLEND IS PREFERRED AT THIS TIME.
...UPPER LEVEL SHORTWAVE LIFTING NORTHEAST ACROSS THE SOUTHERN
PLAINS SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-12Z GFS BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
AS THE DEEP TROUGH AND ASSOCIATED CLOSED LOW EVOLVES ACROSS THE
WEST THIS WEEKEND AND SLOWLY ENCROACHES ON THE HIGH PLAINS, THERE
WILL BE A SHORTWAVE TROUGH ROUNDING ITS BASE, LIFTING NORTHEAST
ACROSS THE SOUTHERN PLAINS ON SUNDAY. THERE IS POTENTIAL FOR
THUNDERSTORMS TO CONVECTIVE ENHANCE THE EXISTING SHORTWAVE OR
DEVELOP A SEPARATE CONVECTIVELY GENERATED VORTICITY MAX. SOME OF
THE GUIDANCE IS A BIT MORE BULLISH WITH THIS IDEA SUCH AS THE 00Z
UKMET AND 00Z CMC, BUT ONLY THE 12Z GFS STANDS OUT ENOUGH WITH A
FASTER TIMING (SIMILAR TO THE ABOVE SYSTEMS) TO BE EXCLUDED FROM
THE PREFERENCE.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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