661
FXUS10 KWNH 201644
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1243 PM EDT WED MAY 20 2020
VALID MAY 20/1200 UTC THRU MAY 24/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..CUT-OFF LOW OVER LOWER OH AND TN RIVER VALLEYS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 20.12Z GFS BLEND BEYOND 22.00Z
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
OVERALL, THE 12Z NCEP GUIDANCE MAINTAINED CONTINUITY WITH THEIR
PREVIOUS RUNS IN THE EVOLUTION OF THE LARGE CUT-OFF LOW OVER THE
LOWER OH AND TN RIVER VALLEYS THROUGH FRIDAY MORNING. GRADUALLY
THE LOW BEGINS TO FILL AND WITH THE APPROACHING UPPER TROUGH
ACROSS THE CENTRAL PLAINS, ITS ENERGY BECOMES ABSORBED. THE GFS
ALLOWS THIS TO HAPPEN MUCH FASTER THAN THE OTHER GUIDANCE, DUE IN
PART, TO THE FASTER PROGRESSION OF THE TROUGH AXIS OVER THE
INTERIOR WEST AND ROCKIES. THE OTHER GUIDANCE (ESPECIALLY THE
20/00Z ECMWF AND UKMET) SHOW A SLOWER PROGRESSION WITH THE LOW
REMAINING CUT-OFF THROUGH MUCH OF THE PERIOD.
GIVEN THE OUTLIER SOLUTION OF THE 20/12Z GFS FROM OTHER GLOBAL
MODELS AND EVEN FROM THE 20/00Z GEFS MEAN, THE WPC BLEND
PREFERENCE WILL REMAIN FOR A NON-GFS SOLUTION BEYOND 22/00Z, WITH
MORE WEIGHT GIVEN TO THE ECMWF/UKMET DETERMINISTIC SOLUTIONS.
..DEEP UPPER TROUGH/CLOSED LOW OVER THE WESTERN U.S. WEDNESDAY
..SECONDARY UPPER TROUGH OVER THE PACIFIC NORTHWEST BY THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NAM/ECMWF/UKMET BLEND
CONFIDENCE: AVERAGE
THE LATEST GUIDANCE SHOWS AVERAGE TO SLIGHTLY ABOVE AVERAGE
AGREEMENT FOR THE LONGWAVE TROUGH OVER THE WEST THAT WILL LIFT
TOWARD THE NORTHERN ROCKIES OVER THE NEXT 1-2 DAYS. TOWARD DAY
2/3, ANOTHER SHORTWAVE DROPPING SOUTHEAST OVER THE PAC NW ABSORBS
THE INITIAL WAVE AND FORMS A LARGE CLOSED LOW WITH SEVERAL LOBES
OF VORTICITY PIVOTING AROUND THE CENTER. IN THE LARGE SCALE SENSE,
THE MODELS ALL HAVE THIS SCENARIO, ALTHOUGH HOW EACH INDIVIDUAL
VORT MAX PLAYS OUT DIFFERS IN STRENGTH AND PLACEMENT. OVERALL, THE
20/12Z GFS WAS THE LEAST FAVORED BECAUSE IT WAS STILL FASTER THAN
THE REST OF THE GUIDANCE AND BECAUSE IT STILL AMPLIFIES THE TWO
SHORTWAVES TOGETHER EARLIER. THE NAM APPEARS USEFUL THROUGH ABOUT
48 TO 54 HOURS BEFORE IT STARTS TO LAG THE ECMWF/UKMET AND
ENSEMBLE MEANS. OVERALL, THE WPC BLEND PREFERENCE IS FOR A NEAR
EQUAL WEIGHTING OF THE NAM/ECMWF/UKMET.
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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