900
FXUS10 KWNH 150649
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 AM EST FRI NOV 15 2019
VALID NOV 15/0000 UTC THRU NOV 18/1200 UTC
..SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..OVERALL PATTERN ACROSS THE CONUS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z NAM, GFS, ECMWF
NAM EXCLUDED ON DAY 3 (AFTER 17.12Z)
CONFIDENCE: AVERAGE
---06Z UPDATE---
NO CHANGE TO THE PRELIMINARY PREFERENCE. THE 00Z ECMWF HAS MADE A
NOTABLE TREND CLOSER TO THE COAST WITH ITS SURFACE LOW OFF THE
CAROLINAS. THIS LENDS SUPPORT TO INCLUDING THE NAM IN THE
PREFERENCE, EVEN THOUGH THE NAM EXITS THE LOW MUCH MORE QUICKLY
AND FURTHER NORTHWEST ON DAY 3. THEREFORE, THE PREFERENCE IS STILL
FOR A BLEND OF THE ECMWF, GFS AND NAM, WITH THE NAM EXCLUDED
BEGINNING ON SUNDAY.
---PREVIOUS DISCUSSION---
THE MOST SUBSTANTIAL MODEL DIFFERENCES ARE RELATED TO A STRONG
UPPER LEVEL LOW APPROACHING THE SOUTHEAST ATLANTIC COAST AND
RELATED CYCLOGENESIS OFF THE COAST OF THE CAROLINAS. OVER THE
REMAINDER OF THE CONUS, MODEL FORECAST PRECIPITATION IS EITHER
VERY LIMITED OR IN FAIRLY GOOD AGREEMENT IN AREAS OF STRONGER
OROGRAPHIC ASCENT IN THE PACIFIC NORTHWEST.
FOR THE SOUTHEAST, THE 00Z NAM CONTINUES TO PRODUCE A SURFACE LOW
CLOSER TO THE COAST, YIELDING HIGHER QPF OVER LAND AREAS. THE ONLY
RELATIVELY COMPARABLE DETERMINISTIC MODEL FORECAST IS FROM THE 12Z
CMC, WHICH HAS ITS SURFACE LOW POSITIONED SLIGHTLY FURTHER
OFFSHORE. THE REMAINING MODELS ARE SLOWER AND FURTHER OFFSHORE,
AND HAVE LESS QPF OVER LAND AREAS. THE TREND ON THE PAST SEVERAL
RUNS OF THE GFS HAS BEEN SLOWER AND THERE IS BETTER ENSEMBLE
SUPPORT FOR A LOW POSITION FURTHER OFFSHORE. NEVERTHELESS, GIVEN
THE STRENGTH OF THE UPPER LEVEL LOW APPROACHING THE COAST AND THE
PROXIMITY OF THE SEA-SURFACE TEMPERATURE GRADIENT TO THE COAST, A
SCENARIO CLOSER TO THE NAM IS NOT UNREASONABLE. THE MODEL
PREFERENCE IS FOR A BLEND OF THE NAM, GFS AND ECMWF TO PLACE
GREATER WEIGHT ON AN OFFSHORE SCENARIO, BUT INCORPORATE SOME
POTENTIAL FOR A CLOSER APPROACH TO THE COAST.
BY SUNDAY, THE NAM BEGINS TO DIVERGE MORE SIGNIFICANTLY FROM OTHER
MODELS, DRAWING THE SURFACE LOW NORTH TOWARD NEW ENGLAND, WHILE
THE REMAINING MODELS HAVE A TRACK MUCH FURTHER SOUTHEAST. THIS IS
RELATED TO DIFFERENCES WITH AN UPSTREAM SHORTWAVE DIGGING THROUGH
THE MIDWEST, AND THE INITIAL POSITION OF THE SURFACE LOW BEING
FURTHER NORTHWEST THAN THE REMAINING MODELS. THE ENSEMBLE SUPPORT
FOR SUCH A SCENARIO IS EVEN MORE LIMITED, AND AS A RESULT THE NAM
IS EXCLUDED FROM THE MODEL PREFERENCE AFTER 12Z SUNDAY.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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