947
FXUS10 KWNH 141836
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 PM EDT SUN JUN 14 2020
VALID JUN 14/1200 UTC THRU JUN 18/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..CLOSED LOW DEVELOPING IN SOUTHERN APPALACHIANS MON/TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH TUESDAY NIGHT
NON-NAM WEDNESDAY
CONFIDENCE: ABOVE AVERAGE
19Z UPDATE: THE UKMET DID SLOW DOWN A BIT MORE TOWARDS THE PRIOR
PREFERENCES, SO IT CAN BE ADDED BACK INTO THE BLEND FOR THE ENTIRE
FORECAST TIME PERIOD. OTHERWISE, LITTLE CHANGE IN THE SPREAD WITH
ONLY THE NAM BEING A WESTERN OUTLIER D3.
PREVIOUS DISCUSSION:
THROUGH 60 HOURS, THERE IS LITTLE DISAGREEMENT IN THE GUIDANCE
EVOLUTION OF A CLOSED LOW DROPPING ACROSS THE SOUTHERN
APPALACHIANS AND INTO GA/SC WHERE IT WILL STALL AND SLOWLY FILL. A
GENERAL BLEND IS ACCEPTABLE THROUGH TUESDAY. ON WEDNESDAY, SOME
DIVERGENCE IN THE SOLUTIONS BEGINS AS THE NAM SENDS A POTENT VORT
LOBE WESTWARD, DRAGGING THE WEAKENING LOW CENTER WITH IT, WHILE
BEING FORCED IN THAT DIRECTION AS WELL BUT STRONGER MID-LEVEL
RIDGING TO THE N/NW. THE UKMET DOES JUST THE OPPOSITE, LIFTING THE
WEAKENING LOW QUICKLY TO THE NORTH, AND WHILE A SLOW NORTHWARD
MOTION IS LIKELY, SOMETHING AS FAST AS THE UKMET SEEMS UNLIKELY
SINCE THE SYSTEM IS COMPLETELY REMOVED FROM THE MEAN FLOW AND
BLOCKED BY RIDGING TO THE NORTH. THIS LEAVES THE ECMWF/GFS/CMC AS
THE BEST CONSENSUS, WHICH ALSO HAS SUPPORT FROM THE ECENS AND GEFS
MEANS. DESPITE THE COMPARABLE MASS FIELDS, QPF DISCREPANCIES DO
EXIST, ESPECIALLY BY D3, AS THE ECMWF WANTS TO SPREAD HEAVIER
RAINFALL FURTHER INLAND INTO THE CAROLINAS/VIRGINIA THAN THE
CMC/GFS. THERE HAS BEEN LITTLE CONSISTENCY IN THE HEAVIEST QPF
AXIS RECENTLY, BUT NOTE A SUBTLY STRONGER JET MAX AND LFQ ROTATING
NORTHWARD AND OFFSHORE D3. THIS COULD ALLOW FOR SOME HEAVIER
QPF/SUBTLY DEEPER SURFACE PRESSURE FALLS NEAR THE COAST TO LIFT
INLAND, SO THE ECMWF SOLUTION CANNOT BE RULED OUT. WILL MAINTAIN
THE PREFERENCES HOWEVER, BUT NOTE THAT THIS BLEND WOULD WASH OUT
SOME OF THE HEAVIER QPF POTENTIAL BY D3.
...INTERACTION OF SHORTWAVE LIFTING THROUGH SW CANADA WITH A
CLOSED LOW ADVECTING ONSHORE WASHINGTON SUNDAY...
..SECONDARY CLOSED LOW MOVING INTO THE NORTHWEST TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC THROUGH 17/00Z
12Z GFS/12Z ECMWF THEREAFTER
CONFIDENCE: ABOVE AVERAGE THROUGH D2, AVERAGE D3
INTERACTION OF A SHORTWAVE LIFTING INTO SASKATCHEWAN AND A CLOSED
LOW MOVING ONSHORE WASHINGTON STATE DRIVES THE BLEND THROUGH
17/00Z. THE GUIDANCE IS VERY WELL CLUSTERED WITH THESE FEATURES
INITIALLY, WITH ONLY THE CMC BECOMING AN OUTLIER ON D2 AS IT SENDS
THE LEADING SHORTWAVE TOO FAR TO THE EAST COMPARED TO CONSENSUS.
THIS LEAVES LESS BINARY INTERACTION BETWEEN IT AND THE APPROACHING
BUT WEAKENING CLOSED LOW, AND ALLOWS THE NEWLY FORMING GYRE/TROUGH
AXIS TO BE DISPLACED FURTHER WEST. OTHERWISE, SENSIBLE DIFFERENCES
ARE MINIMAL AT THIS TIME.
BEYOND 17/00Z, SPREAD BEGINS TO EXPAND. AS ANOTHER CLOSED LOW
DROPS OUT OF THE GULF OF ALASKA AND ONSHORE WASHINGTON TUESDAY, A
LARGE GYRE WILL FORM ACROSS WESTERN CANADA/NORTHWEST CONUS. ENERGY
SHEDDING AROUND THE APPROACHING CLOSED LOW WILL LIFT ONSHORE PRIOR
TO THE CLOSED LOW, AND THE UKMET IS MUCH TOO FAST WITH THIS FIRST
VORT LOBE. THIS ENERGY MOVING TOO QUICKLY EAST CAUSES THE
INTERACTION OF THE APPROACHING LOW AND THE PREVIOUS ONE TO BE
STRETCHED/SHEARED TOO FAR TO THE SOUTHEAST, AND OUT OF TOLERANCE
WITH THE OTHER GUIDANCE WHICH DUMBBELL THE VORT MAXES N/S AROUND
EACH OTHER. OTHERWISE, THE NAM/GFS/ECMWF ARE ALL QUITE SIMILAR
BOTH WITH THE INTERACTION, AND WITH THE INTENSIFICATION OF THE
SHORTWAVE AS IT TILTS NEGATIVELY INTO MONTANA D3. THE NAM DOES
BEGIN TO LAG LATE D3, LIKELY IN RESPONSE TO SUBTLY STRONGER LFQ
JET DYNAMICS AS A JET STREAK PIVOTS AROUND THE CLOSED FEATURE, AND
FOR SLIGHTLY HIGHER HEIGHTS BLOCKING TO THE EAST. WHILE THE
GFS/ECMWF ARE FASTER THAN THE NAM SHIFTING THIS FEATURE EASTWARD,
IMPRESSIVE DYNAMICS SHOULD BE ABLE TO DRIVE HEIGHT FALLS INTO THE
RIDGE AS THE SHORTWAVE PIVOTS E/NE, AND THE AGREEMENT COMBINED
WITH THE ENSEMBLE MEANS PRODUCES THE SUGGESTED BLEND FOR D3.
WEISS
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page