032
FXUS10 KWNH 171831
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 PM EST TUE DEC 17 2019
VALID DEC 17/1200 UTC THRU DEC 21/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z EVALUATION WITH PREFERENCE AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..EASTERN CONUS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
EXCEPTION: 12Z NAM/ECMWF/UKMET WITH CANADIAN COASTAL LOW AFTER
36HRS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE CMC CONTINUES TO BE SLIGHTLY DEEPER/COLDER/MORE
CONCENTRIC...SO IT IS SLOWER WITH THE CANADIAN MARITIME SURFACE
LOW DEVELOPMENT...SO LESS FAVORABLE THERE. SO WILL FAVOR A BLEND
OF THE UKMET/NAM AND ECMWF OVER THE GFS/CMC.
---PRIOR DISCUSSION---
THE MODELS CONTINUE TO BE STRONGLY ALIGNED ACROSS WITH THE SURFACE
WAVE AND HIGHLY ELONGATED VORTICITY STRIPE AND WARM CONVEYOR BELT
REMAINING ALONG THE EAST COAST FOR THE REMAINDER OF THE DAY. THE
VERY STRONG/COMPACT COLD AIR DESCENDING ACROSS ONTARIO INTO THE
GREAT LAKES TOMORROW AND THROUGH NEW ENGLAND THURS IS ALSO FAIRLY
WELL AGREED UPON. THE 12Z GFS REMAINS A TAD WEAKER AND THEREFORE
A BIT FASTER WITH THE ASSOCIATED SHORTWAVE...BUT NOT SUBSTANTIALLY
SO FOR A LATE DAY 2 INTO DAY 3 SPREAD IN THE CONUS. AS THE
SURFACE CYCLONE DEVELOPS ALONG THE SE CANADIAN MARITIMES, THE GFS
BEING FAST IS NORTH WITH THE DEVELOPING WAVE; WHILE THE SLIGHTLY
COLDER SOLUTIONS OF THE CMC,UKMET AND 12Z NAM ARE SLIGHTLY SLOWER.
THE 12Z GFS IS CORRECTING RELATIVE TO THE 00Z/06Z BUT STILL
SHOULD BE REMOVED IF FORECASTING FOR CANADIAN MARITIME REGION.
FOR THE CONUS AND US WATERS, HOWEVER, WILL CONTINUE SUPPORTING A
GENERAL MODEL BLEND FOR THESE SYSTEMS AT ABOVE AVERAGE CONFIDENCE.
...TROUGH OFF WEST COAST SPLITS THROUGH TO NORTH-CENTRAL AND
SOUTHERN PLAINS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
EXCEPTIONS: NON-NAM IN NORTHERN STREAM ON LATE DAY 3 IN NORTHERN
PLAINS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: UKMET TRENDED SLOWER TO MATCH THE GFS, PLACING THE NAM
WELL FASTER/STRONGER THAN THE REMAINING GUIDANCE ACROSS THE
NORTHERN PLAINS ON DAY 3. AS FOR THE SOUTHERN STREAM, THE 12Z
ECMWF TRENDED A BIT BROADER WITH THE REMAINING SHORTWAVE ENERGY
WHICH IN TURN REDUCED THE SOUTHWARD DIG ACROSS NM INTO TX...AND
NOW MATCHES THE LATITUDE OF THE REMAINING GUIDANCE ACROSS THE RED
RIVER BY DAY 3...SO INCREASED CONFIDENCE IN A GENERAL MODEL BLEND
IN THE SOUTHERN STREAM, THOUGH TYPICAL TIMING DIFFERENCES EXIST
(GFS/NAM-FAST; EC/CMC-SLOW).
---PRIOR DISCUSSION---
GOES-WV SUITE DEPICT AN ELONGATED TROF ALONG/JUST WEST OF 130W AND
APPEARS TO BE SHARPENING INTO A MORE CONSOLIDATED BASE. THIS
WOULD FAVOR THE EVOLUTION OF THE UKMET/CMC AND ECMWF (ECENS/CMCE
MEANS) COMPARED TO THE 12Z NAM/GFS THAT STILL HAVE STRONGER ENERGY
(AND SURFACE REFLECTION) SLIGHTLY NORTH, BUT MOSTLY IN THE LOWER
TROPOSPHERIC LEVELS/SURFACE HOWEVER, AS THE WAVE ENTERS THE
WESTERN CONUS AND STRONG PACIFIC JET ADDS SPEED ENERGY/VIGOR TO
THE TROUGHING TOWARD THE PACIFIC NW BY LATE WED INTO THURS. THE
GUIDANCE STARTS TO ALIGN MUCH BETTER BUT STARTS SPLITTING THE
FLOW. THE NORTHERN STREAM ENERGY EVOLVES INTO A MEDIUM WAVELENGTH
SHORTWAVE WITH SOME NEGATIVE TILT ORIENTATION MOVING INTO THE
NORTHERN PLAINS BY FRIDAY. THE 12Z NAM SHOWS SOME LATE-TERM
OVER-AMPLIFICATION BIAS THAT TYPICALLY DOES NOT MANIFEST, THOUGH
IS ALONG THE FASTER FRINGE OF THE GUIDANCE SUITE AS WELL. IT IS
ACCOMPANIED BY THE UKMET, BUT THE 12Z GFS WHICH WAS PARTNERED
SLOWED A BIT AND TRENDED TOWARD THE GEFS MEAN/TIMING. THIS
GENERALLY MATCHES THE CMC/ECMWF/ECENS MEAN...SO WOULD FAVOR A
TREND A NON-NAM SOLUTION IN THE NORTHERN STREAM.
IN THE SOUTHERN STREAM, THE REMAINING SHORTWAVE ENERGY REMAINS
CONSOLIDATED THROUGH SHRINKS IN SIZE AS IT PROGRESSES THROUGH THE
FOUR CORNERS REGION ON THURSDAY. THE GUIDANCE CONTINUES TO
TIGHTEN TOWARD A COMMON SOLUTION, ANCHORED BY CONSISTENT
GEFS/ECENS MEANS. THE OPERATIONAL ECMWF SHOWS SOME NEGATIVE BIAS
OF VERY SMALL BUT COMPACT VORTICITY CENTER THAT EVENTUALLY DIGS
SOUTH, SLOWER ACROSS TX (AWAY FROM THE ECENS MEAN). THE 12Z GFS
SLOWED SUBSTANTIALLY, BUT REMAINS NORTH ALONG THE RED RIVER VALLEY
AT THE END OF DAY 3...MATCHING THE UKMET/NAM AND CMC ALONG WITH
THE MEANS. AS SUCH A GENERAL MODEL BLEND WILL SUFFICE ACROSS THE
SOUTHERN PORTION OF THE TROF. MANY SMALLER INTERNAL
SHORTWAVE/VORTICITY CENTERS IN A HIGHLY ELONGATED/SHEARED
ENVIRONMENT MOVING THROUGH COMPLEX TERRAIN IS A FAIRLY UNCERTAIN
SMALL SCALE FORECAST TO LOCK DOWN BUT OVERALL CONFIDENCE IS
SLIGHTLY ABOVE AVERAGE THROUGH THE LENGTH OF THE TROF, GIVEN THE
AGREEMENT OVERALL IN THE MASS FIELDS.
..PERSISTENT ONSHORE FLOW INTO THE PACIFIC NORTHWEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: LITTLE CHANGE HERE WITH THE AR; THOUGH THE
ECMWF/UKMET/CMC TRENDED A BIT WETTER OVERALL (NARROWING THE PLUME
SLIGHTLY). OTHERWISE, THE GENERAL MODEL BLEND PREFERENCE REMAINS
SOLID AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.
---PRIOR DISCUSSION---
IN THE WAKE OF THE ELONGATED TROF ENTERING THE PACIFIC COAST
WED... A STRONG CLOSED LOW WILL PARK OVER THE GULF OF ALASKA AND
DIRECT STRONG/PERSISTENT ONSHORE MOIST FLOW INTO THE PACIFIC
NORTHWEST AS A STRONG ATMOSPHERIC RIVER EVENT. TIMING OF EMBEDDED
SHORTWAVES ARE TOUGH TO PRECISELY LOCK DOWN, BUT THE LARGE SCALE
MASS FIELDS ARE FAIRLY STRONGLY ALIGNED. THERE ARE SOME TYPICAL
TIMING DIFFERENCES BETWEEN THE GFS/NAM/UKMET AND THE ECMWF/CMC
MAINLY WITH RESPECT TO THE ARRIVAL OF THE FIRST SURGE OF MOISTURE,
MAKING SHORTER-TERM (LESS THAN 6HR) QPF FORECASTS A BIT DIFFICULT
BUT LONGER DURATION 12-24HR TOTALS ARE LIKELY TO RESULT IN
SIGNIFICANT RAINFALL. WITH THE 12Z GFS SLOWING DOWN SIGNIFICANTLY
WITH THE INITIAL SHORTWAVE/NOSE OF THE JET...THE TIMING IS BETTER
OVERALL AND THE GFS COULD BE INCORPORATED BACK INTO THE
PREFERENCE. THIS RESULTS IN A GENERAL MODEL BLEND PREFERENCE FOR
THE MASS FIELDS...PLEASE SEE WPC QPF FORECAST GRIDS FOR
PREFERENCES IN TIMING...BUT CONFIDENCE IS INCREASED TO SLIGHTLY
ABOVE AVERAGE GIVEN SYNOPTIC BETTER AGREEMENT.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
GALLINA
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