020
FXUS10 KWNH 110450
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1149 PM EST TUE DEC 10 2019
VALID DEC 11/0000 UTC THRU DEC 14/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..LARGER SCALE CONUS (CONFIDENCE DISCUSSION)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE BROAD GLOBAL TROF THAT HAS DOMINATED THE EASTERN HALF OF THE
NA CONTINENT GIVES WAY TOWARD A MORE ZONAL PATTERN OVER THE NEXT
FEW DAYS, LEAD BY SMALLER SHORTWAVE ENERGY PACKETS ALONG THE
REMAINING NW-SE STRETCHED TROF CURRENTLY ENTERING THE WEST COAST
(ONE NORTH ALONG THE VANCOUVER ISLAND/PUGET SOUND AND SOUTHERN
NEAR CAPE MENDOCINO IN N CA). EVENTUALLY, THE LEAD NORTHERN AND
SOUTHERN STREAM WAVES PROGRESS INTO THE PLAINS BEFORE GIVING FULL
WAY TO A STRONG PACIFIC JET WITH NUMEROUS VERY SHORT
WAVELENGTH/LOW AMPLITUDE WAVE PARADE INTO THE PACIFIC NORTHWEST,
MIDDAY WED TO LATE FRIDAY WITH THE APPROACH OF A DEEPER LATITUDE
SHORTWAVE TROF ENTERING SAT. HIGH CONFIDENCE IN GENERAL MODEL
BLEND WILL EXIST FOR THE REMAINING GLOBAL SCALE TROF AND FRONTAL
ZONE CROSSING THE EAST COAST/NORTHEAST TODAY, AFTERWARD HOWEVER,
THE TIMING/SPACING OF NUMEROUS SMALLER SCALE FEATURES AND THEIR
INTERACTIONS LEAD TO LARGE INTERNAL VARIATIONS, WITH MODERATE TO
HIGH DIFFERENCES IN THE SENSIBLE WEATHER PREDICTABILITY EVEN
THOUGH THE LARGE SCALE EVOLUTION OF A BROADLY NEGATIVE TILT TROF
AND SOUTHEAST SURFACE LOW DEVELOPMENT IS AGREED UPON. SO
BOTTOM-LINE, CONFIDENCE IS SLIGHTLY BELOW TO BELOW AVERAGE FOR THE
INTERNAL PRECISE PLACEMENT OF IMPORTANT WEATHER ELEMENTS AS THE
SYSTEM COMES TOGETHER BY THE WEEKEND.
...NORTHERN STREAM SHORTWAVES ACROSS NORTHERN TIER INTO GREAT
LAKES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~
PREFERENCE: INITIALLY 00Z GFS/NAM AND 12Z ECMWF THRU 13.06Z
18Z GEFS/00Z NAM AND 12Z ECMWF/ECENS AFTER
CONFIDENCE: SLIGHTLY ABOVE AVERAGE TO AVERAGE
THE NORTHERN STREAM, STARTING WITH THE SHORTWAVE ENTERING THE
PACNW AT THIS TIME, IS BETTER HANDLED THROUGH THE SHORT-RANGE
PERIOD...WITH A SOLID CONSENSUS/GENERAL MODEL BLEND WORKING ACROSS
THE NORTHERN TIER INTO THE GREAT LAKES BY FRI. ON ITS HEELS,
THOUGH, THERE IS MORE VARIATION, MAINLY IN TIMING SPACING BETWEEN
THE PACIFIC SHORTWAVE ENERGY AND THE DIGGING ARCTIC COLD AIR.
HERE THE ECMWF, NAM AND GFS ARE SOLID IN TIMING, BUT THE GFS SHOWS
A TYPICAL THOUGH MINOR TO MODERATE FAST BIAS WITH THE COLD AIR AND
THEREFORE GREATER AMPLIFICATION. THE 00Z NAM, WHILE SPACED
NICELY, SHOWS A GREATER REFLECTION OF THE WAVE IN THE HEIGHT
FIELDS, BUT THAT SEEMS TO BE THE ONLY NEGATIVE IMPACT. SO WOULD
BE SHIFTING MORE TOWARD A 18Z GEFS MEAN, 00Z NAM, 12Z ECMWF BLEND
SOLUTION FOR THIS SYSTEM BUT AT AVERAGE TO SLIGHTLY ABOVE AVERAGE
CONFIDENCE.
..SOUTHERN STREAM/DEVELOPING SOUTHEAST SURFACE LOW FRI/SAT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/12Z ECMWF (12Z ECENS MEAN)
CONFIDENCE: SLIGHTLY BELOW TO BELOW AVERAGE
THE SOUTHERN STREAM SYSTEMS/ENERGY ARE MORE UNCERTAIN, MAINLY
DRIVEN BY THE UNCERTAINTY IN MODELS HANDLING THE INTERNAL WAVES OF
THE ZONAL JET. INITIALLY THOUGH THE LEAD WAVE IS A BIT MORE
CERTAIN IN ITS TIMING THROUGH THE 00Z GFS TRENDED A BACK TOWARD A
STRONGER AND FURTHER SOUTH SOLUTION WHICH SHORTENS THE SPACING
FROM THE NORTHWARD RETURNING SUBTROPICAL SHORTWAVE AND ASSOCIATED
MOISTURE/INSTABILITY FLUX OUT OF THE GULF THURSDAY. THE TIGHTER
SOLUTION OF THE GFS LEADS TO A LONGER RETENTION OF THE WAVE
RELATIVE TO A MORE FAVORABLE 00Z NAM/12Z ECMWF AND CMC SOLUTIONS
THAT FIT THE ENSEMBLE SUITE BETTER; THE UKMET REMAINS UNRESOLVED
WITH THE WAVE (WELL TOO WEAK). GETTING THE INITIAL SETUP IS
GOING TO BE CRITICAL TOWARD THE EVOLUTION/INTERNAL SENSIBLE
WEATHER ACROSS THE SOUTHEAST UP THE EAST COAST BY 12Z
SAT...BECAUSE THE SHORTWAVE EMERGING FROM THE 150KT 250H JET OUT
OF THE PACIFIC/INTERMOUNTAIN WEST, INTERACT AND LEAD TO A GENERAL
LARGER SCALE NEGATIVE TILT TO THE 5H PATTERN. THE GFS BEING
STRONGER UPSTREAM, ENHANCES THE DEFORMATION ZONE ACROSS AL INTO TN
GREATER THAN THE ECMWF WHICH IS WEAKER AND MORE PROGRESSIVE
LEADING TO MORE MOISTURE/FLUX CONVERGENCE OUT OF THE GULF AND
EASTERN ATLANTIC ACROSS THE CAROLINAS. THE 00Z NAM WHICH HAS
INITIAL CONDITIONS A BIT MORE FAVORABLE INITIALLY THAN THE 00Z
GFS; DOES EVOLVE A STRONGER MORE COMPACT UPSTREAM WAVE (THOUGH IN
LINE WITH TYPICAL NEGATIVE DAY 3 BIAS), AND IS A SPLIT BETWEEN THE
GFS AND ECWMF CAMPS. THE CMC IS UNCHARACTERISTICALLY PROGRESSIVE
WITH THE ENTIRE LARGE SCALE TROF AND IS DISMISSED AS THE WAVE
SHOULD BE WAITING FOR THE LARGER SCALE HEIGHT-FALLS EMERGING FROM
THE STRONG UPSTREAM JET. SO ALL CONSIDERED, WILL BE FAVORING THE
ECMWF/ECENS MEAN ACROSS THE SOUTHEAST BY THE LATE WEEK/SAT, THOUGH
INCORPORATING THE NAM MAY HELP HEDGE THE MODERATE TO HIGH INTERNAL
UNCERTAINTY.
..WEST
~~~~~~~~~~~
PREFERENCE: 00Z GFS/NAM AND 12Z ECMWF
CONFIDENCE: AVERAGE
AS STATED IN CONUS DISCUSSION ABOVE, PARADE OF SMALL AMPLITUDE
SHORTWAVES IN STRONG ZONAL JET MAKE DECIPHERING A PREFERENCE
EXTREMELY DIFFICULT GIVEN THE SPACING TO WAVES MAY BE BELOW 6HRS
AND WHERE SYNOPTIC FORCING HITS OROGRAPHIC FORCING ENHANCEMENT IS
BEST HANDLED BY A GENERAL MODEL BLEND AND HIT HAZARDS AT LONGER
TIME SCALES SUCH AS 12/24HR PACKS. STILL, TOWARD THE END OF THE
TRAIN, A STRONGER/GREATER AMPLITUDE SHORTWAVE TRACKS THROUGH WITH
SOME MODERATE NEUTRAL TO NEGATIVE TILT ORIENTATION LATE FRIDAY
INTO EARLY MORNING SAT WITH AN ASSOCIATED SURFACE CYCLONE.
REMARKABLY, THE GLOBAL GUIDANCE IS FAIRLY AGREEABLE WITH THE
TIMING AND MASS FIELDS AS A WHOLE, PROVIDING SOME CONFIDENCE. THE
LARGE DIFFERENCES ARE THE WIDTH OF THE UPPER LEVEL SYSTEM, WITH
THE GFS A BIT MORE SLOWER AND BROADER SUPPORTED MORE BY THE CMC
WHILE THE NAM/ECMWF ARE WELL PLACED/SHAPED BUT NARROWER AND THE
UKMET IS MOST NARROW AND NEGATIVELY TILTED. WILL HEDGE MORE OF A
COMPROMISE BETWEEN THE 00Z NAM/GFS AND 12Z ECWMF.
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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