425
FXUS10 KWNH 070436
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1236 AM EDT TUE APR 07 2020
VALID APR 07/0000 UTC THRU APR 10/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION WITH INITIAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SURFACE WAVE MOVING THROUGH GREAT LAKES LATE TUE/WED THEN SLIDING
OFFSHORE ALONG 40N WED/THURS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND (WEIGHTED HEAVY TO 12Z ECMWF/ECENS)
CONFIDENCE: AVERAGE
A WEAK SURFACE WAVE CURRENTLY IN SD, WILL PROGRESS THROUGH THE
GREAT LAKES LATER TODAY BETWEEN THE STRONGER DEEPER CLOSED LOWS
OVER THE SOUTHWEST AND EASTERN CANADA BUT ALSO PRIOR TO THE
STRONGER UPSTREAM PACIFIC WAVE. SO, THE MASS FIELDS DO NOT
INDICATE STRONG MID-LEVEL SHORTWAVE WITH THIS FEATURE BUT DUAL JET
STRUCTURE) AND LOW LEVEL JET WARM ADVECTIVE PROCESSES MAINTAIN IT
WELL BEFORE IT GROWS DEEPER OFFSHORE SOUTH OF LONG ISLAND BY WED,
ALONG THE BASE/FAVORABLE CYCLONIC CURVATURE ALOFT FROM THE EASTERN
CANADIAN CYCLONE. THE 00Z NAM IS CLEARLY STRONGER/MORE AMPLIFIED
ALOFT INITIALLY, A PERHAPS A TAD NORTH WITHIN THE ENSEMBLE SURFACE
CLUSTER, BUT IS PAIRED WITH THE 12Z UKMET TO GIVE SOME INCREASED
CREDENCE. THE 00Z GFS CONTINUES TO BE FAST RELATIVE TO THE SUITE
AND THE CMC IS VERY SLOW. THE ECMWF/ECENS MEAN ARE MORE CENTRAL
TO THE PACKING AND WILL RECEIVE GREATEST WEIGHTING IN THE
PREFERENCE, BUT TO ACCOUNT FOR SOME UNCERTAINTY, WILL SUPPORT A
NON-CMC BLEND AT AVERAGE CONFIDENCE.
UPPER TROUGH DIGGING ACROSS GREAT LAKES; SURFACE LOW DEVELOPING
OFF NEW ENGLAND COAST DAY 3
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z ECMWF BLEND
CONFIDENCE: AVERAGE
STRONG OMEGA BLOCK INITIALLY OVER NORTHERN CANADA, WILL DIRECT
PACIFIC JET TO UNDERCUT IT THROUGH CENTRAL CANADA. BINARY
SHORTWAVE INTERACTIONS WILL LEAD TO RAPIDLY DEVELOPING/DEVOLVING
CYCLONES ALONG THE SHEAR AXIS UNTIL REACHING THE UPPER GREAT
LAKES/MIDWEST BY LATE WED INTO THURSDAY, STARTING TO STRONGLY
AMPLIFY ALOFT TO A DEEP CLOSED LOW THAT WILL SWING THROUGH THE
LOWER GREAT LAKES BY THURSDAY. IN THE PROCESS A STRONG EMBEDDED
SHORTWAVE WILL DRIVE HEIGHT-FALLS/NEGATIVE TILTING THROUGH THE
MID-ATLANTIC AND HELP TRANSFER THE CENTER OF THE UPPER LOW TO A
MUCH STRONGER CLOSED DEEP CYCLONE IN NEW ENGLAND/GULF OF MAINE BY
00Z FRIDAY. A CLEAR OUTLIER MANIFEST EARLY, MAINLY IN THE INITIAL
SETUP FROM THE DOWNSTREAM WAVE: THE 12Z CMC. A WEAKER CORE
THROUGH MANITOBA/W ONTARIO AND SLOWER EXITING WAVE COMBINE TO
ACCELERATE THE NOSE OF THE JET AND ASSOCIATED NEW TRIPLE POINT LOW
FASTER AND FURTHER SOUTH WITH THE FASTEST COLD FRONT THROUGH THE
MID-ATLANTIC/EAST COAST, WHICH IS NOT PREFERRED. ON THE OPPOSITE
SIDE OF THE SPECTRUM, THE 00Z NAM IS VERY STRONG WITH THE INITIAL
CENTER LOW/OCCLUDED SURFACE WAVE IN ONTARIO, WHICH LEADS TO THE
TRIPLE-POINT AND UPSTREAM SHORTWAVE TO DIG SOUTH AND DEVELOP
SLOWER. THIS IS PAIRED WITH THE UKMET, BUT UNLIKE THE NAM, IT
RAPIDLY DEEPENS THE SURFACE WAVE ALONG THE GULF OF MAINE, LIKELY
WITH OVER-AGGRESSIVE LATENT HEAT RELEASE AND FEEDBACK TO CYCLONE
DEEPENING (WHICH THE UKMET HAS A KNOWN BIAS TOWARD) TO BE THE
STRONGEST SOLUTION BY THE END OF DAY 3.
THE 18Z GFS WHICH HAD BEEN SLOW/DELAYED DUE TO INITIAL INTERACTION
WITH A FASTER SOUTHERN STREAM CLOSED LOW; NO LONGER HAS THIS
CONNECTION AND TRENDED SLIGHTLY FASTER IN THE 00Z RUN, JUST
OUTPACING THE ECMWF AND NOW IS MORE IN LINE WITH THE 18Z GEFS.
GIVEN THE ECMWF/ECENS MEAN SHOW SOLID CONSISTENCY AND ARE CENTRAL
TO THE OVERALL SUITE, THE GFS COMBINED WITH THE ECWMF SEEMS AN
APPROPRIATE BLEND, WHILE KEEPING THE DOOR OPEN TOWARD A STRONGER
SOLUTION WITH FUTURE CYCLES. CONFIDENCE IS AVERAGE GIVEN THE
DYNAMIC EVOLUTION, HARDER PREDICTABILITY (UNDERCUTTING THE OMEGA
BLOCK TO THE NORTH).
SLOW MOVING SOUTHERN STREAM (S CA/DESERT SOUTHWEST) CLOSED LOW.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL THROUGH 09.12Z;
12Z CMC/ECENS MEAN AND 00Z GFS/NAM BLEND
CONFIDENCE: ABOVE AVERAGE BECOMING AVERAGE AFTER 09.12Z
DEEP CLOSED LOW OFF CENTRAL CA WILL CONTINUE TO SLIDE SOUTH ALONG
THE CA COAST LATE WED. MODELS CONTINUE TO HANDLE A SIMILAR
EVOLUTION THROUGH THIS POINT. AS THE INNER CORE DIFFERENCES GROW,
WITH TIMING/MAGNITUDE, THE RESULTANT BINARY INTERACTION
DIFFERENCES MAGNIFY AS THE TYPICALLY DO MAINLY LATE THURSDAY.
THE CONSISTENT OUTLIER, GFS, HAS SEEN A SIGNIFICANT SHIFT BACK
WEST WITH THE 00Z RUN, AND WHILE IT IS QUICKER TO BREAK DOWN THE
CYCLONE, IT IS QUITE CENTRAL TO THE PLACEMENT AS WELL AS HINTING
AT THE PROPER ORIENTATION OF THE INTERNAL WAVE, RELATIVE TO THE
REMAINDER OF THE GUIDANCE SUITE, PARTICULARLY THE 12Z ECENS MEAN.
THE 18Z GEFS WAS MORE SENSIBLE THAN THE 18Z GFS, BUT GIVEN THE
ADJUSTMENT SEEN, IT WOULD NOT BE SURPRISING TO SEE THE 00Z GEFS
SHIFT BACK TOWARD THE ECENS MEAN LATER. THE 00Z NAM, WHILE
STRONGER, TYPICAL OF THE LATE-TERM BIAS, LOOKS SENSIBLE IN
PLACEMENT/TIMING AS THE ECENS MEAN AND THE 00Z GFS AND 12Z CMC,
PROVIDING SOME CONFIDENCE IN A BLEND OF THESE SOLUTIONS. THE 12Z
UKMET IS NOW THE CLEAREST OUTLIER, SHOWING A TYPICAL NEGATIVE BIAS
OF OVER-AMPLIFYING A VORTICITY CENTER, WHICH SENDS THE OVERALL
CLOSED LOW WOBBLING BACK WEST WELL OUTSIDE OF THE CMCE/ECENS/GEFS
SUITE, AND IS NOT CONSIDERED FOR THE PREFERENCE, AT THIS TIME.
THE 12Z ECMWF IS SIMILARLY UNBALANCED FAVORING A WESTWARD WOBBLE
ON DAY 3; AND IS A DISTINCT WESTWARD MEMBER OF THE ENTIRE 12Z
ECENS SUITE. WHEN THIS OCCURS, IT IS TYPICAL TO NOT VERIFY VERY
WELL AND REDUCE ITS CONFIDENCE TOWARD INCLUSION. AS SUCH, A
GENERAL MODEL BLEND IS SUPPORTED THROUGH 09.12Z BUT TRANSITIONING
TO A 12Z CMC/ECENS MEAN AND 00Z GFS/NAM BLEND. THE AFOREMENTIONED
CONCERNS WITH THE GFS/NAM ARE LIKELY TO OFFSET IN THE BLEND TO
HAVE SOME CONFIDENCE; YET, IT IS ONLY CONSIDERED AVERAGE AFTER
9.12Z.
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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