812
FXUS10 KWNH 270647
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 AM EDT MON APR 27 2020
VALID APR 27/0000 UTC THRU APR 30/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
7Z UPDATE: AFTER THE ARRIVAL OF ALL THE 00Z GUIDANCE, THE CMC IS
SLIGHTLY WEAKER WITH THE NOR'EASTER OFF THE COAST OF NEW ENGLAND
AND THE GFS IS STILL A LITTLE BIT FASTER WITH THE SHORTWAVE
TROUGH, WITH SAME PREFERENCES ADJUSTED FOR 00Z CYCLE. FOR THE
MIDWEST SYSTEM, THE GFS REMAINS THE QUICKEST WITH MID-LEVEL HEIGHT
FALLS ACROSS THE NORTH-CENTRAL U.S. AND THE CMC SLIGHTLY WEAKER
WITH THE UPPER LOW, BUT OVERALL GOOD AGREEMENT IN THE MODELS FOR
AN 84-HOUR FORECAST GIVEN THE AMPLIFIED PATTERN IN PLACE. FOR THE
PACIFIC NORTHWEST, THE ECMWF TRENDED MORE IN LINE WITH THE OTHER
MODELS REGARDING TIMING OF THE SECOND SHORTWAVE ON DAY 3.
DEVELOPING NORTHEAST COASTAL LOW THROUGH MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM/00Z ECMWF/00Z UKMET BLEND
CONFIDENCE: MODERATE-HIGH
THE DUAL-SURFACE LOW OVER THE MID-ATLANTIC REGION ON SUNDAY IS NOW
CONSOLIDATING INTO A PRIMARY LOW JUST OFF CAPE COD AS A DEVELOPING
NOR'EASTER. THIS IS IN RESPONSE TO A STRONG SHORTWAVE PIVOTING
AROUND A LARGER UPPER LOW OVER NEW ENGLAND. A TRIPLE POINT LOW IS
LIKELY TO DEVELOP SOUTH OF NOVA SCOTIA BY MONDAY NIGHT, AND THEN
EVOLVE INTO THE PRIMARY LOW BY TUESDAY. THE MODELS OVERALL ARE IN
GOOD AGREEMENT MASS FIELD WISE, WITH THE 00Z GFS A LITTLE FASTER
WITH THE 500MB TROUGH AXIS BY TUESDAY MORNING AND BEYOND, AND THE
CMC SLIGHTLY WEAKER WITH THE 700MB LOW.
TROUGH AXIS CROSSING CANADIAN PRAIRIES, CLIPPING UPPER
MIDWEST/GREAT LAKES THROUGH MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: HIGH
A NORTHERN STREAM SHORTWAVE WILL TRACK ACROSS MINNESOTA AND OVER
THE NORTHERN GREAT LAKES THROUGH MONDAY, AND WILL SUPPORT THE
PASSAGE OF A WEAK COLD FRONT ACROSS THE NORTHERN PLAINS. THERE IS
ENOUGH MODEL AGREEMENT TO MERIT A GENERAL MODEL BLEND.
LOW PRESSURE TRACKING FROM THE NORTHERN PLAINS TO THE GREAT LAKES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/UKMET/12Z ECENS BLEND
CONFIDENCE: MODERATE-HIGH
SOME OF THE SHORTWAVE ENERGY FROM THE LARGE PACIFIC TROUGH
CURRENTLY NEAR BRITISH COLUMBIA CROSSES THE CANADIAN ROCKIES, AND
THEN AMPLIFIES AS A DOWNSTREAM TROUGH ACROSS THE CENTRAL AND
NORTHERN PLAINS BY TUESDAY MORNING. THIS WILL INDUCE SURFACE
CYCLOGENESIS ACROSS SOUTH DAKOTA AND NEBRASKA, CROSSES THE MIDWEST
STATES ON TUESDAY, AND THEN DEVELOPS FURTHER AS IT REACHES
MICHIGAN UNDER THE PRESENCE OF A DEEPENING UPPER TROUGH AND CLOSED
LOW. THE MODELS ARE IN GOOD AGREEMENT MASS FIELD WISE THROUGH
ABOUT 12Z TUESDAY. THE 00Z NAM APPEARS A LITTLE FASTER AND
FARTHER NORTH WITH THE MID LEVEL CLOSED LOW, AND FASTER WITH THE
COLD FRONT REACHING THE EAST COAST BY THE END OF THE FORECAST.
THE GFS IS THE FASTEST TO BRING HEIGHT FALLS TO THE MIDWEST AND
MID-SOUTH. THE 12Z CMC IS ON THE SLOWER AND WEAKER SIDE OF THE
GUIDANCE, AND THE UKMET IS STRONGER. TAKING THESE DIFFERENCES
INTO ACCOUNT, A BLEND OF THE 12Z ECMWF/ECENS/UKMET WORKS WELL AS A
STARTING POINT.
GLANCING EFFECTS (FRONT) OF LEAD SHORTWAVE LATE TUES/WED IN
PACNW...FULL BODIED SHORTWAVE REACHING PACNW BY 00Z THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 12Z WEDNESDAY, THEN A 00Z
UKMET/ECMWF/12Z ECENS BLEND
CONFIDENCE: MODERATE
THE NEXT PACIFIC SHORTWAVE HAS TRENDED A BIT FARTHER NORTH AND NOT
AS AMPLIFIED. GIVEN THE OLDER GULF OF ALASKA UPPER LEVEL GYRE
WILL BE ERODING LATE MONDAY INTO TUESDAY, THE ARRIVAL OF THE
UPSTREAM SHORTWAVE LATE TUESDAY WILL RESET THE LARGER SCALE TROUGH
BUT DISPLACE IT EASTWARD. THIS WILL ALLOW FOR STRONG
SOUTHWESTERLY MOISTURE TRANSPORT OVER SOUTHWEST BRITISH COLUMBIA
AND CLIPPING WESTERN WASHINGTON BY LATE TUESDAY AND EARLY
WEDNESDAY. A SECOND PACIFIC SHORTWAVE WILL QUICKLY APPROACH ON
WEDNESDAY, AND WITH THE LINGERING FRONTAL ZONE DIRECTED TOWARD THE
WASHINGTON COAST, ANOTHER SURGE OF MOISTURE WILL LIKELY REACH
WESTERN WASHINGTON BY WEDNESDAY EVENING. A GENERAL MODEL BLEND
WORKS THROUGH ABOUT 12Z WEDNESDAY, AFTER WHICH THE GFS TRENDS
FASTER WITH THE SECOND SHORTWAVE, AND THE ECMWF SLOWER AND FARTHER
SOUTH WITH THE SURFACE LOW. THE 12Z UKMET AND CMC ARE CLOSE TO
THE ENSEMBLE MEANS AND CAN BE USED IN CONJUNCTION WITH THE ECENS
FOR THE DAY 3 PERIOD.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
HAMRICK
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