275
FXUS10 KWNH 260643
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
242 AM EDT SUN APR 26 2020
VALID APR 26/0000 UTC THRU APR 29/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
7Z UPDATE: THE 00Z UKMET TRENDED MUCH CLOSER TO THE MODEL
CONSENSUS WITH THE DAY 3 LOW DEVELOPING ACROSS THE MIDWEST AND
THEN OVER MICHIGAN BY THE END OF THE FORECAST PERIOD. THE 00Z GFS
REMAINS THE FASTER SOLUTION WITH THE PROGRESSION OF THE SHORTWAVE
TROUGH ACROSS THE NORTHERN PLAINS AND MIDWEST ON TUESDAY, AND THE
00Z CMC IS SLIGHTLY SLOWER WITH THE LOW AND THE COLD FRONT TIMING.
OTHERWISE, THERE ARE NOT ANY MAJOR CHANGES NOTED WITH THE 00Z
NON-NCEP GUIDANCE.
SHORTWAVE AND DEVELOPING LOW PRESSURE MOVING FROM THE OHIO VALLEY
THROUGH THE NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-GFS CONSENSUS
CONFIDENCE: MODERATE-HIGH
A WELL DEVELOPED SURFACE LOW CURRENTLY OVER THE OHIO VALLEY WILL
GRADUALLY WEAKEN ON SUNDAY WHILE A NEW SURFACE LOW EVOLVES NEAR
THE DELMARVA COAST. THIS MILLER-TYPE B CYCLOGENESIS WILL RESULT
IN A NOR'EASTER NEAR THE 40N/70W BENCHMARK BY MONDAY MORNING, AND
SLOWLY TRACK TOWARDS THE NORTHEAST AND SOUTH OF NOVA SCOTIA
THROUGH TUESDAY. THE MAIN DIFFERENCE NOTED WITH THE MODELS IS A
WARMER THERMAL PROFILE ON THE 00Z GFS COMPARED TO THE OTHER
GUIDANCE OWING TO A NORTHWARD DISPLACEMENT OF THE 850 MB LOW.
TROUGH AXIS AFFECTING THE NORTHWEST INTO THE UPPER MIDWEST/GREAT
LAKES THROUGH MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: HIGH
SHORTWAVE AND DEVELOPING SURFACE LOW CURRENTLY OVER ALBERTA WILL
CROSS SOUTHERN CANADA WITH A COLD FRONT CLIPPING THE NORTHERN TIER
OF THE U.S. NORTHERN PLAINS THROUGH SUNDAY EVENING. THERE IS NOW
ENOUGH DETERMINISTIC MODEL AGREEMENT TO MERIT THE USE OF A GENERAL
MODEL BLEND WITH THIS FRONT.
SHORTWAVE ENERGY AFFECTING THE PACIFIC NORTHWEST ON MONDAY INTO
THE PLAINS BY TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL BLEND THROUGH 12Z TUESDAY, THEN 00Z ECMWF/12Z
ECENS/00Z NAM BLEND
CONFIDENCE: MODERATE
THE FIRST OF TWO NOTEWORTHY STORM SYSTEMS TO IMPACT THE PACIFIC
NORTHWEST IS EXPECTED TO ARRIVE ON SUNDAY NIGHT AND INTO MONDAY
MORNING WITH A COLD FRONT QUICKLY MOVING INLAND, AND THE PARENT
SURFACE LOW LIFTING NORTHEAST TOWARDS THE GULF OF ALASKA. SOME OF
THE SHORTWAVE ENERGY FROM THIS TROUGH CROSSES THE CANADIAN ROCKIES
AND SPAWNS A NEW SURFACE LOW ACROSS SOUTHERN ALBERTA BY MONDAY
EVENING AND THIS REACHES THE NORTHERN PLAINS BY TUESDAY AFTERNOON.
SECONDARY CYCLOGENESIS EVOLVES AROUND THE SAME TIME ACROSS THE
MIDWEST STATES AND EVENTUALLY BECOMES THE NEXT MAJOR STORM SYSTEM
TO AFFECT THE EASTERN U.S. THE MODELS ARE IN GOOD AGREEMENT MASS
FIELD WISE THROUGH ABOUT 12Z TUESDAY, AFTER WHICH THE 12Z UKMET IS
FARTHER NORTH AND MUCH STRONGER WITH THE MIDWEST SURFACE LOW
DURING THE DAY 3 PERIOD TUESDAY NIGHT. THE 00Z NAM IS A LITTLE
FASTER WITH THE LOW AND THE 00Z GFS A BIT FASTER WITH THE TRAILING
COLD FRONT ACROSS THE MID-SOUTH. THERE IS RELATIVELY GOOD
AGREEMENT AMONG THE ECMWF/ECENS/NAM TO SUPPORT THIS BLEND AS AN
INITIAL STARTING POINT IN THE FORECAST PROCESS.
COLD FRONT REACHING PACIFIC NORTHWEST LATE TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/12Z ECENS/00Z GFS
CONFIDENCE: MODERATE
THE NEXT MAJOR STORM SYSTEM TO APPROACH BRITISH COLUMBIA FROM THE
NORTHEAST PACIFIC WILL LIKELY BE TUESDAY AFTERNOON AFTER A BRIEF
BREAK FROM THE PRIOR STORM. THE COLD FRONT SHOULD REACH
WASHINGTON AND OREGON BY TUESDAY EVENING, BUT SHOULD WEAKEN AFTER
THAT SINCE IT WILL BE GOING INTO AN UPPER LEVEL RIDGE AXIS OVER
THE INTERMOUNTAIN WEST. THE NCEP GUIDANCE IS A BIT FASTER THAN
THE NON-NCEP GUIDANCE, BUT THERE ARE LESS IN THE WAY OF
LATITUDINAL DIFFERENCES. THE UKMET HAS BEEN CONSISTENTLY SLOWER
WITH THIS SYSTEM. A BLEND OF THE ECMWF/EC MEAN/GFS SHOULD WORK AS
A BASELINE.
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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