Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8
000
FXUS10 KWNH 261857
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 PM EDT WED APR 26 2017

VALID APR 26/1200 UTC THRU APR 30/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

12Z MODEL EVALUATION WITH FINAL PREFERENCES/CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...CYCLONE OVER THE MIDDLE ATLANTIC MOVING NORTHEAST OFFSHORE OF
NEW ENGLAND THROUGH THU...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS HAVE AGREED WELL ON THE FORECAST FOR THIS FEATURE AND
SHOWN STRONG RUN TO RUN CONSISTENCY FOR THE PAST FEW CYCLES. THE
12Z SUITE OF MODELS REMAIN CLOSE TO THE MODEL CONSENSUS.


...LARGE UPPER TROUGH AND FRONTAL SYSTEM OVER THE CENTRAL UNITED
STATES MOVING ACROSS GREAT LAKES/MISSISSIPPI VALLEY LATE TODAY AND
REACHING THE ATLANTIC COAST THU NIGHT/FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-12Z NAM MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

A TREND OVER THE PAST FEW MODEL RUNS IS FOR A SLIGHTLY MORE
ENERGETIC AND NEGATIVELY TILTED MID LEVEL TROUGH AS IT MOVES
ACROSS THE MIDDLE MISSISSIPPI VALLEY TONIGHT AND LIFTS NORTH
ACROSS THE GREAT LAKES LATE THU/THU NIGHT...AND THIS IS REINFORCED
BY THE 12Z MODELS. THE MAIN DISCREPANCY IN MODEL SOLUTION IS THAT
THE 12Z NAM IS SLIGHTLY LESS PROGRESSIVE WITH THE SURFACE FRONTAL
POSITION AND MOISTURE FIELDS. THE 12Z ECMWF...CMC...AND UKMET ARE
IN CLOSE AGREEMENT WITH THE 12Z GFS...SO THE 12Z NAM STILL LOOKS
LIKE THE OUTLIER..AND A BLEND THAT EXCLUDES IT WOULD PROBABLY
YIELD THE BEST COMPROMISE.


...UPPER LOW OVER SOUTHERN ALBERTA MOVING SLOWLY EAST ACROSS
SASKATCHEWAN INTO SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS HAVE AGREED WELL ON THE FORECAST FOR THIS FEATURE AND
SHOWN STRONG RUN TO RUN CONSISTENCY FOR THE PAST FEW CYCLES. THE
12Z SUITE OF MODELS REMAIN CLOSE TO THE MODEL CONSENSUS.


...LARGE UPPER TROUGH DEEPENING OVER THE INTERMOUNTAIN WEST AND
PLAINS THU NIGHT/FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-12Z NAM MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

MULTIPLE SHORTWAVES EMBEDDED IN A STRONG NORTHWESTERLY JET ACROSS
THE CENTRAL GREAT BASIN WILL DEEPEN A LARGE UPPER TROUGH OVER THE
INTERMOUNTAIN WEST AND PLAINS THU NIGHT AND FRI...AND THIS SYSTEM
SHOULD BE A SIGNIFICANT WEATHER PRODUCER OVER THE CENTRAL/SOUTHERN
PLAINS AND INTO THE MISSISSIPPI VALLEY BY FRI NIGHT OR SAT (AND
BEYOND). THE MODELS CONTINUE TO BE IN GENERALLY GOOD
AGREEMENT...WITH THE 12Z RUNS REINFORCING THE TREND FOR A DEEPER
LOW THAT IS DIGGING A BIT FURTHER SOUTH. THIS TREND LOOKS
BELIEVABLE GIVEN THE LIKELIHOOD OF A 150+ KT NORTHWEST JET
COMBINED WITH STRONG AND EXTREMELY MOIST LOW LEVEL INFLOW FROM THE
GULF OF MEXICO.

THERE ARE SOME MINOR DIFFERENCES IN THE MODELS AS THE LEADING EDGE
OF THE UPPER TROUGH REACHES THE PLAINS OF FRI...WITH THE 12Z
NAM/GFS A BIT FASTER AND STRONGER. THE 12Z ECMWF HAS TRENDED
SLIGHTLY TOWARD THE NAM/GFS IN THIS REGARD...BUT IT STILL SHOWS A
WEAKER SURFACE REFLECTION AND A SUPPRESSED MOISTURE FIELD. THE 12Z
NAM IS NOTED TO BE THE STRONGEST WITH THE SURFACE REFLECTION AND
STANDS TO BE ON THE EDGE OF THE LATEST DETERMINISTIC MODEL
GUIDANCE. A BLEND OF THE 12Z GFS AND 12Z ECMWF SHOULD YIELD A
REPRESENTATIVE FORECAST COMPROMISE.


...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC
NORTHWEST SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/12Z ECMWF BLEND
CONFIDENCE: AVERAGE

THE 12Z SUITE OF MODEL SOLUTIONS HAVE TRENDED A BIT DEEPER AND
FURTHER SOUTH WITH THE PARENT LOW REACHING THE CENTRAL BRITISH
COLUMBIA COAST LATE SAT...IN PARTICULAR THE GFS AND EVEN MORE SO
THE UKMET. THE 12Z ECMWF SOLUTION IS NOT AS EMPHATIC WITH THIS
TREND...BUT IT DOES SUPPORT THE SOLUTION SHOWN BY THE 12Z
GFS...AND AT THIS POINT A BLEND OF THOSE TWO MODELS PROBABLY
YIELDS THE BEST COMPROMISE AND A REPRESENTATIVE FORECAST.


WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/

MCDONNAL/OTTO

$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.