Prognostic Meteorological Discussion
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FXUS10 KWNH 221732
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 PM EDT SUN OCT 22 2017

VALID OCT 22/1200 UTC THRU OCT 26/0000 UTC

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

12Z NAM/GFS EVALUATION...WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...UPPER TROUGH CROSSING THE NRN PLAINS/UPPER MS VALLEY TODAY WITH
ATTENDANT COLD FRONT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL CONSENSUS
CONFIDENCE: ABOVE AVERAGE

ONLY MINOR TIMING DIFFERENCES SHOW UP WITH THE LATEST MODELS
REGARDING THE COLD FRONT ACROSS THE GREAT LAKES REGION...BUT THEY
ARE SMALL ENOUGH TO PREFER A GENERAL MODEL COMPROMISE.


...SOUTHERN STREAM LOWER MS VALLEY CLOSED LOW DEVELOPMENT BY MON...
...SURFACE COLD FRONT SWEEPING ACROSS THE MS/TN VALLEYS...
...SURFACE LOW DEVELOPMENT OVER THE TN/OH VALLEYS...
...DEEP PHASED CYCLONE OVER THE GREAT LAKES REGION B-Y TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 40% 00Z ECMWF...40% 12Z NAM...20% 12Z GFS BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE

AN DEVELOPING CLOSED LOW APPROACHING THE LOWER MS VALLEY THIS
AFTERNOON IS EXPECTED TO ADVANCE EAST-NORTHEASTWARD OVER THE NEXT
24-36 HOURS WHILE ELONGATING AND ACQUIRING A NEGATIVE TILT. LOWER
THERE CONTINUES TO BE TIMING DIFFERENCES WITH THE SHORTWAVE AS IT
SWINGS NORTHEASTWARD AHEAD OF AN UPSTREAM AMPLIFYING UPPER TROUGH.
THE GFS HAS BEEN RATHER INCONSISTENT FROM RUN TO RUN AND IS
CURRENTLY TOWARD THE FASTER SIDE OF THE DETERMINISTIC GUIDANCE.
WHILE OTHER MODELS AND ENSEMBLE GUIDANCE HAS SHOWN SLIGHTLY
QUICKER TRENDS SINCE YESTERDAY...IT IS THOUGHT THE 12Z GFS IS TOO
FAST. THE ECMWF HAS ONLY SHOWN MINOR CHANGES OVER THE PAST 3
CYCLES ENDING WITH ITS 00Z/22 CYCLE.

A TIMING CLOSER TO THE 00Z ECWMF/12Z NAM...WITH A SLIGHT NUDGE IN
THE DIRECTION OF THE 12Z GFS IS RECOMMENDED. THIS BLEND STAYS
TOWARD THE MIDDLE TO FRONT EDGE OF THE LATEST ENSEMBLE
GUIDANCE...AND IS FASTER THAN THE 00Z UKMET/CMC...WITH THE 00Z CMC
CONSIDERED LEAST LIKELY TO VERIFY GIVEN OVERALL MODEL TRENDS AND
ITS PLACEMENT TOWARD THE SLOWER END OF THE ENSEMBLE GUIDANCE.
CONFIDENCE REMAINS A BIT LOWER THAN AVERAGE GIVEN THE POOR RUN TO
RUN CONSISTENCY IN A MAJORITY OF THE MODEL GUIDANCE.


...SHORTWAVE CROSSING B.C./PACIFIC NORTHWEST TODAY AND SWEEPING
ACROSS THE NORTHERN PLAINS/MIDWEST MON...
...WEST COAST RIDGE/SANTA ANA WIND DEVELOPMENT MON/TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL CONSENSUS
CONFIDENCE: ABOVE AVERAGE

ALTHOUGH THE 00Z CMC REMAINS A BIT STRONGER WITH THE LOW-MID LEVEL
RIDGE OVER THE WESTERN U.S...THERE IS ENOUGH AGREEMENT TO SUPPORT
A GENERAL MODEL COMPROMISE.


...SHORTWAVE DIGGING TOWARD THE NORTHERN PLAINS TUES NIGHT...
...ASSOCIATED SURFACE LOW OVER SOUTHERN CANADA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z UKMET/00Z ECMWF/12Z GFS
CONFIDENCE: AVERAGE

THE 00Z UKMET SPLITS THE DIFFERENCE IN POSITION AND IS A BIT
WEAKER THAN THE FASTER/SOUTHERN 00Z ECMWF AND SLOWER/NORTHERN 12Z
GFS. A 3-WAY BLEND OF THE 00Z UKMET/00Z ECMWF/12Z GFS FITS TOWARD
THE MIDDLE OF THE LATEST ENSEMBLE SPREAD WITH NO CONSISTENT TRENDS
NOTED IN THE LATEST GUIDANCE.


...SHORTWAVE TROUGH APPROACHING THE PACIFIC NORTHWEST BY WED...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/00Z UKMET/00Z ECMWF MEAN
CONFIDENCE: AVERAGE

THE 00Z ECMWF HAS BEEN CONSISTENTLY TOWARD THE DEEPER SIDE OF THE
DETERMINISTIC/ENSEMBLE SPREAD WITH THE ECMWF MEAN CONSISTENTLY
WEAKER/FLATTER WITH THE SHORTWAVE AS IT REACHES THE NORTHWEST
U.S./SOUTHWEST CANADA. THE 12Z GFS/00Z UKMET IS SLIGHTLY WEAKER
THAN THE 00Z ECMWF MEAN BUT A BLEND OF THE 3 MODELS SHOULD ALLOW
FOR A FAVORABLE COMPROMISE/BLEND REGARDING THIS =SYSTEM TO AFFECT
THE INTERIOR NORTHWEST.


www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

OTTO

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