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FXUS10 KWNH 291709
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
108 PM EDT SAT APR 29 2017

VALID APR 29/1200 UTC THRU MAY 03/0000 UTC

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

12Z NAM/GFS INCLUDING PRELIMINARY MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...STRONG CLOSED LOW REACHING THE PLAINS ON SUNDAY AND UPPER
MISSISSIPPI VALLEY ON MONDAY...SPURRING DEEP SURFACE CYCLONE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z GFS/00Z ECMWF
CONFIDENCE: AVERAGE

WHILE TRENDS HAD PREVIOUSLY BEEN SLOWER WITH THE EJECTION OF THE
CLOSED LOW THROUGH THE CNTRL PLAINS ON SUN...THE PREVIOUSLY
CONSISTENT ECMWF MEAN HAS JOINED THE FASTER TRENDING CAMP OF THE
00Z MODELS AND 12Z NAM/GFS. CURRENTLY...THE 12Z NAM STANDS AS A
SLOWER OUTLIER. GIVEN THE FASTER TRENDS FROM OVERNIGHT CONTINUES
TO BE SUPPORTED IN THE LATEST AVAILABLE 12Z GUIDANCE...THE 12Z NAM
APPEARS A LOW PROBABILITY SOLUTION. WHILE WOBBLING BACK TO A
SLOWER SOLUTION IS POSSIBLE WITH FUTURE DETERMINISTIC MODEL
CYCLES...THERE IS ENOUGH AGREEMENT IN THE LATEST ENSEMBLE
CLUSTERING FOR A POSITION NEAR THE 12Z GFS AND 00Z ECMWF.
CONFIDENCE IS ONLY AVERAGE GIVEN THE INCONSISTENCIES FROM RUN TO
RUN SINCE YESTERDAY.


...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC
NORTHWEST SAT TRANSLATING ACROSS THE S CANADIAN ROCKIES SPURRING
LEE SURFACE WAVE THAT SLIDES OUT OF ALB/SASK ACROSS N TIER LATE
MON/TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS...00Z ECMWF...00Z UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z NAM CONTINUES TO BE MUCH STRONGER THAN THE REMAINING
DETERMINISTIC AND ENSEMBLE MODEL CONSENSUS ACROSS SWRN CANADA ON
MON MORNING. THE RESULT OF THE STRONGER 12Z NAM SHOWS SOME MINOR
INTERACTION WITH THIS WAVE AND A LARGE CLOSED LOW LOCATED OVER THE
UPPER MISSISSIPPI VALLEY LATER MON INTO TUE. OUTSIDE OF THE 12Z
NAM...THIS SOLUTION IS NOT REPRESENTED AND SO A NON 12Z NAM IS
RECOMMENDED. THE 00Z CMC IS ON THE NRN EDGE OF THE SPREAD AND
WHILE THERE IS SOME MINOR ENSEMBLE SUPPORT FOR THE 00Z
CMC...BETTER AGREEMENT EXISTS FOR THE MIDDLE ROAD BEST REPRESENTED
BY THE 12Z GFS...00Z ECMWF AND 00Z UKMET.


...NEXT WEAK PACIFIC WAVE ENTERING PACIFIC NORTHWEST LATE MON AND
CROSSING N ROCKIES BY TUES MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND
CONFIDENCE: AVERAGE

A WEAK SHORTWAVE TOPS THE MEAN RIDGE IN THE EASTERN PACIFIC AND
MOVES SOUTHEAST ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES
MONDAY AND THEN INTO THE NORTHERN TO CENTRAL PLAINS AND CENTRAL
ROCKIES TUE. THE DEGREE OF RIDING UPSTREAM WILL INFLUENCE THE
DEGREE AND TIMING OF DEEPENING OF THIS FEATURE DOWNSTREAM ACROSS
THE ROCKIES. THE 00Z CMC SHOWS TOO DEEP WITH RESPECT TO THE
ENSEMBLES AS THE SHORTWAVE CROSSES THE WEST COAST. SOME LATITUDE
DIFFERENCES ARE BEST RESOLVED WITH A 12Z GFS AND 00Z ECMWF BLEND
GIVEN THESE TWO MODELS SEEM TO REPRESENT THE ENDS OF THE LATEST
ENSEMBLE CLUSTERING.


...PACIFIC CYCLONE OFFSHORE OF THE PACIFIC NORTHWEST LATE TUE...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/ECMWF BLEND
CONFIDENCE: AVERAGE

RELATIVELY MINOR DIFFERENCES EXIST WITH A SURFACE CYCLONE AHEAD OF
A SHORTWAVE ADVANCING AT THE FRONT EDGE OF CLOSED LOW IN THE GULF
OF ALASKA ON TUE. ENSEMBLE SPREAD IS AVERAGE WITH THIS
SYSTEM...AND THE 12Z GFS AND 00Z ECMWF ARE SIMILAR TO THE MIDDLE
OF THE SPREAD.


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

OTTO

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