Prognostic Meteorological Discussion
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FXUS10 KWNH 271846
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 PM EDT FRI MAR 27 2015

VALID MAR 27/1200 UTC THRU MAR 31/0000 UTC

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

12Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


LONGWAVE UPPER TROUGH MOVING ACROSS THE EAST COAST THIS WEEKEND
DEEPENING SURFACE LOW TRACKING UP EAST OF NOVA SCOTIA SAT NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/12Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

DIFFERENCES ARISE ACROSS LONG ISLAND AND SOUTHEASTERN NEW ENGLAND
TOMORROW AND ARE PARTIALLY TIED TO A MID-LEVEL SHORTWAVE LIFTING
FROM THE MID-ATLANTIC COAST TONIGHT AND A DEEPENING SURFACE LOW
CROSSING SOUTHEAST OF THE 40N/70W BENCHMARK SAT MORNING. THE
GFS/ECWMF REPRESENT THE MIDDLE OF THE 12Z DETERMINISTIC MODEL
SPREAD AS RUN TO RUN CONTINUITY CONTINUES TO SHOW SOME CHANGES.
THE 12Z UKMET IS NOW THE MOST WEST WITH THE SURFACE LOW...WHILE
THE 00Z EC MEAN IS THE MOST PROGRESSIVE AND FARTHEST EAST. THE 12Z
ECMWF HAS TRENDED TOWARD THE GFS AND EVEN APPEARS A BIT
DEEPER...WHICH IS A CHANGE FROM ITS PRIOR 00Z RUN. ALL OF THE
DETERMINISTIC MODELS ARE PLAUSIBLE WITH RESPECT TO THE ENSEMBLE
GUIDANCE...AND GIVEN THE SHORT TERM NATURE OF THE FORECAST...IT IS
DIFFICULT TO RULE OUT ANY ONE MODEL.


SHORTWAVE CROSSING THE PACIFIC NORTHWEST TONIGHT
COLD FRONT REACHING THE APPALACHIANS EARLY MON MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/12Z ECMWF
CONFIDENCE: AVERAGE

WHAT HAPPENS DOWNSTREAM WITH A SHORTWAVE REACHING THE PACIFIC
NORTHWEST TONIGHT SEEMS TO COME FROM DIFFERENCES VERY EARLY ON.
THE 00Z ECMWF/UKMET ARE MORE ELONGATED WITH THIS SHORTWAVE BY
00Z/28 COMPARED TO THE 12Z NAM/GFS...AND EVEN SHOW SOME
DIFFERENCES WITH THEIR F012 HR FORECASTS COMPARED TO WATER VAPOR
IMAGERY THIS MORNING. THE 12Z ECMWF/UKMET HAVE TRENDED TOWARD THE
FLATTER/FASTER NAM/GFS BUT REMAIN A BIT SLOWER/DEEPER. THE 12Z CMC
IS NOW THE FASTEST WITH THIS FEATURE. GIVEN FAVORABLE ADJUSTMENTS
BY THE ECMWF/UKMET...THIS RAISES CONFIDENCE TO AVERAGE...BUT THE
12Z UKMET REMAINS A BIT SLOWER/MORE AMPLIFIED WITH HEIGHTS ACROSS
THE CNTRL HIGH PLAINS SUN MORNING. WHILE ENSEMBLE SPREAD
REMAINS...THERE SEEMS TO BE MORE SUPPORT FOR AN IDEA THAT IS MORE
SIMILAR TO THE 12Z GFS/ECMWF WITH THE GFS POSSIBLY A LITTLE FAST.


SHORTWAVE NEAR THE N-CNTRL U.S. MON EVENING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 70% 00Z ECMWF / 30% 12Z GFS BLEND
CONFIDENCE: AVERAGE

THE GFS HAS BEEN TRENDING NORTH WITH THE SHORTWAVE BY
00Z/31...WHILE THE ECMWF HOLDS DECENT RUN TO RUN CONTINUITY WITH A
SWD/FASTER ADJUSTMENT WITH ITS 12Z RUN. THE 12Z CMC IS
DEEPEST...WHICH IS CONNECTED TO A DEEPER UPSTREAM TROUGH ACROSS
THE PACIFIC NORTHWEST. ENSEMBLE SPAGHETTI HEIGHT PLOTS SUPPORT A
12Z GFS/00Z ECMWF BLEND OVER THE N-CNTRL U.S...BUT WITH MORE
WEIGHT TOWARD THE ECMWF...AS THE GFS APPEARS TO BE TOWARD THE
FLATTER SIDE OF THE ENSEMBLE GUIDANCE. MORE MEMBERS ARE A BIT
DEEPER THAN THE GFS...TOWARD THE 00Z ECMWF. THE 12Z ECMWF APPEARS
TO BE A STEP WAY FROM THE PREVIOUS CONSENSUS SO WILL STICK WITH
THE ORIGINAL THINKING.


WEAK MID-LEVEL TROUGH NEAR BAJA CA ON SUNDAY/MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/12Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE GFS/ECMWF ARE IN THE MIDDLE OF THE LATEST DETERMINISTIC
SPREAD...WHICH HAS SHRUNK COMPARED TO YESTERDAY BUT ALL OF THE
DETERMINISTIC GUIDANCE HAS SHOWN POORER THAN AVERAGE RUN TO RUN
CONTINUITY. WILL CONTINUE TO GO TOWARD THE MIDDLE OF THIS SPREAD.


SOUTHWESTERLY FLOW INTO VANCOUVER ISLAND THROUGH MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM...12Z GFS...00Z ECMWF BLEND
CONFIDENCE: AVERAGE

THROUGH MON...THE IDEA OF A BROAD LONGWAVE TROF CROSSING THE
NORTHEASTERN PACIFIC IS WELL SUPPORTED IN THE GUIDANCE. THE MODELS
VARY WITH THE EXACT PLACEMENT OF THIS FEATURE WITH THE 12Z CMC
CONTINUING TO BE THE MOST OUTLYING SOLUTION WITH THE UPPER TROF
DISPLACED NORTHWARD...FOLLOWED BY THE 12Z ECMWF WHICH ADJUSTED A
BIT SLOWER/DEEPER WITH THE APPROACHING UPPER TROUGH. THIS LEADS TO
DIFFERENT TIMING/ORIENTATION WITH SURFACE LOW AND TRAILING COLD
FRONT APPROACHING THE PACIFIC NORTHWEST. WILL STICK WITH THE
PREVIOUS THINKING AND 00Z ECMWF IN THE LATEST PREFERENCE.



...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

OTTO

$$




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