Prognostic Meteorological Discussion
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FXUS10 KWNH 271712
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
111 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 NAM/GFS EVALUATION ALONG WITH PRELIMINARY 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/00Z 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 TWO CAMPS OF SOLUTIONS WITH MINOR RUN TO
RUN CHANGES SEEN IN EACH MODEL. THE GFS IS ON THE SLIGHTLY
DEEPER/STRONGER SIDE AND IS TOWARD THE WRN SIDE OF THE
DETERMINISTIC/ENSEMBLE SPREAD WHILE THE 00Z ECMWF IS A BIT WEAKER
AND MORE PROGRESSIVE. GIVEN BOTH IDEAS ARE PLAUSIBLE WITH RESPECT
TO THE ENSEMBLE GUIDANCE...AND THERE IS AN EVEN SPLIT IN THE
LATEST DETERMINISTIC GUIDANCE...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/00Z CMC
CONFIDENCE: BELOW 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 NAM/GFS APPEAR TO BE IN BETTER
AGREEMENT WITH SATELLITE IMAGERY AND HAVE GAINED SUPPORT FROM THE
00Z CMC DOWNSTREAM ACROSS THE CNTRL CONUS. THE 00Z UKMET EXISTS ON
THE DEEP/SLOW EDGE..AND AT TIMES EVEN OUTSIDE OF...THE ENSEMBLE
SPREAD BY SUN MORNING ACROSS THE CNTRL HIGH PLAINS. THE 00Z ECMWF
MEAN IS A BIT LESS AMPLIFIED THAN THE 00Z ECMWF AND THE 00Z ECMWF
MEAN IS ALSO SLIGHTLY MORE PROGRESSIVE THAN THE 00Z ECMWF.

WHILE ENSEMBLE SPREAD REMAINS...THERE SEEMS TO BE MORE SUPPORT FOR
AN IDEA THAT IS MORE SIMILAR TO THE 12Z GFS. THE GFS COULD STILL
BE A BIT FAST...BUT WHEN BLENDED WITH THE SOMEWHAT SLOWER 00Z
CMC...A WORKABLE BLEND IS REACHED.


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 GOOD RUN TO RUN CONTINUITY. THE 00Z
CMC IS DEEPEST...WHICH IS CONNECTED TO A DEEPER UPSTREAM TROUGH
ACROSS THE PACIFIC NORTHWEST. ENSEMBLE SPAGHETTI HEIGHT PLOTS
SUPPORT A GFS/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.


WEAK MID-LEVEL TROUGH NEAR BAJA CA ON SUNDAY/MONDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS/00Z 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: NON 00Z CMC COMPROMISE
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 00Z CMC
CONTINUING TO BE THE MOST OUTLYING SOLUTION WITH THE UPPER TROF
DISPLACED NORTHWARD. THIS LEADS TO A DIFFERENT SURFACE LOW TRACK
THAN THE ENSEMBLE LOW PLOTS SUPPORT. THE 00Z CMC DEPICT PARALLEL
FLOW ALONG THE LOCAL TERRAIN ACROSS COASTAL WA AND VANCOUVER
ISLAND WHICH LIMITS THE QPF ACROSS THE REGION. THE PREVIOUS WPC
PREFERENCE WILL STAND HERE.



...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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