Prognostic Meteorological Discussion
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000
FXUS10 KWNH 231708
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
108 PM EDT WED JUL 23 2014

VALID JUL 23/1200 UTC THRU JUL 27/0000 UTC

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

...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...UPPER LOW SPINNING OVER SOUTHEASTERN LA...

PRELIMINARY PREFERENCE: A NON-00Z CMC MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

BASED ON THE LATEST WATER IMAGERY...A MID/UPPER LOW WAS SEEN
SPINNING IN THE VICINITY OF SOUTHEASTERN LA. IT HAS BECOME MORE
ELONGATED IN NATURE COMPARED TO PREVIOUS DAYS BUT STILL REMAINS A
FOCUS FOR CONVECTION...PRIMARILY DURING THE PEAK DIURNAL HEATING.
THE GUIDANCE SHOWS THE SYSTEM CONTINUING TO SHEAR AS IT FEELS THE
INFLUENCE OF A BROAD MID-LEVEL RIDGE ACROSS THE FOUR CORNERS
REGION/SOUTHERN PLAINS. WITH THE EXCEPTION OF THE 00Z CMC WHICH IS
FURTHER EAST...THE MODELS AGREE ON MAINTAINING THE VORT ENERGY IN
A SIMILAR LOCATION AS CURRENT. GIVEN THIS ASSESSMENT...A NON-00Z
CMC MODEL COMPROMISE WILL BE RECOMMENDED.


...DEEP AND ANOMALOUS CLOSED LOW MOVING FROM THE PACIFIC NORTHWEST
TO SOUTHERN SASKATCHEWAN...
...SURFACE LOW TRACKING THROUGH THE GREAT PLAINS ON
THURSDAY/FRIDAY...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF WITH THE
06Z GEFS/00Z ECMWF ENSEMBLE MEANS
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

A RATHER STRONG UPPER LOW CURRENTLY APPROACHING THE PACIFIC
NORTHWEST COAST WILL MOVE ONSHORE BY THIS AFTERNOON. THE 12Z NAM
INDICATED THIS FEATURE IS AT LEAST 2 TO 2.5 STANDARDIZED ANOMALIES
BELOW CLIMATOLOGY BASED ON 500-MB HEIGHTS. SUCH ANOMALIES ARE
FORECAST TO PERSIST THROUGHOUT THE SHORT RANGE PERIOD EXTENDING
THROUGH SATURDAY. SOLUTIONS VARY WITH THE SPEED OF THIS FEATURE
WITH THE 12Z NAM/00Z UKMET BEING QUICKER TO SLIDE HEIGHT FALLS
INTO THE CANADIAN ROCKIES. BY 25/1200Z...THE 12Z NAM IS THE
FURTHEST EAST SOLUTION WITH SOME SUPPORT FROM THE 09Z SREF MEAN.
HOWEVER...THIS MAY BE BIASED BY THE FACT THE 09Z SREF MEAN HAS
SOME WEIGHTING FROM THE DETERMINISTIC NAM. THE 12Z GFS/00Z ECMWF
ARE BEST SUPPORTED BY THE ENSEMBLE MEANS. THE 576-DM SPAGHETTI
PLOT SHOWS A RELATIVELY WELL BEHAVED PLOT WITH THE MODELS SUBTLY
IN AGREEMENT. THE 00Z ECMWF ENSEMBLE MEMBERS DO SHOW HINTS AT A
FASTER/MORE AMPLIFIED PROGRESSION BY SATURDAY ACROSS THE MIDDLE MS
VALLEY/UPPER GREAT LAKES. IN SPITE OF THE SIMILARITY BETWEEN THE
12Z GFS/00Z ECMWF WITH THE CORE OF THE LOWER HEIGHTS ACROSS
SOUTHERN CANADA...THEY DIFFER GREATLY WITH THE JET ENERGY CROSSING
THE NORTHERN TIER OF THE U.S. THIS HAS RAMIFICATIONS ON
UNCERTAINTY WITH THE EVOLUTION OF THE SURFACE
FEATURES...PARTICULARLY OVER THE REALM OF THE MESOSCALE. WILL
STICK WITH A COMBINATION OF THE GFS/ECMWF BUT UTILIZE THE ENSEMBLE
MEANS GIVEN THE INCREASING UNCERTAINTY.


...MEAN UPPER TROF OVER NORTHEASTERN NORTH AMERICA...
...ASSOCIATED COLD FRONT...

PRELIMINARY PREFERENCE: A NON-00Z UKMET SOLUTION
FORECAST CONFIDENCE: AVERAGE

A PERSISTENT NEGATIVE HEIGHT ANOMALY ACROSS THE NORTHEASTERN
SECTOR OF NORTH AMERICA WILL BE FEATURED DURING THE PERIOD. A
SERIES OF IMPULSES TRAVERSING WITHIN THE CYCLONIC FLOW WILL MOVE
THROUGH OH VALLEY AND MID-ATLANTIC/NEW ENGLAND. THROUGH
25/1200Z...THE MODELS AGREE QUITE WELL WITH THE EXCEPTION OF THE
00Z UKMET WHICH IS FLATTER WITH THE HEIGHT PATTERN. MORE
UNCERTAINTY LOOMS UPSTREAM WITH A RATHER POTENT IMPULSE SLIDING
THROUGH THE UPPER GREAT LAKES ON FRIDAY EVENING. THE GUIDANCE DOES
NOT SHOW A CLEAR SIGNAL OF WHERE THIS SYSTEM WILL BE LOCATED WITH
BOTH PLACEMENT AND TIMING ISSUES. FOR NOW...WILL RECOMMEND A
NON-00Z UKMET SOLUTION ACCOUNTING FOR THE INITIAL DIFFERENCE BUT
WILL REASSESS LATER AS FUTURE GUIDANCE ARRIVES.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

RUBIN-OSTER

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