Prognostic Meteorological Discussion
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FXUS10 KWNH 191703
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
102 PM EDT TUE AUG 19 2014

VALID AUG 19/1200 UTC THRU AUG 23/0000 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 TROF SLIDING FROM THE UPPER GREAT LAKES TOWARD THE
NORTHEASTERN U.S...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS WITH THE 00Z
ECMWF/UKMET
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A BROAD UPPER TROF INITIALLY OVER THE UPPER GREAT LAKES HAS BEEN
RESPONSIBLE FOR MULTIPLE ROUNDS OF CONVECTION THE PAST 24 HOURS.
THIS CLOSED LOW WILL MIGRATE EASTWARD TOWARD THE LOWER GREAT LAKES
THROUGH WEDNESDAY WITH THE 00Z CMC BEING A TAD SLOWER DURING THIS
EVOLUTION. ADDITIONALLY...THE 12Z NAM BECOMES MORE AMPLIFIED THAN
THE ENSEMBLE MEANS WHICH INCLUDES THE 09Z SREF MEAN WHICH WAS
FLATTER. THE 12Z GFS AND 00Z ECMWF/UKMET OFFER A REASONABLE
COMPROMISE TO THE INCREASING SPREAD LATER ON. WILL FAVOR A BLEND
OF THE 12Z GFS WITH THE 00Z ECMWF/UKMET GIVEN THIS ASSESSMENT.


...SHORTWAVES LIFTING FROM THE CENTRAL ROCKIES INTO THE UPPER
MIDWEST THROUGH THURSDAY...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: AVERAGE

A MYRIAD OF SHORTWAVES MOVING THROUGH THE CENTRAL ROCKIES WILL
NUDGE THE SHORTWAVE RIDGE EASTWARD AS HEIGHTS BEGIN TO FALL ACROSS
THE HIGH PLAINS. AS WAS THE CASE YESTERDAY...THE 12Z NAM IS
FARTHER NORTH WITH THE ENERGY ALLOWING IT TO BECOME ABSORBED INTO
THE SYNOPTIC-SCALE TROF ACROSS WESTERN/CENTRAL CANADA.
LIKEWISE...THE 00Z CMC DOES THIS AS WELL BUT DURING A SLOWER
PROCESS WITH THE VORT ENERGY BEING WEAKER. MEANWHILE...THE 12Z GFS
AND 00Z ECMWF/UKMET FAVOR CARRYING THE SHEARING ENERGY ABOVE THE
MS RIVER VALLEY RIDGE WITH SOME SORT OF WEAKENING SHORTWAVE MOVING
THROUGH THE GREAT LAKES MIDDAY THURSDAY. BASED ON THE ENSEMBLE
MEANS...THE 00Z UKMET MAY BE TOO AGGRESSIVE ATTEMPTING TO BREAK
DOWN THE NORTHERN EXTENT OF THE RIDGE. FOR NOW WILL FAVOR A MIX OF
THE 12Z GFS/00Z ECMWF.


...CLOSED LOW GRADUALLY DROPPING DOWN THE CA COAST...

PRELIMINARY PREFERENCE: 00Z ECMWF
FORECAST CONFIDENCE: AVERAGE

WATER VAPOR IMAGERY SHOWED A TIGHTLY WOUND CLOSED LOW SLIDING DOWN
THE CENTRAL CA COAST. IT SHOULD EVENTUALLY REACH THE SOUTHERN CA
COAST BY MIDDAY WEDNESDAY. THE 09Z SREF MEAN FAVORS A LITTLE MORE
RETROGRESSION OF THE SYSTEM BY LATE WEDNESDAY. ADDITIONALLY...THE
12Z GFS LOOKS VERY SIMILAR TO ITS RUN YESTERDAY WHICH WAS FASTER
AND DEPICTING A MORE AGGRESSIVE SOLUTION. THE ENSEMBLE MEANS FAVOR
SOMETHING SLOWER INCLUDING THE 06Z GEFS MEAN WHICH MAKES THE 12Z
GFS AN OUTLIER. ONE ISSUE THAT ARISES IS THE POSSIBLE INTERACTION
WITH TROPICAL STORM LOWELL. THE 00Z CMC IS WELL NORTHEAST OF THE
NHC TRACK WHICH RESULTS IN HEFTY QPF FOR THE SOUTHWESTERN U.S. THE
00Z ECMWF FOLLOWS THEIR TRACK MOST CLOSELY AND OBEYS THE WELL
CLUSTERED ENSEMBLE MEANS. WPC WILL RECOMMEND THE 00Z ECMWF.


...MEAN TROF ANCHORING THE NORTHWESTERN CONUS...

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

A LONGWAVE TROF ACROSS WESTERN/CENTRAL CANADA WILL BE MAINSTAY
FEATURE FOR THE WEEK AS ADDITIONAL HEIGHT FALLS DROP DOWN INTO THE
PACIFIC NORTHWEST FOR THE END OF THE PERIOD. WILL NOT INCLUDE THE
12Z NAM/00Z CMC INTO THE PREFERENCE AS THEY WERE QUICK IN LIFTING
SHORTWAVE ENERGY INTO THE EASTERN EXTENT OF THE TROF AS PREVIOUSLY
DISCUSSED. THE ENSEMBLE MEANS ARE IN VERY GOOD AGREEMENT FOR AN 84
HOUR FORECAST WITH THE OVERALL STRUCTURE OF THE UPPER TROF. THE
00Z ECMWF FOLLOWS THESE MEANS VERY CLOSELY WHILE THE 12Z GFS SHOWS
THIS BUT WITH MORE ENERGY DISPLACED TOWARD THE WEST. THIS 12Z GFS
SOLUTION DOES THAT APPEAR THAT OUT OF LINE RELATIVE TO THE SPREAD
IN THE 576-DM SPAGHETTI PLOT. WILL RECOMMEND THE COMBINATION OF
THE 12Z GFS/00Z ECMWF BUT ADD THE MEANS TO THE MIX GIVEN THE
INHERENT UNCERTAINTY.


...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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