807
FXUS10 KWNH 211621
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1221 PM EDT SAT SEP 21 2019
VALID SEP 21/1200 UTC THRU SEP 25/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..DEEP TROUGH CROSSING THE PLAINS/MIDWEST THIS WEEKEND
..ENERGY CLOSING OFF OVER THE NORTHEAST EARLY NEXT WEEK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS
NON-GFS BLEND...AFTER 60 HOURS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
MODEL DIFFERENCES WITH THE NORTHERN PLAINS TO UPPER MS VALLEY
TROUGH ARE RATHER SMALL THROUGH MOST OF THE WEEKEND AS THE ENERGY
ADVANCES ACROSS THE PLAINS AND MIDWEST.
BY LATER MONDAY AND TUESDAY AS THE ENERGY CROSSES THE GREAT LAKES
AND MOVES INTO THE NORTHEAST, THE 00Z-12Z GFS BECOMES A BIT MORE
PROGRESSIVE THAN THE REMAINING GUIDANCE. THE 00Z-06Z NON-NCEP
GUIDANCE IS NOW ALL VERY WELL CLUSTERED AND CLOSE TO THAT OF THE
12Z NAM WITH THE TIMING OF THE 700-500 MB LOW. GIVEN THE MAJORITY
OF MODELS/ENSEMBLE MEANS CLUSTER WITH A SLOWER MOTION THAT IS
NOT AS PROGRESSIVE AS THE DETERMINISTIC GFS, A GENERAL MODEL BLEND
IS RECOMMENDED THROUGH ABOUT 60 HOURS, AND THEN A NON-GFS BLEND
THEREAFTER.
..UPPER TROUGH DIGGING INTO THE WEST BY MONDAY
..CLOSED LOW EVOLUTION OVER THE SOUTHWEST BY TUESDAY
..MOISTURE/ENERGY ASSOCIATED WITH HURRICANE LORENA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z NAM/GFS AND 00Z UKMET
CONFIDENCE: AVERAGE...BECOMING BELOW AVERAGE BY MON/TUES
THE INITIAL TROUGH OVER THE SOUTHWEST DEAMPLIFIES AS IT MOVES
NORTHEAST OUT OF THE SOUTHWEST INTO THE PLAINS. THE NATIONAL
HURRICANE CENTER'S FORECAST FOR HURRICANE LORENA HAS THE SYSTEM
COMING ONSHORE INTO NORTHWEST MEXICO AND WEAKENING. AMONG THE
CURRENT GUIDANCE THE 12Z NAM MATCHES THE NHC TRACK THE BEST, SO IT
SHOULD BE GIVEN MORE WEIGHTING.
A SECOND TROUGH COMES ONSHORE IN THE PACIFIC NORTHWEST SUN AND AND
THE AMPLIFIES MONDAY AS IT AMPLIFIES INTO THE SOUTHWEST US.
SEVERAL MODELS/ENSEMBLE MEMBERS INDICATED A CLOSED 500 MB LOW
DEVELOPS, WITH THE MODELS THEN SHOWING TIMING DIFFERENCES
DEVELOPING TUE.
THE 00Z ECMWF IS POSITIONED WEST OF THE 12Z GFS/00Z UKMET/00Z
CANADIAN SOLUTIONS, WHICH ARE NOW PRETTY WELL CLUSTERED. THE 12Z
NAM AND 06Z GEFS MEAN ARE THE FARTHEST EAST SOLUTION BY THE END OF
THE PERIOD. GIVEN AN UPSTREAM RIDGE IS LIKELY TO LEAD TO SLOW
FORWARD MOTION, THE NAM AND 06Z GEFS MEAN SHOULD BE GIVEN THE
LEAST WEIGHTING. BASED ON THE LATEST CLUSTERING OF SOLUTIONS, A
BLEND OF THE 12Z GFS/00Z UKMET/00Z CANADIAN AND 00Z ECMWF WILL BE
PREFERRED.
..UPPER TROUGH OVER THE NORTHERN HIGH PLAINS BY TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
THE MODELS HAVE GOOD AGREEMENT OVERALL WITH THE EVOLUTION OF A
BROAD UPPER TROUGH DEPARTING THE NORTHERN ROCKIES ON MONDAY AND
INTO THE PLAINS TUE, ALONG WITH ITS ASSOCIATED COLD FRONT.
THERE ARE TYPICAL MODEST TIMING/AMPLITUDE DIFFERENCES, BUT THE
MODEL DIFFERENCES ARE MODEST ENOUGH THAT A GENERAL MODEL BLEND IS
PREFERRED.
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML
PETERSEN
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