Prognostic Meteorological Discussion
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000
FXUS10 KWNH 281854
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 PM EDT FRI AUG 28 2015

VALID AUG 28/1200 UTC THRU SEP 01/0000 UTC

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

12Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/CMC AND ECMWF


...SHORTWAVE TROUGH MOVING THROUGH THE MIDWEST/GREAT LAKES
REGION...

PREFERENCE: NON-ECMWF CONSENSUS
CONFIDENCE: ABOVE AVERAGE

THE 00Z ECMWF WAS A DEEPER OUTLIER SOLUTION WITH THIS SYSTEM AS IT
MOVES INTO THE GREAT LAKES REGION. THE 12Z ECMWF HAS TRENDED
WEAKER AND IS ACTUALLY CLOSE TO THE DEPTH OF THE 12Z NAM. THE 12Z
GFS/12Z UKMET AND 12Z CMC ARE ALL A LITTLE WEAKER THAN THE 12Z
NAM. DESPITE THE TREND IN THE ECMWF...THERE ARE VARYING TIMES WHEN
IT STILL REMAINS THE STRONGEST SOLUTION. THUS...A NON-ECMWF
CONSENSUS WILL BE PREFERRED STILL AT THIS TIME.


...UPPER TROUGH OVER THE GULF OF MEXICO...

PREFERENCE: BLEND OF THE 12Z GEFS MEAN AND 00Z ECENS MEAN
CONFIDENCE: BELOW AVERAGE

THE UPPER TROUGH OVER THE GULF OF MEXICO WILL BE MOVING WEST OVER
THE NEXT COUPLE OF DAYS BEFORE GENERALLY STALLING. THE GUIDANCE
REFLECTS SOME COMPLICATED EVOLUTION OF THIS THOUGH. ALL OF THE
MODELS SHOW ENERGY EJECTING OUT OF THE BASE OF THE TROUGH INTO THE
SOUTHEAST U.S. SAT AND SUN WHILE THE OVERALL TROUGH AXIS SLOWLY
SHIFTS WEST. BY MON...THERE IS SPREAD WITH HOW THE VORTICITY IS
ORIENTED WITHIN THE TROUGH. MOST OF THE MODELS SHOW THE TROUGH
ELONGATING FROM THE WESTERN GULF OF MEXICO NORTHWARD INTO THE
LOWER/MID MS VALLEY. THE 12Z NAM TENDS TO BE STRONGER WITH THE
TROUGH...WITH THE GLOBAL MODELS ALL A TAD WEAKER. HOWEVER...THERE
IS SIGNIFICANT SPREAD WITH THE CENTER OF THE TROUGH AND LIKELY A
CLOSED LOW BY THE END OF THE PERIOD. THE 12Z ECMWF HAS A MID LEVEL
CENTER OVER EASTERN TX...THE 12Z GFS IS ALONG THE OK/AR
BORDER...THE 12Z UKMET IS ELONGATED N/S THROUGH MO/AR...AND THE
12Z NAM AND 12Z CMC SHOW A MUCH MORE ELONGATED TROUGH ORIENTED
SW/NE FROM THE WESTERN GULF COAST TO THE TN VALLEY. MUCH OF THE
MODEL SPREAD AND COMPLICATED TROUGH EVOLUTION IS BEING DRIVEN BY
DIFFERENCES IN THE INTERACTION OF THE THE ENERGY OVER THE GULF OF
MEXICO WITH ENERGY DIGGING SOUTH FROM THE MIDWEST WHICH APPEARS TO
BE CONVECTIVELY ENHANCED. AT THIS POINT...IT IS DIFFICULT TO PICK
ANY ONE SOLUTION...SO WILL LEAN TOWARD THE ENSEMBLE MEANS WITH A
BLEND OF THE 12Z GEFS MEAN AND 00Z ECENS MEAN. CONFIDENCE IS VERY
LIMITED.


...SHORTWAVE TROUGHS CROSSING THE PACIFIC NORTHWEST THIS WEEKEND...

PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF
CONFIDENCE: AVERAGE

THE 12Z UKMET IS FASTER THAN THE 12Z NAM/12Z GFS/12Z ECMWF AND 12Z
UKMET WITH THE SHORTWAVE TROUGH AND ASSOCIATED SURFACE LOW THAT
MOVES INTO THE PACIFIC NORTHWEST TONIGHT AND SAT. THIS ENERGY
SHEARS INLAND AHEAD OF ADDITIONAL STRONG HEIGHT FALLS DIGGING
SOUTH FROM THE GULF OF AK AND THROUGH BRITISH COLUMBIA. THIS WILL
COME IN THE FORM OF MULTIPLE SHORTWAVE IMPULSES...AND BY THE END
OF THE PERIOD A BROAD BUT RELATIVELY DEEP TROUGH WILL BE IMPACTING
THE NORTHWEST AND WESTERN CANADA. THE 12Z NAM IS A STRONGER AND
SOMEWHAT SLOWER OUTLIER BY LATER IN THE PERIOD WITH THE LOW CENTER
AND FRONTAL ZONE EJECTING ACROSS THE NORTHERN PLAINS. THE 12Z CMC
IS THE FASTEST SOLUTION WITH THE FRONT...WITH THE 12Z GFS/12Z
ECMWF AND 12Z UKMET A BIT SLOWER...BUT STILL FASTER THAN THE 12Z
NAM. WILL RECOMMEND A COMPROMISE SOLUTION BETWEEN THE 12Z GFS AND
12Z ECMWF AT THIS POINT.


...TROPICAL STORM ERICA...

THE 12Z GFS/12Z ECMWF AND 12Z UKMET TRACK ERICA LEFT OF THE NHC
15Z ADVISORY FORECAST TRACK. THE 12Z NAM AND 12Z CMC ARE CLOSER TO
THE NHC TRACK...BUT BY 48 HRS AND BEYOND THE 12Z NAM AND
ESPECIALLY THE 12Z CMC ARE FASTER AND TO THE RIGHT OF THE NHC
TRACK. PLEASE CONSULT THE LATEST NHC FORECAST ADVISORY/DISCUSSION
FOR MORE INFORMATION ON ERICA.

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

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

ORRISON

$$




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