Prognostic Meteorological Discussion
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FXUS10 KWNH 300435
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1234 AM EDT FRI SEP 30 2016

VALID SEP 30/0000 UTC THRU OCT 03/1200 UTC

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

00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS


...UPPER LOW CROSSING BACK TO THE LOWER GREAT LAKES...
...ADVANCING EAST INTO THE NORTHEAST THIS WEEKEND...

PREFERENCE: 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS TAKE THE UPPER LOW OVER THE OH VALLEY GRADUALLY BACK
NORTH INTO THE LOWER GREAT LAKES REGION BY SATURDAY...AND THEN
EAST INTO THE NORTHEAST ON SUNDAY. THE 00Z GFS GRADUALLY BECOMES
THE FASTEST MODEL TO TAKE THE HEIGHT FALLS INTO THE NORTHEAST. BY
THE END OF THE PERIOD...THE 00Z NAM AND 12Z CMC MAY BE A TAD TOO
SLOW AND IT APPEARS THAT THE 12Z UKMET MAY BE TAKING THE SYSTEM A
TAD TOO FAR NORTH. THE 12Z ECMWF REPRESENTS THE MODEL CONSENSUS
THE BEST AND HAS STRONG SUPPORT FROM THE 18Z GEFS MEAN AND 12Z
ECENS MEAN. WILL LEAN TOWARD THE ECMWF FOR NOW.


...WEAK UPPER TROUGH DEVELOPING OVER THE GULF COAST STATES...

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

IN THE WAKE OF THE UPPER LOW OVER THE OH VALLEY LIFTING OFF TO THE
NORTH AND NORTHEAST...THE GUIDANCE ALLOWS FOR A BROAD
WEAKNESS/UPPER TROUGH TO DEVELOP OVER THE GULF COAST STATES BY
SUNDAY AND MONDAY. THE 00Z NAM AND 12Z CMC APPEAR TO BOTH BE TOO
DEEP WITH THIS SYSTEM. THE 00Z GFS/12Z UKMET AND 12Z ECMWF ARE ALL
A LITTLE WEAKER AND HAVE STRONGER MODEL CLUSTERING AND ENSEMBLE
SUPPORT. WILL LEAN TOWARD THE GFS/UKMET/ECMWF CAMP FOR NOW.


...SHORTWAVE SHEARING FROM THE GREAT BASIN TO THE NORTHERN
PLAINS...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

A SHEARING MID-LEVEL PERTURBATION WILL EJECT ACROSS THE GREAT
BASIN AND ACROSS THE NORTHERN PLAINS THROUGH FRIDAY. DIFFERENCES
AMONG THE MODELS ARE MINOR WITH THIS SYSTEM...AND A GENERAL MODEL
COMPROMISE SHOULD SUFFICE TO RESOLVE THIS AT THIS POINT.


...DEEP UPPER TROUGH/CLOSED LOW MOVING INTO THE WEST...
...LEAD SHORTWAVE CROSSING THE PACIFIC NORTHWEST...

PREFERENCE: BLEND OF THE 00Z NAM/00Z GFS/12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

AN ACTIVE SYNOPTIC PATTERN IS IN PLACE OVER THE EASTERN PACIFIC
WITH A PAIR OF SYSTEMS EXPECTED TO AFFECT THE WESTERN U.S. THIS
WEEKEND. INITIALLY...AN UPPER TROUGH JUST OFFSHORE THE PACIFIC
NORTHWEST WILL PIVOT INLAND ACROSS THE PACIFIC NORTHWEST BY
SATURDAY BEFORE LIFTING NORTHEAST INTO SOUTHWEST AND THEN
SOUTH-CENTRAL CANADA THROUGH SUNDAY. THE MODELS SHOW GOOD
AGREEMENT WITH THE EVOLUTION OF THIS SYSTEM. MEANWHILE...MUCH
STRONGER HEIGHT FALLS ASSOCIATED WITH AN UPPER LOW WILL DIG SOUTH
OFF THE WEST COAST AND THEN INLAND ACROSS THE GREAT BASIN SUNDAY
AND MONDAY. THE 12Z CMC IS LIKELY TOO SLOW WITH THIS SYSTEM...AS
THE OTHER MODELS CLUSTERED ON A SOMEWHAT MORE PROGRESSIVE
EVOLUTION THAT FEATURES A CLOSED LOW OVER THE GREAT BASIN BY EARLY
MONDAY. HOWEVER...THE 12Z UKMET MAY BE JUST A TAD TOO PROGRESSIVE
BY THAT TIME. STRONGER MODEL CLUSTERING WOULD FAVOR A BLEND OF THE
00Z NAM/00Z GFS AND 12Z ECMWF...AND THIS WILL BE THE LATEST
PREFERENCE.


...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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