Prognostic Meteorological Discussion
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FXUS10 KWNH 031844
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
243 PM EDT THU SEP 03 2015

VALID SEP 03/1200 UTC THRU SEP 07/0000 UTC

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

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


...VORT LIFTING FROM THE CENTRAL ROCKIES TO THE NORTHERN PLAINS...

PREFERENCE: 12Z ECMWF
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW GOOD AGREEMENT IN LIFTING A VORT CENTER OVER CO
OFF TO THE NORTHEAST OVER THE NEXT 24 TO 36 HOURS AND ACROSS THE
NORTHERN PLAINS. THERE ARE SOME MODEST DIFFERENCES WITH THE VORT
INTENSITY AS IT LIFTS THROUGH THE NORTHERN PLAINS. THE 12Z GFS
OVERALL IS THE WEAKEST SOLUTION...WITH THE 12Z NAM THE STRONGEST.
THE 12Z ECMWF/12Z UKMET AND 12Z CMC SPLIT THE DIFFERENCE...BUT THE
ECMWF REPRESENTS ESSENTIALLY THE GLOBAL MODEL CONSENSUS AND THIS
WILL BE THE PREFERENCE.


...NEGATIVELY-TILTED TROUGH CROSSING THE NORTHWEST...

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

THE 12Z NAM AND 12Z CMC TEND TO BE STRONGER OUTLIERS ALOFT WITH
THE EVOLVING DEEP TROUGH THAT GOES NEG-TILT ACROSS THE NORTHWEST
AND OUT INTO THE HIGH PLAINS OVER THE NEXT TWO TO THREE DAYS. THE
12Z UKMET APPEARS TO BE A TAD TOO STRONG AT THE SURFACE WITH THE
DEEPENING LOW CENTER. THE STRONGER MODEL CLUSTERING TENDS TO FAVOR
THE 12Z GFS AND 12Z ECMWF WHICH IS A TAD WEAKER THAN THE NAM AND
CMC SOLUTIONS...AND SO A BLEND OF THESE SOLUTIONS WILL BE
PREFERRED.


...MID LEVEL TROUGH/CLOSED LOW CENTER OVER MI...

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

A RATHER COMPACT MID LEVEL TROUGH AND ASSOCIATED CLOSED LOW OVER
LOWER MI IS EXPECTED TO LINGER HERE OVER THE NEXT COUPLE OF DAYS
BEFORE THEN WEAKENING THIS WEEKEND AND GRADUALLY SHEARING THROUGH
SOUTHEAST ONTARIO. THE 12Z NAM AND 12Z CMC TEND TO HANG ONTO
SOMEWHAT STRONGER HEIGHT FALLS WITH THIS SYSTEM BEFORE GRADUALLY
WEAKENING THE ENERGY. OVERALL...THE MODEL SPREAD IS NOT
PARTICULARLY SIGNIFICANT...BUT WILL AGAIN SUGGEST A BLEND OF THE
12Z GFS AND 12Z ECMWF GIVEN BETTER OVERALL CLUSTERING AND ENSEMBLE
SUPPORT.


...RETROGRADING UPPER LOW MOVING INTO THE SOUTHEAST SAT/SUN...

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

THE MODELS INDICATE DEVELOPMENT OF A REX BLOCK ALONG AND JUST
OFFSHORE THE EAST COAST BY SAT. THE UPPER LOW DEVELOPING OFF THE
SOUTHEAST COAST IS FORECAST TO SLOWLY RETROGRADE INTO THE INTERIOR
SOUTHEAST BY LATE SUN. SURFACE LOW PRESSURE ASSOCIATED WITH THIS
APPEARS IN PART TO BE RELATED TO THE REMNANTS OF FORMER T.S.
ERIKA. THE 12Z CMC OVERALL IS THE DEEPEST SOLUTION WITH THE
EVOLUTION OF ALL OF THIS ENERGY. THE 12Z GFS/12Z ECMWF AND 12Z
UKMET ARE ALL A LITTLE WEAKER ALOFT AND WITH THE SURFACE PRESSURE
FIELDS. THE 12Z NAM APPEARS TO BE TOO FAR EAST WITH ITS SURFACE
AND MID LEVEL LOW CENTERS.


...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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