Prognostic Meteorological Discussion
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000
FXUS10 KWNH 280731
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
331 AM EDT THU AUG 28 2014

VALID AUG 28/0000 UTC THRU AUG 31/1200 UTC

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

==============================================
00Z MODEL EVALUATION AND PREFERENCES
==============================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==============================================

...CENTRAL AND NORTHERN U.S. FROM THE PLAINS TO GREAT LAKES...

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

A CLOSED LOW IN COLORADO WILL MOVE EAST AND THEN GRADUALLY
DE-AMPLIFY AS IT LIFTS TOWARD THE GREAT LAKES. AT THE SAME TIME A
NORTHERN STREAM TROUGH WILL RIDE ALONG THROUGH SOUTHERN
CANADA...PUSHING A COLD FRONT INTO MONTANA LATE THURSDAY AND ON
TOWARD THE UPPER MIDWEST BY FRIDAY EVENING. THE 00Z UKMET TRENDED
IN LINE WITH THE PREFERRED CONSENSUS WITH RESPECT TO INTENSITY.
THE 00Z ECMWF TRENDED BACK TOWARD THE PREFERRED PLACEMENT OF THE
SURFACE LOW OVER THE GREAT LAKES ON DAY 3. THE NAM AND CANADIAN
WERE FASTER THAN CONSENSUS ON DAY 3.


...TROUGH EXITING THE NORTHEAST U.S. BY FRIDAY...

PREFERENCE: NONE
CONFIDENCE: HIGH

THE MODELS ARE IN GOOD AGREEMENT WITH RESPECT TO THE
TIMING/AMPLITUDE OF THE 500 MB TROUGH AND ASSOCIATED SURFACE FRONT.


...SLOW MOVING EASTERLY WAVE ALONG THE WESTERN GULF COAST...

PREFERENCE: BLEND OF 00Z ECMWF/UKMET/CANADIAN
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THIS PORTION OF THE MAP FEATURES SOME FORECAST CHALLENGES...AS A
WEAK POINT IN THE FLOW...OR COL POINT EXISTS OVER TEXAS. THE
MODELS VARY IN THEIR DEPICTION OF VORTICITY MAXIMA EAST OF THE COL
AND THEIR SUBSEQUENT MOTION. ONE FEATURE WAS NEARING THE SOUTH
TEXAS COAST AS OF EARLY THURSDAY MORNING...AND WAS WELL DEFINED IN
SATELLITE IMAGERY...PARTICULARLY THE VISIBLE CHANNEL DATING BACK
TO WEDNESDAY AFTERNOON. ANOTHER DISTURBANCE...ARRIVING AS AN
EASTERLY WAVE FROM THE YUCATAN...IS FORECAST BY SEVERAL MODELS TO
DEEPEN AS IT MOVES INTO THE WESTERN GULF OF MEXICO AND THEN LIFTS
THROUGH THE LOWER MISSISSIPPI VALLEY AHEAD OF THE GREAT PLAINS
TROUGH. BOTH OF THESE ARE SMALL FEATURES IN WEAK STEERING
FLOW...AND THE LATTER ONE WAS NOT YET VERY EVIDENT IN
OBSERVATIONAL DATA...SO CONFIDENCE IS LOW. WE
DISCOUNT...HOWEVER...THE 00Z GFS WHICH WAS ILL DEFINED WITH THE
CIRCULATION NEAR TEXAS EARLY IN THE FORECAST. THE OTHER MODELS ARE
NOW QUITE SIMILAR THROUGH DAY 2. THE NAM...HOWEVER...ALLOWS THE
COMBINED SHEAR AXIS DEFINED BY THESE DISTURBANCES TO DRIFT FARTHER
NORTH AND WEST...PERHAPS ALLOWED DUE TO THE WARMER/FLATTER
SOLUTION THAT MODEL HAS IN THE NORTHERN STREAM. THIS YIELDS SOME
SIGNIFICANT QPF DIFFERENCES ON DAY 3. FOR QPF...WPC IS
RECOMMENDING LESS WEIGHT ON THE NAM IN THIS REGION ON DAY 3.


...DEEP TROUGH DIGGING INTO THE NORTHWEST BY FRI AND SAT...

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

MODELS GENERALLY AGREE TO THE TIMING OF A MEDIUM WAVELENGTH TROUGH
THAT IS FORECAST TO SLIDE THROUGH THE WESTERN U.S. WHILE
UNDERGOING SOME BROAD AMPLIFICATION ON FRIDAY/SATURDAY. ALTHOUGH
THE NAM IS INCLUDED IN THIS STATEMENT...IT FEATURES NOTICEABLY
WARMER HEIGHTS AND ALSO MOVES OUT OF PHASE WITH THE OPERATIONAL
MODEL CONSENSUS IN THE UPSTREAM FLOW ON DAY 3. OTHERWISE...THE
GLOBAL MODELS COULD BE BLENDED TO REACH AN OVERALL CONSENSUS...BUT
WE CHOSE TO OMIT THE 00Z CANADIAN WHICH WAS A LITTLE QUICK TO
REACH THE HIGH PLAINS WITH HEIGHT FALLS.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

BURKE
$$





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