Prognostic Meteorological Discussion
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000
FXUS10 KWNH 021850
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EDT SUN AUG 02 2015

VALID AUG 02/1200 UTC THRU AUG 06/0000 UTC

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

12Z MODEL EVALUATION INCLUDING ANALYSIS AND PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SHORTWAVE TROUGH TRACKING FROM NEVADA TO THE NORTHERN PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z NAM/GFS/ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z NAM MOVES TOWARD THE STRONG EDGE OF THE GUIDANCE AFTER
REACHING THE PLAINS TUESDAY NIGHT BUT OTHERWISE SHOWS REASONABLY
GOOD AGREEMENT WITH THE 00Z ECMWF AND THE ENSEMBLE MEANS.  THE 12Z
GFS LIFTS THE SHORTWAVE ENERGY NORTH WITH A STRONGER INTERACTION
WITH THE PACIFIC NORTHWEST CLOSED LOW...SHEDDING ENERGY INTO THE
LOW MUCH MORE THAN OTHER GUIDANCE.  THIS OVERALL REDUCES SOME OF
THE DOWNSTREAM ENERGY ALLOWING IT TO WEAKEN AND SPEED UP
EVENTUALLY OUTPACING THE 12Z NAM BY 00Z ON THE 6TH. THE 12Z ECMWF
ALSO PICKED UP ON THE TREND WITH VERY GOOD AGREEMENT WITH THE
SPEED LOCATION OF THE 12Z NAM BUT BETTER AGREEMENT WITH THE 12Z
GFS IN STRENGTH/AMPLITUDE. AS SUCH A BLEND OF THE 12Z
GFS/NAM/ECMWF REMAINS PREFERRED WITH SLIGHTLY INCREASED
CONFIDENCE.


SHORTWAVE TROUGH TRACKING FROM COLORADO TO THE MID MISSISSIPPI
VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
PREFERENCE: BLEND OF 12Z GFS/00Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE 12Z NAM INITIALIZED WITH 500 MB HEIGHTS 10-20 METERS TOO LOW
OVER A BROAD EXPANSE OF THE FOUR CORNERS REGION. THIS IS MAGNIFIED
DOWNSTREAM WHERE THE NAM BECOMES A BROAD AND DEEP UPPER LEVEL
SOLUTION OVER THE PLAINS AND MID MISSISSIPPI VALLEY...DESPITE
HAVING A REASONABLE SURFACE FORECAST. THE GFS/ECMWF SHOW GOOD
AGREEMENT WITH EACH OTHER AND WITH THEIR RESPECTIVE ENSEMBLE MEANS
UP TO WED MORNING WHEN THE 12Z GFS APPEARS TO HAVE CONVECTIVE
FEEDBACK LIFTING NORTH ACROSS NORTHERN MO/IL BY THE END OF THE
PERIOD. THE 12Z ECMWF HAS ALSO TRENDED A BIT MORE ROBUSTLY AS THE
WAVE EJECTS ACROSS KANSAS ON WED. ADDITIONALLY TRENDING A SHADE
FURTHER NORTH AS WELL.  THE 12Z UKMET RAPIDLY DEVELOPS THE VORT
MAX STRONGLY GENERATING A SURFACE LOW WELL TOO DEEP BY DAY 3.  THE
12Z CMC FALLS IN BETWEEN THE 12Z UKMET AND 12Z ECMWF...TRENDING
MORE CONSOLIDATED LIKE THE UKMET BUT WEAKER/MORE REALISTIC LIKE
THE ECMWF.  ALL CONSIDERED...A CONTINUATION OF CONTINUITY WITH THE
TWO MIDDLE GROUND MODELS...THE 12Z GFS/12Z ECMWF...BLEND IS
PREFERRED.   INCREASED DIFFERENCES AND A TREND STRONGER
CONFIDENCE IN THIS BLEND IS REDUCED TO SLIGHTLY BELOW AVERAGE.


TROUGH AND RENEWED SURGE OF MILD AIR OVER THE GREAT LAKES /
NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
PREFERENCE: BLEND 12Z NAM/GFS/ECMWF...TURNING TO LESS WEIGHT ON
THE NAM AFTER 05/00Z
CONFIDENCE: AVERAGE

THE NAM/GFS/ECMWF ARE IN TIGHT AGREEMENT WITH THE ENSEMBLES ON THE
LARGE SCALE THROUGH DAY 2. THE NAM IS THEN DEEPER AND
SLOWER...MAINTAINING COOLER HEIGHTS OVER THE SOUTHERN AND EASTERN
GREAT LAKES. THIS MAY NOT BE A BAD FORECAST...GIVEN THE RELATIVELY
DEEP AND SLOWLY PROGRESSIVE LONGWAVE PATTERN. THE GFS/ECMWF MAY
PROVE TO BE TOO ANXIOUS TO RAISE HEIGHTS. MUCH DEPENDS ON THE
UPSTREAM SHORTWAVE TRACKING FROM NEVADA TO THE NORTHERN
PLAINS...FOR WHICH THE GFS...ALTHOUGH IT IS ONE OF THE PREFERRED
MODELS...IS A LITTLE NORTH AND EAST AND/OR FASTER THAN AN IDEAL
CONSENSUS POSITION. THE NAM IS QUESTIONABLE GIVEN ITS
LOWER-THAN-CONSENSUS HEIGHTS AROUND OTHER SHORTWAVES...SO
CONFIDENCE IS LOWER ON DAY 3...AND WE RECOMMEND MORE WEIGHT ON THE
GFS/ECMWF WHICH BETTER FIT THE AVAILABLE ENSEMBLE GUIDANCE.


LOW PRESSURE OVER THE NORTHEAST GULF OF MEXICO
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z GFS/ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z NAM PATTERN ALOFT...LIKE ELSEWHERE...APPEARS TO BE A FEW
DECAMETERS TOO LOW THROUGHOUT THE FORECAST PERIOD...REDUCING
CONFIDENCE IN USING IT IN THE BLEND. THOUGH SURFACE FEATURES LOOK
GOOD IN STRENGTH THOUGH MAYBE A SHADE FAST AS IT LIFTS UP THE
COAST...THE 12Z NAM MAY BE USABLE AT THE LOWER LEVELS. THE 12Z GFS
REMAINS SOLID IN CONTINUITY WITH ITSELF PRIOR ECMWF RUNS AND
ENSEMBLE MEANS...INCLUDING THE MOST RECENT 12Z RUN. SIMILARLY THE
00Z CMC AND UKMET REMAIN STRONGEST/CONSOLIDATED IN COMPARISON.  AS
SUCH A BLEND OF THE 12Z GFS/ECMWF REMAINS PREFERRED BUT AT
SLIGHTLY ABOVE AVERAGE GIVEN CONTINUED AGREEMENT WITH LITTLE
CHANGE.


TROUGH PROGRESSING INTO THE PACIFIC NORTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z NAM/GFS/ECMWF
CONFIDENCE: AVERAGE

A CLOSED LOW WILL GRADUALLY MOVE ONSHORE INTO BRITISH COLUMBIA
WHILE MEDIUM WAVELENGTH TROUGHING OVERSPREADS THE U.S. PACIFIC
NORTHWEST AND NORTHERN ROCKIES. THE 12Z GFS/ECMWF AND RESPECTIVE
ENSEMBLES SHOWED GOOD AGREEMENT AS TO THE EVOLUTION HERE...EVEN
INTO THE BASE OF THE TROF WITH THE SHORTWAVE COMING ASHORE INTO
NORTHERN CA/SW OR BY TUE NIGHT/WED MORNING.  THE 12Z ECWMF ALSO
PICKED UP A BIT OF EASTWARD SHIFT MORE IN LINE WITH THE 12Z NAM
INCREASING STRENGTH IN THE RETAINED BLEND OF THE 12Z NAM/GFS/ECMWF
WITH AVERAGE CONFIDENCE.  THE 12Z CMC REMAINS THE NOTABLE OUTLIER
IN POSITION AND STRENGTH...WHILE THE 12Z UKMET WAS A BIT SOUTH OF
THAN CONSENSUS AS IT ROTATES THE MAIN VORT ENERGY FASTER TOWARD
THE US/CANADA BORDER BY DAY 3.


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

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

GALLINA/BURKE

$$




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