Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8
000
FXUS10 KWNH 021652
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1251 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 NAM/GFS EVALUATION INCLUDING ANALYSIS AND PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SHORTWAVE TROUGH TRACKING FROM NEVADA TO THE NORTHERN PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z NAM/GFS AND 00Z ECMWF
CONFIDENCE: 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 RELATIVE
TO THE 00Z ECMWF...AND EVENTUALLY OUTPACING THE 12Z NAM AS WELL BY
00Z ON THE 6TH. A BLEND OF THE 12Z GFS/NAM AND 00Z ECMWF IS
PREFERRED AT THIS TIME...BUT DUE TO BETTER OVERALL AGREEMENT AND
CONTINUITY RECOMMEND MORE EMPHASIS AND HIGHER WEIGHTING UPON THE
00Z ECMWF.


SHORTWAVE TROUGH TRACKING FROM COLORADO TO THE MID MISSISSIPPI
VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
PREFERENCE: BLEND OF 12Z GFS/00Z ECMWF...TURNING TO LESS WEIGHT ON
GFS AFTER 05/06Z
CONFIDENCE: 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 00Z CANADIAN WAS LARGELY OUT OF PHASE WITH THE
GFS/ECMWF-LED CONSENSUS...AND THE UKMET WAS ONE OF THE DEEPEST
SOLUTIONS WITH RESPECT TO THE SHORTWAVE COMING OUT OF
NEVADA...AFFECTING ITS FORECAST FOR THIS SHORTWAVE DOWNSTREAM INTO
THE SOUTHERN PLAINS AND MID MISSISSIPPI VALLEY.   ALL
CONSIDERED...A CONTINUATION OF A 12Z GFS/00Z ECMWF BLEND IS
PREFERRED UNTIL 06Z ON THE 5TH...WHEN THE CONVECTIVE FEEDBACK
BECOMES TOO MUCH OF AN ISSUE...THEN SOLELY 00Z ECMWF AFTER THAT.
CONFIDENCE IN THIS BLEND IS AVERAGE.


TROUGH AND RENEWED SURGE OF MILD AIR OVER THE GREAT LAKES /
NORTHEAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
PREFERENCE: BLEND 12Z NAM/GFS AND 00Z 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/00Z 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 EVEN THOUGH SURFACE FEATURES
LOOK GOOD IN STRENGTH THOUGH MAYBE A SHADE FAST AS IT LIFTS UP THE
COAST BUT IT MAY BE USABLE AT THIS LOWER LEVEL. THE 12Z GFS
REMAINS SOLID IN CONTINUITY WITH ITSELF PRIOR ECMWF RUNS AND
ENSEMBLE MEANS.  SIMILARLY THE 00Z CMC AND UKMET ARE MUCH TOO
STRONG/CONSOLIDATED IN COMPARISON. AS SUCH A BLEND OF THE 12Z
GFS/00Z 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 AND 00Z 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 00Z 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 00Z CMC WAS A
NOTABLE OUTLIER IN POSITION AND STRENGTH...WHILE THE 00Z UKMET WAS
ALSO SLOWER THAN CONSENSUS ON DAY 3.  AS SUCH A BLEND OF THE 12Z
NAM/GFS WITH THE 00Z ECMWF IS PREFERRED AT AVERAGE CONFIDENCE.


...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

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.