Prognostic Meteorological Discussion
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000
FXUS10 KWNH 030530
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
129 AM EDT WED JUN 03 2015

VALID JUN 03/0000 UTC THRU JUN 06/1200 UTC

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

00Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

WELL DEVELOPED NORTHERN STREAM UPPER LOW ROLLING ACROSS NEW ENGLAND
SURFACE LOW PASSING JUST OFF NOVA SCOTIA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF OPERATIONAL MODELS
CONFIDENCE: ABOVE AVERAGE

NO SIGNIFICANT MODEL DIFFERENCES WERE NOTED...ABOVE AVERAGE
CONFIDENCE EXISTS GIVEN THE SHORT TERM NATURE OF THE FORECAST AND
VERY GOOD AGREEMENT AMONG THE LATEST GUIDANCE.


CLOSED LOW FORECAST TO WEAKEN EWD ACROSS THE SOUTHERN
APPALACHIANS-
  SOUTHERN MID-ATLANTIC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/UKMET/12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GFS HAS SLOWED SOME FROM ITS 12Z SOLUTION...PLACING ITS TIMING
INTO BETTER AGREEMENT WITH THE UKMET/12Z ECMWF AS THE SYSTEM
DRIFTS EAST.  HOWEVER...THE NAM HAS REMAINED CONSISTENT WITH ITS
12Z RUN...LEAVING IT ALONG THE LEADING EDGE OF THE GUIDANCE.
GIVEN THE SLOW PROGRESSION OF THIS TROUGH UP UNTIL NOW...AND THE
PRESENCE OF RIDGING ACROSS THE WESTERN ATLANTIC...PREFER TO KEEP
WITH THE SLOWER SOLUTIONS.

SHORTWAVE SHEARING OUT ALONG U.S./CANADIAN BOARDER
NORTHERN HIGH PLAINS CYCLOGENESIS
SOUTHERN STREAM SHORTWAVE EJECTING INTO CENTRAL PLAINS THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NAM
CONFIDENCE: BELOW AVERAGE

THE 00Z NAM HAS BACKED AWAY FROM ITS 12Z SOLUTION WITH A FLATTER
SHORTWAVE TROUGH AND LESS AMPLIFIED SURFACE LOW OVER THE UPPER
MIDWEST EARLY THU.  THIS PUTS IT INTO BETTER AGREEMENT WITH THE
REMAINING OPERATIONAL GUIDANCE.   HOWEVER...NUMEROUS OTHER DETAIL
DIFFERENCES ARE NOTED IN WHAT REMAINS A COMPLEX SITUATION ACROSS
THE PLAINS...WHERE SEVERAL WEAK IMPULSES EMBEDDED WITHIN SOUTHWEST
FLOW ARE EXPECTED TO EJECT OUT FROM THE WESTERN CONUS AND MOVE
ACROSS THE TOP OF A STRONG RIDGE. CONVECTIVE DETAILS MUDDLE THE
FORECAST AND FEATURES ARE DIFFICULT TO TRACK GIVEN THE RELIANCE ON
YET TO BE SEEN CONVECTIVELY DRIVEN VORTICITY MAXIMA. FOR
EXAMPLE...DIFFERENCES EVOLVE WITH THE SHORTWAVE TROUGH FORECAST TO
AMPLIFY AS IT SPILLS OFF OF THE TOP OF THE RIDGE INTO THE
MID-UPPER MS VALLEY THU NIGHT-FRI MORNING.  THE GFS/UKMET ARE
SIMILARLY TIMED...BUT ARE FURTHER TO THE NORTH AND MORE WRAPPED UP
THAN THE NAM/00Z ECMWF ACROSS THE UPPER MS VALLEY EARLY FRI.  IN
CONTRAST...THE 12Z ECMWF IS THE LEAST AMPLIFIED ALOFT AND MORE
PROGRESSIVE ACROSS THE MID MO/MS VALLEYS INTO THE OH VALLEY LATE
THU-FRI.  BY LATE FRI INTO SAT THE 12Z ECMWF BECOMES MUCH MORE
PROGRESSIVE DIGGING ENERGY FURTHER TO THE SOUTH INTO THE SOUTHERN
APPALACHIANS EARLY SAT.  AT THIS POINT...WHILE CONFIDENCE IN ITS
DETAILS ARE VERY LIMITED...THE NAM OFFERS THE BEST COMPROMISE OF
THE LATEST OPERATIONAL RUNS.


UPPER TROUGH RELOADING OVER THE WEST BY WED/THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET BLEND
CONFIDENCE: ABOVE AVERAGE

ONLY MINOR PLACEMENT/TIMING DIFFERENCES EXIST WITH A CLOSED LOW
FORECAST TO FORM OVER CALIFORNIA BY MID-DAY
THURSDAY...HOWEVER...WHILE TRENDING TOWARD THE REMAINING
OPERATIONAL MODELS...THE 00Z UKMET STILL STANDS OUT A BIT FROM THE
OTHER OPERATIONAL MODELS REMAINING SOMEWHAT MORE OPEN IN THE
700-500 MB LAYER. GIVEN THE OVERALL GOOD AGREEMENT AND THE TREND
IN THE UKMET...THE PREFERENCE REMAINS FOR A NON-UKMET BLEND OF
MODELS.


SHORTWAVE TROUGH IMPACTING THE NORTHERN ROCKIES HIGH PLAINS SAT
MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
PREFERENCE: GFS/NAM/UKMET
CONFIDENCE: AVERAGE

THE GFS/NAM/UKMET ARE IN FAIRLY GOOD AGREEMENT WITH A SHORTWAVE
TROUGH FORECAST TO CENTER NEAR THE MT/ND BORDER SAT MORNING.  THE
12Z ECMWF IS A RELATIVE OUTLIER HERE WITH A MORE AMPLIFIED
SOLUTION.

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

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

PEREIRA

$$





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