Prognostic Meteorological Discussion
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000
FXUS10 KWNH 270647
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 AM EDT MON APR 27 2015

VALID APR 27/0000 UTC THRU APR 30/1200 UTC

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

00Z MODEL EVALUATION
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


DEEP TROUGH/CLOSED LOW CURRENTLY OVER THE SOUTHWEST U.S.
LOW PRESSURE DEVELOPING OVER THE SOUTHERN PLAINS BY MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE THROUGH 12Z WED...GFS/ECMWF
COMPROMISE THEREAFTER
CONFIDENCE: AVERAGE

THROUGH EARLY WED...THE MODELS ARE SHOWING BETTER AGREEMENT WITH
THE 00Z NAM TRENDING TOWARD THE SLOWER CONSENSUS.  THE
NAM/GFS/ECMWF/UKMET ARE FAIRLY WELL CLUSTERED THROUGH 12Z WED.
THEREAFTER...THE NAM REMAINS ON THE PROGRESSIVE SIDE OF THE
GUIDANCE WITH THE REMNANT SHORTWAVE MOVING ACROSS THE
SOUTHEAST/SOUTHERN MID-ATLANTIC AND THE SURFACE LOW TRACKING UP
THE SOUTHEAST COAST.


UPPER TROUGH DIGGING INTO THE GREAT LAKES LATE WED-THU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GEFS MEAN/ECMWF
CONFIDENCE: AVERAGE TO BELOW AVERAGE

THERE IS LESS THAN AVERAGE CONFIDENCE ACROSS THE GREAT LAKES/OH
VALLEY LATE WED-THU AS A RESULT OF POOR RUN-TO-RUN CONTINUITY AND
ABOVE AVERAGE MODEL SPREAD WITH RESPECT TO THE EVOLUTION OF A
SHORTWAVE TROUGH FORECAST TO DIG INTO THE GREAT LAKES LATE
WED-THU.  BY LATE WED...THE NAM BEGAN TO TREND TOWARD A MORE
AMPLIFIED SOLUTION OVER THE GREAT LAKES...HOWEVER IT IS THE 00Z
GFS/UKMET THAT ARE SIGNIFICANT DEPARTURES FROM THEIR 12Z
RUNS...NOW SHOWING A DEEP LOW CLOSING OFF OVER THE GREAT LAKES
LATE WED...BEFORE SETTING INTO THE OH VALLEY BY EARLY WED.  AT THE
MOMENT THESE TWO MODELS ARE AT THE DEEP..SOUTHWEST SIDE OF THE
GUIDANCE...WHILE THE REMAINING MODELS ARE TO VARYING DEGREES MORE
SHEERED AND FURTHER TO THE NORTH.  THIS INCLUDES THE 00Z ECMWF
WHICH HAS TRENDED A LITTLE MORE AMPLIFIED...DIGGING THE TROUGH
FURTHER TO THE WEST ACROSS THE UPPER GREAT LAKES EARLY THU...BUT
NOT NEARLY TO THE DEGREE THAT THE GFS/UKMET ARE SHOWING.  WITH THE
00Z GEFS MEAN BETTER SUPPORTING THE 00Z ECMWF...WILL RECOMMEND
LEANING AWAY FROM THE GFS/UKMET.

UPPER TROUGHING OVER THE PACIFIC NORTHWEST TUE/WED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GFS/NAM/UKMET
CONFIDENCE: AVERAGE

THE 00Z GFS IS MORE AMPLIFIED AND SLOWER WITH THE SHORTWAVE TROUGH
FORECAST TO MOVE ONSHORE LATE WED-THU...PUTTING IT INTO BETTER
AGREEMENT WITH THE NAM AND THE 00Z UKMET...WHICH HAS SLOWED AS
WELL.  THE 00Z ECMWF SHOWED A DISSIMILAR TREND AND IS FASTER AND
LESS AMPLIFIED THAN ITS 12Z RUN...WHICH SEEMS LESS LIKELY GIVEN
THE STRENGTH OF AN UPSTREAM RIDGE.


...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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