Prognostic Meteorological Discussion
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FXUS10 KWNH 180440
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 AM EDT FRI AUG 18 2017

VALID AUG 18/0000 UTC THRU AUG 21/1200 UTC

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

...AN EVALUATION OF THE 00Z MODEL GUIDANCE ALONG WITH
PREFERENCES/FORECAST CONFIDENCE...

...700 MB WAVE CROSSING THE CENTRAL PLAINS TO MID MS VALLEY FRI
AND OH VALLEY SAT...

PREFERENCE: BLEND OF THE GFS/ECMWF
FORECAST CONFIDENCE: AVERAGE

ANOTHER DISTURBANCE IS FORECAST TO PUSH THROUGH THE CENTRAL PLAINS
TO THE MIDDLE MS VALLEY FRI  AND OH VALLEY SAT.  THE 00Z NAM HAS A
BULLSEYE IN 700 MB CONVERGENCE AND ASCENT THAT DISTORTS THE WAVE
FIELD 00-06Z SUN OVER NORTH CENTRAL KS...WHICH CARRIES DOWNSTREAM
INTO THE OH VALLEY AFTERWARD.  WITH GOOD CLUSTERING AMONG THE
GFS/UKMET/ECMWF...RECOMMEND BLENDING THESE SOLUTIONS INSTEAD.

...COLD FRONT CROSSING THE NORTHERN HIGH PLAINS FRI TO THE UPPER
MS VALLEY AND CENTRAL PLAINS BY SUN MORNING..WITH WAVY LOW
PRESSURE OVER THE CENTRAL PLAINS SUN NIGHT TO MON MORNING...

PREFERENCE: BLEND OF THE GFS/ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE 12Z CMC IS MUCH SLOWER /AMPLIFIED WITH A WAVE PROGRESSING
ACROSS THE NORTHERN ROCKIES AND HIGH PLAINS DAY 2 AND NORTHERN
PLAINS AND UPPER MS VALLEY DAY 3.  THE OTHER EXTREME AMONG THE
SUITE OF MODELS IS THE 12Z UKMET...WHOSE PATTERN OVER THE UPPER
GREAT LAKES AND UPPER MS VALLEY BECOMES DISTORTED IN RESPONSE TO
AGGRESSIVE AMPLIFICATION OF A WAVE APPROACHING NORTHERN MANITOBA
AND HUDSON BAY.

A BLEND OF THE 00Z GFS/12Z ECMWF SHOULD SUFFICE HERE GIVEN
SOMEWHAT SIMILAR FORECASTS...AND UNCERTAINTIES OF THE WAVE
AMPLITUDE/TIMING IN FAST CONFLUENT FLOW.

...IMPULSE LIFTING OUT OF NORTHERN MX REACHING SOUTHWESTERN NM BY
20/0000Z...

PREFERENCE: BLEND OF ECMWF/NAM
FORECAST CONFIDENCE: ABOVE AVERAGE

LIKE YESTERDAY...THE GFS IS MORE ASSERTIVE THAN OTHER MODELS IN
DEVELOPING A COMPACT 500 MB CIRCULATION CENTER WITH HIGH ABSOLUTE
VORTICITY ORIGINATING FROM CONVECTION IN NORTHERN MEXICO AND THEN
MOVING IT DOWNSTREAM NEAR THE MEXICO/TX/NM BORDER AND NORTHEAST
ACROSS NM ON DAY 3.
THE WAVE IS SHOWN IN SEVERAL OTHER MODELS BUT WITH LESS
CONCENTRATION THAN THE GFS.

...LOW PRESSURE MOVING ACROSS QUEBEC WITH FRONTAL SYSTEMS CROSSING
NEW YORK/NEW ENGLAND FRI AND MOVING OFF THE COAST SAT...

FINAL PREFERENCE: MODEL CONSENSUS
FORECAST CONFIDENCE: AVERAGE

MODELS SHOW LOW PRESSURE MOVING NORTHEAST OUT OF ONTARIO IN QUEBEC
FRI NIGHT. A WARM FRONT AHEAD OF THE SYSTEM CROSSES NY/NEW
ENGLAND...FOLLOWED BY A TRAILING COLD FRONT.  THIS WILL
GOOD AGREEMENT EXISTS AMONG THE MODELS TO SUPPORT A MODEL
CONSENSUS.

www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

PETERSEN


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