Prognostic Meteorological Discussion
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165
FXUS10 KWNH 170443
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1142 PM EST THU NOV 16 2017

VALID NOV 17/0000 UTC THRU NOV 20/1200 UTC

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

00Z INITIAL MODEL PREFERENCES ALONG WITH CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
MODEL INITIALIZATION ERRORS APPEAR NEGLIGIBLE WITH RESPECT TO
THEIR FORECASTS

LEAD SHORTWAVE TRACKING ACROSS SOUTHERN CANADA THROUGH FRIDAY NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

A LEAD NORTHERN STREAM SHORTWAVE TRACKING EASTWARD FROM ALBERTA TO
HUDSON BAY WILL SUPPORT A SURFACE LOW WITH A TRAILING COLD FRONT.
THIS BOUNDARY WILL CROSS THE NORTHERN PLAINS EARLY FRIDAY, AND
THEN REACH THE NORTHERN GREAT LAKES BY FRIDAY NIGHT WHILE THE
PARENT LOW LIFTS WELL TO THE NORTH OVER NORTHERN MANITOBA.  THE
NAM BECOMES SLIGHTLY FASTER WITH THE FRONTAL PROGRESSION BY FRIDAY
NIGHT OVER WISCONSIN AND MICHIGAN, BUT DOES NOT DIFFER ENOUGH TO
DISCOUNT IT FROM THE PREFERENCES.


LARGE STORM SYSTEM OVER THE EASTERN U.S. THIS WEEKEND
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z GFS/12Z ECMWF/12Z EC MEAN
CONFIDENCE: AVERAGE

BEHIND THE LEAD SHORTWAVE IS A MUCH LARGER UPPER LEVEL TROUGH THAT
IS CURRENTLY SITUATED OVER THE PACIFIC NORTHWEST.  THIS INITIALLY
POSITIVELY TILTED TROUGH IS EXPECTED TO TRAVERSE THE CONTINENTAL
U.S. AND BECOME A FULL LATITUDE TROUGH AS IT CROSSES THE PLAINS
AND MIDWEST.  A SURGE OF SHORTWAVE ENERGY BEHIND THE TROUGH IN
NORTHWEST FLOW WILL LIKELY RESULT IN THIS FEATURE ACQUIRING
NEGATIVE TILT AS IT APPROACHES THE NORTHEAST U.S.  THIS WILL
SUPPORT THE DEVELOPMENT OF A STRONG SURFACE LOW TRACKING FROM THE
OHIO VALLEY TO SOUTHERN QUEBEC.  THE NAM BECOMES A NOTABLE
SOUTHERN OUTLIER WITH THE SURFACE LOW BY SATURDAY, AND ALSO
CONSIDERABLY WEAKER.  THE 18Z GEFS MEAN IS ON THE NORTHERN EDGE OF
THE GUIDANCE, AND THE EC MEAN IS NEAR THE MODEL CONSENSUS.  WITH
THE GFS AND ECMWF CLOSE TO THE EC MEAN WITH THE SURFACE LOW, A
BLEND OF THESE THREE MODELS SHOULD SUFFICE WELL FOR NOW.


TROUGH APPROACHING THE PACIFIC NORTHWEST LATER ON SUNDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

A LARGE UPPER LEVEL TROUGH OVER THE GULF OF ALASKA WILL SLOWLY
SETTLE SOUTHWARD OFF THE BRITISH COLUMBIA COAST AS A POSITIVELY
TILTED FEATURE, WITH A SURFACE LOW TRACKING INLAND JUST NORTH OF
VANCOUVER ISLAND.  THE TRAILING COLD FRONT IS EXPECTED TO REACH
WESTERN WASHINGTON BY SUNDAY EVENING.  THE OVERALL MASS FIELD
DIFFERENCES ARE RELATIVELY MINOR FOR THIS SYSTEM AND A GENERAL
MODEL BLEND SHOULD WORK WELL.


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

HAMRICK

$$





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