Prognostic Meteorological Discussion
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FXUS10 KWNH 181849
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 PM EDT FRI AUG 18 2017

VALID AUG 18/1200 UTC THRU AUG 22/0000 UTC

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

12Z FINAL MODEL GUIDANCE EVALUATION ALONG WITH PREFERENCES AND
FORECAST CONFIDENCE

***MID LEVEL SHORTWAVE CROSSING FROM THE UPPER MIDWEST TO THE
GREAT LAKES***

PREFERENCE: BLEND OF THE 12Z GFS AND ECMWF
FORECAST CONFIDENCE: AVERAGE

A MID LEVEL TROUGH BEHIND THE CURRENT TROUGH OVER THE NORTHEAST IS
FORECAST TO TRACK FROM THE UPPER MIDWEST AND AMPLIFY SOME AS IT
CROSSES THE GREAT LAKES ON SATURDAY.  THIS WILL SUPPORT A WAVE OF
LOW PRESSURE AT THE SURFACE OVER THE OHIO VALLEY REGION.  THE NAM
BECOMES MORE AMPLIFIED WITH THE SOUTHERN PORTION OF THE TROUGH,
WHILST THE 12Z CMC IS SLIGHTLY SLOWER WITH THE NORTHERN PORTION.


***COLD FRONT CROSSING THE NORTH CENTRAL U.S. THIS WEEKEND***

PREFERENCE: BLEND OF THE 12Z GFS AND ECMWF
FORECAST CONFIDENCE: NEAR AVERAGE

THE MODELS SHOW A SLOW MOVING UPPER TROUGH TRACKING EASTWARD JUST
NORTH OF THE CANADIAN BORDER, SUPPORTING A COLD FRONT THAT WILL
TRACK ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST. THE 12Z UKMET
BECOMES MORE AMPLIFIED WITH THE UPPER LEVEL TROUGH OVER SOUTHERN
CANADA BY SUNDAY MORNING.  THE NAM BECOMES QUICKER THAN THE MODEL
CONSENSUS WITH THE COLD FRONT PASSAGE.  A BLEND OF THE 12Z GFS/12Z
ECMWF SHOULD SUFFICE HERE GIVEN REASONABLY SIMILAR SOLUTIONS.


***LARGE SCALE UPPER LEVEL TROUGH OVER THE SOUTHWEST U.S. THIS
WEEKEND***

PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

THE MODELS CONTINUE TO ADVERTISE A LARGE SCALE TROUGH OVER
CALIFORNIA AND THE DESERT SOUTHWEST THAT IS EVIDENT IN THE 588DM
CONTOUR.  THERE IS ALSO GOOD AGREEMENT THAT THIS COULD PINCH OFF
INTO A WEAK CLOSED LOW ON SATURDAY NEAR SOUTHERN CALIFORNIA.
THERE IS ENOUGH MODEL AGREEMENT TO WARRANT A GENERAL MODEL
COMPROMISE.


***MID LEVEL TROUGH AND SURFACE COLD FRONT REACHING THE EAST COAST
SATURDAY***

PREFERENCE: NON-UKMET MODEL CONSENSUS
FORECAST CONFIDENCE: ABOVE AVERAGE

AN OCCLUDED SURFACE LOW IS FORECAST TO TRACK NORTHEASTWARD ACROSS
EASTERN ONTARIO AND THEN OVER QUEBEC THROUGH SATURDAY, WITH A
TRAILING COLD FRONT REACHING THE EAST COAST SATURDAY MORNING.
EXCEPT FOR THE 12Z UKMET THAT IS NORTH OF THE MODEL CONSENSUS WITH
THE SURFACE LOW, GOOD AGREEMENT EXISTS AMONG THE OTHER MODELS TO
SUPPORT A NON-UKMET MODEL CONSENSUS.

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

HAMRICK


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