Prognostic Meteorological Discussion
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445
FXUS10 KWNH 201648
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1247 PM EDT THU JUL 20 2017

VALID JUL 20/1200 UTC THRU JUL 24/0000 UTC

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

***THE PARALLEL GFS WAS UPGRADED TO THE OPERATIONAL GFS WITH THE
12Z MODEL CYCLE WEDNESDAY 7/19***

12Z NAM/GFS MODEL EVALUATION WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
WITH THE EXCEPTION OF SOME 850MB TEMPERATURE DISCREPANCIES OVER
THE OHIO VALLEY, NAM/GFS INITIALIZATION ERRORS APPEAR NEGLIGIBLE
WITH RESPECT TO THEIR SHORT RANGE FORECASTS.


CLOSED LOW AND UPPER TROUGH TRACKING FROM BRITISH COLUMBIA TO THE
GREAT LAKES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~
PREFERENCE: 00Z ECMWF/00Z CMC BLEND
CONFIDENCE: NEAR AVERAGE

THE UPPER LEVEL TROUGH CURRENTLY OVER THE VANCOUVER ISLAND REGION
OF BRITISH COLUMBIA IS FORECAST BY THE MODEL GUIDANCE TO CONTINUE
TRACKING EASTWARD ACROSS SOUTHERN CANADA OVER THE NEXT FEW DAYS AS
IT ATTEMPTS TO CLOSE OFF AT TIMES.  THE TROUGH AXIS WILL SUSTAIN
AN AREA OF LOW PRESSURE ACROSS THE CENTRAL AND NORTHERN PLAINS
THROUGH SATURDAY WITH A TRAILING COLD FRONT.  THE UKMET BECOMES
FASTER THAN THE MODEL CONSENSUS BY SATURDAY MORNING ALOFT.  THE
GFS IS FARTHER TO THE NORTH WITH THE TRACK OF THE SURFACE LOW.


SOUTHEAST COASTAL SHORTWAVE RETROGRADING ALONG THE GULF COAST
THROUGH SATURDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT WITH THIS WEAK
SHORTWAVE AT 250MB, AND ONLY DISPLAYING MINOR PLACEMENT AND
STRENGTH DIFFERENCES THROUGH SUNDAY MORNING.  A GENERAL MODEL
COMPROMISE IS ADVISED WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE.


FRONTAL BOUNDARY REACHING THE NORTHEAST ON FRIDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/00Z ECMWF
CONFIDENCE: AVERAGE

THE MAJORITY OF THE MODELS AND THE ENSEMBLE MEANS AGREE WELL ON
THE PLACEMENT AND TIMING OF THIS BOUNDARY, WITH THE 00Z UKMET
SLIGHTLY SLOWER THAN THE MODEL CONSENSUS.  WITH THE GFS AND ECMWF
IN GOOD AGREEMENT WITH THEIR RESPECTIVE MEANS, A COMPROMISE OF
THESE TWO MODELS SHOULD WORK WELL.


WEAK MID-UPPER LEVEL SHORTWAVE NEAR NORTHERN CALIFORNIA BY SUNDAY
MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~
PREFERENCE: 12Z NAM/12Z GFS/00Z ECMWF BLEND
CONFIDENCE: AVERAGE

A WEAK REFLECTION OF AN UPPER LEVEL TROUGH IS EVIDENT IN THE MODEL
GUIDANCE WITH THE 588DM CONTOUR OFF THE COAST OF NORTHERN
CALIFORNIA THIS WEEKEND, WITH VERY SLOW EASTWARD PROGRESSION
EXPECTED.  HOWEVER, THIS FEATURE IS NOT EXPECTED TO PRODUCE
ADVERSE WEATHER CONDITIONS.  THE 00Z UKMET INDICATES THE GREATEST
DEGREE OF TROUGHING.  WHILE THE 00Z ECMWF REMAINS A BIT FASTER
THAN THE REMAINING CONSENSUS INITIALLY, IT SLOWED ENOUGH COMPARED
TO ITS 12Z RUN TO INCLUDE IT AS PART OF THE MODEL PREFERENCE.


UPPER LEVEL RIDGE OVER THE CENTRAL TO EASTERN U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: WELL ABOVE AVERAGE

MODELS CONTINUE TO SHOW EXCELLENT AGREEMENT WITH THE UPPER LEVEL
RIDGE ACROSS THE CENTRAL U.S. THAT GRADUALLY WEAKENS HEADING INTO
THE UPCOMING WEEKEND, WITH THE AREAL COVERAGE OF THE 594DM CONTOUR
SHRINKING BY SATURDAY MORNING AND THEN SUB-594DM HEIGHTS BY
SATURDAY AFTERNOON AND BEYOND.  THE CMC SHOWS A SLIGHTLY GREATER
EXPANSE OF THE RIDGE, BUT CLOSE ENOUGH TO STILL BE CONSIDERED
USEFUL.


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

HAMRICK

$$





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