Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5
000
FXUS10 KWNH 201854
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 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: 12Z ECMWF/12Z CMC/12Z GFS 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
SLIGHTLY FASTER THAN THE MODEL CONSENSUS BY SATURDAY MORNING
ALOFT.  THE GFS IS FARTHER TO THE NORTH WITH THE TRACK OF THE
SURFACE LOW, AS WELL AS THE GEFS MEAN, SO IT CAN BE INCORPORATED
INTO THE FORECAST.


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/12Z ECMWF
CONFIDENCE: AVERAGE

THE MAJORITY OF THE MODELS AND THE ENSEMBLE MEANS AGREE WELL ON
THE PLACEMENT AND TIMING OF THIS BOUNDARY, WITH THE 12Z UKMET
SLIGHTLY QUICKER THAN ITS PREVIOUS RUN.  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/12Z 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 12Z UKMET INDICATES THE GREATEST
DEGREE OF TROUGHING TOWARDS THE END OF THE FORECAST PERIOD.  THE
ECMWF REMAINS CLOSE TO THE MODEL CONSENSUS.


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.


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

HAMRICK

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.