Prognostic Meteorological Discussion
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000
FXUS10 KWNH 171721
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
121 PM EDT THU AUG 17 2017

VALID AUG 17/1200 UTC THRU AUG 21/0000 UTC

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

...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...


...PRONOUNCED SHORTWAVE PUSHING TOWARD THE UPPER MIDWEST...
...ASSOCIATED DEEP SURFACE LOW/ATTENDANT COLD FRONT...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

WATER VAPOR IMAGERY SHOWED A COMPACT UPPER LOW LIFTING THROUGH
NORTHWESTERN WI WITH A TRAILING FRONTAL ZONE/MOISTURE PLUME
EXTENDING DOWN FROM THE GREAT LAKES INTO THE ARKLATEX. MODELS SHOW
THIS SYSTEM CONTINUING TO MOVE NORTHEASTWARD TOWARD SOUTHEASTERN
ONTARIO DURING THE NEXT 24 TO 30 HOURS WITH GENERAL AGREEMENT
NOTED. THIS WILL ULTIMATELY HELP USHER A FRONTAL ZONE EASTWARD
TOWARD THE I-95 CORRIDOR BY FRIDAY EVENING. OVERALL...FAIRLY GOOD
AGREEMENT EXISTS AMONG THE MODELS TO SUPPORT A GENERAL MODEL
COMPROMISE.


...TRAILING SHORTWAVE RACING FROM THE DAKOTAS TO THE NORTHEASTERN
U.S. THROUGH SUNDAY...

PRELIMINARY PREFERENCE: A NON-00Z CMC MODEL COMPROMISE
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

IN THE WAKE OF THE LEAD SYSTEM PUSHING INTO THE GREAT
LAKES...ANOTHER DISTURBANCE IS FORECAST TO PUSH THROUGH THE MIDDLE
MS VALLEY BY FRIDAY EVENING. COMPARED TO OTHER AVAILABLE
SOLUTIONS...THE 00Z CMC IS QUITE A BIT SLOWER RELATIVE TO THE
CONSENSUS. THIS DIFFERENT CONTINUES INTO THE WEEKEND AS THE HEIGHT
FALLS PROJECT THROUGH NEW ENGLAND LATER IN THE WEEKEND. GIVEN SUCH
A DIFFERENCE IN THE FORECAST...WILL FAVOR A NON-00Z CMC MODEL
COMPROMISE.


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

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

A RATHER POTENT LOOKING FEATURE IS EXPECTED TO COME OUT OF MX
WHILE CROSSING INTO SOUTHWESTERN NM BY SATURDAY EVENING. THERE ARE
A COMPLEX ARRAY OF SOLUTIONS WITH A VARIETY OF STRENGTHS AND
POSITIONS. FOR INSTANCE...THE 12Z NAM SITS FARTHEST TO THE NORTH
WHILE THE 00Z CMC IS STILL OVER MX WHILE BEING WEAKER. AT THIS
POINT...A BLEND OF THE 12Z GFS/00Z ECMWF WOULD BE THE BEST
STARTING POINT...BUT WITH BELOW AVERAGE CONFIDENCE GIVEN THE
MESOSCALE NATURE OF THIS SYSTEM.


...BROAD LONGWAVE TROUGH EXTENDING OVER THE WESTERN HALF OF CANADA
FRIDAY THROUGH SUNDAY...
...COLD FRONT SWEEPING THROUGH THE NORTH-CENTRAL U.S. OVER THE
WEEKEND...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: AVERAGE

A STRONG LONGWAVE TROUGH INITIALLY OVER THE NORTHEASTERN PACIFIC
WILL DROP SOUTHEASTWARD IN TIME. THE BETTER CORRIDOR OF HEIGHT
FALLS SHOULD SURGE EASTWARD REACHING MANITOBA BY SUNDAY MORNING.
AS NOTED WITH OTHER SYSTEMS...THE 00Z CMC IS MUCH SLOWER THAN THE
MODEL CONSENSUS WHICH PLACES ITS COLD FRONT WELL TO THE WEST. BY
THE END OF THE FORECAST...THE 12Z NAM/00Z UKMET BEGIN TO
ACCELERATE AHEAD OF THE OTHER GUIDANCE WHICH EVENTUALLY BECOME THE
OTHER EXTREME AMONG THE SUITE OF MODELS. THIS IS FAIRLY WELL
DOCUMENTED WITHIN THE RECENT ENSEMBLE SPAGHETTI PLOTS. A BLEND OF
THE 12Z GFS/00Z SHOULD SUFFICE HERE GIVEN SOMEWHAT SIMILAR
FORECASTS AND SITTING WITHIN THE CENTER OF THE MODEL SPREAD.


...ELONGATED UPPER TROUGH POSITIONED OVER THE SOUTHWESTERN U.S.
LATE IN THE FORECAST...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

TOWARD THE END OF THE PERIOD...A BROAD UPPER TROUGH IS FORECAST TO
EXTEND ACROSS THE SOUTHWESTERN STATES. MODELS ARE IN DECENT
AGREEMENT WITH GOOD CLUSTERING AMONG THE ENSEMBLE MEMBERS VIA THE
582-DM SPAGHETTI PLOT. A GENERAL MODEL COMPROMISE IS WARRANTED
HERE.


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

RUBIN-OSTER



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