Prognostic Meteorological Discussion
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FXUS10 KWNH 221848
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 PM EDT TUE AUG 22 2017

VALID AUG 22/1200 UTC THRU AUG 26/0000 UTC

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

...AN EVALUATION OF THE 12 UTC MODELS ALONG WITH
PREFERENCES/FORECAST CONFIDENCE...

...LONGWAVE TROUGH AFFECTING CENTRAL TO EASTERN NORTH AMERICA...
...ASSOCIATED DEEP SURFACE LOW/COLD FRONT...
...TRAILING SHORTWAVE PUSHING THROUGH THE UPPER MIDWEST 24/0000Z...

PREFERENCE: GENERAL MODEL CONSENSUS
FORECAST CONFIDENCE: ABOVE AVERAGE

OVERALL...THE MODELS REMAIN IN FAIRLY GOOD AGREEMENT WITH THE
TROUGH AND COLD FRONT MOVING ACROSS THE EAST. SOME MINOR
DIFFERENCES EXIST WITH THE TRAILING SHORTWAVE FEATURE MOVING INTO
THE UPPER MS VALLEY LATER WEDNESDAY. HOWEVER THESE DIFFERENCES ARE
NOT SIGNIFICANT AND A GENERAL MODEL BLEND SHOULD SUFFICE FOR THESE
FEATURES.

19Z UPDATE: NO CHANGES IN PREFERENCE.

...QUASI-STATIONARY UPPER LOW IN THE VICINITY OF CA/DESERT
SOUTHWEST...

PREFERENCE: GENERAL MODEL CONSENSUS
FORECAST CONFIDENCE: ABOVE AVERAGE

AN UPPER TROUGH/LOW NEAR CA WILL SLOWLY PROGRESS EAST INTO THE
SOUTHWEST THROUGH MID WEEK. SHORTWAVE ENERGY WITHIN THE TROUGH
WILL HELP SUPPRESS THE UPPER RIDGE IN PLACE OVER THE SOUTHWEST.
EVENTUALLY SOME OF THIS ENERGY EJECTS INTO THE WESTERN PLAINS BY
LATER THURSDAY INTO FRIDAY...AND WILL BRING AN INCREASED
CONVECTIVE THREAT TO THE AREA. IN THE LARGE SCALE MODELS ARE IN
PRETTY GOOD AGREEMENT WITH THEIR EVOLUTION OF THESE FEATURES.
SMALLER SCALE FACTORS WILL LIKELY PLAY A ROLE IN CONVECTIVE
PLACEMENT...AND REFERENCE THE QPFPFD FOR MORE INFORMATION ON THESE
DETAILS.

19Z UPDATE: NO CHANGES.

...STRONG HEIGHT FALLS MOVING INTO WESTERN CANADA/PACIFIC
NORTHWEST BY THURSDAY...

PREFERENCE: NON CMC BLEND
FORECAST CONFIDENCE: AVERAGE

MODELS REMAIN IN PRETTY CLOSE AGREEMENT ON THE LARGER SCALE WITH
THIS FEATURE. THE UKMET REMAINS QUICKER THAN THE BETTER MODEL
CLUSTERING. STILL SOME TIMING/DEPTH DIFFERENCES BETWEEN THE OTHER
GUIDANCE...BUT A NON UKMET BLEND SHOULD WORK FINE FOR NOW.

19Z UPDATE: THE UKMET HAS JOINED THE BETTER MODEL CLUSTERING AND
CAN NOW BE INCLUDED IN ANY BLEND. HOWEVER THINK THE 12Z GEM
REPRESENTS A LESS LIKELY OUTCOME...BEING A SLOWER AND DEEPER
SOLUTION WITH THE TROUGH.



...TROPICAL DISTURBANCE ASSOCIATED WITH THE REMNANTS OF HARVEY...

MODELS REMAIN IN GOOD AGREEMENT IN SHOWING HARVEY REDEVELOPING
INTO A TROPICAL SYSTEM AND THEN MOVING NORTHWESTWARD TOWARDS THE
TEXAS COAST. OF COURSE STILL SOME UNCERTAINTY WITH THE STRENGTH
AND EXACT TRACK OF THIS SYSTEM. THE GENERAL TREND HAS BEEN A
NORTHWARD SHIFT IN THE GUIDANCE OVER RECENT RUNS. HOWEVER HAVE
NOTED THAT THE NEW 12Z RUN OF THE GFS IS A TAD SOUTH OF ITS 06Z
AND 0Z RUNS. FOR NOW A BLEND OF THE GFS/ECMWF (WEIGHTED A BIT MORE
TOWARDS THE FURTHER NORTH GFS BASED ON TRENDS) SEEMS LIKE A GOOD
COMPROMISE THROUGH DAY 3 (0Z SAT)...HOWEVER WILL HAVE TO CONTINUE
TO CLOSELY MONITOR TRENDS.

19Z UPDATE: THE 12Z ECMWF CAME IN VERY CLOSE TO ITS 0Z RUN WITH
REGARDS TO THE TRACK OF THIS SYSTEM...BUT IS A BIT WEAKER. THE
EXACT TRACK REMAINS UNCERTAIN...AND HOPEFULLY WE WILL SEE A BIT
BETTER MODEL CONVERGENCE ONCE A LOW LEVEL CIRCULATION FORMS. AS OF
18Z TUESDAY THE WPC/NHC COORDINATED PREFERRED TRACK IS GENERALLY
IN BETWEEN THE FURTHER EAST 12Z NAM/UKMET AND FURTHER SOUTHWEST
12Z GFS/ECMWF. THIS PREFERENCE IS ALSO PRETTY CLOSE TO THE 12Z
GEFS MEAN AND A QUICKER ADJUSTED 12Z GEM.


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

CHENARD

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