Prognostic Meteorological Discussion
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FXUS10 KWNH 231850
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EDT WED AUG 23 2017

VALID AUG 23/1200 UTC THRU AUG 27/0000 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...

...TROPICAL CYCLONE HARVEY...

TROPICAL DEPRESSION HARVEY HAS REFORMED AND IS FORECAST TO MOVE
NORTHWESTWARD TOWARDS THE TEXAS COAST FRIDAY INTO SATURDAY. STILL
SOME UNCERTAINTY ON THE EXACT STRENGTH AND TRACK OF THIS SYSTEM.
AS THE SYSTEM CONTINUES TO BECOME BETTER DEFINED WE WILL HOPEFULLY
CONTINUE TO SEE MODELS CONVERGE ON A SOLUTION. FOR NOW THE NHC
PREFERRED TRACK IS CLOSE TO A CONSENSUS OF THE GFS/ECMWF THROUGH
12Z SATURDAY. THEREAFTER CONFIDENCE DECREASES WITH WHETHER HARVEY
IS ABLE TO TURN NORTHEASTWARD OR WHETHER IT TENDS TO STALL
OUT...WITH MODELS GENERALLY SHOWING INCONSISTENT SOLUTIONS. THUS
WILL NEED TO CONTINUE TO CLOSELY MONITOR TRENDS.

19Z UPDATE: THE NEW 12Z ECMWF TRENDED SOUTHWEST FROM ITS PREVIOUS
RUN...WITH THE CMC ALSO TRENDING IN THAT DIRECTION. THE 12Z UKMET
ALSO TRENDED A TAD SOUTHWEST...ALTHOUGH IS STILL THE FURTHEST EAST
SOLUTION AMONGST THE GLOBAL GUIDANCE. IF ANYTHING THESE NEW RUNS
SEEM TO ADD TO THE UNCERTAINTY WITH THIS FORECAST. STILL DO NOT
THINK WE HAVE SEEN A CONSISTENT ENOUGH TREND TO FULLY JUMP ONTO
THIS SOUTHWEST TREND. HOWEVER THE SLOWER AND WEST TREND IS
NOTICEABLE AND CERTAINLY WORTH MONITORING. PLEASE SEE THE LATEST
NHC FORECAST FOR THE LATEST PREFERRED TRACK FOR HARVEY.

...EAST COAST TROUGH AND TRAILING SHORTWAVE MOVING ACROSS THE
GREAT LAKES THURSDAY...

PREFERENCE:GENERAL MODEL CONSENSUS
FORECAST CONFIDENCE: ABOVE AVERAGE

MODELS GENERALLY APPEAR TO BE IN GOOD AGREEMENT WITH THESE
FEATURES AND THUS A GENERAL MODEL BLEND CAN BE PREFERRED.

19Z UPDATE: NO CHANGES NEEDED.


...STRONG HEIGHT FALLS MOVING INTO PACIFIC NORTHWEST BY
THURSDAY...MID LEVEL TROUGH CROSSING THE NORTHERN PLAINS FRI...

PREFERENCE: BLEND OF 12Z GFS/ECMWF/UKMET
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

MODELS REMAIN IN PRETTY CLOSE AGREEMENT WITH THE 500 MB TROUGH
MOVING ONSHORE IN THE PACIFIC NORTHWEST EARLY THU AND THEN
TRACKING ACROSS SOUTHERN CANADA THROUGH FRIDAY. SUBTLE PIECES OF
SHORTWAVE ENERGY ON THE SOUTHERN EDGE OF THIS TROUGH WILL COMBINE
WITH WEAK FEATURES MOVING OUT OF THE ROCKIES TO RESULT IN THE
FORMATION OF A MORE WELL DEFINED SHORTWAVE TROUGH OVER THE
NORTHERN PLAINS LATER FRIDAY INTO SATURDAY. THE 0Z CMC SEEMS TO BE
SUFFERING SOME FEEDBACK ISSUES WITH CONVECTION MOVING ACROSS THE
PLAINS ON FRIDAY. IT IS ALSO DEEPER WITH THE TROUGH MOVING INTO
THE NORTHWEST. THUS IN GENERAL THE 0Z CMC SEEMS TO REPRESENT AN
UNLIKELY SOLUTION ACROSS THIS PORTION OF THE COUNTRY. THE 12Z NAM
IS NOTICEABLY WEAKER WITH THE TROUGH DEVELOPING OVER THE NORTHERN
PLAINS AND IS ALSO CONSIDERED A LESS LIKELY OUTCOME. PREFER TO
STAY CLOSER TO THE BETTER CLUSTERED GFS/ECMWF/UKMET SOLUTIONS. THE
GFS IS A TAD QUICKER THAN THE ECMWF/UKMET...WITH SOMETHING IN THE
MIDDLE APPEARING MOST LIKELY AT THIS TIME.

19Z UPDATE: THE 12Z CMC LOOKS IMPROVED FROM ITS 0Z RUN WITH THE
EVOLUTION OF THESE FEATURES. HOWEVER STILL PREFER TO STAY WITH THE
GOOD CLUSTERING SEEN WITH THE GFS/ECMWF/UKMET.

...BREAKDOWN OF SOUTHWEST RIDGE AND EMBEDDED SHORTWAVES EJECTING
EAST TOWARDS THE SOUTHERN PLAINS...

PREFERENCE: MODEL CONSENSUS
FORECAST CONFIDENCE: ABOVE AVERAGE

MODELS ARE IN GOOD AGREEMENT WITH THE BREAKDOWN OF THE SOUTHWEST
RIDGE AND EMBEDDED SHORTWAVES EJECTING EAST ACROSS THE SOUTHERN
PLAINS THROUGH SATURDAY. SMALLER SCALE DIFFERENCES EXIST WITH THE
INDIVIDUAL SHORTWAVE FEATURES...HOWEVER THESE DIFFERENCES ARE
RELATIVELY MINOR AND ON A BROADER SCALE A GENERAL MODEL BLEND
SHOULD SUFFICE.

19Z UPDATE: NO CHANGES.


...MID LEVEL CIRCULATION FORECAST TO FORM NEAR FL EAST COAST...

PREFERENCE: 12Z GFS/UKMET/ECMWF MODEL CONSENSUS
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A WEAK TROPICAL WAVE REMAINS IN THE VICINITY OF FLORIDA. SOME
SIGNS WE COULD SEE SOME SLIGHT ORGANIZATION OF THIS FEATURE WITH
THE DEVELOPMENT OF A MID LEVEL CIRCULATION OVER THE NEXT FEW DAYS.
OVERALL THERE APPEARS TO BE GOOD CLUSTERING AMONGST THE
GFS/ECMWF/UKMET...AND THUS WILL CONTINUE TO PREFER A BLEND OF
THESE SOLUTIONS. THE NAM ORGANIZES THE SYSTEM A BIT MORE THAN THE
OTHER GUIDANCE...AND WHILE NOT IMPOSSIBLE...IT SEEMS TO REPRESENT
A LESS LIKELY OUTCOME.

19Z UPDATE: NO CHANGES.

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

CHENARD

$$





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