Prognostic Meteorological Discussion
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FXUS10 KWNH 271844
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 PM EDT WED JUL 27 2016

VALID JUL 27/1200 UTC THRU JUL 31/0000 UTC

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

12Z FINAL MODEL EVALUATION AND PREFERENCES


...MULTIPLE SHORTWAVES MOVING EAST OVER THE SOUTHWEST
RIDGE...DROPPING SOUTHEAST INTO A DEVELOPING EAST COAST TROUGH...
...SHORTWAVE ENERGY MOVING NORTH THROUGH THE LOWER MS
VALLEY...BECOMING ABSORBED INTO THE EAST COAST TROUGH...

PREFERENCE: CONSENSUS OF THE 12Z GFS/ECMWF/UKMET
CONFIDENCE: AVERAGE

A COMPLEX PATTERN OVER THE CONUS FOR THE SHORT TERM PERIOD...WITH
THE FORECAST AGAIN EXPECTED TO BE INFLUENCED BY SMALL SCALE
CONVECTIVE FEATURES/VORTS...WHICH WILL BE DIFFICULT TO TRACK. ON
THE LARGE SCALE THERE IS PRETTY GOOD AGREEMENT AMONGST THE
MODELS...WITH A SOUTHWESTERN U.S. UPPER RIDGE...AND A DEVELOPING
BROAD TROUGH OVER THE EASTERN HALF OF THE NATION. HELPING TO
DEVELOP THIS TROUGHING WILL BE MULTIPLE SHORTWAVES RIDING UP AND
OVER THE RIDGE AND DIGGING SOUTHEAST ACROSS THE MS VALLEY AND INTO
THE EAST. THERE IS GOOD AGREEMENT AS WELL THAT THE MID LEVEL
TROUGH/CLOSED LOW OVER THE LOWER MS VALLEY WILL BE PULLED NORTH
AND GRADUALLY ABSORBED INTO THE TROUGH.

THE DISAGREEMENT COMES FROM THE TIMING/STRENGTH OF THE WAVE MOVING
NORTHEAST OUT OF THE LOWER MS VALLEY...AS WELL AS THE WAVES MOVING
SOUTHEAST OUT OF THE PLAINS...AND HOW THESE FEATURES INTERACT
WITHIN THE DEVELOPING TROUGH OVER THE EAST. THE GFS REMAINS THE
QUICKEST SOLUTION...AND IN FACT THE 12Z RUN IS EVEN SLIGHTLY
QUICKER THAN THE 0Z RUN. THE 0Z ECMWF/GEM REMAIN THE SLOWEST
SOLUTIONS. THE GENERAL TREND HAS BEEN TOWARDS A QUICKER
SOLUTION...SUGGESTING THE 0Z ECMWF/GEM ARE LIKELY TOO SLOW WITH
THE EASTWARD PROGRESSION OF THE TROUGH AND DEVELOPING SURFACE LOW
ACROSS THE MID ATLANTIC. THE NEW 12Z UKMET/NAM ARE CLOSER TO THE
GFS WITH REGARDS TO TIMING...JUST SLIGHTLY SLOWER. ALSO HAVE
SLIGHT DIFFERENCES IN THE ORIENTATION OF THE TROUGH BY 12Z
FRIDAY...WHICH ENDS UP HAVING A PRETTY SIGNIFICANT QPF IMPACT
ACROSS SOUTHERN NEW ENGLAND. THE SLOWER ECMWF/GEM END UP A BIT
FURTHER NORTH THAN THE GFS/UKMET. BY THIS TIME THE 12Z NAM APPEARS
TO BE AN OUTLIER...BEING TO STRONG WITH THE WAVE AND LOW IN
GENERAL...AND THUS WILL RULE IT OUT FOR NOW. THINK THE ECMWF/GEM
ARE LIKELY TOO FAR NORTH...WITH THE TIMING ISSUES IN THESE MODELS
LIKELY IMPACTING THIS LATITUDE DIFFERENCE AS WELL. PREFER A
SOLUTION CLOSER TO THE 12Z GFS/UKMET FOR THE TIME BEING...ALTHOUGH
A SMALL INCLUSION OF THE 0Z ECMWF IS REASONABLE TO ACCOUNT FOR THE
POTENTIAL OF A SLIGHTLY SLOWER/NORTH TRACK. WOULD EXPECT TO SEE A
QUICKER AND SOUTH TREND IN THE NEW 12Z ECMWF/GEM. WILL REEVALUATE
FOR THE FINAL ISSUANCE IF THIS TREND IS NOT SEEN.

UPSTREAM ADDITIONAL SHORTWAVES WILL BE DIGGING DOWN FROM THE
PLAINS AND ACROSS THE MIDWEST THURSDAY INTO SATURDAY HELPING
REINFORCE THE WEAK TROUGHING. OVERALL THE MODELS ARE IN PRETTY
GOOD AGREEMENT WITH THE HANDLING OF THIS TROUGHING...WITH THE
ECMWF PROBABLY SLIGHTLY TOO SLOW IN GENERAL. ALTHOUGH AS
EXPECTED...DIFFERENCES EXIST IN THE EXACT TRACK/INTENSITY OF THE
INDIVIDUAL SHORTWAVE IMPULSES. OVERALL THOUGH A GENERAL MODEL
BLEND COULD BE USED.

1830Z UPDATE: BOTH THE 12Z ECMWF AND GEM DID INDEED TREND QUICKER
WITH THE TROUGH AND DEVELOPING SURFACE REFLECTION ACROSS THE EAST.
THE 12Z GEM APPEARS TO BE STRUGGLING WITH THE HANDLING OF THE
SHORTWAVE ENERGY RESULTING IN A SOLUTION TOO FAR NORTH. THE 12Z
ECMWF MAY HAVE TRENDED SLIGHTLY SOUTH...BUT HAS GENERALLY STAYED
PUT WITH A FURTHER NORTH SOLUTION. IT IS SLIGHTLY MORE AMPLIFIED
WITH THE WAVE WHICH ALLOWS FOR THE SLIGHTLY FURTHER NORTH
SOLUTION. FOR NOW WILL PREFER SOMETHING IN BETWEEN THE NORTHERN
ECMWF AND SOUTEHRN GFS/UKMET. OF COURSE THE QPF FORECAST IS ALSO
DEPENDENT ON CONVECTIVE PROCESSES AND INSTABILITY. SO EVEN A
FURTHER NORTH LOW/WAVE TRACK DOES NOT NECESSARILY MEAN THE FURTHER
NORTH QPF WILL VERIFY. SEE THE QPFPFD FOR MORE DETAILS ON THE WPC
QPF FORECAST FOR THIS SYSTEM.

...SHORTWAVE TROUGH AIMING FOR THE NORTHWEST BY SAT...

PREFERENCE: BLEND OF THE 12Z GFS/NAM/ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GUIDANCE HAS A SHORTWAVE TROUGH CROSSING THE GULF OF AK AND
DROPPING SOUTHEAST ACROSS BRITISH COLUMBIA BY FRIDAY..WITH THE
ENERGY CLIPPING THE NORTHWEST U.S. ON SAT. OVERALL THE BEST MODEL
CLUSTERING AND SOLUTIONS CLOSEST TO THE ENSEMBLE MEANS ARE THE 12Z
GFS/NAM AND THE 0Z ECMWF. THE 12Z UKMET AND 0Z GEM EVOLVE THE
ENERGY WITHIN THE TROUGH DIFFERENTLY...AND WHILE NOT
IMPOSSIBLE...SEEM TO REPRESENT LESS LIKELY SOLUTION.

1830Z UPDATE: 12Z ECMWF TRENDED SLIGHTLY QUICKER AND SOUTH WITH
THE TROUGH. THE 12Z GEFS MEAN IS SLOWER THAN THE 12Z DETERMINISTIC
GFS...WHICH COULD SUGGEST THE ECMWF IS TOO FAST. HOWEVER APPEARS
THAT RECENT TRENDS ARE FOR A QUICKER SYSTEM...SO WILL NOT RULE OUT
THE ECMWF AT THIS TIME. A BLEND OF THE 12Z GFS...ECMWF AND NAM
STILL LOOKS LIKE THE BEST BET FOR NOW.

CHENARD

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

$$





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