Prognostic Meteorological Discussion
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FXUS10 KWNH 251846
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 PM EDT TUE JUL 25 2017

VALID JUL 25/1200 UTC THRU JUL 29/0000 UTC

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

12Z MODEL EVALUATION...WITH PREFERENCES AND CONFIDENCE

***THE 12Z ECMWF WAS NOT AVAILABLE FOR THIS ISSUANCE***
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...SHORTWAVE EXITING THE NORTHEAST TODAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

ANY REMAINING MODEL DIFFERENCES ARE SMALL ENOUGH TO SUPPORT A
GENERAL MODEL BLEND WITH THIS SYSTEM.


...LOW/MID-LEVEL TROUGHING ACROSS THE GULF COAST...
...ENERGY ADVANCING EAST ACROSS GA/SC THROUGH WED/THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS ALL TAKE AN ELONGATED LOW TO MID LEVEL TROUGH AXIS
ACROSS THE GULF COAST STATES GRADUALLY SOUTH AND EAST OVER THE
NEXT COUPLE OF DAYS...WITH THE MODELS SUPPORTING A MORE
CONCENTRATED POCKET OF ENERGY...ESPECIALLY IN THE 700/500 MB LAYER
OVER CENTRAL/SOUTHERN GA AND SOUTHERN SC LATER TONIGHT AND ON WED.
BY THURS...THE ENERGY SHOULD BE MORE ALIGNED SW/NE AS AN OPEN
TROUGH AXIS OVER THE SOUTHEAST COASTAL PLAIN. MODEL SPREAD IS VERY
SMALL WITH RESPECT TO THE MASS FIELD DETAILS...SO WILL PREFER A
GENERAL MODEL BLEND AT THIS POINT.


...UPPER LOW TRAVERSING SOUTHERN CANADA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS
            BLEND OF THE 12Z GFS/00Z ECMWF...AFTER 60 HOURS
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN GOOD AGREEMENT WITH THE EVOLUTION OF THE
PROGRESSIVE UPPER LOW CURRENTLY SITUATED OVER MANITOBA. THE
GUIDANCE TAKES THIS OFF TO THE EAST THROUGH ONTARIO AND QUEBEC
WITH SOME INTRUSION OF TROUGHING INTO THE NORTHEAST BY THURS AND
FRI. MODEL SPREAD WITH THIS IS RATHER MINOR THROUGH THURS...BUT BY
FRI THERE IS MORE SPREAD WITH THE DETAILS OF ADDITIONAL ENERGY
DIGGING SOUTHEAST THROUGH QUEBEC WHICH WILL REFOCUS AN UPPER LOW
OVER QUEBEC AS THE ORIGINAL ENERGY WEAKENS/DAMPENS OUT SOMEWHAT.
THE 12Z GFS AND 00Z ECMWF CLUSTER WELL TOWARD THE END OF THE
PERIOD WITH THIS FEATURE...SO WILL FAVOR A GENERAL MODEL
COMPROMISE THROUGH ABOUT 60 HOURS...AND THEN A GFS/ECMWF BLEND
THEREAFTER.


...AMPLIFYING TROUGH OVER THE GREAT LAKES/NORTHEAST/MID-ATLANTIC...
...SURFACE LOW CROSSING THE CENTRAL PLAINS TO THE MID-ATLANTIC...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GEFS MEAN AND 00Z ECENS MEAN
CONFIDENCE: BELOW AVERAGE

A RELATIVELY MODEST MID LEVEL LOW CENTER AND ASSOCIATED TROUGH
ALONG THE BRITISH COLUMBIA/ALBERTA BORDER IS EXPECTED TO PLAY A
SIGNIFICANT ROLE WITH THE EVOLUTION OF AN AMPLIFYING TROUGH OVER
THE GREAT LAKES/NORTHEAST AND MID-ATLANTIC REGION BY THURS AND
FRI...AND WITH THE ADVANCE OF SURFACE LOW PRESSURE FROM THE
CENTRAL PLAINS EAST ACROSS THE OH VALLEY AND INTO THE MID-ATLANTIC
REGION THROUGH THE PERIOD. THIS ENERGY ALOFT WILL ADVANCE RATHER
PROGRESSIVELY EAST-SOUTHEAST WED AND THURS...INITIALLY TRACKING
NEAR THE U.S./CANADIAN BORDER WED AND THEN DIGGING DOWN ACROSS THE
UPPER MS VALLEY ON THURS. THEREAFTER...THE ENERGY IS FORECAST BY
ALL OF THE GLOBAL MODELS TO AMPLIFY VIGOROUSLY DOWN ACROSS THE
GREAT LAKES...UPPER OH VALLEY AND THE MID-ATLANTIC REGION AND
INCLUDING PARTS OF THE NORTHEAST. THE 12Z NAM TENDS TO DIG ENERGY
A TAD FARTHER SOUTH THAN THE GLOBAL MODEL CONSENSUS...BUT AMONG
THE GLOBAL MODELS THE 12Z UKMET IS THE FARTHEST NORTH SOLUTION
WITH ITS HEIGHT FALLS. THE 12Z UKMET THOUGH HAS TRENDED
SLOWER...FARTHER SOUTH AND WEAKER WITH ITS SURFACE LOW. THE 12Z
GFS FOR ITS PART HAS ALSO TRENDED SIGNIFICANTLY SLOWER THAN ITS
PREVIOUS COUPLE OF RUNS WITH THE DOWNSTREAM AMPLIFICATION OF THE
TROUGH...AND AT THE SURFACE IT IS MORE SUPPRESSED WITH THE LOW
TRACK AND ALSO WEAKER WITH IT INVOLVING AN AREA FROM ACROSS THE
MID MS/OH VALLEYS. THE 12Z CMC AND 00Z ECMWF ARE FASTER WITH THE
HEIGHT FALLS...AND ARE STRONGER WITH THEIR RESPECTIVE SURFACE
LOWS. THE ECMWF ALSO IS EXHIBITING SOME EVIDENCE OF CONVECTIVE
FEEDBACK. CONFIDENCE IS LIMITED GIVEN THE TREND OF THE LATEST GFS
AND UKMET....BUT THE PREFERENCE WILL BE TO LEAN TOWARD THE MODEL
CONSENSUS WHICH RIGHT NOW WOULD BE BEST REPRESENTED BY A BLEND OF
THE ENSEMBLES MEANS INCLUDING THE GEFS MEAN AND ECENS MEAN. THE
GEFS MEAN IS MORE SUPPORTIVE OF THE GFS/UKMET CLUSTER...WITH THE
ECENS MEAN FAVORING THE NAM/CMC/ECMWF CAMP. WILL ATTEMPT
COMPROMISE IN BETWEEN.


...UPPER LOW/TROUGH OVER CA THROUGH WED...
...SHEARING DOWNSTREAM OVER THE NORTHERN INTERMOUNTAIN REGION...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE UPPER LOW/TROUGH AXIS OVER CENTRAL/NORTHERN CA THIS MORNING
WILL REMAIN IN PLACE AND GRADUALLY WEAKEN THROUGH WED BEFORE THEN
ADVANCING NORTHEAST AND SHEARING DOWNSTREAM ON THURS ACROSS THE
NORTHERN INTERMOUNTAIN REGION. THIS WILL OCCUR AS THE SUBTROPICAL
RIDGE OVER THE SOUTHERN U.S. SHIFTS FARTHER WEST IN TANDEM WITH
WEAK TROUGHING ARRIVING ACROSS THE PACIFIC NORTHWEST. SOME REMNANT
ENERGY OF THIS FEATURE WILL LIKELY EJECT OVER TOP THE RIDGE AND
ACROSS THE NORTHERN HIGH PLAINS BY FRI. THERE IS GOOD MODEL MASS
FIELD AGREEMENT WITH THIS SYSTEM AND ITS EVOLUTION AND SO A
GENERAL MODEL BLEND WILL BE PREFERRED.


...SHORTWAVE ARRIVING ACROSS THE PACIFIC NORTHWEST ON THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

A STRONG SURGE OF HEIGHT FALLS DROPPING DOWN ACROSS WESTERN AK AND
INTO THE GULF OF AK WILL ALLOW A PACIFIC SHORTWAVE WELL TO ITS
SOUTHEAST TO EJECT EASTWARD AND INTO THE PACIFIC NORTHWEST BY
THURS AND SOUTHWEST CANADA ON FRI. THERE IS GOOD MODEL MASS FIELD
AGREEMENT AT THIS TIME...AND SO A GENERAL MODEL BLEND WILL BE
PREFERRED.


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

ORRISON

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