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000
FXUS10 KWNH 271711
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
111 PM EDT THU APR 27 2017

VALID APR 27/1200 UTC THRU MAY 01/0000 UTC

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

12Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...WEAKENING CYCLONE EXITING FROM OFFSHORE NEW ENGLAND
TODAY/TONIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

ONLY MINOR DIFFERENCES REMAIN WITH THIS SYSTEM AND A GENERAL MODEL
BLEND CAN BE USED GIVEN THE SIMILAR GUIDANCE.


...LARGE UPPER TROUGH/FRONTAL SYSTEM CROSSING THE GREAT
LAKES/UPPER MS VALLEY TODAY/TONIGHT...
...COLD FRONT REACHING THE MID-ATLANTIC/NORTHEAST ON FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

REMAINING DIFFERENCES WITH THIS SYSTEM RELATE TO THE TIMING OF THE
COLD FRONT INTO THE EAST/NORTHEAST U.S. WITH THE 00Z UKMET A
LITTLE SLOWER THAN THE CONSENSUS. HOWEVER...THESE AND OTHER MINOR
DIFFERENCES WITH THE SURFACE LOW TRACK INTO ONTARIO ARE MINOR
ENOUGH TO ALLOW A GENERAL MODEL BLEND FOR THE PREFERENCE.


...UPPER LOW OVER SOUTHERN ALBERTA MOVING SLOWLY EAST ACROSS
SASKATCHEWAN BY SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-00Z CMC CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 00Z CMC STANDS OUT GREATEST FROM THE LATEST DETERMINISTIC
GUIDANCE BY SUN MORNING WHEN SOME OF THE ENERGY WITHIN THE
WEAKENING SHORTWAVE SHEARS ENEWD WHILE THE REMAINING ENERGY
REMAINS ACROSS SASKATCHEWAN. THERE IS GOOD ENSEMBLE SUPPORT FOR A
NON 00Z CMC BLEND.


...LEADING EDGE OF LARGE UPPER TROUGH ACROSS THE CNTRL HIGH PLAINS
ON FRI...
...WEAK SURFACE LOW TRACKING FROM THE CNTRL HIGH PLAINS TO THE
MIDWEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z ECMWF BLEND
CONFIDENCE: AVERAGE

SOMEWHAT EARLY IN THE EVOLUTION OF THE LARGE UPPER LEVEL TROUGH
OVER THE ROCKIES...DESCRIBED IN THE BELOW SECTION...FROM FRI INTO
SAT THERE ARE SOME DIFFERENCES WORTH MENTIONING ACROSS THE PLAINS
INTO THE MIDWEST. FROM 00Z/28-00Z/29...THE 00Z ECMWF STANDS OUT
FROM THE REMAINING MODEL GUIDANCE ACROSS THE CNTRL HIGH PLAINS
WITH A WEAKER LOW-MID LEVEL LOW REFLECTION. THIS AREA APPEARS TO
BE DRIVEN BY CONVECTION...BUT THE 00Z ECMWF STANDS AS A
DETERMINISTIC OUTLIER WITH RESPECT TO A WEAK SURFACE LOW
TRANSLATING FROM THE CNTRL HIGH PLAINS TONIGHT...AND ACROSS THE
MID-MISSISSIPPI VALLEY FRI EVENING. GIVEN THERE IS NOT A STRONG
ENSEMBLE CONSENSUS FOR A NON-00Z ECMWF BLEND AND CONVECTIVE
UNCERTAINLY PLAYS A ROLE...CONFIDENCE IS ONLY AVERAGE IN THE
PREFERENCE.


...AMPLIFYING TROUGH OVER THE INTERMOUNTAIN WEST THURS/FRI...
...CLOSED LOW EVOLUTION INTO THE CENTRAL/SOUTHERN PLAINS BY SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF
CONFIDENCE: AVERAGE

THERE CONTINUES TO BE GOOD LARGE SCALE AGREEMENT WITH THE
EVOLUTION OF A LARGE CLOSED LOW/TROUGH EVOLVING ACROSS THE
CNTRL/SRN ROCKIES AND INTO THE PLAINS THIS WEEKEND. DETAIL
DIFFERENCES WORTH NOTING INCLUDE THE 12Z NAM ON THE FASTER/MORE
PROGRESSIVE SIDE OF THE LATEST DETERMINISTIC AND ENSEMBLE GUIDANCE
THROUGH SUNDAY OVER THE PLAINS. THE 12Z NAM IS NOT PREFERRED FOR
THIS REASON. THE 12Z GFS  AND 00Z UKMET ARE ALSO ON THE FASTER
SIDE OF THE MODELS TO KICK THE UPPER LOW EWD ACROSS THE PLAINS
INTO THE MIDWEST...WHILE THE 00Z CMC/ECMWF REMAIN SLOWER. WHILE
THE CMC/ECMWF HAVE BEEN TRENDING SLOWER OVER THEIR PAST 3
CYCLES...ENDING WITH THE 00Z/27 CYCLE...THE GFS/UKMET HAVE BEEN
GENERALLY CONSISTENT AND FASTER. BOTH SLOWER AND FASTER SOLUTIONS
ARE WELL WITHIN THE LATEST ENSEMBLE CLUSTERING...WHICH HAVE BEEN
TRENDING SLIGHTLY SLOWER OVER THEIR PAST 4 CYCLES VERIFYING
SUNDAY. AT THIS TIME...NO CLEAR DIRECTION STANDS OUT AND GIVEN THE
REASONABLY SIMILAR TRACKS IN THE GFS/ECMWF...A BLEND OF THE TWO IS
PREFERRED FOR NOW.


...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC
NORTHWEST SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 00Z UKMET BLEND
CONFIDENCE: AVERAGE

THE 00Z UKMET STANDS AS A NEAR OUTLIER TO THE SOUTH WITH A 500 MB
TROUGH AMPLIFYING ACROSS THE NORTHWEST COAST OF THE CONUS COMPARED
TO THE LATEST ENSEMBLE AND DETERMINISTIC SOLUTIONS. A NON 00Z
UKMET BLEND IS PREFERRED GIVEN THE RELATIVELY SIMILAR NON 00Z
UKMET SOLUTIONS. ALTHOUGH THERE HAVE BEEN SOME WOBBLES NORTH/SOUTH
WITH THE NON 00Z UKMET MODELS...THEY ALL SHOW RATHER SIMILARLY.


WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/

OTTO

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