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270
FXUS10 KWNH 271900
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 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 MODEL EVALUATION WITH FINAL 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 12Z UKMET
SLIGHTLY SLOWER THAN THE CONSENSUS. HOWEVER...THESE AND OTHER
MINOR DIFFERENCES WITH THE SURFACE LOW TRACK INTO ONTARIO ARE
SMALL ENOUGH TO ALLOW A GENERAL MODEL BLEND FOR THE PREFERENCE.


...UPPER LOW OVER SOUTHERN ALBERTA MOVING SLOWLY EAST ACROSS
SASKATCHEWAN BY SAT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

ADJUSTMENTS IN THE 12Z CMC COMPARED TO ITS 00Z CYCLE WERE IN THE
DIRECTION OF THE REMAINING DETERMINISTIC GUIDANCE BY SUN MORNING
ACROSS SASKATCHEWAN. THERE IS GOOD ENSEMBLE SUPPORT FOR A GENERAL
MODEL 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: GENERAL MODEL 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 STOOD OUT
FROM THE REMAINING MODEL GUIDANCE ACROSS THE CNTRL HIGH PLAINS
WITH A WEAKER LOW-MID LEVEL LOW REFLECTION. THE 12Z ECMWF ADJUSTED
TOWARD THE REMAINING MODEL GUIDANCE BUT REMAINS SOMEWHAT WEAKER
THAN THE DETERMINISTIC CONSENSUS. WHILE SOME OF THE MODELS APPEAR
TO BE SUFFERING FROM CONVECTIVE FEEDBACK GIVEN AREA APPEARS TO BE
DRIVEN BY CONVECTION...THE 12Z CONSENSUS SHOWS REASONABLE
AGREEMENT NOW 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 STRONGER 12Z CMC OR 12Z GFS-LIKE SOLUTION...AND GIVEN THE
FACT THAT 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 12Z 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 12Z 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. THE 12Z ECMWF/CMC REMAINED
REASONABLY SIMILAR TO THEIR PREVIOUS CYCLES. 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 12Z UKMET BLEND
CONFIDENCE: AVERAGE

THE120Z 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 12Z
UKMET BLEND IS PREFERRED GIVEN THE RELATIVELY SIMILAR NON 12Z
UKMET SOLUTIONS. ALTHOUGH THERE HAVE BEEN SOME WOBBLES NORTH/SOUTH
WITH THE NON-UKMET MODELS...MOST NOTABLY IN THE 12Z ECMWF...THE
UKMET IS ON THE DEEPER EDGE OF THE ENSEMBLES AND THE ECMWF REMAINS
WITHIN REASON ALTHOUGH ALSO TOWARD THE DEEPER SIDE OF THE
ENSEMBLES.


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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