Prognostic Meteorological Discussion
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FXUS10 KWNH 231845
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 PM EDT TUE MAY 23 2017

VALID MAY 23/1200 UTC THRU MAY 27/0000 UTC

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

12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...CLOSED UPPER LOW OVER THE UPPER MIDWEST DIGGING ACROSS THE
MIDDLE/LOWER MS VALLEY LATE WED...MOVING TO THE EAST COAST
THU...EXITING NEW ENGLAND FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON 12Z NAM BLEND OF THE MODELS
CONFIDENCE: AVERAGE

MODELS AGREE WELL THROUGH WED AS THE UPPER LOW DIGS TO A POSITION
OVER THE MIDDLE/LOWER MS VALLEY. MODELS  DIVERGE SLIGHTLY THU AND
FRI...AS SHORTWAVE ENERGY MOVING THROUGH THE BASE OF THE TROUGH
AFFECTS ITS DEVELOPMENT AND PROGRESSION. EVEN THEN...MODEL
AGREEMENT IS GOOD OVERALL SHOWING THAT THE UPPER TROUGH WILL TAKE
ON A NEGATIVE TILT ON THU...WITH THE UPPER LOW NEAR THE OHIO
VALLEY AND SHORTWAVE ENERGY/VORTICITY SWINGING THROUGH THE BASE OF
THE TROUGH OVER THE MIDDLE ATLANTIC. THE 12Z SOLUTIONS OF THE
ECMWF...CMC...AND UKMET ALL TRENDED SIMILAR TO THE 12Z GFS
RUN...WITH MORE SHORTWAVE ENERGY/VORTICITY MOVING THROUGH THE BASE
OF THE TROUGH WED NIGHT RESULTING IN A MORE PROGRESSIVE SOUTHERN
END OF THE TROUGH AND A MORE NEGATIVE TILT TO THE FEATURE OVERALL.
THE 12Z NAM NOW STANDS OUT AS THE LEAST PROGRESSIVE OF THE
SOLUTIONS...AND THE ONLY MODEL THAT HAS NOT EXHIBITED THIS RECENT
TREND. THEREFORE A GENERAL MODEL BLEND THAT EXCLUDES THE NAM IS
PROBABLY BEST.


...SUBTLE SHORTWAVE FEATURES AND SOUTHERN BRANCH JET MOVING ACROSS
THE SOUTHEAST TODAY...
...SURFACE LOWS TRAVERSING THE GULF COAST INTO THE SOUTHEAST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

WHILE SOME MINOR DIFFERENCES STILL EXIST...MODELS HAVE CONVERGED
ON SIMILAR SOLUTIONS WITH THIS ACTIVITY MOVING ACROSS THE
SOUTHEAST AND MID ATLANTIC. THUS A GENERAL MODEL BLEND SHOULD WORK
FINE.


...UPPER TROUGH MOVING ACROSS THE NORTHWEST THROUGH MID WEEK...
...DEVELOPING LONGWAVE TROUGH OVER THE WEST...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE

AN UPPER LOW OVER HAIDA GWAII WILL DIG SOUTHEAST ACROSS BRITISH
COLUMBIA TONIGHT...THEN MOVE SLOWLY EASTWARD ACROSS ALBERTA AND
SASKATCHEWAN WED AND THU. THE UPPER LOW WILL LEAVE A TRAILING
TROUGH MOVING SLOWLY EASTWARD OVER THE NORTHWEST WED...WITH
ADDITIONAL SHORTWAVE ENERGY CARVING OUT A SOMEWHAT DEEPER TROUGH
OR CLOSED LOW OVER THE REGION THU AND FRI. MODELS ARE INITIALLY IN
VERY GOOD AGREEMENT WITH THIS SYSTEM...BUT MODEL SOLUTIONS DIVERGE
LATE THU THROUGH FRI AS SHORTWAVE ENERGY DROPPING INTO THE TROUGH
PLAYS A MORE IMPORTANT ROLE. MAINLY...THE MODELS DIFFER WITH
REGARD TO WHETHER AND HOW QUICKLY AN UPPER LOW WILL CLOSE OFF OVER
ID. THE 12Z NAM AND 12Z UKMET ARE SIMILAR AND THE MOST AGGRESSIVE
WITH THE SHORTWAVE ENERGY...FORMING A CLOSED LOW ALONG THE OR/ID
BORDER LATE THU. THE 12Z ECMWF HAS TRENDED IN THAT DIRECTION AS
WELL BUT NOT AS AGGRESSIVELY...CLOSING OFF A LOW OVER ID EARLY
FRI. THE 12Z CMC IS SOMETHING OF A COMPROMISE BETWEEN THOSE MODELS
AND THE 12Z GFS...WHICH IS THE LEAST AGGRESSIVE WITH SHORTWAVE
ENERGY AND THE IDEA OF CLOSING OFF A LOW. GIVEN THE TREND IN THE
12Z MODEL RUNS...ESPECIALLY THE ECMWF...I DON`T THINK WE CAN
DISCOUNT ANY PARTICULAR MODEL SOLUTION. THEREFORE A GENERAL MODEL
BLEND IS RECOMMENDED BUT WITH ONLY AVERAGE CONFIDENCE.


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

MCDONNAL

$$





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