Prognostic Meteorological Discussion
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743
FXUS10 KWNH 260423
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1123 PM EST SAT FEB 25 2017

VALID FEB 26/0000 UTC THRU MAR 01/1200 UTC

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

00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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

THE MODELS SHOW STRONG SIMILARLY WITH THIS SYSTEM TO SUPPORT A
GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE.


FAST MOVING MID-LEVEL SHORTWAVE TRACKING FROM THE NRN PLAINS THIS
MORNING THROUGH THE NW GREAT LAKES TONIGHT INTO ONTARIO BY MON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THERE APPEARS TO BE A SLIGHT DIFFERENCE AT THE SURFACE WITH
RESPECT TO FRONT ORIENTATION IN THE 12Z UKMET AS THE SYSTEM
CROSSES OUT OF THE NW GREAT LAKES BUT THIS APPEARS MINOR AS THE
MAJORITY OF THE DEPTH OF THE 12Z UKMET IS AGREEABLE TO AN
OTHERWISE QUITE STRONG SIMILARITY IN SOLUTIONS.  AS SUCH A GENERAL
MODEL BLEND IS SUPPORTED AT ABOVE AVERAGE CONFIDENCE.


SHORTWAVE OFF CENT CALIFORNIA COAST THIS MORNING SWINGING THROUGH
THE SOUTHWEST LATE TONIGHT REACHING THE SRN PLAINS LATE SUN/EARLY
MON BEFORE HEADING INTO CONFLUENT FLOW ACROSS THE CENTRAL U.S.
LATE MON INTO TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE

THE MODELS ARE IN FAIR TO STRONG AGREEMENT AS THE SHORTWAVE ROUNDS
THE BASE OF THE WESTERN TROF TONIGHT AND BEGINS TO ACCELERATE AND
SHEAR INTO INCREASINGLY CONFLUENT FLOW ACROSS THE GREAT PLAINS
INTO THE TN RIVER VALLEY BY MONDAY.   THE SUBTLE DIFFERENCES IN
HOW THE WAVE SHEARS OUT WITH SOME MESOSCALE UPSCALE GROWTH OF
CONVECTION IN THE SOUTHERN STATES IS THE REMAINING DIFFERENCES IN
THE MASS FIELDS WHICH MAY BE A BIT TOO SMALL TO ACCURATELY CHOOSE
THE PRECISE SOLUTION IN FAVOR OF A LARGER BLEND OR HIGHER
PROBABILITY IN THE ENSEMBLE SOLUTIONS.  THE TYPICAL BIASES ARE
ALSO ON DISPLAY TOO AS THE 00Z NAM IS A BIT FURTHER NORTH WITH THE
FORCING AND THE 00Z GFS IS FAST WHILE THE 12Z ECMWF/CMC ARE A BIT
SLOWER FAVORING CONVERGENCE/FORCING ALONG THE SOUTHWESTERN OR TAIL
END OF THE MID-LEVEL TROF.   AS SUCH A GENERAL MODEL BLEND IS
PREFERRED WITH THE MASS FIELDS THOUGH CONFIDENCE REMAINS AVERAGE
GIVEN THE IMPORTANT SMALLER SCALE DIFFERENCES THAT REMAIN.


NEXT SHORTWAVE DROPPING OUT OF COASTAL BC TO THE NWRN U.S. COAST
SUNDAY INTO MON WITH ADDITIONAL ENERGY FROM THE NW PHASING WITH
OFFSHORE UPPER LOW THAT WILL SWING THROUGH SOUTHERN CA BY TUES
BECOMING NEUTRALLY ORIENTED FROM THE NORTHERN PLAINS TO SOUTHERN
ROCKIES BY WED MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/UKMET AND 18Z GEFS BLEND
CONFIDENCE: AVERAGE

WV MOSAIC DEPICTS A BROAD BUT WELL ORGANIZED SHORTWAVE ROLLING
DOWN THE BC COAST AT THIS TIME AND A TIGHT CUT-OFF UPPER LOW THAT
SHOWS SOME W-E ELONGATION AROUND 35N AND 142W.   MODELS CONTINUE
TO HANDLE BOTH SYSTEMS QUITE SIMILAR THROUGH ABOUT 12Z MONDAY AS
THE SYSTEM REMAIN SEPARATE ENTITIES WITH THE NORTHERN SHORTWAVE
SHIFTING INTO THE NORTHERN GREAT BASIN AND SNAKE RIVER PLAIN AND
THE UPPER CONTINUING TO ELONGATE AND SHEAR TOWARD A SW TO NE
ORIENTATION OFF THE S CA COAST.   BOTH WILL CONTINUE TO PHASE AND
ELONGATE AND GROW UPSCALE TOWARD A DEEPER GLOBAL TROF THAT WILL
PROGRESS EASTWARD.  THROUGH THIS TIME PERIOD A KICKER WAVE WILL
REINFORCE THE NORTHERN PORTION OF THE TROF AND EXPAND HEIGHT FALLS
INTO THE NORTHERN PLAINS AS SPUR A SFC CYCLONE TO EMERGE FROM THE
CENTRAL ROCKIES AND LIFT INTO THE MIDWEST BY TUESDAY AND GREAT
LAKES BY WED.   OVERALL THE MODEL SPREAD IS SMALL AND THE MASS
FIELDS ARE FAIRLY TIGHTLY ALIGNED...IT IS THE 12Z ECMWF/UKMET THAT
ARE A BIT MORE AGGRESSIVE AND STRONGER WITH THE SURFACE WAVE INTO
THE GREAT LAKES TOWARD WED.  THE 12Z CMC IS UNCHARACTERISTICALLY
FAST WITH THE SURFACE WAVE INTO THE GREAT LAKES BUT SHOW SIMILAR
TIMING/PLACEMENT OF THE FRONTAL ZONE THROUGH MIDWEST TO THE
CENTRAL PLAINS AS THE UKMET/ECMWF. THE 00Z NAM IS GENERALLY WEAKER
WITH THE FIRST WAVE AND SUPPORT A SLOWER EASTWARD PROGRESSION OF
THE FRONTAL ZONE WITH A  SECONDARY SFC LOW INTO THE MIDWEST BY
MIDDAY WED.  THE 00Z GFS INDICATED A FAIRLY SIZABLE SHIFT FASTER
BY DAY 3 WITH THE OVERALL TROF COMPARED TO THE PRIOR RUNS...WHICH
INITIALLY IS QUITE COMPARABLE TO THE 12Z ECMWF/UKMET LIFTING THE
FIRST SURFACE WAVE OUT TOWARD THE GREAT LAKES BUT BEGINS TO STALL
OVER LP OF MI BY 12Z WED.  THIS IS RELATED TO A STRONGER FORECAST
SOUTHERLY JET LEADING TO A PROGRESSIVE SHIFT OF THE BASE OF THE
TROF BECOMING NEUTRALLY ORIENTED THROUGH THE LENGTH OF THE TROF BY
WED AND FASTER TRANSLATION OF THE COLD FRONT THROUGH THE CENTRAL
PLAINS AND OZARKS BY 12Z WED.  WHILE BRINGING THE GFS INTO BETTER
AGREEMENT INITIALLY WITH THE UKMET/ECMWF AND ENSEMBLE SUITE
(INCLUDING THE 18Z GEFS MEAN); THE AGGRESSIVE/FAST NATURE BY THE
END OF DAY 3 MAY BE A BIT TOO MUCH TO INCORPORATE TO THE
PREFERENCE AT THIS TIME WITHOUT GARNERING ADDITIONAL SUPPORT FROM
OTHER GUIDANCE.  ALL CONSIDERED A BLEND OF THE 12Z ECMWF/UKMET AND
18Z SEEMS AN APPROPRIATE COMPROMISE IN SOLUTIONS AT AVERAGE
CONFIDENCE OVERALL.


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

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

GALLINA


$$





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