848
FXUS10 KWNH 141908
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
308 PM EDT TUE APR 14 2020
VALID APR 14/1200 UTC THRU APR 18/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z FINAL MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..SHORTWAVE SHEARING INTO THE MIDWEST/OHIO VALLEY DAY 3
---------------------
MODEL BLEND PREFERENCE: 00Z ECMWF/ECMEAN/UKMET
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE PREVIOUS PREFERENCES REMAIN UNCHANGED AS THE
ECMWF/UKMET REMAINED VERY CLOSE TO THEIR PREVIOUS RUNS.
PREVIOUS DISCUSSION:
A SHORTWAVE DROPPING THROUGH THE INTER-MOUNTAIN WEST WILL SHEAR
OFF TO THE EAST FRIDAY AS IT BECOMES ABSORBED BY THE WESTERLIES IN
THE BASE OF A LONGWAVE EASTERN TROUGH. AT THE SAME TIME, AN UPPER
JET STREAK WILL STRENGTHEN SOUTH OF THE MID-LEVEL TROUGH, WITH THE
COMBINATION OF THESE FORCINGS CAUSES WEAK SURFACE LOW DEVELOPMENT
MOVING THROUGH THE OHIO VALLEY FRIDAY. THE CMC IS WEAK WITH THE
DEPTH OF THIS FEATURE, AFFECTED BY POOR OVERALL SYNOPTICS UPSTREAM
ACROSS THE INTERMOUNTAIN WEST. THE GFS BECOMES TOO PROGRESSIVE AS
THE SHORTWAVE MOVES EAST, BECOMING A FAST OUTLIER WHEN COMPARED TO
THE REMAINING GUIDANCE ENVELOPE. THE NAM ALSO BECOMES QUICK DURING
D3, BUT ALSO DEVELOPS AN UPPER JET STREAK WHICH IS TOO INTENSE,
PLACING MORE INTENSE ASCENT A BIT FURTHER SOUTH, WHICH DISPLACES
THE SURFACE LOW AND PRODUCES PRECIPITATION WHICH IS MORE ROBUST
THAN THE REMAINING GUIDANCE. THIS LEAVES THE CONSISTENT
ECMWF/ECMEAN/UKMET AS THE PREFERRED BLEND FOR THIS SYSTEM.
WESTERN/CENTRAL CONUS
--------------------
MODEL BLEND PREFERENCE: GENERAL BLEND D1-2, ECMWF/ECMEAN/UKMET D3
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
19Z UPDATE: THE CMC HAS BECOME MUCH MORE CLOSELY ALIGNED WITH THE
OTHER GUIDANCE IN ITS EVOLUTION OF BOTH THE PACIFIC SHORTWAVE AND
MOUNTAIN WEST SHORTWAVE. THERE IS VERY LITTLE SPREAD IN THE
POSITION OR INTENSITY OF THE PACIFIC FEATURE THROUGH THE FIRST 2
DAYS, BEFORE SPREAD BEGINS TO INCREASE IN THE INTENSITY AND
EASTWARD PROGRESSION AS THE LOW OPENS. FOR THE VORTICITY LOBE
SHEARING INTO THE MOUNTAIN WEST AND THEN EASTWARD, THE GUIDANCE IS
VERY WELL CLUSTERED, AGAIN, THROUGH THE FIRST 60 HOURS BEFORE
LONGITUDINAL DIFFERENCES BEGIN TO ARISE.
PREVIOUS DISCUSSION:
SIGNIFICANT PACIFIC RIDGE WILL DOMINATE OVER THE NEXT SEVERAL
DAYS, WHILE MID-LEVEL IMPULSES ROTATE AROUND IT AND DOWN INTO THE
WESTERN CONUS. TWO DISTINCT FEATURES WILL EMBED WITHIN THE FLOW
RACING FROM THE NW. THE FIRST OF THESE IS A CLOSED LOW WELL OFF
THE CA COAST, AND IT WILL DROP SOUTHWARD BEFORE PUSHING ONSHORE
INTO BAJA/SOCAL D3. OUTSIDE OF THE 00Z/CMC, THE GUIDANCE IS IN
GOOD AGREEMENT WITH THIS FEATURE THROUGH THE FIRST 2 DAYS, BUT
LITTLE TO NO PRECIPITATION WILL OCCUR ON THE COAST WITH THIS. BY
D3, PRECIPITATION SPREADS ONSHORE AND THE UKMET BECOMES A BIT
STRONG COMPARED TO THE CONSENSUS, AND THE GFS STARTS TO PUSH TOO
FAST, BUT STILL A GENERAL NON-CMC BLEND IS REASONABLE.
FOR THE SECOND SHORTWAVE DROPPING FROM THE CANADIAN ROCKIES AND
INTO THE INTERMOUNTAIN WESTERN CONUS, SIGNIFICANT SNOW IS LIKELY
WITH THIS FEATURE AND THROUGH THE FIRST 2 DAYS A GENERAL MODEL
BLEND IS ACCEPTABLE, EXCLUDING THE VASTLY DIFFERENT CMC. HOWEVER,
BY D3 /FRIDAY/ THE GFS BEGINS TO SHEAR THE SHORTWAVE TOO STRONGLY
TO THE EAST, STRINGING OUT THE VORTICITY LOBE FASTER THAN THE
REMAINING GUIDANCE. THE NAM LAGS A PIECE OF ENERGY WELL W/SW OF
THE PRIMARY SHORTWAVE CAUSING SOME INTERACTION AND RETROGRESSION
OF THE STRONGEST FORCING, WHICH IS OUT OF TOLERANCE WITH THE
REMAINING SUITE. FOR THESE REASONS A ECMWF/ECMEAN/UKMET IS
PREFERRED FOR MOST OF THE WEST D3 AS THEY ARE CONSISTENT AND MATCH
WELL TO EACH OTHER.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
WEISS
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