116
FXUS10 KWNH 211646
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1245 PM EDT SAT MAR 21 2020
VALID MAR 21/1200 UTC THRU MAR 25/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z INITIAL MODEL EVALUATION WITH LATEST PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PHASING STREAMS OVER THE MISSISSIPPI VALLEY MON, SUPPORTING EAST
COAST/NORTHEAST STORM TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/UKMET BLEND WITH 12Z GFS ONLY THRU 23.12Z.
CONFIDENCE: SLIGHTLY BELOW AVERAGE
ACTIVE SOUTHERN STREAM IS EJECTING A SHORTWAVE ACROSS THE FOUR
CORNERS REGION INTO THE PLAINS TODAY AND THIS WAVE WILL CONTINUE
TO DRAW DEEP MOISTURE BOTH OFF THE GULF, BUT THE SUBTROPICAL
PACIFIC TO SUPPORT AN INVERTED SURFACE TROF/WAVE THROUGH THE
MISSISSIPPI VALLEY MONDAY. THE NORTHERN STREAM WILL ALSO BE
DIGGING ACROSS CENTRAL CANADA INTO THE NORTHERN HIGH PLAINS TO
HELP BROADEN A DEEPER LATITUDE/PHASED TROF ACROSS THE GREAT LAKES
BY LATE MONDAY. TIMING AND INTERACTION BETWEEN STREAMS WITH THE
INCLUSION OF LATENT HEAT RELEASE IN CERTAIN PORTIONS OF THE WAVE
WILL CONTINUE TO BE LEAD TO LARGE UNCERTAINTY TO PRECISE IMPACTFUL
SENSIBLE WEATHER. THIS INCLUDES THE DEVELOPMENT OF THE COASTAL
SURFACE CYCLONE, BOTH IN LOCATION AND DEPTH BY TUESDAY. THE 12Z
GFS CONTINUES TO BE SLIGHTLY FASTER IN THE NORTHERN STREAM AND SO
DOES NOT DIG AS SHARPLY, YET ALSO SHOWS A BIAS NOTED THIS WINTER
OF BEING A BIT TOO WARM WITH THE WARM CONVEYOR BELT/ISENTROPIC
ASCENT CHANNEL WHICH HAS THE POTENTIAL TO LEAD TO GREATER
UNCERTAINTY WITH PRECIPITATION TYPE ACROSS THE NORTHEAST. THE 12Z
NAM CONTINUES TO SHOW A BIAS OF BEING A BIT TOO STRONG THROUGH THE
DEPTH, LIKELY DUE TO INCREASED LATENT HEAT RELEASE IN THE
MID-LEVEL COLUMN THROUGH THE MIDWEST/OHIO VALLEY, WHICH SUPPORTS A
STRONGER CYCLONE AS WELL AS STRONGER TRAILING ANTI-CYCLONE. THIS
IS A CLEAR OUTLIER IN MASS FIELDS; YET HAS SEEN THE ECMWF/UKMET
TRENDING TOWARDS IT IN THE DEVELOPMENT OF THE SURFACE CYCLONE.
THE 00Z CMC IS SLOW, EVEN MORE SO THAN NORMAL IN THE SOUTHERN
STREAM. SO WITH REDUCED NORTHERN STREAM PHASING; THE NORTHERN
STREAM EXITS FASTER ALLOWING FOR FAVORABLE UPPER LEVEL DIVERGENCE
TO DEEPEN THE CYCLONE OVER SOUTHERN NEW ENGLAND ON TUESDAY. THE
UKMET/ECWMF AND ECENS HAVE SEEN THE TREND NORTHWARD AND STRONGER
WITH THE CYCLONE AS A WHOLE WHICH CONTINUES TO BE MOST CENTRAL IN
THE EVOLUTION. GIVEN THE UNCERTAINTY INHERENT IN PHASING STREAMS;
WILL GO WITH THE MORE CENTRAL EVOLUTION OF THE UKMET/ECWMF AS
PREFERENCE; THOUGH INCLUSION OF THE GFS IS LIKELY SUPPORTIVE UNTIL
AROUND 54HRS (23.12Z) WHEN THE NORTHERN STREAM/SOUTHERN STREAM ARE
MOST DECOUPLED AND THE COASTAL CYCLONE DEVELOPS WELL SOUTH OF THE
CLUSTER (THOUGH SUPPORTED BY THE 06Z GEFS). CONFIDENCE IS
SLIGHTLY BELOW AVERAGE GIVEN THE LOWER PREDICTABILITY OF THE
COMBINING STREAMS.
CLOSED LOW OFF SW CA TODAY, TRACKS ACROSS SOUTHWEST INTO MID-MS
VALLEY, MON AND TUES. RESPECTFULLY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS AND 00Z UKMET/12Z ECMWF BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THE LARGE CLOSED LOW CURRENTLY NEAR 35N135W WILL START TO ADVANCE
EASTWARD IN THE NEXT THIS EVENING REACHING CENTRAL/SOUTHERN CA BY
EARLY MONDAY. HOWEVER, EVEN BY THIS POINT THIS IS A SOLID
DIFFERENCE IN THE MASS FIELDS, WITH THE 00Z CMC ALREADY
SIGNIFICANTLY SLOWER, WHICH CONTINUES THROUGH THE REST OF THE
SHORT-TERM FORECAST PERIOD. THE 12Z NAM IS ALSO A BIT STRONGER
BUT ALSO FASTER. THE CONCERN THOUGH WITH THE NAM IS THE POOR
DOWNSTREAM SETUP, AS THE OVER-STRONG PRECURSORY RIDGE LEADS TO
STRONGER RETURN FLOW, FURTHER NORTH AND WHILE THE SURFACE LOW
LEVEL MASS FIELDS JIVE WELL, THE EFFECTIVE BOUNDARIES/QPF ARE NOT,
AND SO LIKE THE CMC IS NOT SUPPORTED. THE 12Z GFS SAW A SIZABLE
SLOWING ESPECIALLY AS THE WAVE ENTERS THE PLAINS LATE MONDAY INTO
TUESDAY, WHICH MAKES IT A TAD SLOWER THAN THE REMAINING GUIDANCE
BUT IS STILL NOT AS SLOW/DEEP AS THE GEFS MEAN/BULK OF SOLUTIONS
WHICH ALSO LAG THE UKMET/ECMWF. STILL THIS FAIRLY SMALL FOR DAY
3...AND A 12Z GFS AND 00Z ECMWF/UKMET IS PREFERRED AT THIS TIME AT
SLIGHTLY ABOVE AVERAGE CONFIDENCE.
PACIFIC NW CLOSED LOW, MON/TUES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM THROUGH 24.00Z
12Z GFS AND 00Z UKMET/ECMWF BLEND THEREAFTER
CONFIDENCE: SLIGHTLY ABOVE TO ABOVE AVERAGE
THE NORTHERN STREAM STRONG SHORTWAVE BOWLING THROUGH BRISTOL
BAY/AK PENINSULA WILL CONTINUE TO HUG THE AK PANHANDLE AND BC
COAST CLOSING OFF INTO A SMALL BUT COMPACT CLOSED LOW REACHING THE
PACIFIC NW BY MONDAY. ONLY THE 12Z NAM CONTINUES TO SHOW A
BROADER INNER CORE/RING OF ENERGY, WHICH EVENTUALLY SLIDES
EASTWARD RELATIVE TO THE OTHER GUIDANCE AS THE WAVE ELONGATES FROM
THE UPSTREAM JET PULLING THE LARGER TROF PATTERN SOUTHWEST INTO
THE PACIFIC BY 00Z TUESDAY; WHILE THE INNER CORE STRETCHES EAST OF
THE COAST RANGE IN BC AND ACCELERATING FASTER/STRONGER INTO THE
SOUTHERN CANADIAN PRAIRIES JUST NORTH OF THE US BORDER BY THE 00Z
WED. THE CMC IS ONCE AGAIN ALSO SLOW, POSSIBLE DUE TO THE
DOWNSTREAM BLOCKING/SLOWER EXITING WAVE. SO A NON-NAM BLEND
PREFERENCE THROUGH 24/00Z BECOMES A 12Z GFS AND 00Z UKMET/ECMWF
BLEND THEREAFTER AT SLIGHTLY ABOVE TO ABOVE AVERAGE CONFIDENCE.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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