555
FXUS10 KWNH 221646
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1145 AM EST SAT FEB 22 2020
VALID FEB 22/1200 UTC THRU FEB 26/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...WEAK MID LEVEL SHORTWAVE AND ATTENDANT FRONT CLIPPING THE GREAT
LAKES/NORTHERN ME SUN/MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND (WEIGHT TOWARD 12Z GFS/00Z ECMWF)
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
SHORTWAVE CURRENTLY TRACKING THROUGH THE CANADIAN ROCKIES,
AMPLIFIES ACROSS THE CANADIAN PRAIRIES INTO THE WESTERN GREAT
LAKES BY LATE SUNDAY WITH A COLD FRONT CONCURRENTLY DRAPING
THROUGH THE NORTHERN TIER INTO THE GREAT LAKES. THE 12Z NAM HAS
SIGNIFICANTLY INCREASED DEPTH OF THE EVOLVING CLOSED LOW BY MIDDAY
MONDAY RELATIVE TO THE OTHER GUIDANCE; BECOMING OUT OF TOLERANCE
FOR A BLEND. THE 00Z UKMET LEANS A BIT FASTER ALLOWING FOR A
GREATER NEGATIVE TILT ORIENTATION OF THE TROF CLIPPING THE
NORTHEAST AS WELL, BUT IS MORE IN LINE OVERALL WITH THE REMAINDER
OF THE GUIDANCE. THE 12Z GFS CONTINUED SIMILAR EVOLUTION TO PRIOR
GUIDANCE AND SO THE OVERALL PREFERENCE WILL SUPPORT A NON-NAM
BLEND BUT WEIGHTED MORE TOWARD THE ENSEMBLE MEANS, WHICH ARE WELL
REPRESENTED BY THE 12Z GFS/00Z ECMWF. CONFIDENCE IS SLIGHTLY ABOVE
AVERAGE.
...CLOSED MID LEVEL LOW REACHING THE ROCKIES SUN, WEAKENING OVER
THE UPPER MS/OH VALLEY MON INTO TUES...
...SURFACE LOW TRACKING FROM NORTHEAST NM INTO OHIO VALLEY BY
TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND THROUGH 25.00Z; THEREAFTER SEE SECTION
BELOW
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
CLOSED LOW IN THE CALIFORNIA BIGHT WILL SLIDE THROUGH THE FOUR
CORNERS REGION AND SUPPORT SURFACE CYCLOGENESIS ALONG THE NE NM
FRONT RANGE INTO SUNDAY. THIS LOW WILL ADVANCE ACROSS THE
SOUTHERN PLAINS INTO THE LOWER OHIO VALLEY BY LATE MONDAY INTO
EARLY TUESDAY WITH SOLID MODEL AGREEMENT IN TIMING AND DEPTH, EVEN
AS THE UPPER LOW BEGINS WEAKENING RAPIDLY. A TAPPING OF THE DEEP
MOISTURE OFF THE GULF ALONG THE WESTERN PERIPHERY OF THE STUBBORN
7H RIDGE ACROSS THE SOUTHEAST WILL ALLOW FOR STRONG CONVECTION
ALONG/AHEAD OF THE FRONTAL ZONE. THERE IS MORE TRADITIONAL TIMING
DIFFERENCES WITH THIS FEATURE, E.G. ECMWF SLOWER/GFS FASTER, ETC,
BUT IS NOT TOO BAD THROUGH 25.00Z (TUES); WITH EXCEPTION TO THE
00Z CMC WHICH IS TOO SLOW OVERALL. IT IS MOST STARK SO AFTER
24.12Z DEPICTING A VERY SLOW, EVEN STALLING OF THE SYSTEM IN
DEFERENCE TO THE UPSTREAM WAVE ON TUESDAY, MAKING IT LESS
FAVORABLE.
MODEL SPREAD THROUGH THE MS VALLEY INTO THE OHIO VALLEY (NOT
NECESSARILY THE GULF COAST INTO THE SOUTHEAST) BECOMES QUITE BROAD
AND UNCERTAIN, DRIVEN MAINLY BY THE DIGGING APPROACHING SHORTWAVE
OUT OF THE NORTHERN STREAM. SO THE PREFERENCE AFTER 25.00Z WILL
BE VERY SIMILAR TO THE SECTION BELOW, BUT WILL BE FAVORING THE
MORE CONSISTENT, SLIGHTLY SLOWER EVOLUTION OF THE ECMWF/ECENS MEAN
AND THE 06Z GEFS OVER THE FASTER SOLUTIONS.
...MID-LEVEL SHORTWAVE CROSSING THE PACIFIC NORTHWEST SUNDAY,
DIGGING INTO NORTHERN/CENTRAL PLAINS MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-UKMET; THEN 00Z ECMWF/ECENS & 06 GEFS AFTER 24.12Z
CONFIDENCE: BECOMING SLIGHTLY BELOW AVERAGE AFTER 24/12Z.
COMPACT CLOSED LOW AND ASSOCIATED SURFACE LOW REACHES VANCOUVER
ISLAND SUNDAY. HERE THE 00Z UKMET IS DISPLACED FROM AN OTHERWISE
VERY TIGHT CLUSTERING; ITS SLOWNESS LEADS TO FURTHER DOWNSTREAM
ISSUES OUT OF THE ROCKIES INTO THE PLAINS, SO INITIALLY A
NON-UKMET BLEND IS PREFERRED FROM THE START. THE 00Z CMC BEING
VERY SLOW AND RAPIDLY WEAKENING WITH THE PRECURSORY WAVE, RESULTS
IN THIS NORTHERN STREAM WAVE TO BE SLOW EXITING THE ROCKIES AND IS
NOT PREFERRED AFTER CYCLONE LANDFALL ON MONDAY.
THE 12Z NAM/GFS BOTH ARE VERY STRONG/FAST WITH THE NOSE OF THE JET
PROVIDING INCREASED DIFFLUENCE ALOFT AND ASCENT OUT OF THE ROCKIES
INTO THE CENTRAL PLAINS AND OHIO VALLEY BY TUESDAY, THIS ALLOWS
FOR FASTER AMPLIFICATION/DEEPENING OF THE CLOSED LOW THROUGH THE
CENTRAL PLAINS, WHICH HELPS TO DEVELOP A SURFACE REFLECTION BACK
AND TO THE NORTHWEST ACROSS THE MIDWEST BY DAY 3. THE NAM'S
AGGRESSIVE NATURE/OVER-DEEPENING BIAS ON DAY 3, SUGGESTS THIS
EVOLUTION IS LESS LIKELY, ESPECIALLY COMBINED WITH THE GFS KNOWN
NEGATIVE BIAS OF BEING TOO FAST. THE 06Z GEFS SUGGESTS A MORE
GRADUAL SHIFT NORTHWARD TOWARD THE NORTHERN STREAM SYSTEM, A TAD
FASTER THAN THE ECMWF/ECENS. GIVEN THE ECWMF/ECENS BIAS TOWARD
BEING A TAD SLOW, BUT ALSO BEING MOST CONSISTENT RUN TO RUN OVER
THE LAST FEW DAYS PROVIDES SOME CONFIDENCE IF BLENDED WITH THE
GEFS (OVER THE 12Z GFS). STILL, THERE IS ALWAYS SIZABLE
UNCERTAINTY WITH BINARY INTERACTION BETWEEN THE STREAM AND SMALL
SHIFTS CAN LEAD TO IMPACTFUL DIFFERENCES IN QPF SWATHS...AS SUCH
CONFIDENCE IN THE ECMWF/ECENS/GEFS BLEND IS SLIGHTLY BELOW
AVERAGE.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
GALLINA
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