Prognostic Meteorological Discussion
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FXUS10 KWNH 010501
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 AM EST SUN FEB 01 2015

VALID FEB 01/0000 UTC THRU FEB 04/1200 UTC

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

...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...UPPER LOW/DEVELOPED SURFACE CYCLONE DEPARTING FROM NEW
ENGLAND...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: HIGH

WATER VAPOR IMAGERY DEPICTED A NEGATIVELY-TILTED TROF CROSSING
EAST OF NOVA SCOTIA. EVENTUALLY THIS SYSTEM BECOMES ABSORBED BY A
BAND OF HEIGHT FALLS CURRENTLY MOVING THROUGH SOUTHWESTERN QUEBEC.
MODELS SHOW SUFFICIENT AGREEMENT WHICH SUPPORTS A GENERAL MODEL
COMPROMISE HERE.


...AMPLIFIED TROF MOVING FROM THE CENTRAL PLAINS TO THE
NORTHEASTERN U.S. ON SUNDAY/MONDAY...
...STRENGTHENING FRONTAL WAVE...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF
FORECAST CONFIDENCE: AVERAGE

A SERIES OF SHORTWAVES MOVING THROUGH THE CENTRAL PLAINS/MIDDLE MS
VALLEY WILL QUICKLY GAIN AMPLITUDE AS AN UPSTREAM IMPULSE DROPS
DOWN FROM THE NORTHERN ROCKIES. THIS AMPLIFIED TROF IS FORECAST TO
RACE EASTWARD REACHING THE OH/TN VALLEYS BY 02/1200Z AS A SURFACE
WAVE BEGINS TO GATHER STRENGTH. THE OVERALL EFFECT OF THIS SYSTEM
WILL BE A BAND OF WINTRY PRECIPITATION FROM THE CENTER OF THE
COUNTRY EASTWARD ACROSS THE UPPER GREAT LAKES/OH VALLEY AND INTO
NEW ENGLAND. THROUGH THE FIRST 24 TO 36 HOURS...THE 12Z CMC IS
NOTABLY SLOWER WITH THE PATTERN ALOFT WHICH LEADS TO A MORE
WESTWARD DISPLACED SURFACE CYCLONE. FURTHER...THE 00Z NAM DEPICTS
A DUAL-LOW STRUCTURE MOVING THROUGH THE MID-ATLANTIC ON MONDAY
MORNING WHICH APPEARS TO BE A MINORITY SOLUTION. AND LIKE PREVIOUS
DAYS...THE 12Z UKMET HAS SHOWN A BIAS TO BE ON THE NORTHERN SIDE
OF THE SPREAD WHICH LEAVES THE 00Z GFS/12Z ECMWF AS THE BEST
COMBINATION OF MODELS TO UTILIZE. SUCH A SOLUTION FITS WELL IN THE
ENSEMBLE LOW PLOT AND IS CONSISTENT WITH THE ENSEMBLE MEANS.


...SLOW-MOVING CLOSED LOW OVER MX...
...EVOLVING INTO AN OPEN WAVE ACROSS EASTERN MX BY 04/0000Z...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF WITH THE
12Z ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

AN EXPANSIVE NEGATIVELY ANOMALY REMAINS A MAINSTAY FEATURE ACROSS
MUCH OF MX THROUGHOUT THE FORECAST. THE 500-MB HEIGHTS OF THIS
SYSTEM SUGGEST DEPARTURES ON THE ORDER TO 3 TO 3.5 STANDARDIZED
ANOMALIES BELOW CLIMATOLOGY FOR EARLY FEBRUARY. SUCH ANOMALIES
SHOULD CONTINUE BEFORE DECREASING AS THE CLOSED LOW BEGINS TO OPEN
UP LATE IN THE PERIOD. THROUGH 02/1200Z...MODELS ARE IN REASONABLE
AGREEMENT BEFORE TIMING DIFFERENCES EMERGE. ON THE QUICKER SIDE OF
THE ENVELOPE ARE THE 00Z NAM AND 18Z GEFS/21Z SREF MEANS WHILE
OTHER MODELS STAY OFF TO THE WEST. AS THE WAVE OPENS UP OVER
EASTERN MX...THE 00Z GFS/12Z ECMWF AND 12Z ECMWF ENSEMBLE MEAN END
ON THE SLOWER SIDE. PLAN ON LEANING TOWARD THE SLOWER SIDE GIVEN
THE FORECAST INVOLVES A CUT-OFF LOW. A BLEND OF THE 00Z GFS/12Z
ECMWF WITH THE 12Z ECMWF ENSEMBLE MEAN IS RECOMMENDED.


...LOW-AMPLITUDE WAVES MOVING THROUGH THE PACIFIC NORTHWEST
THROUGHOUT THE PERIOD...

PRELIMINARY PREFERENCE: THROUGH DAY 2: GENERAL MODEL
COMPROMISE...THEREAFTER: A NON-12Z ECMWF/ECMWF ENSEMBLE MEAN
FORECAST CONFIDENCE: AVERAGE

AT THE START OF THE PERIOD...AN UPPER RIDGE WILL ANCHOR THE
PACIFIC NORTHWEST AND CENTRAL GREAT BASIN. THIS RIDGE AXIS IS
FORECAST TO GRADUALLY FLATTEN AS A SERIES OF LOW-AMPLITUDE WAVES
TRAVEL THROUGH THE PACIFIC NORTHWEST AND EVENTUALLY INTO INTERIOR
LOCATIONS. THE FLAT NATURE OF EACH WAVE CREATES A SLEW OF
DIFFERENCES AMONG THE MODELS. THROUGH DAY 2...FEEL A GENERAL MODEL
COMPROMISE WILL SUFFICE. BY DAY 3...ALL OF THE GUIDANCE SHOWS AN
UPPER RIDGE DEVELOPING ACROSS THE EASTERN PACIFIC WITH THE
EXCEPTION OF THE 12Z ECMWF/ECMWF ENSEMBLE MEAN WHICH FLATTENS THE
RIDGE. WILL FAVOR A NON-12Z ECMWF/ECMWF ENSEMBLE MEAN FOR DAY 3.


...UPPER TROF CROSSING THE UPPER MIDWEST BY WEDNESDAY MORNING...
...ATTENDANT COLD FRONT MOVING THROUGH THE CENTER OF THE CONUS...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF
FORECAST CONFIDENCE: AVERAGE

TOWARD THE END OF THE PERIOD...A BROAD AXIS OF HEIGHT FALLS MOVE
THROUGH THE UPPER MIDWEST AS A STRONG UPPER TROF CROSSES OVERHEAD.
TIMING DIFFERENCES ARE NOTED WITH THE 00Z NAM BEING DECIDEDLY
SLOWER THAN ANY OTHER DETERMINISTIC/ENSEMBLE SOLUTIONS. THERE IS
SOME SPREAD IN THE ENSEMBLE MEANS WITH THE 18Z GEFS BEING SLOWER
THAN THE 12Z ECMWF ENSEMBLE MEAN. IT IS WORTHY NOTING THE 00Z GFS
HAS TRENDED AWAY FROM THIS GEFS SOLUTION MORE TOWARD THE ECMWF
ENSEMBLE MEAN. WILL FOLLOW THE GROUPING FORMED BY THE 00Z GFS/12Z
ECMWF.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

RUBIN-OSTER

$$





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