Prognostic Meteorological Discussion
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FXUS10 KWNH 310500
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1159 PM EST FRI JAN 30 2015

VALID JAN 31/0000 UTC THRU FEB 03/1200 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.


...NEGATIVELY-TILTED TROF OVER NEW ENGLAND EARLY IN THE PERIOD...
...ASSOCIATED COASTAL LOW...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

A RATHER POTENT AXIS OF HEIGHT FALLS MOVING OFFSHORE OF THE
MID-ATLANTIC HAS SPREAD LIGHT TO MODERATE SNOW ACROSS UPPER NEW
ENGLAND THIS EVENING. THE SYSTEM BECOMES FURTHER WRAPPED UP AS A
CLOSED MID-LEVEL CENTER DEVELOPS EAST OF MA BY 31/1200Z. MODELS
ARE IN AGREEMENT THAT THE NEGATIVE ANOMALY LIFT CONTINUE LIFTING
NORTHWARD TOWARD NOVA SCOTIA. IN PARTICULAR...THE PAST FEW
ENSEMBLE LOW PLOTS HAVE SHOWN A DEFINITIVE TREND IN THE QUICKER
DIRECTION TO ACCELERATE THE AREA OF LOW PRESSURE TOWARD THE NORTH.
OVERALL DIFFERENCES WHILE THE SYSTEM AFFECTS NEW ENGLAND ARE
MINIMAL WHICH SUGGESTS A GENERAL MODEL COMPROMISE HERE.


...CLOSED LOW MOVING FROM THE DESERT SOUTHWEST TOWARD
WESTERN/CENTRAL MX...

PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECWMF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

AN EXPANSIVE UPPER LOW SPINNING OVER THE DESERT SOUTHWEST HAS BEEN
ACCOMPANIED BY AN ANOMALOUS TONGUE OF MOISTURE LIFTING INTO THE
SOUTHWESTERN CONUS. AGREEMENT EXISTS THAT IS BROAD AXIS OF
VORTICITY WILL SINK SOUTHWARD TOWARD BAJA CA/FAR WESTERN MX. HOW
LONG THIS SYSTEM LINGERS OVER THE REGION BEFORE IT SLIDES EASTWARD
ACROSS MX IS A BIT MORE UNCERTAIN. THE MULTI-MODEL TRENDS BASED ON
SPAGHETTI PLOTS SUGGEST A QUICKER TREND IN THE ENSEMBLES. ON THE
FASTER SIDE OF THE ENVELOPE ARE THE 00Z NAM AND 21Z SREF/18Z GEFS
MEANS WHILE THE SLOWEST MODEL IS THE 12Z UKMET WHICH CONTINUES TO
BE ITS RECENT TRACK RECORD WITH THIS SYSTEM. BY 03/1200Z...THE 21Z
SREF/18Z GEFS MEANS ARE ON THE FAR EASTERN SIDE OF THE SPREAD. IT
APPEARS THE 00Z GFS HAS TRENDED AWAY FROM THIS FASTER SOLUTION
BECOMING CENTERED IN THE MIDDLE ACCOMPANYING THE 12Z ECMWF. WILL
FOLLOW THE COMBINATION OF THE 00Z GFS/12Z ECMWF SOLUTIONS.
CONFIDENCE WILL KEPT A TAD BELOW AVERAGE GIVEN THE COMPLEXITY OF
FORECASTING A SLOW-MOVING UPPER LOW.


...DEEPENING TROF MIGRATING FROM THE MIDDLE MS VALLEY TO THE
MID-ATLANTIC ON SUNDAY/MONDAY...
...STRENGTHENING SURFACE WAVE CROSSING THE MID-ATLANTIC...

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

HEIGHT FALLS CURRENTLY MOVING THROUGH BRITISH COLUMBIA WILL
EVENTUALLY CARVE OUT A MORE DEFINED TROF ACROSS THE CENTER OF THE
COUNTRY BY EARLY SUNDAY. THE MOST OUTLYING MODEL AT THIS POINT IN
TIME IS THE 12Z UKMET WHICH SHOWS MUCH MORE DEFINITION IN THE
SHORTWAVE ALONG WITH A QUICKER PROGRESSION. LOOKING AT THE
SURFACE...A PRONOUNCED WAVE OF LOW PRESSURE WILL SLIDE EASTWARD
FROM THE LOWER OH VALLEY TOWARD THE MID-ATLANTIC HEADING INTO LATE
SUNDAY/EARLY MONDAY. AS EXPECTED...THE QUICKER 12Z UKMET IS AHEAD
OF OTHER GUIDANCE WHILE BEING NORTH OF THE STRONGER MODEL
CONSENSUS. THE TREND NORTHWARD IN THE MODELS FROM LAST NIGHT DOES
APPEAR TO HAVE HELD UP DURING THE PAST COUPLE OF MODEL CYCLES.
CONTINUE TO RECOMMEND A BLEND OF THE 00Z GFS/12Z ECMWF GIVEN THEIR
CONSISTENT SOLUTIONS RELATIVE TO PRIOR RUNS. THE 00Z GFS IS A BIT
QUICKER THAN THE 12Z ECMWF BUT BLENDING THE TWO SHOULD AVERAGE OUT
THEIR DIFFERENCES.


...LOW-AMPLITUDE WAVES AFFECTING THE PACIFIC NORTHWEST EARLY NEXT
WEEK...

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

AN UPPER RIDGE ANCHORING THE WESTERN U.S. BETWEEN 30 AND 40 N
LATITUDE WILL GRADUALLY BREAK DOWN AS A SERIES OF LOW-AMPLITUDE
IMPULSES TRACK ACROSS THE PACIFIC NORTHWEST LATE SUNDAY ONWARD.
EXCEPT FOR THE 12Z UKMET WHICH IS MORE AMPLIFIED THAN ONE OF THESE
WAVES...THE MODELS ARE REASONABLY CLOSE TO ONE ANOTHER OVERALL.
GIVEN SUCH SIMILARITIES...WPC WILL RECOMMEND A COMBINATION OF
HIGHER-RESOLUTION DETERMINISTIC GUIDANCE TO ACCOUNT FOR THE BETTER
HANDLING OF THE COMPLEX TERRAIN. THAT IS...A BLEND OF THE 00Z
NAM/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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