Prognostic Meteorological Discussion
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FXUS10 KWNH 310644
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
144 AM EST SAT JAN 31 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 MODEL GUIDANCE ALONG WITH FINAL
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...

FINAL 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 TONIGHT. 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 WILL 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...

FINAL PREFERENCE: BLEND OF THE 00Z GFS/ECWMF
FORECAST CONFIDENCE: 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 A 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/00Z GEFS
MEANS WHILE THE SLOWEST MODELS ARE THE 00Z ECMWF/UKMET. BY
03/1200Z...THE 21Z SREF/00Z GEFS MEANS ARE ON THE FAR EASTERN SIDE
OF THE SPREAD. INTERESTINGLY...WHILE THE MULTI-MODEL TRENDS HAD
SUGGESTED A MOVE IN THE FASTER DIRECTION...THE 00Z GUIDANCE HAS
TAKEN A SHIFT TOWARD THE SLOWER SIDE. THE 00Z GFS/ECMWF/CMC ALL
EXHIBITED SUCH BEHAVIOR. THE WAFFLING OF THE MODELS IS NOT
TERRIBLY SURPRISING GIVEN THE DIFFICULTY OF FORECASTING THE SPEED
OF A CLOSED UPPER LOW. PLAN ON STICKING WITH THE PREVIOUS
PREFERENCE WHILE INCORPORATING THE LATEST ECMWF. THIS WILL ACCOUNT
FOR THE SLOWING TREND GIVEN THE 00Z GFS/ECMWF BOTH SLOWED DOWN
RELATIVE TO THEIR PREVIOUS CYCLES. CONFIDENCE WILL BE SHIFTED TO
BELOW AVERAGE GIVEN THE GROWING UNCERTAINTY.


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

FINAL PREFERENCE: BLEND OF THE 00Z GFS/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 00Z UKMET WHICH SHOWS MORE DEFINITION IN THE SHORTWAVE
ACROSS THE MO VALLEY. 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.
HAVE SEEN MODELS CONVERGING ON A SOLUTION CARRYING THE LOW ALONG
THE VICINITY OF 40N WITH VARIABLE TIMING SUGGESTED. THE SLOWER
TREND IN THE 00Z ECMWF INCREASES THE SPREAD BETWEEN THE 00Z
GFS/ECMWF ON DAY 3. HOWEVER...WILL PLAN ON CONTINUING TO SPLIT THE
DIFFERENCE BETWEEN THESE TWO SOLUTIONS.


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

FINAL PREFERENCE: BLEND OF THE 00Z NAM/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.
OVERALL...THE MODELS ARE REASONABLY CLOSE TO ONE ANOTHER WITH THE
LARGER SCALE PATTERN WITH MORE VARIANCE NOTED WITH THE INDIVIDUAL
SHORTWAVES. GIVEN THE BROADER SIMILARITIES...WPC WILL RECOMMEND A
COMBINATION OF HIGHER-RESOLUTION DETERMINISTIC GUIDANCE TO ACCOUNT
FOR THE BETTER HANDLING OF THE COMPLEX TERRAIN OUT WEST. THAT
IS...A BLEND OF THE 00Z NAM/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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