Quantitative Precipitation Forecast
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FOUS11 KWBC 122005
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
405 PM EDT SAT APR 12 2014

VALID 00Z SUN APR 13 2014 - 00Z WED APR 16 2014



...ROCKY MOUNTAINS/HIGH PLAINS...

ON DAYS 1/2...THE LARGE-SCALE UPPER TROUGH RESPONSIBLE FOR THE
COLD FRONTAL PASSAGE AND ASSOCIATED UPSLOPE FLOW HAS GOOD OVERALL
AGREEMENT FROM THE MODELS/ENSEMBLE FORECASTS ON DAY 1.  THE
COMBINED UPPER DIVERGENCE AND 700 MB VERTICAL MOTION MAXIMA LEADS
TO HEAVY SNOW ACROSS THE RANGES OF WY INTO NORTHERN CO ON DAY 1
AND CONTINUING SOUTH ACROSS THE RANGES OF CO INTO NORTHEAST NM
SANGRE DE CRISTO RANGE BEFORE ENDING DAY 2. TIMING DIFFERENCES
DEVELOP ON THE DEPARTURE OF THE UPPER TROUGH FROM THE SOUTHERN
ROCKIES ON TO THE PLAINS. ON THE HIGH PLAINS...THE PRIMARY
CONSIDERATION WITH REGARDS TO SNOW IS THE P-TYPE WITH MODELS
SHOWING PRECIP BEGINS WHEN THE AIR MASS IS TOO WARM FOR SNOW...AND
AFTER THE AIRMASS COOLS...THEN VERTICAL MOTION DECLINES SHORTLY
AFTERWARD.  MANUAL PROGS GAVE MORE WEIGHTING TO THE 12Z ECMWF/GFS
QPF/TEMPERATURE PROFILES WITH MINOR CONTRIBUTIONS FROM THE SREF
MEAN.  THE NAM WAS AN OUTLIER DAY 2 WITH THE HIGH MAGNITUDE 500 MB
TROUGH AND COLDER AIR MASS...WHICH RESULTS IN GREATER SNOW
POTENTIAL THAN OTHER SOLUTIONS IN KS/MO.

THE HIGHER PROBABILITIES ARE WITHIN THE AREAS WHERE CONFIDENCE IS
HIGHER ON BOTH QPF AND COLD TEMPERATURE PROFILES IN THE RANGES AND
NEARBY FOOTHILLS OF WY/CENTRAL CO/NORTHEAST NM.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


...UPPER MIDWEST/UPPER GREAT LAKES...

LOW PROBABILITIES OF 4 INCHES OF SNOW ARE DEPICTED ACROSS PORTIONS
OF UPPER MIDWEST AND UPPER GREAT LAKES SUNDAY NIGHT THROUGH MONDAY
IN ASSOCIATION WITH WEAK SURFACE LOWS MOVING NORTHEAST ALONG THE
FRONT ACROSS MICHIGAN LATE SUNDAY TO EARLY MONDAY.  RELIED UPON A
MULTI-MODEL CONSENSUS INVOLVING THE 00-12Z ECMWF/12Z GFS/12Z GFS
ENSEMBLE MEAN/SREF MEAN FOR LIQUID EQUIVALENT AMOUNTS AND PRECIP
TYPE.  COLD AIR WILL GRADUALLY ENTRAIN INTO THE REGION NORTH AND
WEST OF THE FRONTAL BOUNDARY AND FRONTAL WAVES...WITH THE PRECIP
TYPE CHANGING FROM RAIN TO SNOW.  ENOUGH ASCENT AND MOISTURE
APPEAR TO COINCIDE WITH MORE FAVORABLE THERMAL PROFILES FOR SNOW
TO SUPPORT LOW TO MODERATE PROBABILITIES OF 4 INCHES ACROSS
NORTHERN MI.  THE 12Z UKMET WAS THE FURTHEST NORTHWEST WITH THE
LOW POSITIONS/TRACK AND GIVEN THE LEAST WEIGHTING.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

...NORTHERN NEW ENGLAND...

ON DAY 1...STRONG LOW-MID LEVEL WARM ADVECTION DEVELOPS WITH THE
POSSIBILITY OF THE WARMING CAUSING THE INITIALLY BELOW FREEZING
AIR MASS TO RISE ABV FREEZING 900-750 MB IN THE GFS FCST
SOUNDINGS...RESULTING IN MIXED PRECIPITATION TYPES.  WHERE A
LONGER DURATION OF SNOW IS EXPECTED THERE ARE PROBABILITIES OF 4
INCHES OF SNOW AND WHERE THE 850-750 MB LAYER WARMS ABV FREEZING
TO MELT FALLING SNOW WHILE SFC TEMPS REMAIN AT FREEZING
PROBABILITIES FOR FREEZING RAIN ARE INDICATED.  THE MODELS STILL
HAVE CONSIDERABLE SPREAD ON THE TOTAL QPF...WITH THE NAM/GFS
HIGHER THAN THE ECMWF/UKMET IN MAINE.

ON DAY 3...THE WAVY COLD FRONT DRIFTS EAST ACROSS NEW YORK AND NEW
ENGLAND.  STRONG POST-FRONTAL COLD ADVECTION OCCURS AND RAIN
CHANGES TO SNOW...FIRST AT HIGHER ELEVATIONS ON THE ADIRONDACKS
AND GREEN MNTNS...POSSIBLY EVENTUALLY INTO LOWER ELEVATIONS BEFORE
THE EVENT ENDS. PROBABILITIES ARE LOW CONSIDERING THE LACK OF A
WELL DEVELOPED LOW FCST ALONG THE FRONT TO GENERATE A STRONG CROSS
FRONTAL CIRCULATION TO SUSTAIN ASCENT IN THE COLDER AIRMASS.
FRONTAL TIMING DIFFERENCES PERSIST AMONG THE MODELS/ENSEMBLE
MEMBERS.


THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PETERSEN



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