Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 010840
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
340 AM EST WED MAR 01 2017

VALID 12Z WED MAR 01 2017 - 12Z SAT MAR 04 2017

...NORTHWEST/NORTHERN ROCKIES...

A SERIES OF SHORTWAVES AND WEST-NORTHWESTERLY FLOW WILL SUPPORT
SNOW...WITH LOCALLY HEAVY ACCUMULATIONS POSSIBLE OVER THE
OLYMPICS...NORTHERN CASCADES AND THE NORTHERN ID AND NORTHWESTERN
MT RANGES OVER THE NEXT FEW DAYS. BY LATER THU INTO FRI...GUIDANCE
SHOWS A WELL-DEFINED TROUGH DIGGING OFFSHORE. INCREASED FLOW AHEAD
OF THE TROUGH IS EXPECTED TO TAP DEEPER MOISTURE...DRAWING IT INTO
THE REGION AND RAISING THE POTENTIAL FOR HEAVIER
PRECIPITATION...WITH HEAVY SNOW ACCUMULATIONS LIKELY FOR PORTIONS
OF THE WA CASCADES AND FAR NORTHERN ID AND NORTHWEST MT. THREE DAY
ACCUMULATIONS OF 2-4 FEET ARE LIKELY ACROSS THE HIGHER PEAKS OF
THE NORTHERN CASCADES.

...UPPER GREAT LAKES...

A LONGWAVE TROUGH WILL MOVE TOWARDS THE MS VALLEY TODAY...WITH
SEVERAL SHORTWAVES EMBEDDED WITHIN THE BROADER SCALE TROUGH. A
LEAD AREA OF LOW PRESSURE IS CURRENTLY MOVING ACROSS MI EARLY THIS
MORNING. AS A STRONG SHORTWAVE CURRENTLY OVER NE/IA MOVES EAST IT
SHOULD SUPPORT THE DEVELOPMENT OF ANOTHER SURFACE LOW ALONG THE
BAROCLINIC ZONE...WITH THIS LOW DEEPENING OVER MI THROUGH THE DAY
TODAY. COLDER AIR WRAPPING IN BEHIND THIS SYSTEM WILL SUPPORT
ACCUMULATING SNOWFALL IN THE DEVELOPING COMMA HEAD FROM CENTRAL WI
INTO NORTHERN MI. INCREASING LOW/MID LEVEL FRONTOGENESIS TO THE
NORTHWEST OF THE DEVELOPING LOW WILL LIKELY SUPPORT A PERIOD OF
HEAVY SNOWFALL. SNOWFALL RATES SHOULD EXCEED 1" AN HOUR IN SPOTS
FOR A PERIOD ACROSS EAST CENTRAL WI BETWEEN 12Z-18Z AND ACROSS
NORTHERN MI BETWEEN 16Z AND 21Z. THIS SHOULD PRODUCE A SWATH OF
6-10" OF SNOW FROM EAST CENTRAL WI INTO NORTHERN MI. MODELS ARE IN
PRETTY GOOD AGREEMENT...ALTHOUGH THOUGHT THE 0Z GFS WAS PROBABLY
TOO FAR NORTH WITH ITS SNOWFALL AXIS. THUS PREFERRED AN AXIS
CLOSER TO THE 0Z ARW/UKMET/ECMWF. WPC PROBABILITIES SHOW A 70-80%
CHANCE OF 6"+ ACROSS PORTIONS OF NORTHERN MI...WITH A 40-60%
CHANCE OF EXCEEDING 8".

...OH VALLEY/CENTRAL APPALACHIANS...

GUIDANCE SHOWS A CLIPPER SYSTEM DIVING SOUTHEAST FROM CENTRAL
CANADA INTO THE NORTHERN PLAINS THURSDAY MORNING TO OFF THE MID
ATLANTIC COAST ON FRIDAY. THIS FEATURE IS EXPECTED TO PRODUCE A
SWATH OF LIGHT SNOW AS IT MOVES FROM THE NORTHERN PLAINS INTO THE
MID ATLANTIC REGION. OROGRAPHIC ENHANCEMENT ACROSS PORTIONS OF
NORTHERN WV AND SOUTHWEST PA IS EXPECTED TO RESULT IN HIGHER
TOTALS ACROSS THAT REGION. OVERALL ONLY EXPECTING UP TO AN INCH OR
TWO ALONG THE TRACK OF THIS FEATURE...WITH AMOUNTS LOCALLY
EXCEEDING 4" CONFINED TO THE FAVORED TERRAIN OF NORTHERN WV INTO
SOUTHWEST PA.

MODEL DIFFERENCES REMAIN WITH THE EXACT STRENGTH AND TRACK OF THIS
SYSTEM. LEANING AGAINST THE 0Z NAM SOLUTION...AS ITS FURTHER NORTH
SOLUTION HAS LITTLE SUPPORT FROM THE OTHER GUIDANCE OR ENSEMBLE
SYSTEMS. THE GFS IS THE DEEPEST WITH THE TROUGH...RESULTING IN A
FURTHER SOUTH TRACK. MEANWHILE THE ECMWF APPEARS TO LIKELY BE TOO
WEAK WITH THE FEATURE...RESULTING IN IT UNDER DOING QPF/SNOW
AMOUNTS. THOUGHT THE 0Z UKMET AND GEFS MEAN WAS A GOOD COMPROMISE
FOR THE TRACK OF THE SYSTEM...ALTHOUGH THE UKMET IS LIKELY TOO
HEAVY WITH AMOUNTS. THE WPC PREFERENCE IS PRETTY CLOSE TO A NON
NAM BLEND...WITH A GEFS MEAN/GFS/ECMWF/UKMET BLEND HELPING
COUNTERACT THE VARIOUS MODEL ISSUES MENTIONED ABOVE...AND
RESULTING IN A DECENT MIDDLE GROUND SOLUTION FOR THE TIME BEING.

CHENARD







$$





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