Quantitative Precipitation Forecast
Issued by NWS

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669 FOUS11 KWBC 240905 QPFHSD PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 404 AM EST FRI FEB 24 2017 VALID 12Z FRI FEB 24 2017 - 12Z MON FEB 27 2017 DAYS 1 THROUGH 3... UPPER MS VALLEY/UPPER GREAT LAKES FRIDAY... NORTHERN NEW ENGLAND SATURDAY... AN AREA OF LOW PRESSURE WILL MOVE FROM THE MID MS VALLEY THIS MORNING...INTO MI THIS EVENING AND INTO SOUTHERN CANADA ON SATURDAY. A SWATH OF MODERATE TO HEAVY SNOWFALL WILL CONTINUE TO THE NORTHWEST OF THIS LOW TRACK...WITH MODERATE TO HIGH PROBABILITIES OF AN ADDITIONAL 6"+ FROM FAR NORTHEAST IA AND FAR SOUTHEAST MN...NORTHEASTWARD INTO CENTRAL WI AND THE UP OF MI. OVERALL MODELS GENERALLY REMAIN IN GOOD AGREEMENT ON THIS AXIS...ALTHOUGH SOME UNCERTAINTY ON THE EXACT LOCATION OF THE HIGHEST AMOUNTS WITHIN THIS SWATH. BASED ON LATEST RADAR TRENDS THE MOST LIKELY LOCATION FOR AN ADDITIONAL 8"+ IS PROBABLY FROM FAR SOUTHEAST MN INTO WEST CENTRAL WI...WHERE STRONG OMEGA WITHIN THE DENDRITIC GROWTH ZONE AND SOME SLANTWISE INSTABILITY SHOULD CONTINUE TO RESULT IN HEAVY SNOWFALL INTO THE MORNING HOURS. A CORRIDOR OF MIXED PRECIPITATION SHOULD CONTINUE FROM POTIONS OF NORTHEAST IA INTO SOUTHERN WI AND CENTRAL/NORTHERN MI. BASED ON TEMPERATURE PROFILES WOULD EXPECT THIS TO PREDOMINANTLY BE SLEET...ALTHOUGH A NARROW CORRIDOR OF FREEZING RAIN IS PROBABLE. BASED ON RECENT RUNS OF THE HIGH RES 4KM NAM AND THE SREF...DOES APPEAR TO BE A LOW TO MODERATE CHANCE OF A QUARTER INCH OF ICE ACCRETION ACROSS NORTHERN MI...WHERE A SIGNIFICANT ENOUGH WARM NOSE ALOFT IS EXPECTED TO MOVE IN. OVERALL LOOKING AT MAINLY A RAIN EVENT FOR NEW ENGLAND WITH THIS SYSTEM. THE EXCEPTION IS ACROSS NORTHERN MAINE...WHERE PRECIPITATION MAY START AS A WINTRY MIX THIS AFTERNOON INTO TONIGHT...BEFORE TRANSITIONING TO RAIN. NOT EXPECTING SIGNIFICANT SNOW OR ICE ACCUMULATIONS. AS THE TROUGH TAKES ON MORE OF A NEGATIVE TILT COULD SEE SOME POST FRONTAL PRECIPITATION DEVELOP ON SATURDAY NIGHT...AND ENOUGH COLD AIR COULD MOVE IN TO RESULT IN A CHANGEOVER TO SNOW ACROSS THE HIGHER TERRAIN OF NORTHERN NY INTO NORTHERN NEW ENGLAND. ALTHOUGH CURRENTLY LOOKS LIKE BY THE TIME THE COLDER AIR MOVES IN THE PRECIPITATION WILL BE NEARLY OVER. THUS ONLY EXPECTING LIGHT SNOWFALL ACCUMULATIONS AT THIS TIME. WEST... BROAD TROUGHING WILL REMAIN OVER THE WEST INTO THE WEEKEND...WITH A COUPLE SYSTEMS EXPECTED TO PUSH SOUTH BRINGING A SNOW THREAT. THE FIRST SYSTEM WILL MOVE DOWN THE PACIFIC NORTHWEST COAST INTO TONIGHT...WITH A SECOND MOVING INTO THE PACIFIC NORTHWEST SATURDAY NIGHT INTO SUNDAY. WITH THE DEEPENING TROUGH...SNOW LEVELS WILL DROP...GETTING PRETTY CLOSE TO THE COASTLINE OF NORTHWEST CA AND SOUTHWEST OR...AND NOT TOO FAR AWAY FROM SEATTLE AND PORTLAND. THE GENERAL LACK OF MOISTURE WILL KEEP AMOUNTS FROM GETTING EXTREME...WITH THREE DAY TOTALS GENERALLY STAYING IN THE 6-12" RANGE FROM PORTIONS OF THE WA/OR CASCADES SOUTH INTO NORTHERN CA AND SOUTHWEST OR. LIGHT TO MODERATE ACCUMULATIONS ARE ALSO LIKELY ACROSS PORTIONS OF THE NORTHERN GREAT BASIN AND NORTHERN ROCKIES...AS WELL AS ACROSS THE COLORADO ROCKIES. QUITE A BIT OF MODEL SPREAD...AND A GENERAL LACK OF RUN TO RUN CONSISTENCY WITH THE HANDLING OF THE INDIVIDUAL WAVES WITHIN THE TROUGHING. ALTHOUGH HAVE GENERALLY SEEN THE 0Z VERSIONS OF THE NAM/GFS/ECMWF CONVERGE CLOSER TOGETHER. THUS THE WPC FORECAST REPRESENTS A SOLUTION CLOSE TO A CONSENSUS OF THESE SOLUTIONS. CHENARD $$

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