PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
412 AM EDT TUE MAR 12 2013

VALID 12Z TUE MAR 12 2013 - 12Z FRI MAR 15 2013

DAYS 1 TO 3...

...PACIFIC NORTHWEST TO THE NORTHERN ROCKIES...

SNOW LEVELS WILL INITIALLY BE LOW ENOUGH TO SUPPORT A SMALL AREA
OF SLIGHT AND EVEN MDT RISK OF 4 INCHES...PLUS A SLIGHT RISK OF 8
INCHES...IN THE NORTHERN CASCADES MOUNTAINS OF WA AND NORTHWEST
MT.  AS HEIGHTS/THICKNESS VALUES INCREASE AS A RESULT OF
AMPLIFICATION OF AN UPPER RIDGE...THE ENVIRONMENT BECOMES
INCREASINGLY HOSTILE TO SNOW OVER THE PAC NW.  BY DAY 2...ONLY A
SLIGHT RISK OF 4 INCHES IS INDICATED AT THE HIGHER ELEVATIONS OF
THE NORTHERN ROCKIES.  THE FOCUS SHIFTS BACK TO THE NORTHERN
CASCADES ON DAY 3 AS HEIGHTS START COMING DOWN BUT STILL IT ONLY
LOOKS LIKE A SLIGHT RISK OF 4 INCHES AT BEST.

...UPPER GREAT LAKES DAY ONE...

A DEEP CLOSED LOW CENTER WILL CONTINUE TO DRIFT NEWD DEEPER INTO
CANADA AS IT FILLS.  BUT THE COLD CYCLONIC FLOW AROUND THIS LOW
WILL CONTINUE TO RESULT IN SNOW ACROSS PARTS OF THE UPPER GREAT
LAKES WITH SOME ENHANCEMENT FROM LAKE SUPERIOR.  QPF IS GENERALLY
LIGHT BUT COLD TEMPS SUGGESTS THAT SNOW TO WATER RATIOS MAY BE
SUFFICIENTLY LARGE TO RESULT IN SOME 4 INCH OR MORE SNOWFALL
AMOUNTS CLOSE TO THE LAKE SHORE. 

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

BANN