THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


PROBABILISTIC HEAVY SNOW AND ICE DISCUSSION




PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
452 PM EDT WED APR 23 2014

VALID 00Z THU APR 24 2014 - 00Z SUN APR 27 2014


DAYS 1 THROUGH 3...

...UPPER MIDWEST TO GREAT LAKES...

A CLOSING MID LEVEL SYSTEM INITIALLY OVER THE NORTHERN PLAINS WILL
CONTINUE TO SCOOT EAST ON THURSDAY...BRINGING ANOTHER ROUND OF
WINTRY WEATHER TO PARTS OF THE UPPER MIDWEST AND WESTERN GREAT
LAKES INTO FRIDAY.  INCREASING DIFLUENCE ALOFT AHEAD OF THE SYSTEM
AND DIVERGENCE ASSOCIATED WITH THE UPPER LEVEL JET WILL INDUCE
CYCLOGENESIS OVER THE NORTHERN GREAT PLAINS.  IN RESPONSE TO THE
TIGHTENING PRESSURE GRADIENT...SOUTHERLY LOW LEVEL WINDS WILL BE
DRAWING MOISTURE FROM THE PLAINS INTO THE UPPER MIDWEST.  WITH THE
THERMAL FIELDS BEING MARGINALLY SUPPORTIVE OF SNOW TO BEGIN
WITH...THINK THAT THE ENVIRONMENT WILL BE WORKING AGAINST SNOW IN
MOST AREAS ON DAY 1...23/00Z TO 24/00Z...ACROSS MOST OF THE AREA
UNTIL LATE IN THE PERIOD.  AS SUCH...ONLY A SLIGHT RISK OF 4
INCHES SEEMED WARRANTED EXCEPT FOR A LOW END MODERATE NEAR THE
BWCA IN THE MN ARROWHEAD.  THE BETTER CHANCE FOR SNOW COMES LATE
THU INTO FRIDAY ONCE THE SURFACE AND UPPER SYSTEM SLIDE
EAST...ALLOWING FOR COLDER AIR TO COME OUT OF CANADA AND INTERACT
WITH THE MID LEVEL CENTER AND DEFORMATION ZONE.  THE AMOUNT OF
ACCUMULATION REMAINS TOUGH TO PINPOINT GIVEN THE POTENTIAL FOR A
MIX OF RAIN AND SNOW EARLY ON AND THE FACT THAT TEMPERATURES DO
NOT GET MUCH BELOW FREEZING. WHILE THE AMOUNTS DIFFERED...THE TIP
OF THE MN INTO PARTS OF THE U.P. OF MI HAD THE BEST CHANCE OF
HAVING 8 INCH SNOWFALL AMOUNTS OR MORE. EVEN THOUGH THE MODELS
STILL SUGGEST SOME LIGHT FREEZING PCPN IS POSSIBLE...THE 12Z
MODELS WERE NOT AS AGGRESSIVE WITH THE AREAL COVERAGE OR AMOUNTS
OF FREEZING RAIN AS THEY WERE ON TUESDAY.  BY DAY 3 MOST OF THE
SNOW WILL BE PULLING AWAY FROM THE AREA WITH ANY ADDITIONAL
SNOWFALL AMOUNTS GENERALLY BEING LIGHT.

...PACIFIC NORTHWEST TO THE SIERRA/NEVADA RANGE TO GREAT BASIN AND
CENTRAL/NORTHERN ROCKIES...

PROPAGATING SHORTWAVE TROFS AND THE APPROACH OF A LONG WAVE TROF
WILL BRING A RISK OF SNOW TO PARTS OF THE WESTERN UNITED STATES AS
HEIGHTS/THICKNESS VALUES LOWER. THAT RESULTS IN SNOW
LEVELS...INITIALLY IN THE 5500 FT TO 8000 FT RANGE...TO LOWER TO
THE VALLEY FLOOR IN SOME PLACES.  BEST CHANCE FOR THE HEAVIEST
SNOW SHOULD BE IN THE CASCADES TO NORTHERN SIERRA/NEVADA RANGE ON
DAY 2 AND ACROSS THE CENTRAL/SOUTHERN SIERRA/NEVADA.  THE RISK OF
THE SNOW PUSHES EAST TOWARDS THE GREAT BASIN BUT WITH LESSER
SNOWFALL AMOUNTS. 

NORTHERN NEW ENGLAND...

SOME SNOW IS POSSIBLE ACROSS PARTS OF NORTHERN NEW ENGLAND TONIGHT
INTO EARLY THURSDAY MORNING AS AN AIRMASS WITH HI RH...EMBEDDED
WITHIN A COLD CYCLONIC CIRCULATION OF AN UPPER LOW OFF THE
COAST...ENCOUNTERS THE COMPLEX TERRAIN.  THE RISK OF SNOW TAPERS
OFF THU MORNING AS THE LOW CONTINUES TO MOVE AWAY.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

BANN








Last Updated: 452 PM EDT WED APR 23 2014