PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
439 AM EDT FRI APR 20 2018

VALID 12Z FRI APR 20 2018 - 12Z MON APR 23 2018

DAYS 1-3...

...GREAT BASIN/FOUR CORNERS AND CENTRAL TO SOUTHERN ROCKIES...

A STRONG CLOSED MID TO UPPER LOW, CENTERED NEAR THE
NEVADA/UTAH/ARIZONA BORDER EARLY THIS MORNING WILL DELIVER SNOW TO
PARTS OF THE FOUR CORNERS REGION AND CENTRAL/SOUTHERN ROCKIES FROM
LATER TODAY INTO THE DAY ON SATURDAY. 

THE GLOBAL MODELS AND ENSEMBLES STILL CAPTURE THIS FEATURE RATHER
WELL WITH OVERALL MINIMAL SPREAD, ESPECIALLY CONCERNING THE
PROGRESSION OF THIS LARGE SCALE FEATURE. THE SYSTEM WILL THEN
SLOWLY PROGRESS INTO THE FOUR CORNERS REGION TODAY AND THEN
PROGRESS THROUGH THE CENTRAL/SOUTHERN ROCKIES INTO THE
CENTRAL/SOUTHERN PLAINS SAT.

THE LARGE CLOSED 500 MB CIRCULATION WILL YIELD SOME DYNAMICALLY
DRIVEN AND UPSLOPE SNOWFALL FROM THE SOUTHERN WASATCH INTO THE CO
ROCKIES TODAY AND TONIGHT, ESPECIALLY FOR THE SWRN SAN JUANS OF
CO. BY SATURDAY, ENHANCED VERTICAL LIFT FROM THE PASSING MID-LEVEL
LOW AND STEADY UPSLOPE FLOW SHOULD CONTINUE TO PRODUCE HEAVY SNOW
ACROSS CO TERRAIN AND PERHAPS SPREAD TO THE PALMER DIVIDE UP TO
THE CHEYENNE RIDGE.

THIS IS WHERE PTYPE ISSUES BEGIN TO EMERGE, AS A NUMBER OF
SOLUTIONS ALLOW SNOW TO SPREAD DOWN THE FOOTHILLS AND LEE SIDE OF
THE CENTRAL ROCKIES. WPC STAYED CLOSER TO THE ECMWF THAN ANYTHING
ELSE IN TERMS OF BOTH MASS FIELDS AND THERMALS.  
 
THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT ON EACH OF THE THREE DAYS.

BANN