ACR B757-200 WX VANES IN STRONG WIND ON A SLICK SURFACE AND SLIDES OFF OF TXWY.

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WHILE TAXIING TO RWY 10L AT PDX ACFT SLID OFF INTO THE GRASS. TXWY WAS EXTREMELY ICY; WIND WAS 110 DEGS AT 27 KTS. I BELIEVE THE ACFT WX COCKED INTO THE WIND. THIS IN COMBINATION WITH WHAT APPEARS TO BE A SLIGHT SLOPE INTO THE GRASS CAUSED THE ACFT TO SLIDE. THE ARPT WAS EXTREMELY ICY DUE TO FREEZING RAIN. THERE WERE NO FIELD CONDITION RPTS GIVEN WHEN WE WERE CLRED TO TAXI. THE ARPT SHOULD HAVE BEEN CLOSED UNTIL DEICED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS FLC WAS FLYING A B757-200 WHEN THEY SLID OFF OF THE TXWY. THE RPTR SAID THAT THE ARPT MAINT CREWS HAD BEEN SCRAPING AND SANDING FOR ALMOST 2 HRS WHEN HE DECIDED TO DEPART AND HE THINKS THAT THEY SIMPLY MISSED THIS SECTION OF TXWY. ANOTHER FACTOR IN HIS DECISION TO GO WAS THAT THE COMPANY WAS ATTEMPTING TO RELOCATE THE INTL ROUTE ACFT TO LAX BECAUSE OF THE STORM AND THAT HE WAS RUNNING OUT OF DUTY TIME. THE RPTR FURTHER SAID THAT HE THOUGHT THE PRIMARY FACTORS WERE THE SLICK SURFACE AND THE STRONG WINDS THAT CAUSED HIM TO WX VANE AND SLIDE SIDEWAYS ONTO THE GRASS. THERE WAS NO DAMAGE OR INJURY JUST INCONVENIENCE FOR THE PAX HE SAID.