H25B CREW OFF THE END OF A 6548 FT RWY AFTER AN APCH TO MINIMUMS AND LNDG IN A HVY SNOW STORM.

Narrative

DURING LNDG IN HVY SNOWFALL; WE ENCOUNTERED A TOTAL LOSS OF BRAKING ABILITY DUE TO A VERY SLIPPERY RWY WHILE ROLLING OUT AFTER LNDG. ONCE THE ACFT HAD SLOWED TO TAXI SPD SOLELY BY AERODYNAMIC BRAKING; WE WERE UNABLE TO SLOW ANY FURTHER AND ENTERED THE STOPWAY AT A TAXI SPD AND STOPPED ONLY WHEN THE NOSEWHEEL WENT PAST THE 200 FT STOPWAY ONTO THE GRASS. NO DAMAGE WAS NOTICED AND AFTER A THOROUGH MAINT INSPECTION; WE FLEW THE ACFT OUT THE NEXT DAY. ONCE WE WERE STOPPED; WE NOTICED FROM VISUAL OBSERVATION OF A WINDSOCK THAT THERE HAD BEEN A L QUARTERING TAILWIND DURING THE LNDG ROLLOUT. WE IMMEDIATELY RPTED OUR SIT TO THE CTL TWR BY RADIO AND ADVISED BRAKING ACTION AS NIL ON ALL SECTIONS OF THE RWY. ALL PREVIOUS RPTS INDICATED BRAKING ACTION AS FAIR; INCLUDING A PIREP FROM A PLANE OF THE SAME TYPE THAT HAD LANDED ONLY A FEW MINS PRIOR ON THE SAME RWY. WINDS HAD BEEN RPTED AS 80 DEGS FROM THE NOSE AT 9 KTS. A NEW ATIS WAS ISSUED AFTER WE HAD BEGUN THE APCH; BUT WE WERE UNABLE TO OBTAIN THE INFO SINCE THE ATIS BROADCAST HAD NOT BEGUN. TWR SIMPLY ADVISED OF A NEW ATIS IN A GENERAL BROADCAST BUT DID NOT MENTION ANY CHANGE IN WIND CONDITIONS. SUBSEQUENT METAR RPTED THE WIND AS 110 DEGS L OF THE NOSE AT 10 KTS; BUT PERSONAL OBSERVATIONS PLACED THE WIND DIRECTION AT ABOUT 135 DEGS L OF NOSE AT 10 KTS AS SEEN ON THE WINDSOCK FROM THE GND AT THE TIME OF THE INCIDENT. IT APPEARS THAT INCORRECT WIND RPTS COMBINED WITH INACCURATE BRAKING ACTION RPTS CONTRIBUTED TO THE OVERRUN.