Narrative:

Morning takeoffs from crw can frequently be fogged in, but never have I seen WX deteriorate so quickly. A quick check of the previous hour's WX indicated that the RVR on the departure end of runway 5 was variable below my 1 mi visibility due to high mins. The current hourly had no RVR report in the remarks and conditions were clear and unlimited visibility. These conditions continued right up to initial taxi. It was then that we noticed the upslope fog on the northern portion of the airport. We were cleared to back taxi and takeoff on runway 5, and the tower added that the last 4000 ft were obscured by fog. Both crew members felt that we still had our 1 mi visibility for takeoff when taxiing onto and turning around on runway 5. Our aircraft was at gross weight and we don't have very effective brakes, so when the visibility went below 1 mi, we were at V1 minus 15. At V1 minus 5 we lost nearly all forward visibility reference. Aborting wasn't a safe option in my mind, the entire airport is on a hilltop with no overruns, and just remaining on the runway would be difficult enough. The takeoff was continued uneventfully. (My) the departure brief never considered an abort due to loss of visibility so during that indecisive period between, V1 minus 15 and V1 minus 5, the WX deteriorated so quickly, that it made the 'continue' decision for me. In the future, my briefs will be more thorough and I will have greater respect for fast moving upslope fog.

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Original NASA ASRS Text

Title: AN LTT ACR CREW TOOK OFF INTO DENSE GND FOG. BELOW THE PLT'S LIMITS. THIS WAS FAST MOVING UPSLOPE FOG.

Narrative: MORNING TKOFS FROM CRW CAN FREQUENTLY BE FOGGED IN, BUT NEVER HAVE I SEEN WX DETERIORATE SO QUICKLY. A QUICK CHK OF THE PREVIOUS HR'S WX INDICATED THAT THE RVR ON THE DEP END OF RWY 5 WAS VARIABLE BELOW MY 1 MI VISIBILITY DUE TO HIGH MINS. THE CURRENT HRLY HAD NO RVR RPT IN THE REMARKS AND CONDITIONS WERE CLR AND UNLIMITED VISIBILITY. THESE CONDITIONS CONTINUED RIGHT UP TO INITIAL TAXI. IT WAS THEN THAT WE NOTICED THE UPSLOPE FOG ON THE NORTHERN PORTION OF THE ARPT. WE WERE CLRED TO BACK TAXI AND TKOF ON RWY 5, AND THE TWR ADDED THAT THE LAST 4000 FT WERE OBSCURED BY FOG. BOTH CREW MEMBERS FELT THAT WE STILL HAD OUR 1 MI VISIBILITY FOR TKOF WHEN TAXIING ONTO AND TURNING AROUND ON RWY 5. OUR ACFT WAS AT GROSS WT AND WE DON'T HAVE VERY EFFECTIVE BRAKES, SO WHEN THE VISIBILITY WENT BELOW 1 MI, WE WERE AT V1 MINUS 15. AT V1 MINUS 5 WE LOST NEARLY ALL FORWARD VISIBILITY REF. ABORTING WASN'T A SAFE OPTION IN MY MIND, THE ENTIRE ARPT IS ON A HILLTOP WITH NO OVERRUNS, AND JUST REMAINING ON THE RWY WOULD BE DIFFICULT ENOUGH. THE TKOF WAS CONTINUED UNEVENTFULLY. (MY) THE DEP BRIEF NEVER CONSIDERED AN ABORT DUE TO LOSS OF VISIBILITY SO DURING THAT INDECISIVE PERIOD BTWN, V1 MINUS 15 AND V1 MINUS 5, THE WX DETERIORATED SO QUICKLY, THAT IT MADE THE 'CONTINUE' DECISION FOR ME. IN THE FUTURE, MY BRIEFS WILL BE MORE THOROUGH AND I WILL HAVE GREATER RESPECT FOR FAST MOVING UPSLOPE FOG.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.