Narrative:

Took off from boulder, co (1v5) with complete WX briefing, advised VFR was ok to ida area until near noon. Terminal at ida was clear with possible light snow showers later in the day. Checked WX en route at fl bridges, wy. Understood WX was down at ida (1500' in snow showers) but pocatello was still reasonably good (2500+). Was also advised of pilot report west of kemmerer, wy that WX was clear west of the mountains. Maintained VFR at 10,500 to 12,500 over the mountains, noted minor impact ice on struts and windshield when flying thru virga and skirting occasional light snow showers. Intersected V-21, which parallels the valley, into pocatello. As an experienced mountain flyer (20 yrs) I had both the appropriate charts and the WAC chart (CF16) so that I was aware of my location relative to high terrain at all times. Attempted to contact pocatello tower approximately 30 DME south of the pih VOR for WX information, since what I was seeing was not what was forecast. Finally established contact at approximately 15 DME, and was advised that WX was 700 indefinite with limited visibility. Was advised that slc would require approximately 20 mins for SVFR clearance due to traffic. Within 10-30 seconds of the last transmission to pocatello tower, a sudden, very heavy snow shower started all around the aircraft. Experiencing a total loss of ground contact and forward visibility, initiated an immediate, full power climb on a 330 heading, toward 10,000' knowing that that would keep me clear of any intervening high ground. Pocatello tower then asked my present flight conditions, and I replied 'now IFR (or IMC)'. Was instructed to contact slc center, vectored to proceed inbound at 10,000 on V-21 to the VOR and then outbnd to tyhee and shoot the approach. The flight was terminated, with no additional problems, after shooting the ILS 21 approach. The expectation, based on all available WX information, that the WX was clearing plus the fact that we had a fair ceiling, good ground clearance and good forward visibility was also a factor in not filing IFR until we were very suddenly in IMC.

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Original NASA ASRS Text

Title: PLT OF SMA ON VFR FLT PLAN ENTERED AREA OF SNOW SHOWERS, ICING. VFR IN IMC. OBTAINED APCH CLRNC AND LANDED WITHOUT FURTHER INCIDENT.

Narrative: TOOK OFF FROM BOULDER, CO (1V5) WITH COMPLETE WX BRIEFING, ADVISED VFR WAS OK TO IDA AREA UNTIL NEAR NOON. TERMINAL AT IDA WAS CLEAR WITH POSSIBLE LIGHT SNOW SHOWERS LATER IN THE DAY. CHECKED WX ENRTE AT FL BRIDGES, WY. UNDERSTOOD WX WAS DOWN AT IDA (1500' IN SNOW SHOWERS) BUT POCATELLO WAS STILL REASONABLY GOOD (2500+). WAS ALSO ADVISED OF PLT REPORT W OF KEMMERER, WY THAT WX WAS CLEAR W OF THE MOUNTAINS. MAINTAINED VFR AT 10,500 TO 12,500 OVER THE MOUNTAINS, NOTED MINOR IMPACT ICE ON STRUTS AND WINDSHIELD WHEN FLYING THRU VIRGA AND SKIRTING OCCASIONAL LIGHT SNOW SHOWERS. INTERSECTED V-21, WHICH PARALLELS THE VALLEY, INTO POCATELLO. AS AN EXPERIENCED MOUNTAIN FLYER (20 YRS) I HAD BOTH THE APPROPRIATE CHARTS AND THE WAC CHART (CF16) SO THAT I WAS AWARE OF MY LOCATION RELATIVE TO HIGH TERRAIN AT ALL TIMES. ATTEMPTED TO CONTACT POCATELLO TWR APPROX 30 DME S OF THE PIH VOR FOR WX INFO, SINCE WHAT I WAS SEEING WAS NOT WHAT WAS FORECAST. FINALLY ESTABLISHED CONTACT AT APPROX 15 DME, AND WAS ADVISED THAT WX WAS 700 INDEFINITE WITH LIMITED VISIBILITY. WAS ADVISED THAT SLC WOULD REQUIRE APPROX 20 MINS FOR SVFR CLRNC DUE TO TFC. WITHIN 10-30 SECONDS OF THE LAST XMISSION TO POCATELLO TWR, A SUDDEN, VERY HEAVY SNOW SHOWER STARTED ALL AROUND THE ACFT. EXPERIENCING A TOTAL LOSS OF GND CONTACT AND FORWARD VISIBILITY, INITIATED AN IMMEDIATE, FULL POWER CLIMB ON A 330 HDG, TOWARD 10,000' KNOWING THAT THAT WOULD KEEP ME CLEAR OF ANY INTERVENING HIGH GND. POCATELLO TWR THEN ASKED MY PRESENT FLT CONDITIONS, AND I REPLIED 'NOW IFR (OR IMC)'. WAS INSTRUCTED TO CONTACT SLC CENTER, VECTORED TO PROCEED INBND AT 10,000 ON V-21 TO THE VOR AND THEN OUTBND TO TYHEE AND SHOOT THE APCH. THE FLT WAS TERMINATED, WITH NO ADDITIONAL PROBLEMS, AFTER SHOOTING THE ILS 21 APCH. THE EXPECTATION, BASED ON ALL AVAILABLE WX INFO, THAT THE WX WAS CLEARING PLUS THE FACT THAT WE HAD A FAIR CEILING, GOOD GND CLRNC AND GOOD FORWARD VISIBILITY WAS ALSO A FACTOR IN NOT FILING IFR UNTIL WE WERE VERY SUDDENLY IN IMC.

Data retrieved from NASA's ASRS site as of August 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.