Narrative:

Flying at 17500 ft MSL west of buildups and west of the continental divide; on a VFR flight to ZZZ deviated from direct to ZZZ to avoid some buildups over the states front range. Equipment on board included a garmin 430 and 496 GPS (with WX). VFR on top at 17500 ft until crossing denver front range mountains. Cloud layer began to rise and to stay VFR I climbed to 18000 ft; then 19000 ft to stay on top out of cloud deck. Contacted approach immediately; but was at 19000 ft before they had a chance to identify. Yes I penetrated class a without authority/authorized. ATC graciously provided a transponder code and I descended IFR without incident to ZZZ. What should I have done differently: done a 180 degree turn and contact ATC before entering class a. What will I do differently in the future: WX is subject to different actual conditions versus forecast along the front range rockies. I purposely skirted all WX to the west of the intended route and forecast called for VFR. I updated WX consistently along the route with metars; radar and cloud cover. I did not choose an eastern plains route along V81 publication-brk-bjc because winds aloft were from the west and I felt any percip would build to thunderstorms in the early afternoon not making for a choice route. Yellow nexrad display was in pueblo front range area. I thought I would have a lowering cloud deck approaching the front range at fort collins; no matter; in future contact ATC early.

Google
 

Original NASA ASRS Text

Title: A VFR-ON-TOP PILOT CLBED TO FL190 ATTEMPTING TO STAY CLEAR OF CLOUDS BEFORE CALLING ATC FOR A CLRNC.

Narrative: FLYING AT 17500 FT MSL W OF BUILDUPS AND W OF THE CONTINENTAL DIVIDE; ON A VFR FLT TO ZZZ DEVIATED FROM DIRECT TO ZZZ TO AVOID SOME BUILDUPS OVER THE STATES FRONT RANGE. EQUIP ON BOARD INCLUDED A GARMIN 430 AND 496 GPS (WITH WX). VFR ON TOP AT 17500 FT UNTIL XING DENVER FRONT RANGE MOUNTAINS. CLOUD LAYER BEGAN TO RISE AND TO STAY VFR I CLBED TO 18000 FT; THEN 19000 FT TO STAY ON TOP OUT OF CLOUD DECK. CONTACTED APCH IMMEDIATELY; BUT WAS AT 19000 FT BEFORE THEY HAD A CHANCE TO IDENT. YES I PENETRATED CLASS A WITHOUT AUTH. ATC GRACIOUSLY PROVIDED A XPONDER CODE AND I DSNDED IFR WITHOUT INCIDENT TO ZZZ. WHAT SHOULD I HAVE DONE DIFFERENTLY: DONE A 180 DEG TURN AND CONTACT ATC BEFORE ENTERING CLASS A. WHAT WILL I DO DIFFERENTLY IN THE FUTURE: WX IS SUBJECT TO DIFFERENT ACTUAL CONDITIONS VERSUS FORECAST ALONG THE FRONT RANGE ROCKIES. I PURPOSELY SKIRTED ALL WX TO THE W OF THE INTENDED RTE AND FORECAST CALLED FOR VFR. I UPDATED WX CONSISTENTLY ALONG THE RTE WITH METARS; RADAR AND CLOUD COVER. I DID NOT CHOOSE AN EASTERN PLAINS RTE ALONG V81 PUB-BRK-BJC BECAUSE WINDS ALOFT WERE FROM THE W AND I FELT ANY PERCIP WOULD BUILD TO TSTMS IN THE EARLY AFTERNOON NOT MAKING FOR A CHOICE RTE. YELLOW NEXRAD DISPLAY WAS IN PUEBLO FRONT RANGE AREA. I THOUGHT I WOULD HAVE A LOWERING CLOUD DECK APCHING THE FRONT RANGE AT FORT COLLINS; NO MATTER; IN FUTURE CONTACT ATC EARLY.

Data retrieved from NASA's ASRS site as of May 2009 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.