PA34 EXPERIENCES ALTDEV IN TURB ON APCH TO IAD.

Narrative

THERE WAS A 'NORTHEASTER' IN AREA COVERING VIRGINIA AND MARYLAND. CEILING 800 FT; MODERATE RAIN AND TURB; AND IT GOT WORSE AS YOU DSNDED BELOW 3000 FT. I MADE ANOTHER APCH 1 HR EARLIER AT MIV. FLYING IN THIS WX IS NOT UNUSUAL FOR ME; AND CONSIDER MYSELF GOOD TO EXCELLENT IN LNDGS WITH GUSTY WINDS OF UP TO 32 KTS; AND HAVE DONE IT BEFORE IN VFR CONDITIONS OVER VARIOUS PARTS OF THE COUNTRY. THE WIND WAS OUT OF THE NE ABOUT 22 KTS. AS I APCHED 2000 FT; THE CTLR ASKED ME TO KEEP MY SPD UP DUE TO JETS BEHIND ME GOING FASTER. I DID NOT CHANGE PWR SETTING WHICH WAS 31 MANIFOLD AND 2500 RPM. I TOLD THE CTLR I COULD MAINTAIN 155 KTS AND I WAS DOING 170-190 ON THE GND. I WAS CLRED FOR THE APCH BUT WANTED TO REMAIN LEVEL AT 2000 FT OVER MIDDLE MARKER SO I COULD VIEW THE GS MOVING CORRECTLY; TO BE SURE IT IS WORKING (A CHK I DO ON EVERY APCH). ALL OF A SUDDEN; I STARTED CLBING TO 2150 FT VERY QUICKLY; BUT MY AIRSPD INDICATED AT 187 KTS; WHICH IS 12 KTS BELOW RED LINE. I REDUCED PWR AND PUSHED DOWN BUT WAS STILL CLBING DUE TO SOME WIND GUSTS OR TERRAIN CREATING UPDRAFTS. NO TSTMS WERE PRESENT; NOR WERE ANY FORECASTED. I COULD NOT MAKE A RPT 'UNABLE TO MAINTAIN ALT' TO THE CTLR BECAUSE HE WAS BUSY XMITTING. I BROUGHT THE PWR DOWN MORE; BUT NOT BEFORE I HIT 2350 FT; 350 FT ABOVE MY ASSIGNED ALT. WHEN THE CTLR FINALLY GOT TO ME; HE SAID I HIT 2400 FT BUT I WAS ASSIGNED 2000 FT. TCAS SHOWED NO CONFLICT. ATC SAID 'DON'T WORRY' AND CANCELED APCH CLRNC; AND I PROCEEDED LATER WITH NO INCIDENT. COULD HAVE BEEN AVOIDED IF I TOLD CTLR I NEEDED SLOWER SPD FOR APCH.