DURING ARRIVAL, THERE WERE INDEFINITE DELAYS AT WHITE PLAINS, NY, SO THE PLT DIVERTED TO NEWBURGH, NY. HE WAS VECTORED FOR AN ILS RWY 9 APCH. WHILE EN ROUTE, THE PLT REQUESTED & WAS GIVEN THE ILS FREQ, MINS FOR THE APCH, THE ARPT ELEVATION(491 FT MSL), THE NEWBURGH WX & THE FREQ FOR THE OUTER COMPASS LOCATOR (EVEN THO, CURRENT APCH CHARTS WERE ON BOARD). HE WAS CLEARED FOR THE APCH, BUT THE ACFT HIT TREES & CRASHED, 2.58 MI WEST OF RWY 9. ELEVATION OF THE CRASH SITE WAS ABOUT 580 FT. THE MIN DSCNT ALT (MDA) FOR THE APCH WAS 682 FT. AN EXAM OF THE WRECKAGE REVEALED NO PREIMPACT PART MALFUNCTION OR FAILURE. THE PLT WAS REQUIRED TO WEAR LENSES TO CORRECT HIS VISION. THE AREA FORCAST CALLED FOR ICING, TURBULENCE, LOW LEVEL WIND SHEAR, LOW CEILINGS, RAIN, DRIZZLE, FOG & A CHANCE OF LIGHT FREEZING RAIN/DRIZZLE. REPORTEDLYTHE PLT RECEIVED A FULL WX BRIEFING, BUT WAS NOT BRIEFED ON SIGMETS JULIETT 7 & LIMA 4 WHICH CALLED FOR MODERATE TO SEVERE TURBULENCE & LOW LEVEL WIND SHEAR AND OCCASIONAL MODERATE TO SEVERE MIXED/CLEAR ICG IN CLDS & PRECIP BLO 8000 FT.