What was found
FLIGHT 3144 LGA - CHS SHORTLY AFTER CLIMBING THROUGH 20,000 FT WITH WINDSHIELD HEAT ON, THERE WAS A BANG AND THE FIRST OFFICERS FRONT WINDSCREEN WAS CRACKED (SPIDER WEBBED). IMMEDIATELY REDUCED SPEED, DECLARED EMERGENCY, AND DIVERTED TO JFK DUE TO LGA BELOW LANDING MINIMUMS. RAN ALL NECESSARY CHECKLISTS AND LANDED AT JFK WITHOUT INCIDENT. MX REMOVED AND REPLACED F/O'S WINDSHIELD IAW EMB-145 MM CH 56-10-01. PRESSURIZED ACFT FOR LEAK CHECKS, NO LEAKS FOUND. WINDSHIELD HEAT CHECKED OK.