Many varieties of American English have the lot-cloth split. It is present in New York, Philadelphia and Baltimore. For speakers who have the lot-cloth split, the vowel in lot is a low vowel, and the vowel in cloth is a mid vowel.
The rounded mid vowel often occurs before voiceless fricatives. It is present in words such as boss, coffee, office and broth. However, it also occurs in words such as chocolate, dog and long.
The lot-cloth split seems to exhibit an open-syllable constraint. In open syllables the vowel is usually low and unrounded unless it is derived from a word with a mid rounded vowel. For example, the words crossing and coughing have the mid vowel because it is present in cross and cough. In the words fossil and possible, the o is in an open syllable and pronounced with a low vowel.
The lot-cloth split maintains a distinction in the vowels of lot and cloth. It does not merge them as is the case with the cot-caught merger. In Received Pronunciation, the lot-cloth split was once maintained but no longer. Though it is maintained in New York English, it is not in Boston English. The varieties of American English that maintain the split reflect an earlier stage of the pronunciation of the English language.