The cold snap will last until at least next Tuesday in the upper North, Bangkok and its surrounding provinces, with temperatures dropping on average by 2-4C, according to the Meteorological Department.
The South, meanwhile, can expect more rain and heavy downpours in some areas over the next four days.
The weather bureau said Thursday the upper North, Bangkok and surrounding provinces will continue to experience cold temperatures until Tuesday with a chance of rain.
More rain is on the way over many areas of the South, with heavy downpours also forecast in some provinces with strong winds over the Gulf of Thailand. The wind is also whipping up waves as high as four metres.
The department has warned of damage to crops unsuited to cold weather. People should also be mindful of their health as many have fallen sick with illnesses aggravated by a drop in temperature.
Fishermen using small boats were also advised not to put to sea until Tuesday.
According to the department, fog has blanketed many parts of the North and Northeast gripped by the cold spell which has produced frost on mountains.
The weather bureau said that for the rest of January, there will be less rainfall. Most of this rain will fall in provinces on the Gulf of Thailand due to lingering high pressure from China.
Meanwhile, holidaymakers are warned to take precautions on mountain roads in the North where fog could hamper visibility, 3rd Army commander Wijak Siribansop said.
He said many tourists visit natural attractions located high in the mountains, including thousands on Doi Inthanon, the country's highest peak, just outside Chiang Mai city.
Lt Gen Wijak said heavy traffic on roads leading to the mountains increases the risk of road accidents.
The army is working with defence volunteers to arrange 185 roadside rest stops and service areas under 3rd Army supervision in the northern provinces.
Checkpoints were set up to search vehicles for any drugs or other illegal items Thursday and will remain in place for the next seven days, Lt Gen Wijak said.
The army area is also running an information service centre for people seeking directions or other traffic information.
In the northeast, the cold weather has contributed to an upsurge in tourist volume in Kalasin where attractions including Laem Non Wiset, a scenic spot by Lam Pao dam, have welcomed many visitors who have started arriving for the New Year celebration.
Meanwhile, floods have subsided in the southern provinces of Songkhla, Phatthalung, Nakhon Si Thammarat and Surat Thani.
However, rainfall is forecast in some of these areas in coming days, prompting authorities to make contingency plans.
