Snow began falling across Southwestern Pennsylvania early Sunday in a winter storm that is expected to bring an accumulation of 4 inches or more by early Tuesday. But as of Sunday afternoon, the accumulation was less than initially predicted. The National Weather Service in Moon on Sunday afternoon issued a snowfall map calling for an accumulation of about 5 inches in much of Allegheny County during the two-day period ending at 7 a.m. Tuesday. In Westmoreland County, about 4 inches of snow is expected, with heavier accumulation in the county’s eastern ridges. The service dialed back its snowfall forecast from an earlier prediction of between 7 and 8 inches in Allegheny County and between 5 and 7 inches in most of Westmoreland County. Around 4:30 p.m. Sunday, the National Weather Service reported it had measured 2.3 inches for the official Pittsburgh climate site at its office in Moon. A winter weather advisory was extended through Tuesday morning. An additional 3-to-6 inches is expected, with the heaviest amounts Sunday evening. The ridges of Westmoreland and Fayette counties were upgraded to a winter storm warning, the weather service said. Shortly before 6 p.m., the weather service said it had reports of up to a foot of snow in the ridges of West Virginia. Areas along the Interstate 70 corridor and south should transition to rain as warm air advances, the service noted. The temperature was expected to top out at 32 degrees Sunday afternoon, dropping off just a few degrees by Sunday night, according to the National Weather Service. The service is calling for highs of 33 degrees on Monday and 28 degrees on Tuesday, with a low of 21 degrees Monday night. Pittsburgh Public Works said it planned to have more than 60 trucks out clearing snow during the day Sunday, after about 50 were dispatched earlier to pre-treat road surfaces. Allegheny County said at least 24 of its salt trucks with plows were prepared for treating the first wave of snow. PennDOT implemented travel restrictions on several major roadways Sunday and urged drivers to avoid unnecessary travel during the storm. The only Southwestern Pennsylvania highway affected as of noon Sunday was I-70. According to PennDOT, a ban on empty commercial vehicles was in effect on I-70 between the Pennsylvania Turnpike in New Stanton and the Maryland state line. A similar ban was announced for the following roads: • Interstate 80 between Interstate 81 and the New Jersey state line. • The entire lengths of Interstates 78, 81, 83, 84 and 380. Restrictions could change or more roads could be added depending on the weather. Up-to-date information will be available at 511pa.com. Staff writer Brian C. Rittmeyer contributed. Jeff Himler is a Tribune-Review staff writer. You can contact Jeff at 724-836-6622, jhimler@triblive.com or via Twitter .