UPDATE 4 p.m. THURSDAY:

Crystal Lake Police have issued the following advisory to motorists:

"Please avoid Route 31 between Crystal Lake and McHenry until further notice, due to the hill being unpassable."

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Original Story Posted 2 p.m. Thursday:

Apparently today's winter storm has kept weather forecasters guessing when it comes to the Northern Illinois area.

On Wednesday a storm warning was issued for McHenry and Lake counties, and then downgraded to a weather advisory late last night.

But, at about 1 p.m. today, The National Weather Service in Chicago has issued a Winter Storm Warning in effect for both counties through midnight Thursday. The Winter Weather Advisory is no longer in effect, the NWS stated.

Heavy snow is expected across McHenry County this afternoon and into the evening before tapering off. This storm is expected to have a "large impact" on the evening rush hour traffic, according to the NWS. 

Snow accumulations of 4 to 8 inches are likely with higher amounts possible in isolated areas. The snow will fall at a rate of 1 to 2 inches per hour this afternoon, resulting in reduce visability to under one half mile and rapid accumulation of snow on area roads.

Travel could be hazardous, the NWS stated.