ITHACA, N.Y. — Sometimes when we report bad weather in the Sunday forecast, we keep our fingers crossed and hope it doesn’t pan out. No such luck this time, folks. Santa’s in for a bumpy ride this year. Heavy rain and high winds are expected tomorrow through Christmas morning. A Flood Watch has been issued for 12 PM Thursday afternoon through 12 PM Friday.

A broad and powerful storm system will be moving across the Western Great Lakes northeastward into Canada. The system extends from Hudson Bay down to the Gulf of Mexico, allowing it to draw in a significant amount of mild, unstable air into its counterclockwise circulation, as well as ample moisture from the warm waters of the gulf.

Showers will move into Tompkins County late Thursday morning. A long period of steady, moderate to heavy rain will occur from Thursday afternoon through Thursday night. As the cold front passes with the movement of the storm center past our longitude, rain will change over to snow and taper off Friday morning.

The latest forecast model runs show increased rainfall amounts Thursday and Thursday night, with mild temperatures and strong, gusty southerly winds. Conditions are favorable for a rapid snowmelt. Since there’s still a lot of snow on the ground from last week’s storm, this creates a significant flooding risk.

More explicitly, rainfall amounts of 1.5 to 2 inches are expected from Thursday afternoon to Friday morning. The existing snowpack has 1 to 3 inches of water stored within it, and with temperatures spiking into the 50s and warmer rainwater percolated through the snowpack, a lot of water will be released very quickly, with models showing the local combined rain/melt total near 3 inches in six hours. In addition, the snowpack will limit the ground’s ability to effectively absorb this rain/meltwater, creating more runoff. The snowpack will also become much heavier as its liquid water content increases with rain and meltwater, raising the risk of roof damage and collapse.

The biggest risk with this storm is with urban and small stream/creek flooding along roadways and in urban areas where storm drains are clogged or jammed by snow and ice. Additional flooding is possible as rain and meltwater flow into low-lying areas.

Wind gusts of 30-40 MPH Thursday afternoon and Thursday night may snap some tree branches and blow around light outdoor objects (i.e. garbage cans, Christmas decorations). Scattered power outages are possible.

The onset of cold air has shifted later into Christmas Day with the latest forecast, falling below freezing around noon. Temperatures will hold steady in the 40s and 50s through the day and evening Christmas Eve, and begin falling rapidly after midnight. Temperatures will plunge into the 20s after sunrise Christmas Day, bottoming out in the teens Christmas Night. Wet roads and surfaces may rapidly ice over around noon Friday as a “flash freeze”. Black ice is possible.

Adjust your holiday plans accordingly. Remove snow and ice from flat or low-pitched roofs, gutters and storm drains as much as possible. Move vehicles away from weak trees and icicles. Secure or put away light objects that may topple or become airborne with gusty winds.

Give yourself much more time than usual if traveling. If a road is ponding over, do not attempt to cross it and find alternative travel routes – the water may be deeper than it looks. Be very careful if outdoors Christmas Day, as widespread surface ice is likely on roads and sidewalks (and the rain will have washed away any salt on those surfaces beforehand). For further updates, check the Public Briefing of the NWS Binghamton office.

As if the pandemic raging wasn’t enough of a reason to stay home this holiday, Mother Nature’s giving you some extra incentive.

Brian Crandall

Brian Crandall reports on housing and development for the Ithaca Voice. He can be reached at bcrandall@ithacavoice.com.