September is a time of change – but are we ready for frost?

Weather Blog

PORTLAND, Ore. (KOIN) – For the first time since this spring, a select few might feel Jack Frost nipping at a nose or two by Thursday. And if you’re like most opinionated weather enthusiasts, you have some feelings about this. Chances are, you fall into one of two camps:

Camp #1: Hates summer, eagerly follows Farmer’s Almanac for the first sign of snow. Waits with baited breath at Sylvan hill to report the 1st snow flake on social media.

Camp #2: Lives for summer and happens to be plant savvy. Has plan laid out to protect greenery from frost damage.

Like it or not, September is a time for change. The sun angle is lower on the horizon, daytime is getting shorter, and we’re just a week from the autumn equinox. Aside from one anomalous cold morning in the middle of August when Portland tied a record low of 48º (1951) on Aug. 23 at PDX, we haven’t felt temperatures in the low 40’s since the middle of May. The last freezing temperature was April 11.

Looking ahead to Thursday morning – some outlying areas of the Willamette Valley, and higher terrain may drop into the 30’s. This will be difficult to achieve unless a few key elements line up perfectly. Wind needs to be calm, sky clear, low dew points. So when is the first normal frost and freeze of the season? On average Portland’s temp drops to 36º as early as October 26, and freezing by Nov. 15. The earliest recorded temperature of 36º in Portland was Sept. 17, 1965. Earliest freeze was October 8, 1985.

Keep in mind you can experience frost on surfaces like the grass or your car when the temperature measured at your local airport is several degrees above freezing. How? Coldest air sinks and metal surfaces get cold easily. Weather observations like temperatures are taken about 5 feet above ground level.

Warm hugs needed for NE Washington

No watches or warnings for Portland, but far northeast Washington will be under a freeze watch starting Wednesday night lasting through Thursday morning.

FREEZE WATCH: Northern Panhandle-Northeast Mountains-Okanogan Highlands – Including the cities of Sandpoint, Rathdrum, Bonners Ferry, Priest River, Eastport, Colville, Deer Park, Chewelah, Newport, Kettle Falls, Republic, Inchelium, and Wauconda

WHAT…Temperatures in the low 30s.

WHERE…Sandpoint, Rathdrum, Bonners Ferry, Priest River, Eastport, Colville, Deer Park, Chewelah, Newport, Kettle Falls, Republic, Inchelium, and Wauconda.

WHEN…From Wednesday night through Thursday morning.

IMPACTS…Freeze or frost could damage sensitive outdoor vegetation if left exposed.

PRECAUTIONARY/PREPAREDNESS ACTIONS… A Freeze Watch means sub-freezing temperatures are possible. Take steps now to protect tender plants from the cold.

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