A deep trough stretched from Saskatchewan to central California, allowing for ridging, clearing skies, and light winds over the Northern Rockies. All this occurred with an unseasonably cold air mass. This early cold spell with high 20s affected gardens and agriculture, as low temperatures reached values not typical until 2 or 3 weeks later in autumn. News media reported early harvest of crops near Missoula, including: lettuce, tomatoes, and squash.

Frost/Freeze in KOOTENAI/CABINET REGION, MONTANA
From 13-SEP-16 03:00:00 to 13-SEP-16 08:00:00 (MST-7)
Reported by: RAWS

Libby, MT temperature sensor reported low of 29 F.

Frost/Freeze in KOOTENAI/CABINET REGION, MONTANA
From 13-SEP-16 03:00:00 to 13-SEP-16 08:00:00 (MST-7)
Reported by: AWSS

Yaak, MT temperature sensor reported a low of 22 F.

Frost/Freeze in LOWER CLARK FORK REGION, MONTANA
From 13-SEP-16 03:00:00 to 13-SEP-16 08:00:00 (MST-7)
Reported by: RAWS

Thompson Falls, MT temperature sensor reported low of 27 F.

Frost/Freeze in FLATHEAD/MISSION VALLEYS, MONTANA
From 13-SEP-16 02:00:00 to 13-SEP-16 08:00:00 (MST-7)
Reported by: ASOS

Kalispell International Airport temperature sensor reported a low of 27 F.

Frost/Freeze in MISSOULA / BITTERROOT VALLEYS, MONTANA
From 13-SEP-16 04:00:00 to 13-SEP-16 07:00:00 (MST-7)
Reported by: Broadcast Media

Media reported on local farms in the Missoula Area taking steps to harvest tomatoes, lettuce, and squash early. Temperatures only dropped to 30 F in Missoula proper, but farmers were impacted even by just below freezing temperatures.

Frost/Freeze in POTOMAC / SEELEY LAKE REGION, MONTANA
From 13-SEP-16 02:00:00 to 13-SEP-16 08:00:00 (MST-7)
Reported by: Trained Spotter

Spotters from the Potomac and Greenough, MT reported heavy frost with temperatures dropping to 20 F and possibly lower in the early morning hours.

Frost/Freeze in FLATHEAD/MISSION VALLEYS, MONTANA
From 13-SEP-16 01:30:00 to 13-SEP-16 08:00:00 (MST-7)
Reported by: ASOS

Kalispell International Airport saw a low of 27 degrees while a temperature sensor in Ronan recorded a low of 25 degrees Fahrenheit.

Frost/Freeze in POTOMAC / SEELEY LAKE REGION, MONTANA
From 13-SEP-16 02:00:00 to 13-SEP-16 08:00:00 (MST-7)
Reported by: RAWS

The RAWS sensor in Seeley Lake reported a low of 21 degrees F. Spotters from the Potomac and Greenough areas reported heavy frost with temperatures dropping to 20 degrees F and possibly lower in the early morning hours.

Frost/Freeze in KOOTENAI/CABINET REGION, MONTANA
From 13-SEP-16 03:00:00 to 13-SEP-16 08:00:00 (MST-7)
Reported by: AWOS

Low temperatures fell below freezing across northwest Montana including 25 deg. F at Eureka, 22 deg. F at Yaak and 29 deg. F in Libby.

Frost/Freeze in LOWER CLARK FORK REGION, MONTANA
From 13-SEP-16 03:00:00 to 13-SEP-16 08:00:00 (MST-7)
Reported by: RAWS

A temperature sensor in Trout Creek reported a low of 25 deg. F while in Thompson Falls, the temperatures fell to 27 deg. F.

Frost/Freeze in MISSOULA / BITTERROOT VALLEYS, MONTANA
From 13-SEP-16 03:00:00 to 13-SEP-16 07:00:00 (MST-7)
Reported by: Broadcast Media

The local media in Missoula reported that local farms took steps to harvest tomatoes, lettuce, and squash early because of the forecast sub-freezing temperatures. Temperatures dropped to 30 deg. F at the Missoula International Airport and to 28 deg. F in Stevensville.