High Wind — Upr Tanana Vly Fortymile, Alaska

2012-09-16 to 2012-09-17 · Upr Tanana Vly Fortymile, Alaska

Wider weather episode

A 975 mb low near Unalakleet at 2100AKST on the evening of the 16th moved north to near Kivalina and weakened to 981 mb by 0300AKST on the morning of the 17th. A strong cold front moved from west to east across the interior and was associated with high winds. As the cold front moved east across the eastern Alaska Range around 2200AKST on the 16th, it is suspected that a mountain wave that had developed to the lee of the Alaska Range on the north side broke out of it's stable layer to descend to near ground level over eastern zone 223 and southwestern zone 224, primarily affecting the community of Tanacross in zone 224 and Dry Creek in zone 223, along with the stretch of the Alaska Highway between these two locations.

Zone 220: A peak wind gust of 56 kt (64 mph) was observed at the Eagle Summit SNOTEL at 2200AKST on the 16th.

Zone 223: A peak wind gust of 62 kt (71 mph) at the Delta Junction ASOS at 1353 AKST on the 16th. There were reports of power outages in the Delta Junction and Salcha areas. Some trees were downed in the Delta area; one damaged a vehicle. A lighted business sign was blown out as well. At Dry Creek, near mile 1378 of the Alaska Highway, a home weather station reported an unofficial peak gust of 99 kt (114 mph) around 2300AKST on the 16th. Damage to this community included several portions of shingles or roofing removed from the larger buildings, selected patio and shed damage, the total removal of shingles from one residence, and many downed trees, some up to 18 inches in diameter. The trees fallen or toppled were in roughly the same northeast direction. Damage amounts are unknown but are roughly estimated at $15,000, to include the sign and vehicle damage at Delta Junction, and the various roof, patio and shed damage at Dry Creek.

Zone 224: Damage from the windstorm associated with the breaking mountain wave resumed along the Alaska Highway starting at mile 1347 of the Alaska Highway near the Robertson River, as a number of trees were downed, and this continued along the highway to mile 1323...about 2 miles southeast of Tanacross. Near the Robertson River, several residences suffered partial roof damage as well as damage to outbuildings. At the village of Tanacross, the windstorm came about 2300AKST on the 16th, and lasted for 3 to 5 hours. No wind reporting station exists in this area, but the damage is similar to that observed at Dry Creek, only most of the residences were older and there were fewer large buildings. A preliminary State of Alaska damage assessment noted about 50 of the 53 residences had some damage, usually a portion of roof covering missing, as well as 25 of these homes had no power due to damage to their electrical service. Two dogs were killed, one directly by a fallen tree, another one indirectly when a tree fell and caused the leash a dog was attached to, to move upward, suspending the dog in the air at the collar. The Tanacross School suffered partial removal of it's sheet metal roof. An empty fuel drum large enough to hold 10,000 gallons of fuel and estimated to weigh roughly one ton, was blown across the Tanacross airstrip approximately one-quarter mile. Damages are estimated at roughly $50,000 which includes the homes, electrical services, and the school's roofing. Also of note is all the standing trees were bent over by 20 to 40 degrees from vertical...this particular area typically has high winds of 50 mph or less...so they are not wind-hardened as at Delta Junction. The long-time residents (60 to 75 years) of Tanacross said it was the strongest wind event they remembered. As at Dry Creek, the fallen or snapped trees were mainly laying in the same direction, to the northeast.

Zone 225: There were four reports of rocks falling on vehicles on the Denali Park Road. The wind gusted as high as 55 kt (63 mph) at the Eielson Visitors Center Remote Automated Weather System (RAWS). It is likely that the wind gusted over 61 kt (70 mph) at Windy Pass, but the DOT Road Weather Information System (RWIS) at Antler Creek was inoperable during the event.

There were also reports of power outages in Nenana, Fairbanks, and North Pole, but there were no reports of damage or winds that reached warning criteria.

Source: NOAA Storm Events Database, event_id 414451. Narrative written by the NWS forecast office that issued the report.