Flooding in Alaska, August 8 to 10, 2018

Name: Flooding in Alaska, August 8 to 10, 2018
Start: 2018-08-08T12:00
End: 2018-08-10T04:00
Location: Alaska

August 8 to 10, 2018 · NWS AJK · 2 events in 2 counties and zones

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
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Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 2

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS AJK wrote it up.

A deep trough of low pressure with a long fetch from the North Pacific to the Gulf of Alaska produced a very strong and wet weather system. The atmospheric river slammed into northern southeast Alaska panhandle from August 7th and persisted through the 10th. The area received moderate to heavy rainfall with stations reporting two to four inches of precipitation at sea level with five inches at higher elevations. Along with the heavy rainfall there was very high freezing levels which ranged from eight to ten thousand feet. These high freezing level accompanied with the heavy rain increased the runoff from any snow left in the mountains and ice melt from area glaciers. All of the rain and snow/ice melt produce moderate flooding along the Taiya River and flooded the Chilkoot trail, part of the Klondike Gold Rush National Historical Park, near Dyea Alaska. The river crested around seventeen point thirty five feet which is above moderate flood stage of seventeen feet in the evening hours on July 23rd. The Mendenhall Lake also rose above moderate flood stage of ten feet and produced moderate flooding along the Mendenhall Lake area. The Mendenhall Lake gauge crested at ten point forty-two feet in the afternoon of August 10th.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Juneau, AK wrote its last area forecast discussion before the first event at Aug 8, 5:44 AM AKST, 6 hours 16 minutes earlier.

Area forecast discussion, Aug 8, 5:44 AM AKST, 6 hours 16 minutes before

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
644 AM AKDT Wed Aug 8 2018

.SYNOPSIS...An atmospheric river will continue to impact the
Panhandle through Thursday. A flood warning is in effect until 1
AM Thursday for the Taiya River, and a flood watch is in effect
from Wednesday afternoon through late Thursday night along the
Mendenhall River associated with prolonged heavy rainfall.

&&

.SHORT TERM...Heavy rain associated with a deep layer moisture
stream is currently impacting the northern Panhandle Wednesday
morning. The atmospheric river, which has already poured 7 inches
of rain over Yakutat in the past 48 hours, is slowly drifting
southeastward and will continue to gradually slide further south
through Thursday. Rainfall totals are expected to range between 4
to 6 inches from the Fairweather area to Sitka and further
inland, including Gustavus and Juneau. Lesser values of 1 to 2
inches are expected in the lower terrain areas near Skagway and
Haines, as well as across most of the southern Panhandle. The
300MB jet stream will continue to dig an upper trough over the
Gulf and swing through the Panhandle Friday morning pushing most
of the precipitation out of SE AK.

Along with the rain, winds will pick up ahead of the front,
especially within the inner channels. Small craft level winds
currently ongoing from southern Chatham Strait through northern
Lynn Canal are forecast to continue through Wednesday night.
Temperatures will hover in the upper 50s to low 60s with a small
diurnal range while the rain and overcast skies persist. Overall
model agreement continues to be good through the short term
period. Minor adjustments were made for local effects.

.LONG TERM.../ Friday to Wednesday / A trough aloft moving from
Southwest Alaska across the Gulf of Alaska will dig south
slightly and sort of latch on to the energy with the cutoff low
aloft over the Eastern Pacific on Wednesday and then the entire
trough moves inland on Friday although the southern end may be
moving slow as the there is a strong ridge anchored over the
Western US. The ridge right behind the trough looks like it may be
strong enough to stop much of the light rain that will be falling
into early Friday. A present have only brought cloud cover down
to roughly 50 percent so should see some sun/or stars depending on
the time of day.

Another weak short wave will be moving in the southwest flow to
the panhandle again for the end of the weekend. This will
increase clouds and the chance of rain for the panhandle.
Low/shortwaves aloft moving out of Eastern Russia and to the
western Bering Sea are being handled differently across the
various model solutions, and from run to run differences are
creeping in. This in leading to larger differences downstream for
the panhandle. There for have leaned toward the forecasts into
next week to be primarily based on the blends from the WPC
solutions.

Friday to Saturday, Day 3-4, more GFS/ECMWF solutions were used
as there was fair agreement on the patterns and and movement of
the systems.

&&

.HYDROLOGY...A flood warning is in effect until 1 AM Thursday for
the Taiya River, and a flood watch is in effect from Wednesday
afternoon through late Thursday night along the Mendenhall Lake
and River.

The Taiya River is at 16.8 feet as of 6 am Wednesday morning. It
is forecast to crest around 17.3 feet Wednesday afternoon. Minor
flood stage is 16.5 feet, with moderate flood stage at 17.0 feet.
If the Taiya River reaches 17.0 feet, the National Park Service
advises against boating and other recreational water based
activities along the river. Trail orientation and navigation
begins to become difficult and may hinder route finding for
several hundred meters. Water will be knee deep or higher in
places along the lower portion of the trail.

The Mendenhall Lake stage is 8.0 ft as of 6 am Wednesday morning.
It is forecast to crest around 9.4 feet late Wednesday night.
Minor flood stage is 9.0 feet, and moderate flood stage is 10.0
feet. At the forecasted peak stage for Mendenhall Lake, the yards
along View Drive will start to flood and cause minor flooding. If
the lake reaches 10 feet though, water will inundate Mendenhall
Campground with up to 3 feet of water covering the low areas, and
up to 1.5 feet of water covering Skaters Cabin Road. Portions of
the West Glacier Trail will be impassible.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Flood Watch from 1 PM AKDT this afternoon through late Thursday
     night for AKZ025.
     Strong Wind until 4 PM AKDT this afternoon for AKZ018.
MARINE...Small Craft Advisory for PKZ011>013-021-022-031>036-041>043.

&&

DDH/Bezenek

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The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

2 flood. Local standard time, as filed.

Flood, Taiya Inlet

When: August 8, 12:00 PM AKST to August 10, 4:00 AM AKST
Where: Taiya Inlet County, 4.52 mi NNW of Skagway to 4.87 mi N of Skagway
Cause: Heavy Rain / Snow Melt
Reported by: River/Stream Gage
Coordinates: 59.512, -135.343

After a very dry period for the northern inner channels of Southeast Alaska moderate to heavy rains moved over the area on August 7th. The high rain rates continued for the next forty-eight to seventy-two hours. Rainfall totals from this time frame ranged from two to three inches near sea level with four to five inches in the headwaters at higher elevations. The very warm temperatures created very high freezing levels that increase runoff from snow or ice melt. The Taiya River started to rise through the early morning hours of August 7th and went above minor flood stage of sixteen point five feet by the late afternoon. The river continued to rise at a stair step fashion through the night and into the morning hours of August 8th. By the early afternoon the water levels rose above moderate flood stage of seventeen feet and then leveled off some as the rain rate relax some through the early evening hours of August 8th. There was a big push of moisture that moved over the area in the early morning hours of August 9th and the river began to rise very steeply. The Taiya River crested in the late morning on August 9th at eighteen point twenty-one feet almost a foot and half over the moderate flood stage of seventeen feet. The rain slowly diminished through the overnight hours of August 10th and the river slowly receded to be below minor flood stage by the morning hours of August 10th. The National Park Service reported that there was significant flooding along the Chilkoot trail with waist deep water along the lower portions of the trail. The international trail was closed for a few days due to the flooding and potential dangers.

Flood, Juneau Borough

When: August 8, 11:00 PM AKST to August 9, 7:00 PM AKST
Where: Juneau Borough County, 13.29 mi NNW of Douglas to 12.14 mi NW of Douglas
Cause: Heavy Rain / Snow Melt
Reported by: River/Stream Gage
Coordinates: 58.434, -134.571

After a very dry period for the northern inner channels of Southeast Alaska moderate to heavy rains moved over the area on August 7th. The high rain rates continued for the next forty-eight to seventy-two hours. Rainfall totals from this time frame ranged from two to three inches near sea level with four to five inches at higher elevations. The very warm temperatures created very high freezing levels that increase runoff from snow or ice melt. There was also a release of water from the glacier dammed lake in Suicide Basin that added runoff into the Mendenhall River system, but less water than the first release earlier in the summer. The Mendenhall Lake started to rise slowly through August 7th, by the morning of August 8th the rate of rise on the lake and along the river increased as the heavy rain moved over the area. The Mendenhall Lake went above minor flood stage of nine feet in the afternoon and continued on the steady rise through the overnight hours and went over moderate flood stage of nine feet. The Mendenhall Lake crested at ten point forty-two feet by the afternoon on August 9th. As the heavy rain started to diminish the water levels began to recede and the lake and river went below minor flood stage in the early morning hours of August 10th. There was minor to moderate flooding around Mendenhall Lake and the upper portions of the river above Back Loop Road. The Mendenhall campground was evacuated due flooding of up to two feet at the entrance and within the campground, also the Skaters Cabin Road was flooded. View Drive was flooded with one foot of water and the road cut off. There was more flooding along the dredge lakes trail area and a few other trails around the Mendenhall Glacier Visitor Center run by the USDA Forest Service.

What these are

Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Alaska in 2018 Every state in 2018 This day in weather history Warnings in Alaska, August 2018

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 774319, 774320.