Flood in Alaska, July 19, 2018

Name: Flood in Alaska, July 19, 2018
Start: 2018-07-19T08:00
End: 2018-07-19T22:00
Location: Alaska

July 19, 2018 · NWS AJK · 1 event in 1 county or zone

Where it happened

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

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 1

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.

Throughout spring and the first part of the summer Suicide Basin, a side valley that is dammed by the Mendenhall Glacier, filled with water from snow melt and rainfall. In the afternoon hours of July 17th visual reports showed signs of the basin beginning to drain as the glacier dam was starting to fail. The river gauge in the Mendenhall Lake started to show this inflow of water from the basin through the evening hours and by the morning of the 18th the event was well on its way. For the next 2 days the Mendenhall Lake and River rose five in a half feet and crested at 10.92ft in the afternoon of the 19th.

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 Jul 19, 4:10 AM AKST, 3 hours 50 minutes earlier.

Area forecast discussion, Jul 19, 4:10 AM AKST, 3 hours 50 minutes before

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
510 AM AKDT Thu Jul 19 2018

.SHORT TERM...Satellite imagery and surface analysis indicate
upper low moving E across Haida Gwaii early this morning with
ridge building over the gulf. Some clearing overnight
combined with saturated BL from recent rains has resulted in some
patchy fog development early this morning. Heaviest fog has been
in PAPG and PAWG with visibilities below 1SM. Expect fog to
dissipate by mid morning. Energy wrapping around the upper low
will maintain shower activity across the panhandle today.
Increased instability near the low along with some energy wrapping
around will increase chances of TSTM development over BC that
could migrate WWd into Misty Fjords area so added mention of SChc
TSTM this afternoon/evening. Otherwise, showers will diminish from
N-S today as the ridge influence increases across the region. As
the ridge begins to take hold NWly winds will increase. Nudged
temps towards NBM resulting in temps into the mid 60s today and
into the low to mid 70s Fri except along the outer coast. Stratus
evident over the gulf will advect E-SE into the weekend and will
likely limit warming potential along the gulf coast.

.LONG TERM.../Thursday through next Tuesday/ The main change
to the forecast resulted from a more eastward positioned ridge
axis over the eastern gulf instead of the central gulf. Perhaps
the ridge breaks into the Panhandle sometime early to mid next
week, but solutions differ, and all we can rely on is ensemble
clustering at this point. New model runs continue to suggest
frontal action becomes more organized to our west but confidence
is not high enough to go with any more than a slight chance of
rain by mid-week.

As a result of this, we continued the trend of raising
temperatures early next week, and now extend 70 degrees to the
Panhandle interior through at least Monday. We even warmed
temperatures a degree or two through the already advertised toasty
weekend.

Winds needed little change except to introduce southeasterlies
over the gulf on the west side of the ridge axis. We would not be
shocked at some point to see small craft westerlies develop at
ocean entrances should the interior heat and chilly gulf stratus
provide solid pressure gradient support. But otherwise, we expect
winds to be mainly on the lighter side.

We used an ensemble of mainline models for the gulf winds Saturday
and relied on increasing influence of WPC thereafter. No changes
to the weekend's dry forecast and our conservative approach keeps
most of the Panhandle PoP free through most of Tuesday. Forecast
confidence is good through the weekend, and diminishes early to
mid next week.

&&

.HYDROLOGY...As of 4 AM Thursday...Suicide Basin continues to
release water into Mendenhall Lake. Webcam imagery indicates
Suicide Basin continues to drain and at 3 AM Mendenhall Lake was
at 8.39 feet and rising. Flood stage at the lake is 9.0 feet.
There is the potential for flooding to begin by late Thursday
morning, and it is expected to reach a near record peak stage of
around 12 feet Thursday night into early Friday morning. Water
levels should fall rapidly after it crests. However, there is
uncertainty in the initial glacial lake volume, which may result
in varying crest height and timing.

Once the lake stage reaches 9.1 feet, water will cover West
Glacier Spur Road between Skater's Cabin and the West Glacier
Trailhead. Also, water will flow into the Mendenhall Lake
campground. Once the lake stage reaches 10.9 feet, View Drive will
be flooded and impassible with significant flooding to some homes
in the area.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Flood Watch from this afternoon through Friday afternoon for
     AKZ025.
MARINE...Small Craft Advisory for PKZ041.

&&

BC/JWA

Visit us at http://www.weather.gov/Juneau

The radar

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

Open the radar archive at this moment

Event by event

1 flood. Local standard time, as filed.

Flood, Juneau Borough

When: July 19, 8:00 AM AKST to 10:00 PM AKST
Where: Juneau Borough County, 13.39 mi NNW of Douglas to 12.01 mi NW of Douglas
Cause: Heavy Rain / Snow Melt
Reported by: River/Stream Gage
Coordinates: 58.433, -134.580

In the early morning hours of July 18th the Mendenhall Lake and River began to slowly rise as the glacier dammed lake in Suicide Basin about 2 miles from the terminus started to drain. Mendenhall Lake and River continue to rise for the next day and a half as the dammed lake emptied. The water levels reach minor flood stage of nine feet by the morning of July 19th and by the mid-afternoon around 5pm Mendenhall Lake crested at ten point ninety two feet. After the lake and river crested the water level receded very quickly and was below minor flood stage just before midnight on the 19th. 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 three feet at the entrance and within the campground with some damage done to the road system. The West Glacier spur road and the area around Skaters Cabin was flooded with three feet water. View Drive was flooded with two feet of water and the road cut off. There was minor flood damage to some homes that border the river along the road. There was also more flooding along the dredge lakes trail area and and 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, July 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: 774303.