Flood in Alaska, September 29 to 30, 2015

Name: Flood in Alaska, September 29 to 30, 2015
Start: 2015-09-29T18:00
End: 2015-09-30T11:00
Location: Alaska

September 29 to 30, 2015 · 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

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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.

A series of weather fronts moved over the Southeast Alaska starting late on September 27th with the last one moving over the area early on the 30th. A strong upper trough of low pressure moved out of the Northern Bering and dug into the Northwestern Gulf of Alaska on the 27th and 28th. This tipped over the upper level ridge over the Gulf of Alaska and increased the onshore flow. The trough continue to deepen through the 29th and 30th before lifting into Canada. As the trough strengthened and dug into the North Pacific it tapped into some sub-tropical moisture and lifted it into the Gulf of Alaska. There was very high precipitable water values that fed the lifting warm fronts over the northern inner channels of Southeast Alaska. The first warm front moved over the area in the afternoon of September 27th morning hours and stalled there through the evening of the 28th. Another wave along the cold front developed and very strong surface low pressure system over the Northern Gulf of Alaska pushed another warm front over the area in the early mornings of the 29th. The very strong associated cold front pushed over the area and into Canada by the early morning of the 30th. There was significant amount of rain in the headwaters of the Taiya River basin about four to five inches in thirty-six hours and produced moderate flooding conditions along the Chilkoot Trail in Klondike National Park.

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 Sep 29, 3:05 PM AKST, 2 hours 55 minutes earlier.

Area forecast discussion, Sep 29, 3:05 PM AKST, 2 hours 55 minutes before

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
405 PM AKDT TUE SEP 29 2015

.SHORT TERM...THE RATHER ACTIVE WEATHER PATTERN WILL BEGIN TO EXIT
THE REGION OVER THE NEXT 24 HOURS. 984 MB LOW IN THE NORTHWEST
GULF WILL CONTINUE TO TRACK EASTWARD THROUGH THURSDAY WHILE
WEAKENING. THERE WERE TWO MAIN FRONTAL WAVES ASSOCIATED WITH THE
LOW MOVING EASTWARD. THE FIRST CROSSED OVER THE PANHANDLE TODAY
PRODUCING HEAVY RAIN AND STRONG WINDS. THE SECOND WAVE WILL MOVE
OVER THE REGION EARLY THIS EVENING BRINGING THE NEXT ROUND OF
STRONG WINDS AND HEAVY RAIN AFTER A BRIEF LULL THIS AFTERNOON. THE
SECOND WAVE WILL CROSS MOVE TO THE SOUTH PRODUCING SOME OF THE
HIGH RAINFALL AMOUNTS SEEN OVER THE NORTH TO THE SOUTH, WITH
DIMINISHING RAIN RATES BEHIND. RAIN FALL AMOUNTS FROM THE SYSTEM
RANGED FROM 2 TO NEARLY 6 INCHES SO FAR, WITH ANOTHER 1 TO 2
INCHES EXPECTED THIS EVENING. SOME QUESTION ON THE TIMING OF THIS
WAVE MOVING OUT OF THE SOUTH SOONER THAN LATER. LAST WRAP AROUND
THE LOW WILL MOVE OVER THE NORTHERN AND CENTRAL PANHANDLE THROUGH
WEDNESDAY. UNSTABLE ATMOSPHERE WITH COLD AIR ALOFT BEHIND THE
FRONT WILL TRANSITION RAIN TO SHOWERS OVERNIGHT WITH THIS LAST
WRAP. ENOUGH INSTABILITY WITH CAPE VALUES AROUND 400 J/KG AND LI
NEAR -1 C TO PUT IN MENTION OF THUNDERSTORMS MOVING ACROSS THE
GULF AND REACHING THE NORTHEAST COAST BY TOMORROW AFTERNOON.

GALE FORCE WINDS AROUND THE LOW OVER THE AK GULF WILL DIMINISH
TONIGHT AS THE LOW WEAKENS. OVER THE INNER CHANNELS WINDS DROPPED
SLIGHTLY THIS AFTERNOON BETWEEN THE TWO WAVES BUT WILL PICK BACK
UP AGAIN THIS EVENING. SOUTHERLY GRADIENT BETWEEN PAGY AND PAJN
REACHED -7.4 RESULTING IN STORM FORCE WIND GUSTS FOR N LYNN
CANAL. GALE FORCE WINDS OVER MOST OF THE CENTRAL AND NORTHERN
INNER CHANNELS THROUGH THE DAY WITH HIGHER GUSTS. CAPE SPENCER
GUSTS REACHED UP TO 60 KTS AT ONE POINT. PAGY REACHED ITS HIGH
WIND WARNING CRITERIA WITH 60 MPH GUSTS THIS AFTERNOON. THE
GRADIENT WILL DECREASE AS THE SYSTEM MOVE EAST WITH WINDS
DIMINISHING THROUGH WEDNESDAY. IN ADDITION TO THE TIGHT SURFACE
GRADIENT LLJ MOVING OVER THE PANHANDLE ENHANCED THE STRONGER
WINDS. THE SOUTHERN PANHANDLE WINDS WILL MUCH WEAKER COMPARED TO
THE NORTH TODAY BUT WITH A 700 MB 50 KT JET MOVING OVER EXPECT
WINDS IN ZONE 27 AND 28 ALONG WITH WINDS IN CLARENCE STRAIT TO
PICK UP.

NEW MODELS HAD A HANDLE ON THE CURRENT SYSTEM AND STILL MATCHED UP
OVERALL FROM PRESS AND WINDS. DID BUMP UP WINDS SPEEDS SLIGHTLY
THIS EVENING. WHILE MOST MODELS KEPT RAIN OVER THE SOUTHERN
PANHANDLE THROUGH THE DAY WED POSSIBLE THEY ARE TOO HIGH WITH THE
SPEED OF THE SYSTEM. FORECAST CONFIDENCE IS AVERAGE

.LONG TERM...WEAKENING LOW WILL MOVE ACROSS THE NE GULF WED NIGHT
THEN TURN SE ALONG THE OUTER COAST THU BUT WILL LIKELY DISSIPATE
BY LATE THU AFTERNOON. HIGH PRESSURE WILL BUILD OVER THE YUKON WED
NIGHT INTO THU...THEN WEAKEN AND SHIFT E FRI INTO THE WEEKEND.
UPPER RIDGE WILL BUILD OVER THE ERN GULF FOR LATE WEEK...BUT WILL
LIKELY FLATTEN ESPECIALLY BY SUN. MODELS DIFFER ON THIS HOWEVER.
ENDED UP USING THE 12Z NAM FOR THE WED NIGHT THRU FRI
PERIODS...WITH MOSTLY LATEST WPC FOR FRI NIGHT ONWARD.

SHOWERS WILL CONTINUE OVER THE NW HALF OF THE AREA WED
NIGHT...WITH SOME SHOWERS SPREADING SE INTO THE SRN AREA LATE WED
NIGHT AND THU MORNING. THE SHOWERS WILL DIMINISH THU AS SFC LOW
DISSIPATES AND LOWER LEVEL NLY FLOW INCREASES. THU NIGHT AND FRI
LOOK TO BE DRY UNDER PARTLY CLOUDY OR BETTER CONDITIONS FOR MOST
OF THE AREA. ALSO WILL HAVE SOME COLDER AIR MOVE IN FROM THE N THU
NIGHT. SOME AREAS COULD SEE TEMPS DROP BELOW FREEZING THU
NIGHT...MAINLY IN WIND SHELTERED AREAS OVER THE N. 25-35 KT NLY
WINDS ARE LIKELY ESPECIALLY OVER THE NRN HALF OF THE AREA THU
NIGHT AND FRI MORNING.

FOR THE WEEKEND...A WEAKENING SHORTWAVE WILL MOVE THRU THE RIDGE
BUT MODELS DIFFER ON HOW MUCH OF THE SYSTEM WILL SURVIVE INTO SE
AK. ATTM...DID BRING IN LOW POPS TO MAINLY THE FAR NW PART OF THE
AREA FOR FRI NIGHT AND SAT. WPC KEEPS POPS GENERALLY LOW THRU THE
WEEKEND INTO EARLY NEXT WEEK...BUT LATER SHIFTS WILL NEED TO
MONITOR THIS AS SOME MODELS SUGGEST MORE SHORTWAVE ENERGY WILL GET
THRU THE RIDGE INTO SE AK SUN INTO EARLY NEXT WEEK.

&&

.AVIATION...WIND PROGS OF 35-50 KNOTS AT 2000 FEET MSL HAVE
PROMPTED WIND SHEAR ALERTS IN MOST OF THE TAFS THROUGH 18 TO 24
HOURS.

&&

.HYDROLOGY...FOR YAKUTAT SOUTHWESTERLY STORM SURGE, ALONG WITH
VERY HIGH TIDE AND HEAVY RAIN FALL WARRANTED A COASTAL FLOOD
WARNING. REPORTS OF WASHED OUT ROADS WERE ALREADY REPORTED FOR THE
AREA. PUT IN A BROAD FLOOD ADVISORY FOR MOST OF THE CENTRAL AND
NORTHERN PANHANDLE DUE TO THE HEAVY RAINFALL. MOST RIVERS AND
STREAMS SAW RAPID RISES TODAY, THEN LEVELED OUT DURING THE
RAINFALL LULL BETWEEN FRONTAL BANDS, BUT ARE EXPECTED TO RISE
AGAIN WITH THE NEXT ROUND. RIVERS OF NOTE ARE THE SITUK NEAR
YAKUTAT WHICH HIT BANKFULL OF 70 FT TO DAY, RISING 3 FEET, AND
EXPECTED TO HIT ABOVE MINOR FLOOD STAGE TO 72 FEET TONIGHT. IN
JUNEAU JORDAN CREEK HAD A QUICK RISE BUT LOTS OF FLUCTUATION
AROUND BANKFULL AT 9 FT, EXPECTED TO RISE ABOVE MINOR FLOOD STAGE
TO 9.9 FEET. WHILE THE MENDENHALL IS NOT EXPECTED TO REACH
BANKFULL TONIGHT IT HAS BEEN SHOWING A 24 HOUR DELAY, SO
POTENTIAL RISES CONTINUING INTO WEDNESDAY WHILE OTHER RIVERS HAVE
ALREADY DROPPED. THE TAIYA RIVER NEAR SKAGWAY HAS BEEN TRICKIEST
SINCE MODEL QPF OVER THE RIVER BASIN HAS SHOWN LARGE VARIATIONS.
THE RIVER, AS MOST OTHERS, HAS SHOWN A RAPID RISE JUST NEARING
BANKFULL. CURRENT NUMBER PUT THE RIVER ALMOST AT MODERATE FLOOD
STAGE OF 17 FEET, BUT AS THESE FRONTAL WAVES ARE PREDICTED TO
START MOVING SOUTH MAY NOT BE ENOUGH RAINFALL TO REACH THAT HIGH.

THE HEAVY RAIN, SATURATED GROUND, AND STRONG WINDS ALSO HAVE MADE
POTENTIAL FOR MUD SLIDES. SMALL MUD SLIDES ALREADY REPORTED NEAR
THE THANE CAMPGROUND IN JUNEAU.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 7 PM THIS EVENING TO 1 AM AKDT WEDNESDAY FOR
     AKZ027.
         AREAL FLOOD ADVISORY UNTIL 9 AM AKDT WEDNESDAY FOR AKZ017>025.
         STRONG WIND UNTIL 10 PM AKDT THIS EVENING FOR AKZ025.
         STRONG WIND UNTIL 7 PM AKDT THIS EVENING FOR AKZ017-022-023.
         STRONG WIND UNTIL 1 AM AKDT WEDNESDAY FOR AKZ019.
         HIGH WIND WARNING UNTIL 1 AM AKDT WEDNESDAY FOR AKZ018.
         STRONG WIND FROM 7 PM AKDT THIS EVENING THROUGH WEDNESDAY
     MORNING FOR AKZ018.
MARINE...STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-031-034-036-042-043-051>053.
         SMALL CRAFT ADVISORY FOR PKZ032-033-035-041.

&&

PRB/RWT

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, Taiya Inlet

When: September 29, 6:00 PM AKST to September 30, 11:00 AM AKST
Where: Taiya Inlet County, 4.16 mi NNW of Skagway to 3.85 mi N of Skagway
Cause: Heavy Rain
Reported by: River/Stream Gage
Coordinates: 59.501, -135.362

There was constant rain in the headwaters of the Taiya River basin from September 27-30. The water levels began to rise on the 28th from the first stalled warm front and continue on a stead climb through the 29th from about three to four inches in 48 hours. The more significant cold front with a lot more upper level energy and orographic lifting produced about one to one and a half inch of rain in 12 hours. That amount of rain in the headwaters with already saturated soils produced large and fast rises on the Taiya River. The runoff pushed the water level over minor flood stage in the early evening hours then over moderate flood stage overnight into early morning of September 30. Once the rain rates associated with the cold front diminished the river levels receded back below flood stage by mid morning on the 30th. The Chilkoot trail was flooded with significant amount of water over the trail with thigh deep in places along the lower portions of the trail near the river.

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 2015 Every state in 2015 This day in weather history Warnings in Alaska, September 2015

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: 602739.