Flood of 1948

On this date 77 years ago, Fairbanks was experiencing the worst flood in the short history of the city up to that time.  It would go on to be exceeded by the August 1967 flood, but May 1948 remains the second worst flood, and the worst springtime flooding event.

The event was not a breakup flood, although breakup was very late that year, occurring on May 10 on the Chena River in Fairbanks, and May 13 on the Tanana River at Nenana.  Rather, the flooding arose about a week later from tremendous snowmelt runoff in the hills.

The stage was set a month or more earlier, as very heavy precipitation occurred from late March into April.  Valley-level temperatures were marginal for snow during the sustained precipitation of April 7-14, but it would have been cold enough in the hills for snow to continue accumulating.  Here's the data from the Fairbanks climate record:

Notice the cold that developed in mid-April, preserving the snowpack at a time of year when it would normally be starting to diminish, depending on elevation.  Overnight temperatures were still falling below 20°F in early May - hence the late breakup - but then spring finally emerged on May 9, and there was no looking back.

It's difficult to say how much snow may have actually been on the hills above Fairbanks by the time the big thaw arrived.  The preceding winter was quite warm until February, and not particularly wet, so it seems unlikely there was a big snowpack going into March; but the 3" of new precipitation in Fairbanks in late March and April would have added at least 4-5" of liquid to the elevated snowpack, perhaps much more.  There have been other years since with snowpacks that were greater, but back in 1948 the combination of sudden melt and a lack of modern flood defenses produced a very unfortunate outcome.

Here's a silent clip from the Alaska Film Archives documenting the event.

https://www.youtube.com/watch?v=S-u7m0uL7Kc

Flood Follow-Up

A few different items of comment today.  First, a significant snowfall is under way across the south-central region today, signaling the start of winter proper for many valley locations in that area.  If Anchorage's snow cover hangs around in the coming weeks, it will mark an earlier than normal onset of permanent snow pack; the normal date is about November 9th.  Of course Anchorage occasionally lacks snow cover even in the depths of winter, but it's unusual, occurring most recently in 2015-16 and for a few days in late December 2019.

As for Fairbanks, the normal date for establishing permanent snow cover is October 18, and it was right on time this year.  However, the most recently reported snow depth of 10" is the highest for the date since 1992, and more fell today.  (But 11" was on the ground in September 2015.)

Looking back at last week's historic west coast storm, it's worth highlighting blog comments by Rick and Gary.  Rick Thoman confirmed that long-time Kotzebue residents reported the highest water in living memory, which is why it was such a devastating event for some in the community:

https://www.adn.com/alaska-news/rural-alaska/2024/10/26/after-flood-kotzebue-residents-take-stock-of-damaged-homes-and-property-and-take-care-of-one-another/

Although the meteorology was different, we might say this was Kotzebue's version of ex-Typhoon Merbok, which caused such havoc for coastal locations farther south about two years ago:

https://ak-wx.blogspot.com/2022/09/more-on-ex-merbok.html

The article highlighted by Gary indicates that flooding was not quite as bad this time around from Nome down to Unalakleet:

http://www.nomenugget.net/news/high-winds-cause-erosion-and-flooding-region

Rick also commented that storms in November 1973 and 1974 may be the most analogous events in the modern climate record.  Certainly the storm of November 10-11, 1973, shows a rather similar sequence of events: low pressure over the Chukchi Sea created strong winds out of the south early on the 10th, and then the winds went around to the west and blew fiercely with a strong north-south pressure gradient, pushing water into Kotzebue Sound.  Here are MSLP maps:

Compare to the recent event:

Interestingly, the wind speed itself was not particularly unusual with last week's storm, and there have been many past events with equally strong, or stronger, winds from a westerly direction in Kotzebue.  I think therefore it was the very low pressure, the large size of the storm, and the long duration of southerly fetch that allowed such a large surge to develop before the winds turned westerly and pushed the water onto the coast.

Kotzebue Flood

In yesterday's post I remarked that I hadn't yet seen specific reports of storm impacts for the west coast, but it turned out that the worst was yet to occur in the northwest, and specifically in Kotzebue:

https://www.adn.com/alaska-news/rural-alaska/2024/10/23/after-severe-flood-displaces-80-people-kotzebue-begins-recovery/

Stormy weather began way back on Saturday in Kotzebue, and the highest winds (gusts to 55 mph) occurred on Monday morning, but it wasn't until yesterday that flooding became severe as the winds went around to the west.

I think what happened here is that a prolonged and very strong southwesterly flow built up a considerable surge of water in the southern Chukchi Sea while the storm's center was at its most intense over Russia's northeastern coast on Monday.  When the circulation finally pushed east towards the North Slope on Tuesday, and the winds went around to the west in Kotzebue Sound, that elevated water rushed into the Sound and inundated the city rapidly.  The "shockingly fast" rise of the water sounds very much like a classic storm surge event that is more commonly seen in landfalling tropical cyclones.

Below is a sequence of model analysis maps showing the pressure and winds at 6 hour intervals from 10am on Monday through 10pm last night.  Judging from the severe impacts, it seems this was essentially a worse-case scenario for Kotzebue flooding.

Southeast Deluge

I don't usually comment on weather in Southeast Alaska, but the past few days brought an extremely intense rain storm that broke longstanding records in the northern part of the region.  All-time records for calendar-day precipitation fell at Juneau, Skagway, and Haines, and unfortunately damage from flooding and a major landslide occurred in Haines.  Here's a summary from NWS Juneau as of 11am yesterday, and more rain fell after that.

The two animations below show precipitable water (the total vertical atmospheric water content) during two 24-hour periods, illustrating the tropical moisture source and the remarkable persistence of the "atmospheric river" directed into the Southeast.

Nice firehose of moisture arriving along the Alaska Panhandle, as revealed by the MIMIC Total Precipitable Water product: https://t.co/gcVpyzhiIs #AKwx pic.twitter.com/Qk23AvBY66

— Scott Bachmeier (@CIMSS_Satellite) December 1, 2020

48 hour rainfall totals from 5-14", wind gusts of 65 mph, 30+ inches of snow, debris flows, flooding, you name it we saw it. The image shows deep moisture surging into the SEAK from the tropics. #AtmosphericRiver #akwx .@KTOOpubmedia .@KHNS_FM .@cbjuneau .@UWCIMSS pic.twitter.com/JkudNcIhar

— NWS Juneau (@NWSJuneau) December 2, 2020

 

Here's another really nice animation:

Meanwhile over the Pacific... upstream of the high-amplitude pattern over North America... an atmospheric river which resulted in the #Haines landslide in #akwx, and now lots of swirls pic.twitter.com/f2I3ZTrzEl

— Stu Ostro (@StuOstro) December 4, 2020

 

If we look at past episodes of extreme rainfall in Juneau in early winter (October through December), it's interesting to note that 5 of the top 6 (since 1950) highest 2-day precipitation totals occurred during La Niña conditions, and 3 of these were rather strong La Niña episodes similar to the one we're currently experiencing.  Those 3 events were Oct 19-20, 1998, Nov 29-30, 1988, and Dec 27-28, 1999.

This is an interesting point because La Niña more often brings drier, not wetter, conditions to Southeast Alaska for the second half of the rainy season as a whole (i.e. early winter).  Since 1950, 10 of the 15 strongest La Niña's in October-December were drier than normal overall in Juneau, and the map below shows the spatial pattern of early winter precipitation for strong La Niña years.  More investigation would be needed to be sure, but this may be an example of weather extremes having a different sensitivity to climate forcing than seasonal weather averages.

I mentioned last month that Fairbanks also has an enhanced frequency of heavy precipitation events during La Niña winters.  The chart below illustrates this for 2-day snowfall totals of 6-9" (blue) and over 9" (purple).

 

The same relationship (warmer ENSO -> lower chance of heavy snow) is evident in both early winter and late winter.

Update: NWS Juneau provided a list of sites that recorded all-time record daily rainfall amounts.

Spring Floods

Summer-like warmth has suddenly arrived in interior Alaska, and with plenty of snow still in place across the higher hills, creeks and rivers are in flood.  Fairbanks recorded 82°F on Sunday and 80°F yesterday; this is only the second time in the modern climate record (1930-present) that more than one day has reached 80°F before May 20.  The other time was the ridiculous early heat wave of 1995 (88°F on May 11).

Looking at the SNOTEL snowpack data up on Munson Ridge (east of Fairbanks at 3100' elevation), there's a long way to go to eliminate the very substantial snowpack: more than 12" of liquid equivalent water remains at this time.  The massive snowpack accumulation in late winter really was remarkable: as the chart below demonstrates, the snowpack went from being only modestly above normal in mid-March to nearly twice the normal amount just one month later.  It didn't reach the excess of 2018, which I reported on here, but it's an impressive snowpack nonetheless (click to enlarge).

I've commented before on the fact that above-normal snowpack has become the norm in recent years - where "normal" is defined as the 1981-2010 median.  The winter before last (2018-19) turned out to be the first below-normal snowpack in the Chena Basin since 2009-10, although it was barely below normal on April 1.

So with this winter now in the books, it's been 10 consecutive winters without a seriously deficient snowpack in this part of Alaska.  But of course the same is not true elsewhere; the Kenai peninsula had a dry winter this year, and my impression (although I haven't examined the data) is that the low-snow theme has been as dominant there as the excess snow near Fairbanks.  Here's the April 1 snowpack map from NRCS:

And here are the SNOTEL sites that contributed to the above basin-wide analysis:

The Fairbanks Flood of 1967: The Rainfall

Hi, Rick T. here. You don't have to live in Fairbanks very long to hear about the great flood of August 1967. Even for a community long accustomed to significant flooding, this was extreme. Something like 95% of the city was flooded, causing millions of dollars in damage. Rasmussen Library at UAF has posted a number of videos from the flood on Alaska Film Archives YouTube channel. The NWS Fairbanks Forecast Office and the Alaska-Pacific River Forecaster Center have also put together a very nice online storybook with a short description of the meteorology and hydrology and lots of photos. There has also been work by the NWS, the City of Fairbanks and FNSB Borough to survey and put up high water mark signs around town, and many of these have been installed in the past couple weeks, such as this one downtown on the north bank of the Chena River.

In this post, I want to look at the rainfall that lead to this flooding from a climate perspective. The rainfall August 11-13, 1967 stands out as the highest of record for daily and multi-day totals. The only rainfall records this event does not hold are short duration records, which are all thunderstorm related. To set the stage, here is the background: the second half of July 1967 saw well above normal rainfall: 3.07" fell between July 16 and 31. That's still the fifth highest "second half of July" total. However, that was followed by a dry start to August: only 0.02" of rain fell during the first week of the month. But then the skies opened. Below is a plot of the hourly and cumulative rainfall for the week of August 8-15, 1967 (data extracted from Fairbanks August 1967 Local Climatological Data). More than half an inch of rain fell on the 9th. This was followed by about 36 hours with very little rain. Starting late in the afternoon on the 11th, moderate rain fell without much of a break until the morning of the 13th, though light rain continued to dribble on into the 15th before the fire hose finally shut down.

The following totals were recorded at the Airport, all of which still stand as the highest of record:

• 24 hour: 3.44" 11pm AKST August 11 to 11pm AKST August 12
• 36 hour: 4.40" 4pm AKST August 11 to 4am AKST August 13 
• 48 hour: 4.76" 3pm AKST August 11 to 3pm AKST August 13
• Single calendar day: 3.42" August 12  
• Two consecutive calendar days: 4.29" August 11-12
• Three consecutive  calendar days: 4.98" August 11-13

So beyond "highest of record", what's the climatological context? Was this a one-in-a-million event, or is there some reasonable likelihood it will be broken?  To answer this I've compiled annual extremes of a few of these parameters and then fitted a generalized extreme value (GEV) distribution. If that's greek, no worries: GEV is a standard technique for analyzing extreme event frequency and generating estimates of return periods.

Maximum 24-hour precipitation (not necessarily calendar day) has been recorded in Fairbanks since the Weather Bureau office opened in the summer of 1929. For two and three day totals, I've included the cooperative data from the Ag Experiment Station starting with 1915, when daily precipitation began to be regularly recorded. In the graphic below I show an example of the annual times series, in this case the maximum 24 hour precipitation (upper left) and then the GEV analysis for the annual  maximum 24 hour precip (upper right) and annual maximum two and three day consecutive days (bottom row). The red line shows the fitted return period, while the open circles are the observations (which are plotted in rank order).  I should point out that there is no significant trend in any of the annual values.

So what are the return periods for the precipitation amounts that occurred in August 1967?

With  87 years of data:

• 3.44" in 24 hours is expected to occur on average once in 203 years

With 102 years of data:

• 4.29" in two consecutive days is expected to occur on average once in 269 years
• 4.98"  in three consecutive days is expected to occur on average once in 352 years

I'm actually not a fan of return periods. It's not technically wrong, but many people would look at those numbers and say "gee, I'll never see that." In fact, the return periods are just an alternate way of expressing the probability of occurrence. So if I tell you that there is 13% chance that Fairbanks Airport will receive precipitation totaling 3.44" or more in 24 hours hours once in the next 30 years, that's equivalent to saying the return period is 203 years, but the take-home message is different. Now 13% in 30 years is not high (and that makes the dubious assumption that there is no change in extreme precipitation events in a warming world), but it is hardly unthinkably rare.

Postscript:
The GEV analysis I've presented here differs somewhat from that published in the 2012 NOAA Atlas 14 primarily in that I used a longer period of record (for extremes analysis, the longer the better), and, as near as I can tell, the maximum 24 hour precipitation (as distinct from calendar day) was not used in compiling that work.

The maximum 24 hour precipitation for August 1967 is listed as 3.42" in the August 1967 Local Climatlogical Data publication and has been carried through ever since. In fact the hourly precipitation data in the same publication shows that the correct amount is 3.44", 11pm on the 11th to 11pm on the 12th.

Flooding in Barrow

A strong low pressure system north of Barrow is bringing strong westerly winds to Alaska's Arctic coastline and causing coastal flooding in Barrow.  Here's a webcam image from a few minutes ago (live link here):

The map below shows this morning's surface analysis, courtesy of Environment Canada.  The central pressure of the storm is 984 mb, which is quite strong but certainly not record-breaking for this location and time of year.  The August record for low pressure in the area 65-90°N, 140-180°W is 971 mb, according to the 1948-present global reanalysis; this was observed in 1975.

More Rain for Fairbanks

After completing the wettest summer on record, Fairbanks is getting started on some new records. A staggering 2.24" of rain has fallen since noon on Monday (September 1st). This already puts Fairbanks into the Top 10 for wettest September's on record and makes for the wettest 24 hours ever in the month of September.

There have now been 4 days with at least 1" of rain from midnight to midnight this year. No other year has seen more than 3 days with 1"+ of precipitation on a calendar day. Since 1915, a total of 48 days have exceeded 1" of precipitation.

If we drop the threshold down to 0.75", there have been 9 days in 2014. The next highest year is 1962 with 6 days at or above 0.75".

If you take the ten wettest days of 2014, it adds up (10.59") to just a shade under the normal annual precipitation total. No other year has seen as much as 9" when the 10 wettest days are added together.

Figure 1. Precipitation from Mesowest of the 24-hour period ending at 9:45 a.m. on September 2nd.

Nenana River Flooding

Hydrograph courtesy of the Alaska-Pacific RFC

The Nenana River at Healy reached the highest stage of record Saturday, causing problems in the Denali National Park east end area.The hydrograph on the left shows a peak stage of 14.9 feet, well above the previous record of 14.4 feet set September 15, 1990. The Fairbanks Daily News-Miner is reporting threats to the Parks Highway north of the Denali National Park entrance as the river erodes the banks. In spots the river is threatening the road, which in a stretch between the Glitter Gulch and Healy is perched on a narrow ledge between the river and the scree slopes. The high stage on the river is the result of copious rains in the headwaters: A SNOTEL (Monahan Flats), which is in the Sustina drainage but only a few miles from the upper Nenana watershed, measured 4.8 inches of rain September 13-21. The recent high freezing levels were likely a secondary factor.

Tina Graham photo from the Fairbanks-Daily News-Miner

It's a Soaker

 May only rarely brings soaking stratiform rains that send Interior Rivers out of their banks, but this is one of them. Here is the Saturday morning hydrograph from the Chena River near the Mile 40 Bridge. In addition to much more rain than anticipated, this rain also accelerated high elevation snowmelt. At the Munson Ridge SNOTEL, at 3100' MSL south of Chena Hot Springs, there was still a snow depth of four inches being reported Friday morning, which is now down to one inch, which is at the noise level. Fairbanks Airport set a new precipitation record Friday with 0.52 inches of rain.

Other rain amounts in the area include
Salcha River RAWS: 1.23 inches
Mile 40 Chena Hot Springs Road: 0.99 inches
Birch Lake RWIS: 0.94 inches
Woodsmoke near North Pole: 0.77 inches
Fort Knox Mine: 0.70 inches
Keystone Ridge: 0.68 inches
Aurora: 0.62 inches
Fairbanks Mid-town: 0.59 inches

Potentially Calamitous Storm for Western Alaska

The numerical models have been forecasting a major storm in the northern Bering Sea for mid-week since Thursday, and are now coming into focus. Here is the 3AM AST (1200 UTC) run of the GFS, with a 944mb low just northwest of St Lawrence Island at 3am Wednesday. This is very likely to produce major coastal flooding on the southern Seward Peninsula coast. The models are also forecasting the low to remain very strong as it moves into the Chukchi Sea, and this could well cause major flooding at Kivalina Wednesday night or Thursday, and even the western North Slope coast after that. The current sea ice coverage analysis from the US Navy shows no significant ice cover in the Bering or Chukchi Seas.




This will be a dangerous storm.

Rains in the Eastern Interior

Eastern Interior Alaska was soaked Wednesday night and Thursday with widespread moderate to heavy rain. Above are hydrographs from the Fortymile River at the Taylor Highway and Birch Creek near 101 Mile Steese Highway. The Fortymile is about to go over flood stage. The much smaller Birch Creek has already crested.

Total rainfall Wednesday and Thursday include…

Ben Creek RAWS (above Coal Creek on the Yukon River): 2.58 inches
Birch Creek RAWS (east of central above the Steese Highway Bridge): 1.43 inches
Chicken RAWS: 1.07 inches
Preacher Creek RAWS (northeast of Circle City): 0.81 inches

The rain got about as far west as the east side of Fairbanks, with most places east of town receiving around a tenth of an inch of rain early Thursday evening. There was no appreciable rain from Fairbanks westward.

Porcupine River Crest

The Porcupine River, the largest tributary of the Yukon, has been running high for weeks now. The recent crest at the gauge near the Alaska/Yukon border is the highest non-break-up related crest in more than a decade. Here is the hydrograph from the Alaska-Pacific RFC showing the crest on Wednesday.

Spectacular Rainfall in the Fortymile Country

The Chicken RAWS wound up with 2.75" of rain for the 24 hours ending at 120am ADT, and an event total of 2.83". The cooperative observer at Chicken, who lives several miles from the RAWS, reported an event total of 3.20" with, unsurprisingly, flooding on area creeks. The cooperative observer at OBrien Creek, on the Taylor Highway between Chicken and Eagle, reported about 3.20" of rain for the event. the Fortymile River at the Taylor Highway Bridge had the highest crest of record. This is really remarkable for this part of the world. The Alaska-Pacific RFC map of 24 hour precip ending 4AM Monday illustrates the storm nicely.

Update 830am Tuesday

The News-Miner reports flooding has closed the Taylor Highway north of Chicken, with some folks stranded:


http://www.newsminer.com/view/full_story/8742860/article-Taylor-Highway-blocked-by-washouts--motorists-stranded?instance=home_news_window_left_top_1

Updated 330pm Tuesday

I added the hydrograph for the Fortymile River showing the record crest.