The Nenana tripod went out yesterday, marking the break-up of the Tanana River at its confluence with the Nenana River. As I noted last week, it's highly likely that the break-up was earlier than it would have been without such abundant run-off from excessive late winter snowfall across the region.
This claim is supported by the fact that this year's break-up occurred with the least number of thawing degree days (TDDs) on record in nearby Fairbanks: the total TDDs through yesterday in Fairbanks was 74.0, which narrowly beats out 2002 (74.5) and 2006 (75.0). We might say this year's thaw season leading up to break-up was the coolest on record.
Here's an updated chart of the relationship between TDDs and precipitation amount from March 1 to break-up.
An interesting nuance here is that most of the years with high precipitation and low TDDs also saw relatively late break-up, in contrast to this year. The chart below classifies the years as "early" or "late" simply based on whether break-up was before or after the long-term median of May 3 (and yes, there's a significant trend).
It seems that it's typical for wet years to also be cool in April, and this delays break-up in comparison to dry years; i.e. dry and warm tend to occur together in late winter and early spring. This complicates the picture a bit, because the stronger sunshine at later dates allows late break-ups to occur with lower TDDs independently of precipitation effects. So the precipitation/TDD relationship isn't quite as simple as "more run-off means earlier break-up"; the relationships are complex.
A final bit of chart analysis (see below) illustrates that the very latest break-ups reliably occur after low TDD totals; but this year was unusually early for such low TDDs. I suggest this is almost certainly because of the increased run-off related to the wet conditions of the past 6 weeks.
Objective Comments and Analysis - All Science, No Politics
Primary Author Richard James
2010-2013 Author Rick Thoman
Tuesday, April 28, 2020
Sunday, April 26, 2020
Length of Summer - Brian B Blog
Most readers will be familiar with Dr Brian Brettschneider of UAF, who has become a sought-after authority on Alaska climate. Brian recently wrote an article on his own blog that I thought would be worth linking here:
Are Summer/Winter Longer/Shorter Than They Used To Be?
Using a simple method, Brian demonstrates that the "summer" and "winter" temperatures of a prior climate period (1960-1989) in Alaska have become considerably longer and shorter respectively in the most recent 30-year period (1990-2019). The changes have been particularly dramatic in winter across Alaska, and most notably of course on the North Slope.
Brian's work provides a nice visualization and easy-to-understand interpretation of temperature changes over the past several decades. In my opinion, it would also be interesting to extend the work to build in the different perceived length of summer/winter at different latitudes. For example, the introduction acknowledges that Houston has a longer summer than Omaha, and Chicago has a longer winter than Oklahoma. Most people would say Alaska has a very long winter and a short summer; and despite the dramatic warming on the North Slope, winter certainly hasn't disappeared there, as Brian's simple method would imply.
Obviously it would be difficult to come up with a good metric to capture subjective opinions of summer and winter, but perhaps a threshold temperature could be added that would demand a "summer" or "winter" classification, regardless of how long that season might be. For example, perhaps:
- Normal daily mean temperature above 27°C -> summer
- Normal daily mean temperature below -10°C -> winter
The winter threshold would then produce a (1981-2010 climate) winter season from October 28 to March 21 in Fairbanks, and October 22 through May 3 in Utqiaġvik. Perhaps readers would like to comment on this or other ideas to refine the analysis without losing too much of the attractive simplicity.
Are Summer/Winter Longer/Shorter Than They Used To Be?
Using a simple method, Brian demonstrates that the "summer" and "winter" temperatures of a prior climate period (1960-1989) in Alaska have become considerably longer and shorter respectively in the most recent 30-year period (1990-2019). The changes have been particularly dramatic in winter across Alaska, and most notably of course on the North Slope.
Brian's work provides a nice visualization and easy-to-understand interpretation of temperature changes over the past several decades. In my opinion, it would also be interesting to extend the work to build in the different perceived length of summer/winter at different latitudes. For example, the introduction acknowledges that Houston has a longer summer than Omaha, and Chicago has a longer winter than Oklahoma. Most people would say Alaska has a very long winter and a short summer; and despite the dramatic warming on the North Slope, winter certainly hasn't disappeared there, as Brian's simple method would imply.
Obviously it would be difficult to come up with a good metric to capture subjective opinions of summer and winter, but perhaps a threshold temperature could be added that would demand a "summer" or "winter" classification, regardless of how long that season might be. For example, perhaps:
- Normal daily mean temperature above 27°C -> summer
- Normal daily mean temperature below -10°C -> winter
The winter threshold would then produce a (1981-2010 climate) winter season from October 28 to March 21 in Fairbanks, and October 22 through May 3 in Utqiaġvik. Perhaps readers would like to comment on this or other ideas to refine the analysis without losing too much of the attractive simplicity.
Wednesday, April 22, 2020
Lots of Water
Interior Alaska is finally escaping the grip of winter, with snow disappearing quickly and break-up beginning to advance on some rivers. Remarkably abundant snowfall in late winter combined with recent rains has led to an excess of run-off and the potential for flooding if temperatures rise too high too quickly. Here's the NWS flood potential map from last week:
Fairbanks is already down to a snow depth of only 4 inches, but the snow pack remaining in the hills is quite monumental: the Munson Ridge SNOTEL site at 3100' elevation near Fairbanks is reporting 15" of liquid equivalent water. That's a lot of water to come down the creeks and rivers in the next month.
According to the SNOTEL instrument, 6.8" of liquid-equivalent precipitation has fallen on the hill since March 1 - this is quite remarkable for the (usually dry) time of year. It's believable too; here's a chart of recent precipitation at the top-quality CRN site (1140' elevation).
The massive influx of melt water will almost certainly bring forward the date of break-up at the Nenana tripod, owing to the increased stress caused by high water. There's some evidence of this effect in the history of the Nenana break-up; the chart below shows that when precipitation is very high after March 1, the heat input (thawing degree days) required to reach break-up tends to be lower than normal.
This year Fairbanks has seen 2.86" of precipitation since March 1, which is the highest on record for March 1 - April 21. The previous record for this period was in 1967, which happens to be the year of the great August flood in Fairbanks (hmm...)
Here's the latest break-up summary from the NWS.
Fairbanks is already down to a snow depth of only 4 inches, but the snow pack remaining in the hills is quite monumental: the Munson Ridge SNOTEL site at 3100' elevation near Fairbanks is reporting 15" of liquid equivalent water. That's a lot of water to come down the creeks and rivers in the next month.
According to the SNOTEL instrument, 6.8" of liquid-equivalent precipitation has fallen on the hill since March 1 - this is quite remarkable for the (usually dry) time of year. It's believable too; here's a chart of recent precipitation at the top-quality CRN site (1140' elevation).
The massive influx of melt water will almost certainly bring forward the date of break-up at the Nenana tripod, owing to the increased stress caused by high water. There's some evidence of this effect in the history of the Nenana break-up; the chart below shows that when precipitation is very high after March 1, the heat input (thawing degree days) required to reach break-up tends to be lower than normal.
This year Fairbanks has seen 2.86" of precipitation since March 1, which is the highest on record for March 1 - April 21. The previous record for this period was in 1967, which happens to be the year of the great August flood in Fairbanks (hmm...)
Here's the latest break-up summary from the NWS.
HYDROLOGIC OUTLOOK NWS ALASKA PACIFIC RIVER FORECAST CENTER ANCHORAGE AK 1 PM AKDT WED APR 22 2020 ..SPRING BREAKUP OUTLOOK FOR ALASKA... Breakup Update: The Forty Mile river upstream of the Taylor Highway has broken up as well as the Kuskokwim River near Nikolai. The Tozitna River has broken up with an ice jam forming and releasing. The Aniak River is reported to have broken up dynamicaly and is mostly open at the confluence with the Kuskokwim. Ice is beginning to lift on the Kuskokwim, Yukon and Koyukuk Rivers. The 2020 Alaska Spring Breakup flood potential is forecast to be generally above average south of the Brooks Range and average flood potential for the North Slope. The Flood Potential forecast is based on observed snowpack, ice thickness reports, and long-range temperature forecasts and focuses on the Kuskokwim, Tanana , Yukon, Koyukuk, Copper, and North Slope rivers. Recent observed and forecast temperatures suggest a generally earlier than normal, more dynamic type breakup for locations statewide. Timing of breakup statewide is expected to be several days earlier than normal. Breakup along the Yukon River upstream of Fairbanks is expected to be 1 to 3 days earlier than median dates; generally 3 days earlier at locations downstream from Fairbanks to Anvik; and 3 to 5 days earlier at locations downstream from Anvik to the mouth. Breakup along the Kuskokwim River at Nikolia downstream to Tuluksak are expected to be 1 to 2 days earlier than median dates and 2 to 5 days earlier downstream from Tuluksak to the mouth. Temperatures - Statewide, temperatures over the past few weeks generally have been normal to below normal. However, temperatures over the next several weeks are expected to be normal in areas north of the Brooks Range and above normal for the remaining parts of the state. Statewide, temperatures for April and May are expected to be above normal. Ice - The April 1st ice thickness data indicate that ice thickness is near normal across the state. A few measurements across interior Alaska ranged from 32 inches at Galena, which is 82% of average; 33 inches at Nenana, which is 80% of average; 48 inches at Eagle, which is 117% of average. Snow - April 1st snowpack by the Natural Resources Conservation Service (NRCS) indicates greater than normal snowpack across interior Alaska ranging from 117% in the central Yukon Basin to 197% of average in the Kuskokwim Basin. The Yukon government is also reporting greater than normal snowpack across the Upper Yukon River Basin in Canada. The snowpack is near normal along the North Slope and below normal along the Gulf Coast and throughout Southeast Alaska. Climate Outlook: April and May weather is the most important factor determining the severity of river ice breakup. Dynamic breakups have a high potential for ice jam flooding and typically require cooler than average temperatures during March and into the first few weeks of April followed by an abrupt transition to warmer than normal temperatures in late April to early May. Thermal breakups have a low potential for ice jam flooding as river ice generally rots in place. The Climate Outlook for Spring 2020 suggests a more dynamic type breakup this year. Observed temperatures in March thru the first week of April were generally below normal to normal. The second and third weeks of April were generally warmer than normal. Temperature forecasts for the last week in April indicate near normal temperatures statewide with equal chances for above and below normal for early may. The mid-March 3-month Climate outlook indicates increased chances of above average temperatures throughout Alaska. Further information can be found at the following web sites: Weather- https://www.weather.gov/aprfc/AGAK78PACR Snow- https://www.weather.gov/aprfc/nrcs_ak_swe https://www.weather.gov/aprfc/snow_depth https://www.wcc.nrcs.usda.gov/snow/ Ice thickness- https://www.weather.gov/aprfc/icethickness Climate prediction- http://www.cpc.ncep.noaa.gov/ River Ice Breakup Flood Threat: The two generalized types of river ice breakup are dynamic (mechanical) and thermal. A dynamic breakup moves from the headwaters of a river downstream in a somewhat linear fashion. Ice jam flooding occurs more often during a dynamic type breakup than a thermal type. A thermal type breakup results in the river ice rotting in place primarily due to gradual to rapid warm ups and little snowmelt runoff. Thermal type breakups usually result in fewer ice jams and less chance of flooding. Statewide, breakup this year is expected to lean generally to the dynamic type. Temperatures statewide over the past few weeks generally have been normal to below normal. However, temperatures over the next several weeks are expected to be normal in areas north of the Brooks Range with above normal temperatures for the remaining parts of the state. Temperatures statewide for April and May are expected to be above normal. South of the Brooks Range, the expected more dynamic type breakup, above normal temperatures, and above average snowpack has increased the potential for flooding this year to above average, while flooding potential north of the Brooks Range is expected to be average. THE FOLLOWING TABLE GIVES AN ESTIMATION OF FLOOD POTENTIAL FOR VARIOUS LOCATIONS AROUND THE STATE AND BASIN RUNOFF VOLUMES. --------------------------------------------------------------------- SNOWMELT RUNOFF VOLUME...EXPECTED WATER VOLUME FROM SNOWMELT DURING THE MELT SEASON. FLOOD POTENTIAL...THE LIKELIHOOD OF FLOODING FROM SNOWMELT AND/OR ICE JAMS. THIS IS INITIALLY CALCULATED BASED ON THE FLOOD FREQUENCY FOR THE 2000 TO 2019 HISTORICAL RECORD AND ADJUSTED TO REFLECT CURRENT CONDITIONS. * MEDIAN BREAKUP DATES ARE FOR THE PERIOD 1980 THROUGH 2019 AND ARE CALCULATED FOR LOCATIONS WITH AT LEAST 5 YEARS OF DATA. ** ACTUAL BREAKUP DATE FOR THIS YEAR --------------------------------------------------------------------- SNOWMELT FLOOD MEDIAN NO. OF FORECAST RIVER - REACH RUNOFF POTENTIAL BREAKUP YEARS BREAKUP VOLUME DATE* USED DATE ------------- ---------- --------- ------- ------ -------- SOUTHEAST PANHANDLE ABOVE KENAI RIVER AVERAGE LOW OPEN TO SKILAK LAKE ANCHOR RIVER BELOW LOW MOSTLY OPEN MATANUSKA RIVER ABOVE AVERAGE LOW SUSITNA RIVER ABOVE AVERAGE GOLD CREEK MOD SUNSHINE LOW-MOD 05/02 31 04/26-05/02 YENTNA RIVER ABOVE AVERAGE LAKE CREEK LOW-MOD 04/30 29 04/27-05/03 SKWENTNA RIVER ABOVE AVERAGE SKWENTNA LOW-MOD 04/29 25 04/23-04/29 COPPER RIVER BASIN AVERAGE GAKONA RVR @ HWY LOW 04/29 32 04/23-04/29 GULKANA RVR @ HWY LOW 04/29 30 04/23-04/29 CHENA RIVER ABOVE AVERAGE CHENA LAKES PROJECT MOD FAIRBANKS LOW 04/25 27 OPEN TANANA RIVER ABOVE AVERAGE CHISANA @ NORTHWAY LOW-MOD 04/26 27 04/17-04/23 SALCHA LOW-MOD FAIRBANKS LOW-MOD 04/28 19 04/26-04/02 NENANA LOW-MOD 04/29 40 04/24-04/30 MANLEY LOW-MOD 05/02 29 04/26-05/02 KUSKOKWIM RIVER ABOVE AVERAGE NIKOLAI LOW-MOD 04/22 34 **04/21 MCGRATH MOD 05/04 40 04/30-05/06 STONY RIVER LOW-MOD 05/01 32 04/27-05/03 SLEETMUTE MOD 05/01 31 04/27-05/03 RED DEVIL MOD 05/03 34 04/28-05/04 CROOKED CREEK MOD 05/03 34 04/29-05/05 ANIAK MOD 05/04 37 04/29-05/05 KALSKAG LOW-MOD 05/04 31 04/30-05/06 TULUKSAK LOW-MOD 05/06 28 05/01-05/07 AKIAK LOW-MOD 05/08 34 05/01-05/07 KWETHLUK MOD 05/03 8 04/30-05/06 BETHEL LOW-MOD 05/09 40 05/01-05/07 NAPAKIAK LOW-MOD 05/10 25 05/03-05/09 YUKON RIVER (UPPER) ABOVE AVERAGE DAWSON, YT LOW-MOD 05/03 40 04/29-05/05 EAGLE MOD 05/03 40 04/28-05/04 CIRCLE MOD-HIGH 05/07 36 05/02-05/08 FORT YUKON MOD 05/10 36 05/04-05/10 BEAVER LOW-MOD 05/09 24 05/04-05/10 STEVENS VILLAGE LOW-MOD 05/10 23 05/05-05/11 RAMPART LOW-MOD 05/10 25 05/04-05/10 YUKON RIVER (MIDDLE) ABOVE AVERAGE TANANA LOW-MOD 05/07 35 05/01-05/07 RUBY LOW-MOD 05/08 34 05/02-05/08 GALENA MOD 05/10 39 05/04-05/10 KOYUKUK MOD 05/08 14 05/04-05/10 NULATO MOD 05/10 23 05/04-05/10 KALTAG LOW-MOD 05/11 34 05/05-05/11 ANVIK LOW-MOD 05/13 32 05/07-05/13 YUKON RIVER (LOWER) ABOVE AVERAGE HOLY CROSS LOW-MOD 05/14 33 05/06-05/12 RUSSIAN MISSION LOW-MOD 05/14 34 05/06-05/12 MARSHALL MOD 05/14 28 05/06-05/12 PILOT STATION LOW-MOD 05/13 23 05/07-05/13 MOUNTAIN VILLAGE LOW-MOD 05/15 33 05/08-05/14 ALAKANUK/EMMONAK MOD 05/20 32 05/12-05-18 KOYUKUK RIVER ABOVE AVERAGE BETTLES LOW-MOD 05/09 38 05/01-05/07 ALLAKAKET LOW-MOD 05/09 33 05/03-05/09 HUGHES MOD 05/10 33 05/03-05/09 SEWARD PENINSULA ABOVE AVERAGE BUCKLAND MOD 05/15 30 05/09-05/15 KOBUK RIVER ABOVE AVERAGE KOBUK MOD 05/13 36 05/07-05/13 SHUNGNAK LOW-MOD 05/16 29 05/10-05/16 AMBLER LOW-MOD 05/16 35 05/10-05/16 NOATAK RIVER ABOVE AVERAGE NOATAK LOW-MOD 05/13 23 05/17-05/19 BROOKS RANGE - NORTH AVERAGE COLVILLE @ UMIAT LOW-MOD 05/24 19 05/16-05/22 COLVILLE @ COLVILLE LOW-MOD 06/02 22 06/26-06/01 SAGAVANIRKTOK RIVER AVERAGE DALTON HWY LOW-MOD For more detail and to see a Flood Potential Map, refer to our Website at https://www.weather.gov/aprfc/FLOODPOTENTIAL The next Spring Breakup Outlook is scheduled at 2PM AKDT Friday April 24th, 2020
Saturday, April 18, 2020
Alaska Community Wind Tool
Yesterday UAF's International Arctic Research Center announced a new website tool for exploring the wind climate of recent decades across Alaska, as well as projected changes to wind behavior in the rest of this century. It's a nice resource for learning about wind in many of Alaska's inhabited places, with data available from 67 sites.
http://windtool.accap.uaf.edu/
The aspect that interests me the most is the monthly wind rose visualization; this is a great way to see how wind typically varies through the year in different places. For instance, the diagrams from Utqiaġvik, Deadhorse, and Kaktovik show interesting differences that I wasn't fully aware of until now. Click to enlarge the images below.
At Utqiaġvik, easterly to northeasterly winds are strongly dominant at all times of the year, with the preferred direction being east-northeast from September through May, and east in June through August. But at the two sites farther east along the Arctic coast, the wind rose is strongly bi-directional in most months: mostly ENE or WSW at Deadhorse, and approximately WNW or E at Kaktovik. It's amazing how reliable the ENE direction is in Deadhorse in May through July; the same is true for the easterlies in Kaktovik in May and June.
Another spot with a remarkably reliable wind regime is Unalakleet in the winter; it's basically all easterlies all the time, and often quite strong. In this case the wind regime is localized, being created by cold air flowing down the Kaltag Portage from the interior.
http://windtool.accap.uaf.edu/
The aspect that interests me the most is the monthly wind rose visualization; this is a great way to see how wind typically varies through the year in different places. For instance, the diagrams from Utqiaġvik, Deadhorse, and Kaktovik show interesting differences that I wasn't fully aware of until now. Click to enlarge the images below.
At Utqiaġvik, easterly to northeasterly winds are strongly dominant at all times of the year, with the preferred direction being east-northeast from September through May, and east in June through August. But at the two sites farther east along the Arctic coast, the wind rose is strongly bi-directional in most months: mostly ENE or WSW at Deadhorse, and approximately WNW or E at Kaktovik. It's amazing how reliable the ENE direction is in Deadhorse in May through July; the same is true for the easterlies in Kaktovik in May and June.
Another spot with a remarkably reliable wind regime is Unalakleet in the winter; it's basically all easterlies all the time, and often quite strong. In this case the wind regime is localized, being created by cold air flowing down the Kaltag Portage from the interior.
Sunday, April 12, 2020
CRN Data Visualization
Here's a follow-up to a post from a few weeks ago, where I mentioned that I was working on a web interface to visualize the high-quality climate data coming out of the Alaska CRN network. Here's a first draft:
http://worldagweather.com/crn/
Note that the page is not designed for mobile viewing - sorry if that's an inconvenience. And various refinements are needed; this is just a first attempt that provides static, pre-generated images for fixed intervals. I'd like to move to a more interactive charting capability at some point, but that will depend on how much time I have.
Also note that I haven't included the two newest sites in southwestern Alaska, one in the Yukon-Kuskokwim Delta, and one at Aleknagik (near Dillingham). This is because I prefer to have at least a couple of years of data to calculate a seasonal "normal" for each of the weather variables.
The page should update every day by around 7am AKST, but let me know if you see any problems.
http://worldagweather.com/crn/
Note that the page is not designed for mobile viewing - sorry if that's an inconvenience. And various refinements are needed; this is just a first attempt that provides static, pre-generated images for fixed intervals. I'd like to move to a more interactive charting capability at some point, but that will depend on how much time I have.
Also note that I haven't included the two newest sites in southwestern Alaska, one in the Yukon-Kuskokwim Delta, and one at Aleknagik (near Dillingham). This is because I prefer to have at least a couple of years of data to calculate a seasonal "normal" for each of the weather variables.
The page should update every day by around 7am AKST, but let me know if you see any problems.
Monday, April 6, 2020
Winter Hangs On
Winter is hanging on with considerable tenacity across Alaska, with another strong trough bringing a blast of renewed cold air from west to east yesterday and today. Nome hasn't climbed out of the single digits Fahrenheit yet today, and Fairbanks is hovering near 15°F in the westerly breeze this evening. These are very chilly conditions for the time of year, although in Fairbanks it's nowhere near the level of April 2013, when the 7th of the month brought a high of only 11°F and a low of -10°F.
This morning's 500m analysis from Environment Canada shows the upper-level trough centered over the Brooks Range, and the plotted observations indicate a 500mb temperature of -42°C at both Fairbanks and Anchorage (click to enlarge below). This is the coldest mid-tropospheric air so late in the winter since 2013 at both sites, and it's a continued symptom of the strong and cold Arctic vortex that has dominated the boreal high latitudes for most of the winter.
But on the bright side for those who are tired of all this, a huge warm-up is looking quite likely for next week. Remarkably, NOAA's probabilistic forecast is showing a median temperature forecast of 62°F in Fairbanks next Friday (the 17th), and that means they're calculating a 50-50 chance that it will be even warmer than that. We'll see... 10 days is a long way out in Alaska weather forecasts.
Update 4/7: here's the link for the probabilistic forecast:
https://sats.nws.noaa.gov/~naefs_ekdmos/meteoform_naefs_v2_oper.php
The probability distribution values can be accessed via "Text Products" on the left menu. Here's yesterday's Max/Min Temp CDF (Cumulative Distribution Function) product for Fairbanks:
This morning's 500m analysis from Environment Canada shows the upper-level trough centered over the Brooks Range, and the plotted observations indicate a 500mb temperature of -42°C at both Fairbanks and Anchorage (click to enlarge below). This is the coldest mid-tropospheric air so late in the winter since 2013 at both sites, and it's a continued symptom of the strong and cold Arctic vortex that has dominated the boreal high latitudes for most of the winter.
But on the bright side for those who are tired of all this, a huge warm-up is looking quite likely for next week. Remarkably, NOAA's probabilistic forecast is showing a median temperature forecast of 62°F in Fairbanks next Friday (the 17th), and that means they're calculating a 50-50 chance that it will be even warmer than that. We'll see... 10 days is a long way out in Alaska weather forecasts.
Update 4/7: here's the link for the probabilistic forecast:
https://sats.nws.noaa.gov/~naefs_ekdmos/meteoform_naefs_v2_oper.php
The probability distribution values can be accessed via "Text Products" on the left menu. Here's yesterday's Max/Min Temp CDF (Cumulative Distribution Function) product for Fairbanks: