Tuesday, July 30, 2013

Record Warm Spell for Anchorage

* Updated 7/31

Much as already been made regarding the breaking of the record for consecutive 70-degree days for Anchorage. Today is day number 14 in a row and the forecast for the next several days indicates that the record will be extended. What has not been noted anywhere is that the last two weeks has been the warmest two week period ever measured in Anchorage when looking at the average daily temperature. Here is the list:

14-Day Ave Temp            Date Range              Rank
          64.96             7/17/2013 - 7/30/2013      1 * (minor edit on 7/31)
          64.89             7/7/2003 - 7/20/2003        2
          64.82             6/20/1953 - 7/3/1953        3
          64.75             7/18/1936 - 7/31/1936      4

In addition, Anchorage (and Fairbanks) are closing in on their warmest summer-to-date records. Here is an update of the chart uploaded a few days ago.

Note: Each of the thin lines represents the cumulative average temperature for the summer season at a specific point in the season for the 10 warmest summers on record. Here is an example of how it works.

Date            Temperature       Season-to-Date Temp.     Calculation
June 1               66                              66.0                       66 / 1
June 2               62                              64.0                       (66+62) / 2
June 3               71                              66.3                       (66+62+71) / 3
June 4               67                              66.5                       (66+62+71+67) / 4
June 5               65                              66.2                       (66+62+71+67+65) / 5

At the beginning of the summer there is a lot of variation since the value in the denominator is small. Over the course of the summer the lines tend to converge.

Monday, July 29, 2013

North Slope Cold Front

It's a raw summer day in Barrow with drizzle, mist, 34 °F, and winds gusting to 30 mph.  The UAF webcam reveals bits and pieces of sea ice along the beach.

A strong cold front went through yesterday just after midday, bringing a sharp temperature drop after late-morning warmth of near 60 °F.  In advance of the front, a substantial amount of rain accompanied the warm, moist airmass: the daily precipitation total of 0.55" and the two-day total of 0.70" are the highest respective precipitation amounts in Barrow in over three years.

Today's pocket of cold air is apparent in the following time-height temperature cross-section for Barrow, which shows a computer forecast for the lower atmosphere beginning at 10 am ADT yesterday; time increases to the right and the vertical axis is pressure in mb.  Surface temperatures near or a little below freezing are possible for the rest of today and into tonight.

Saturday, July 27, 2013

Summer-to-Date Temperatures

Through July 27th, both Fairbanks and Anchorage are well on their way to Top 5 warmest summers on record. As is stands now, Fairbanks is in 4th place with a season-to-date temperature of 65.3F. In first place is the questionable summer of 1915 with 1975 and 2004 close behind – each of those years is approximately a full degree ahead of 2013. For Anchorage, the season-to-date temperature of 59.95F is only 0.2F below the record pace of 2004. The chart below shows the Top 10 warmest summers for each city with the running mean of June 1st through August 31st. The 2013, and 1981-2010 normals are shown and thick solid and thick dashed lines respectively.

Arctic Sea Ice Update

There is much more ice in the Beaufort Sea presently (July 27th) than last year at this time. Here's the Alaska-centered graphic from the University of Illinois Cyrosphere Today:

The  difference in the Beaufort Sea coverage between last year and this year is shown at the endpoints of this plot:
Arctic-wide, the sea ice coverage is not quite as low as the record low last year, but it is close, thanks to much less ice on the Atlantic side of the Arctic. This year continues the pattern we've seen since 2007, with different parts of the Arctic having different year to year melt patterns, but for the basin as a whole the ice coverage continues to decrease. The melt season has another six to nine weeks to go, and a vigorous storm earlier this week well north of Alaska may have broken up a lot of northern Beaufort Sea ice, so the accelerating decline evident on the Beaufort Sea ice area plot is likely to continue.

Friday, July 26, 2013

Kenai Rainfal

Last night just before midnight AKDT, the Kenai Municipal Airport recorded 1.23" of rain in one hour (and 1.83" in two hours). This is an extraordinary amount. To put it into perspective, according to the newly released NOAA precipitation atlas for Alaska (http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_ak.html), an hourly reading of 1.17" has a 1/1,000 chance of occurring in any given year for the city of Kenai (1,000-year recurrence interval). The 1,000-year recurrence interval for a two hour rainfall is 1.48". Wow! One of the resources that NOAA used to generate their numbers can be found at the following link: ftp://hdsc.nws.noaa.gov/pub/hdsc/data/ak/dur01h_ams_na14v7.txt . According to that rather abbreviated list, here is a list of the top 1-hour rainfall events in Alaska (I accidentally deleted the date column, sorry):

Station Hourly Rain (in.)
80-1940 PREACHER        , AK   1.67
50-6586 NORTHWAY AP     , AK   1.48
80-2440 TELIDA  , AK   1.33
80-0100 ALCAN HWY   1.32
80-2440 TELIDA  , AK   1.32
50-0352 ANNETTE ISLAND AP       , AK   1.22
80-0460 CHATANIKA       , AK   1.22
80-2620 VUNZIK LAKE     , AK   1.21
50-9941 YAKUTAT STATE AP        , AK   1.20
50-9941 YAKUTAT STATE AP        , AK   1.20
80-1280 KAIYUH  , AK   1.20

Chilly Morning at Eagle

A quick update to note the overnight minimum temperature of 34 °F at Eagle airport; this breaks the daily record of 36 ° set in 1958 and 1968.  However, most of Eagle's daily record minima in late July are 34 ° or lower, so this morning's chill is not all that unusual.  In 2005 the temperature dropped to 29 ° on July 21 and 30 ° on July 31.

Reader Gary asked about a 2013 precipitation chart, so here it is for Fairbanks.

Peak Precipitation

The resurgence of warm, dry weather over interior Alaska as August approaches is somewhat uncharacteristic for the time of year, as it is more typical to see wetter weather as summer advances.  Indeed the mean annual distribution of precipitation in northern and interior Alaska peaks in late summer, just a few weeks after the seasonal peak in temperature.  At interior locations, the tendency for greater cloudiness and more frequent rainfall is a major reason for the marked decline in average temperature in August; unlike most low- and mid-latitude Northern Hemisphere locations, August is considerably cooler than both June and July in the Alaskan interior.  More frequent rainfall tends to keep daytime temperatures lower, and the greater cloudiness and diminishing solar elevation and length of day combine to significantly reduce the solar insolation.

The charts below illustrate the mean annual cycle of precipitation for six observing stations in interior or northern Alaska; the first shows the mean total precipitation by month, and the second shows the mean frequency of measurable (0.01 inches or more) precipitation by month.  The amount of precipitation peaks in August for all six stations, and August is also the time of peak frequency of precipitation, except for Barrow where precipitation frequency peaks in October.  It is interesting to note that Fairbanks shows a sharper decline in precipitation amount and precipitation frequency from August to September than the rest of the stations, indicating a marked change to drier conditions in September.  The average daily precipitation amount peaks on about July 30 in Fairbanks, but the peak occurs in mid-August for the other locations.

Looking more closely at Fairbanks, the next chart shows the mean daily distribution of precipitation frequency and amount around the year.  The seasonal peaks are quite pronounced, with minimum precipitation falling in April and the maximum occurring only three and a half months later.  The secondary peak in precipitation frequency in October is interesting and may reflect a period of disturbed weather that tends to accompany the precipitous mid-autumn decline in temperature.

Thursday, July 25, 2013

Low Lightning

Reader Gary noted that there has been very little thunder in Fairbanks-land this summer. Fairbanks Airport has had thunder just ine day, and even here on Keystone Ridge I've heard thunder just once. Here is the plot of lightning strikes from the Alaska Fire Service for the two weeks from July 10 through July 24.

The total of 552 would be lackluster for any one day, much less for two weeks in July. Unfortunately, the strike counts this year (and going forward) are not really comparable to previous years data due to significant changes in the AFS lightning detection system. The new system is much more sensitive that the previous system, going so far as to detect separate branches off of the same leader stroke. Additionally, there were numerous technical glitches earlier this summer that made the data suspect.

The two systems were run in parallel for part of last summer, and while there was considerable day to day variation, the new system is counting something like 1.5 times as many strikes as the old system.

Tuesday, July 23, 2013

All-Time Maximum Temperatures

In June, a number of cities in Alaska set all-time maximum temperature records; including: Talkeetna, Valdez, Yakutat, Unalakleet, and many others. Missing from that list were the two largest cities in Alaska. However, it turns out that several of the stations in and around Anchorage and Fairbanks did indeed set all-time station maximum temperatures. In Anchorage, the temperature at Merrill Field reached 87 degrees Fahrenheit which broke their all-time record. Of the four sites that have been the official climate location for Anchorage (Park Strip, Merrill Field, Anchorage International Airport, and the NWS Forecast Office), no higher temperature has ever been recorded. Similarly, a number of the stations in and around Fairbanks set their all-time daily maximums this June. The map below shows the station maximums for both Anchorage and Fairbanks. Readings that have a data quality "flag" have been excluded (Note: The 99 at the Experiment Station in Fairbanks, while highly dubious, is still in the record books). Even though neither city technically broke their all-time daily maximum temperature at their respective climate recording sites, an argument can be made that they each experienced their hottest day on record (6/18/13 for Anchorage and 6/26/13 for Fairbanks).

Monday, July 22, 2013

Spring-Summer Temperature Transition

Author: Richard J.  I'm very grateful for the opportunity to contribute to this blog - thanks Rick!  When I stumbled across the site last year, I was delighted to read Rick's insights and commentary, and to begin engaging in some very interesting discussions of Alaska weather and climate.  As a non-resident of Alaska, I can't make any claim to expert local knowledge on the subject, but I hope my contributions will be worthwhile and interesting nonetheless.

For a first post, I thought I would highlight the extraordinary jump from unusually cold spring conditions to unusually warm summer conditions in Fairbanks this year.  I imagine the pace of change might have been dizzying even for locals used to extreme weather variations.  In a "typical" year (which rarely exists, of course), the average temperature would increase by about 21° F from the "spring" average (which I'm calling April and May) to early-mid summer (June 1 - July 15).  This year the temperature increase was over 34° F, and by far the highest in the Weather Bureau/NWS era (1930-present).  The chart below shows the annual values, and 2013 really stands out; the previous record increase was 28.5° F in 1986.

The 2013 change is especially unusual in light of 2010-2012, which saw a much more gentle transition from spring to summer.  The seasonal temperature increase in 2010 was the smallest in the record, only 14.2° F.

The remarkable change this year was created by the sequence of the coldest April-May period on record in Fairbanks (except for 1911), followed by one of the warmest early summer periods on record.  Among the unusual events was the latest first day with mean daily temperature above freezing (April 24), and then less than two months later there were 6 consecutive days with a high temperature of 86°F or above (June 15-20) which has only happened once before in 1918.

So in summary, the swing from one temperature extreme to the other since spring in Fairbanks has no precedent in the modern era.  From a meteorological standpoint, the reversal in extremes seems to be related to persistent high-latitude blocking around the northern hemisphere, which has created many persistent and extreme anomalies in different locations.  Another factor seems to be the evolution of sea surface temperatures in the North Pacific in recent months, which seem to have favored cold in the spring and warmth in the summer.  But that's a subject for another post...

Sunday, July 21, 2013

The Warmest Daily Minimum Temperature in Alaska

Continuing the discussion that Brain's post and thread in the comments about the warmest minimum, the Brian neatly disposed of most of the contenders for 70ºF or higher. The one data point still standing was the University Experiment station on July 11, 1983.

Richard pointed out the min of 70ºF is at observations with both the minimum at Fairbanks International and College Observatory; at the time the College Observatory obs site was less than a mile and about 150' higher elevation.

However, an examination of the original observation form for the Experimental Station shows that the observation day low for July 11, 1983 should have been at least 65, as this was the temperature at the time of observation on the 10th (this should have been caught by NCDC at the time but was not). 

So, if I understand Brian correctly, this means that there are no plausible observation in the GHCN database with daily min temperatures in Alaska of.70ºF or higher What about non-NCDC type data?

The June 1991 heatwave  produced several very warm nights. The highest calendar day minimum I can find is from the Cottonwood RAWS, located on a ridge north of the Yukon River (my memory is that it has been moved to its current location sometime after 1991 but I can't seem to  find online documentation of that). On June 21, 1991 the lowest hourly temperature was 70ºF at 3am and 4am, However, RAWS platforms, then or now, do not record absolute temperature extremes: all we have to go on are the hourly observation. Offhand, I can't think of any why to query the RAWS archive (or SNOTELs) to get at the highest daily minimum temperature. 

So, we're left with the low of 70ºF on June 25, 1992 at Fairbanks Airport as the only "continuously monitored" daily minimum temperature  of 70ºF or higher.  How does this compare with cooperative observations that day?

For June 25th minimum temperatures. we have
University Experimental Station 66ºF
Fairbanks Midtown 64ºF
Fairbanks Airport Upper Air: 58ºF
College Observatory: 58ºF

So this proves that the Fairbanks Airport data is bogus, right? Ahh, no. The hourly observations from the ASOS show 6-12 mph winds every hour from 10pm to 6am, which kept the air at the ASOS well mixed. The joy of mirco-meteorology.

Saturday, July 20, 2013

Maximum Minimums

Rick, thank you for the opportunity to contribute to your blog. Following the posts have been extremely educational as my focus is usually a little farther south. That being said, I would like to note the unusual low temperature that occurred recently. On Friday the low temperature in Anchorage was 61 degrees. This is the highest value on record for the station (Anchorage Forecast Office); although their period of record is only 15 years. The highest official reading for Anchorage was the 63 degree reading at Merrill Field in June 1953. Friday's 61 degree reading goes into the record books as the second warmest minimum temperature on record. Here is the list of the warmest low temperatures at the official Anchorage climate site:

1) 6/27/1953 63
2) 7/19/2013 61
3) 7/15/2003 61
4) 8/4/1999 61  
5) 8/15/1967 61
6) 6/26/1953 61

Pouring through the data generously provided by NCDC, the variability of low temperatures around a relatively small geographical area can be displayed cartographically. The two images below show the highest minimum temperature recorded for the stations around both Anchorage and Fairbanks. The length of record for stations varies tremendously. For Fairbanks, only stations with 10+ years of readings were included. For Anchorage, only station with 5+ years were used. As mentioned earlier, the 61 degree temperature for Anchorage Forecast Office is a station record and the 70 degree temperature for Fairbanks measured on June 25th is also a station record.

Blog Changes

Some changes are in the works for Deep Cold the blog as I've struggled to make time to gin up posts.

To help out with that, a couple of folks with expertise and interest in Alaska weather and climate have agreed to volunteer as Deep Cold post authors. Dr. Brian B. is a long time Anchorage resident with a PhD in Environmental Geography. Dr. Richard J. is a lower-48 consulting meteorologist with expertise in numerical weather modeling and weather risk management.  His travels to Alaska have inspired an avid interest in far northern weather and climate.  The geographic scope of the blog will be increased a bit, with more posts about Alaska weather and climate south of the Alaska Range and probably other high latitudes (roughly north of 60N) areas too.

There are many weather and climate blogs online, so I hope this experiment fills a niche and  keeps quality information on Alaska weather and climate available.


Wednesday, July 17, 2013

Getting Drier

The lack of rainfall in Fairbanks-land is adding up, so to speak. At the Airport only 0.98" of precipitation fell May first through July 15th. This is the third lowest total of record for this period, behind 1957 (0.63") and 1991 (0.94") and only 33% of the 1981-2010 normal. Here's a plot of difference from the long term (1915-2013) mean for this period for each season since 1915:

Precipitation elsewhere in the area is not much better. Here on Keystone Ridge there's been 2.29" in the same period, a paltry 44% of normal. In the upper Chena Basin, the Munson Ridge SNOTEL south of Chena Hot Springs, at 3100" MSL has measured just 3.2" precip since May 1, just 48% of normal.

Sunday, July 14, 2013

Updated Fairbanks Temperatures

Here's a plot of daily mean temperatures for 2013 (thru Saturday) referenced around normal. Note that the cool spell earlier this month only barely nicked below the one standard deviation "typical temperatures" range. 

This is a bit of a placeholder as I'm trying to decide if I should continue this blog. With my new (since April) job I get a lot of this kind of thing, and it's a requirement that I keep this and work separate. Plus the "burn-out" factor.

Friday, July 5, 2013

The Apex of Climatological Warmth at Fairbanks

Here in the land of the continental climate, mean annual temperatures are now at their peak, just two weeks after summer solstice. Here's a plot of the NCDC 1981-2010 normal daily mean temperature for June and July at Fairbanks:

The slower decline after the peak in early July is due to increased cloud cover, higher dew points and higher soil temperatures in late July than early June. This results in normal low temperatures falling more slowly than normal high temperatures (so the mean diurnal range is less).

Wednesday, July 3, 2013

Warmest Fairbanks Weeks

Here's my take:

The  Weather Bureau/NWS era (1930-present) records are:

Warmest 7-day average maximum temperature (none overlapping weeks):
  1. 87.9ºF June 20-26, 1991 & June 30-July 6, 1986
  2. 87.4ºF June 14-20, 1969
  3. 87.0ºF June 30-July 6, 1990
  4. 86.7ºF July 24-30, 1954
  5. 86.4ºF July 12-18, 1993
  6.  86.1ºF July 19-25, 1968
Warmest 7-day average minimum temperature (none overlapping weeks):
  1. 65.0ºF June 24-30, 2013
  2. 62.0ºF July 11-17, 1975
  3. 61.7ºF June 21-27, 1991
  4. 61.1ºF July 4-10, 1975
  5. 61.0ºF July 18-24, 1975
  6. 60.9ºF June 25-July 1, 1983
The anomalies nature of the low temperatures in late June really stands out. Only 1.1ºF separate #2 from #6, while with high temperatures less than two degrees separate the top six.

The pre-Weather Bureau data from the Agricultural Farm (now called University Experimental Station) is plagued by data quality issues. There is zero doubt in my mind that the weekly average of 90.1ºF July 26-August 1, 1919 is bogus. No other location in Interior even had one day with a high of 90ºF, and this includes Nenana and Salcha. The average of 88.6ºF July 11-17, 1918 is less obviously bad, but is part of what look to be a host of anomalously warm summer temperatures recorded in 1911-1919 at the Ag Farm.

Tuesday, July 2, 2013

June Weather Factoids

Working on catching up with all the weather while I was gone, so here a few lesser publicized factoids:

  • Thunderstorm at Barrow the evening evening of June 13th is the earliest in the season thunderstorm of record there. Barrow also had the warmest June of record.
  • Umiat RAWS had a high of 90ºF on the 20th, and Sagwon SNOTEL had 85ºF same day.
  • Highest reliable temperature so far is 97ºF at the Amber Lake coop site, southwest of Talkeetna. 
  • Both Nome and Kotzebue tied their all-time record highs, 86ºF and 85ºF respectively.
  • Almost 808,000 acres burned in June; The Lime Hills (201,000 arces) and Moore Creek (160,000 acres) are the largest fires.
    View from Ester Dome Tuesday evening, Courtesy of the FAA