Tuesday, April 30, 2013

Cold is Not the New Normal

There will be a lot to write about once April is in the books, but for now here's something to chew on. April is going to finish up as the coldest in Fairbanks since 1924. Following on the cold December and the cold January 2012, I thought I'd look at thermally "extreme" months in recent years.

In the past decade, 2003-2012 plus the first four months of this year, here are the number of times a given month was in either the top ten warmest or coldest in the Weather Bureau/NWS era (since 1930). So red is the "warm month" count and blue the "cold month" count.

The total count is: since January 2003, 21 month have been in the warmest ten and 10 have been in the coldest ten. Interestingly, only two months in the warm season (April 2013 and September 2004) have been in the cold column. while 11 months have been in the warmest ten.

Sunday, April 28, 2013

Significant Record Low at Fairbanks

Courtesy of Pro Music, Fairbanks
Updated with additional observations and faciods…

Temperatures dropped to near zero overnight. The low temperature at the Fairbanks Airport of +2ºF easily broke the previous record of 8 above set in 1924, and is among the coldest temperatures so late in the season (more below). Other low temperatures include:

Chena Hot Springs: -8ºF
Goldstream Creek: -6ºF
Woodsmoke CWOP: -3ºF
Mile 43 Steese: -2ºF
Fort Wainwright: -1ºF
Eielson AFB: +1ºF
UAF West Ridge: +2ºF
Wickersham Dome: +6ºF
Keystone Ridge: +8ºF

The low of +2F at the airport makes this among the lowest temperatures so late in the season. The only lower temperatures later than April 28th are a low of 0ºF on May 3, 1945 and the -1ºF on May 9, 1964. At UAF West Ridge and Eielson, with obs since the 1940s, these are the lowest temperatures of record this late in the season.

Obviously the sustained cold  weather has kept break-up at bay. The photo from Pro Music Sunday morning, looking south across the Chena River, hardly even shows any frozen melt water on top of the ice.

Friday, April 26, 2013

Fairbanks Standardized Temperature Departures: Blue Edition

Here's the standardized daily mean temperature departures updated through Thursday. Fairbanks is definitely headed toward a top five coldest Aprils of record, and that's no surprise given all that blue on the chart. 19 days so far this month have been 1.0 or more standard deviations below normal, while only the first three days of the month were above average at all.

Wednesday, April 24, 2013

A Record Falls, Another Remains

Courtesy of the FAA
The average daily temperature on Tuesday at Fairbanks was 32ºF, which means that 2013 is now the latest in the spring that Fairbanks has ever gone with zero accumulated thaw degree days.  The high Wednesday has been 39ºF (early morning right with the cold frontal passage), and the low through 7pm AKDT has been just 32ºF. However, it is possible that the temperature could get down to 25ºF by midnight, so the streak might continue.

The inch of snow today is not a record for April 24th. That remains 1.9" in 1941.

Sunday, April 21, 2013

Fairbanks Staying Cool

Here's an update of temperatures through Saturday, April 20th.  In this plot, in addition to trying out new software, I've plotted the daily mean temperatures along with the 1981-2010 mean ± 0.43 standard deviations (the grey area).

This basically corresponds to the Climate Prediction Center's tercile categories, with red colors showing temperatures in the CPC "much above" tercile and blue showing temperatures in the "much below" tercile. Of course, you don't need a weatherman to tell you that mild weather has been short supply for quite a while now.

Saturday, April 20, 2013

Fairbanks Snow Melt…Getting There…But Not Quite Yet

Milder weather has come to Fairbanks-land, and so the long process of snow melt and river ice break-up will, after a couple week delay, get underway. Here was the view on Smith Lake, at the west end of the University of Alaska Fairbanks campus on Thursday afternoon (April 18th), when trail conditions were still "perfect".
Courtesy of Ed Plumb
Temperatures finally cracked freezing early Friday afternoon and we now look to be into the thaw-freeze diurnal cycle, with mild days and clear cool nights. This will allow for slow ripening the snow pack, a necessary step in before substantial runoff can commence. One measure of how this process is progressing are thaw degree days, which are simply the sum of daily mean temperatures above freezing. Below is a plot of cumulative thaw degrees at Fairbanks through April 20th for each of the last 108 years, expressed as the difference from the mean.

Through Saturday, Fairbanks has cumulative total of zero thaw degree days since March 1, 47 below the mean . How unusual is this? Well, it's not unprecedented: 1960 and 1954 also had zero thaw degree days through April 20th. However, we don't want to get too hung up on "zero". After all, "one" is not very much different than "zero. Next is a histogram of the above data:

So having accumulated very few thaw degree days at this point is not unusual;  11 percent of springs have five or less through April 20th. So, while it is unusual not to have any significant snow melt thus far, it is well within the range of past experience. If Saturday's numerical weather models are vaguely correct, we'll start to accumulate those thaw degree days pretty quickly next week and with it snow pack ripening.

Tuesday, April 16, 2013

Cold April in Context

The average temperature the first half of April in Fairbanks was10.8ºF. This is a remarkable 16.3 degrees below normal and the fourth coldest of record (second coldest in the WB/NWS era). The chart plots the mean temperature the first half of April and the 10-year running mean.

The years with coldest first half of April and the mean temperatures are:

1911:  4.4ºF

1985:  9.8ºF
1924:  9.9ºF
2013: 10.8ºF
1986: 11.0ºF

The 10 year running mean shows nicely that there has been little trend in April temperatures over the past 50 years except for the decade or so of warm Aprils in the 1990s. This year is a good example of an "outlier" that we have no reason to think is tied to a larger pattern (unlike say, Barrow temperatures in October).

Here's a link to the NWS Alaska Region Facebook graphic showing how the cold weather this month is distributed across Alaska. Northwest and Southeast Alaska have not been notably cold but in between it sure has been.

Saturday, April 13, 2013

The Cold April week

Updated with Saturday, April 13th stats

Fairbanks has chilled through the coldest April week since the 1920s. The average temperature Saturday, April 6th through Friday, April 12th was +2.6ºF. This is the coldest week wholly within April (no end-of-March days) since April 2-8, 1927, when the average temperature was also 2.6ºF. The coldest April week was in 1924, when the average temperature April 1-7 was -1.5ºF. If we include the last couple of days of March, then this is the coldest "mostly April" week since March 30-April 5, 1985, when the average temperature was 1.7ºF. This was not quite the coldest week so late in the season: April 7-13, 1911 had an average temperature of 1.0ºF.

Update: Saturday came in with a high of 25ºF and a low of -13ºF. So, the week of April 7-13th is now the coldest (and this should be the bottom), with an average temperature of +2.2ºF.  This the coldest April week since April 3-9, 1924, when the average temperature was +1.9ºF.  

The lowest temperature this week was 21 below on the 10th, the lowest April temperature since 1992. The only daily record temperature set was the low of 15 below on the 11th, which broke the previous record of 12 below set in 1936.

From my favored standardized anomaly viewpoint, the average daily temperature on Thursday, April 10 was 3.0 standard deviations below normal. This is the largest daily negative anomaly since June 4, 2006 (-3.4). However, this was only the absolute largest anomaly since May 28, 2011 (+3.1). A quick analysis of the weekly anomaly, using the full Weather Bureau/NWS era, 1930-2013 as a base comes to -2.9. This is no where close to the greatest negative weekly anomaly in April: April 20-26 1924 and 1948 both came in at -4.0.

Update: The average temperature of +2.2ºF for April 7-13 is 3.0 standard deviations below the 1930-2013 mean. 

How did this happen: cold low aloft. Here's the mean 500mb heights for April 6-12:
Courtesy NCEP/NCAR reanalysis
There have been no upper air records set or even approached. Rather, it's the duration of the cold pattern that has produced the cold April week.

Thursday, April 11, 2013

Coldest Morning This Late in Two Decades

Courtsey of the FAA
I'll be posting a wrap-up of the current cold snap this weekend, but in the meantime, it's worth noting that the low (through 6am) Thursday at the Fairbanks Airport has been -20F. This is the lowest temperature this late in the season since 1992, when the temperature fell to 23 below on April 13th. It's slightly colder in the usual places, with 24 below at Goldstream Creek and the Woodsmoke CWOP near North Pole.

Sunday, April 7, 2013

Interior Alaska Temperature Anomalies: Hills vs. Valleys

I was talking with a colleague this past week about standardized anomalies as a way of grouping locations into broad climate regimes (e.g. the Alaska climate divisions work in Bieniek 2012).  A primary question is to what extant different elevations anomalies are correlated. This is hard to answer for Alaska because there are so few stations above their respective valley floors with long periods of record. However, I thought I'd give it a go for Fairbanks-land.

Here's a plot of the difference in monthly mean temperature standardized anomalies (anomalies computed from the NCDC 1981-2010 normals) between Keystone Ridge and Fairbanks Airport (14 miles apart) for entire period of record for Keystone Ridge (June 1996 to present). This is not an ideal test as Keystone Ridge is only 1200' higher elevation than the Fairbanks Airport. However, data for both sites are complete and there is no differing time of observations to confound the question. The way this plot is constructed, positive values indicate the higher elevation station is warmer than expected compared to the valley, and vice versa. In winter, this is straightforwardly interpretable as variations in mean monthly inversion strength. In summer, the situation is more complex but certainly differences in the number of rainy days will effect the differences in anomalies.

The overall correlation between monthly temperature anomalies at the valley and higher elevation site is an very impressive 0.94. Looking at individuals months, May and October have correlations of 0.99, while December has the lowest correlation at 0.88. In the above plot there are some interesting outliers. The largest negative anomaly is November 2003. This was a wet and cloudy month, with only minimal inversions most of the time. The largest positive anomaly is December 2005, with exceptionally strong inversions (and hardly any precipitation) prevailed the second half of the month. Just eyballing the plot, there may be some longer term signal. Since late 2007 there have been a (seemingly) large number of months with negative differences, while 2004 and 2005 had a large number of months with positive differences.

Variations in daily anomalies are greater, as the plot below since 2011 shows, I've presented a slightly different view in this case, with the actual Fairbanks Airport daily anomalies in green and the Keystone Ridge difference in red. Again, positive values indicate that Keystone Ridge is warmer than expected compared to the valley, and vice versa.

Note: it would be better to use the anomalies calculated from  means and standard deviations for the overlapping period of record (again, June 1996 to present), but it turns out that the difference from using the 1981-2010 normals is, in this case, negligible, and since I otherwise use the current NCDC normals for calculating standardized anomalies, I chose in this case to remain consistent. 

Saturday, April 6, 2013

Cold April Morning

Fairbanks-land awoke Saturday to the coolest weather this late in the season in several years. A decent pressure gradient across the Interior kept winds blowing in some valley locations overnight, but where winds dropped off temperatures dipped well into the teens below. But hey, with more than 14 hours of sunshine to enjoy, I'm not complaining.

Lows Saturday morning included:

Goldstream Creek: -16F
Eielson AFB: -18F
Fort Wainright: -14F

Valley locations where winds persisted were notably milder:

Woodsmoke CWOP:  +1F (near North Pole)
Mile 42 Steese Highway: -2F
Fairbanks Airport: -3F

Higher elevations were mostly breezy and nippy:

Keystone Ridge: -3F
Wickersham Dome: -5F
Cleary Summit: -5F

Tuesday, April 2, 2013

Fairbanks Winter Wrap-up

It's April now, so the 2012-13 cold season is in the books. Here's how temperatures shook out: 

Unrelenting cold weather early in the season gave way to a much more mixed temperatures starting just before New Years. Overall, the average temperature from October 1 through March 31 was an even 0.0°F. This is 1.4 degrees colder than last winter and the third coldest October through March period since 1976. The first half of the winter, October through December, with an average temperature of -1.1°F was the coldest since 1961 and the third coldest in the 82 years of the Weather Bureau/NWS era. In stark contrast, the second half of the cold season, January through March, the average temperature of 1.1°F was the mildest January through March period in Fairbanks since 2006.

To mind my the highlight of the season was the dreaded ran January 14th. There are still stretches of Murphy Dome Road that are ice covered from this rain (though that is now improving rapidly).