Autumn Warming

Barrow observed a maximum temperature of 57 °F yesterday, which is almost the highest temperature of the year so far; the highest was 58 °F on July 16.  It has been 45 years since Barrow recorded a summer without reaching 60 °F, so it would be quite noteworthy if it happens this year.  Barrow also exceeded 50 °F for each of the past three days, which is the first time they have been able to string together two or more days above 50°.

The relative warmth in Barrow led me to wonder when the warming effect of reduced sea ice typically shows up on the calendar in Barrow.  As we all know, Arctic sea ice has been much below normal in recent years and is well below-normal again this year (see chart below), despite earlier model forecasts of increased ice (as we've discussed before).  The lack of autumn sea ice in the Arctic waters near Barrow has caused pronounced autumn warming in Barrow in recent years.  The second chart below shows that September and November temperatures in Barrow have been higher than the long-term mean in just about every year since 1997, and the October mean temperatures have been tremendously elevated since 2002.  In previous posts Rick has pointed out the collapse of the inter-annual variance of the October temperatures at Barrow, and of course this is directly attributable to the huge loss of sea ice; the open water in October simply prevents any seriously cold air from settling in over Barrow.

A more precise look at the seasonal timing of the recent warming can be found by looking at the mean daily temperature anomalies at Barrow since 2002; the dark blue line in the chart below shows that warming at Barrow relative to the 1981-2010 normal is maximized in the second half of October and starts to diminish at the beginning of November.  Note that I applied a +/- 15 day smoothing to the 2002-2013 mean anomalies to remove some of the sampling variability; the unsmoothed daily mean anomaly from 2002-2013 actually peaks at +11.1 °F on October 28.  The chart also shows the same data for several other coastal Arctic stations, from Kotzebue around to Deadhorse; the other stations show very similar patterns, with pronounced recent warming in October, although the timing of the peak is a little earlier at Kivalina and Kotzebue in the northwest.

The following two charts show that, interestingly, a similar October peak in recent warming is found at both Fairbanks-area stations and a collection of various other Alaska stations north of 64 °N.  I am a little surprised by this, because I would not necessarily expect the pronounced warming effect from the sea ice reduction to extend so far to the south.  However, the very similar timing of the peak warming at all the stations seems quite suggestive of being caused by the same phenomenon throughout, and there is very high confidence that the sea ice reduction is indeed the cause of the October warming on the North Slope.  The only other possibility I can see is that the weather pattern has coincidentally (and strongly) favored southerly flow and warmer conditions in mid-late October on average in the past 11 years.  A little more investigation will be required to rule out this possibility.

Advancing Night

The long summer day is now fading in Arctic Alaska, as a daily period of darkness advances north across Alaska with the change of seasons.  Last night was the first night that civil twilight was observed at Barrow, i.e. the sun briefly dipped more than 6° below the northern horizon.  However, it will be another 2-3 weeks before it starts to get reasonably "dark" at night in Barrow.

Here are a couple of "night" pictures from the Barrow sea-ice webcam in the past few days: the first, a beautiful scene, taken about an hour and a half before sunrise on Monday, and the second taken a little before solar midnight last night.

Barrow-Area Temperatures - Part 2

[Updated August 19 with polar plots, per reader request.]

A few readers of my original post about the Barrow urban heat island effect suggested that wind speed and direction are important in determining the relative temperatures at the Barrow ASOS and CRN stations.  This is undoubtedly true based on the Hinkel et al study, but I thought I could follow up with an analysis of the 12 years of overlapping data (Hinkel used only a single winter).  To do this, I calculated a daily mean wind vector from the surface observations in the twice-daily balloon soundings, then categorized the wind by both speed and direction and finally obtained the mean temperature difference between the two stations for each wind category.  (Note that a more accurate daily wind vector could be obtained from the hourly ASOS observations; the balloon soundings generally go up only at 3 am and 3 pm AKST.)

The results are shown below, for daily maximum and minimum temperatures in high summer (top 2 charts) and two months from deep winter (bottom 2 charts).  The blue, red, and green lines show the mean temperature differences (ASOS minus CRN) for weak (0-10 kt), moderate (10-20 kt), and strong (20+ kt) winds respectively.  I required at least 10 instances in a single category to compute a mean temperature difference, so there are large gaps in the results for higher (less common) wind speeds.  The purple columns indicate the frequency distribution of the wind direction categories; note that the categories are overlapping.

Based on this analysis, the most pronounced temperature differences between the Barrow ASOS and CRN stations are found for maximum temperatures in summer when winds are out of the east or east-southeast; in this scenario the trajectory of air reaching Barrow airport passes over a lot more land than the trajectory of air reaching the CRN station, and so the airport enjoys the benefit of more solar heating.  The difference is greatly lessened, however, when wind speeds increase, as expected.  When winds come from the west, there is little difference in summer temperatures between the two locations, and high temperatures are even a little lower at the airport with a stiff breeze from the west.

The daily minimum temperature differences for winter show a pattern that is nearly opposite to the high temperatures in summer, with temperature differences minimized for east or east-southeast flow, but with the airport staying a few degrees warmer when there is a light breeze from the west.  The maritime influence is greatly lessened in winter owing to sea ice cover, but it still plays a role in elevating the CRN temperatures when the trajectory is from the east or east-southeast.  Another way of looking at this is that we would normally expect Barrow temperatures to be noticeably higher in winter owing to the heat island effect, but when the flow is from the east or southeast, the air reaching the airport passes over more land and has time for radiative cooling, which brings the airport temperature down relative to the CRN location.

I'm sure there are several more interesting features of the data that could be discussed, but I'll leave it to readers to point these out and suggest hypotheses about their origin.

Update: reader Eric suggested using polar graphs to show the data; this is a great idea and I was able to get close to a true polar graph using the radar chart function in Excel.  See below, along with the station location map for ease of reference.

Northwest Warmth

Kotzebue has been enjoying an extraordinary spell of warm late summer weather lately, and has broken some longstanding records in the process.  The first half of August was the warmest on record, by more than 1.5 °F, based on complete data since 1949 and patchy data back to 1929 (and some earlier years).  The previous record was exceeded for the daily mean temperature as well as for the August 1-15 average daily maxima and minima separately; the previous record was set in 1968 for all three of these metrics.  The chart below shows the temperature anomaly since June 1; until the recent heatwave developed, the summer was averaging a little cooler than normal.

In addition to the August 1-15 record, the week ending August 12 was the warmest week on record that was either wholly or partly within August, with a mean temperature of 66.2 °F compared to 65.7 °F for August 17-23, 2004.  The week ending August 14 also had the highest weekly average low temperature on record for a week ending in August (59.9 °F compared to 58.9 °F in 1977), but the weekly average high temperature was not quite as high as in the 2004 warm spell.  Also, the recent weekly average temperatures did not break the all-time records from June and July of previous years, although the week ending August 12 was the warmest week since early July of 1990.

Brian also points out via email and his Facebook page that the two-week period ending today in Kotzebue has had the warmest 14-day average high temperature since 1898 (at any time of year); so the warm spell is just about unprecedented in this respect.

And one more statistic: the number of days with high temperature of 70 °F or above is already a record for August (8 compared to 7 in 2004), and the number of nights with low temperature of 60 °F or above is easily a record for August (6 compared to only 3 in 1933).

It's interesting to look at the vertical profile of temperature anomalies from the twice-daily Kotzebue balloon soundings this summer, and to compare with the observations from the Barrow soundings about 300 miles to the north-northeast (see charts below).  At Kotzebue, the anomalies aloft have matched up very well with the surface anomalies, and have exceeded +8 °C at times recently.  The upper-air temperatures at Barrow have followed a similar path, with considerable warmth aloft in August, but interestingly the low-level temperatures have continued to track below-normal at Barrow this month.  This illustrates the "de-coupling" of the low-level air from the upper-level air that tends to persist at Barrow owing to the climatological inversion that remains all the way through late August (see discussion here).

Long-Term Precipitation Trends – Part I: Alaska

** Updated 8/17 with charts reflecting percentage changes instead of raw number changes **

Continuing with the theme of precipitation trends, I wanted to look at the rate of change of various precipitation thresholds over the last number of years to see if they are more or less frequent. To evaluate the rate of change, I looked at 4 different precipitation thresholds over the course of the Fairbanks climate record (good precipitation records extends back to 1915). Figure 1 shows the annual number of days for four different precipitation classes in Fairbanks (>= 0.01", >= 0.05", >= 0.25", and >= 0.50"). The only one of the trend lines that was significant at the 95% level (p<=0.05) was the number of days per year with at least 0.01" of precipitation. All the other thresholds were close to the even line but none showed a statistically significant trend (positive or negative). End of story, right?

Figure 1. Precipitation frequency (days per year) at Fairbanks for four different precipitation classes from 1915 to 2013. They are: 1) at least 0.01", 2) at least 0.05", 3) at least 0.25", and 4) at least 0.50".

A dangerous practice in the field of climatology is to make sweeping generalizations by looking at a single station's data. So, let's look to see how things have changed across a wide swath of Alaska. Unfortunately there are not many stations with a record as long as Fairbanks. We can increase the sample size to 21 stations when we set the begin date at 1951 instead of 1915. Figure 2 shows the stations we will use to look at the statewide trend in precipitation events.

Figure 2. Stations (21) used to assess long-term precipitation frequencies.

Looking at the statewide data, I was originally looking at "heavy" events so the categories are a little different. Actually, I was looking for national trends so the criteria were set somewhat higher than would ordinarily be appropriate for Alaska. In any event, the categories are: 1) at least 0.05", 2) at least 0.50", 3) at least 1.00", and 4) at least 2.00". That makes for a little bit of an apples to oranges comparison with Figure 1 – but let's progress nonetheless. Figures 3 through 6 below show the annual percentage difference of all stations from the 1951-2013 station average. To eliminate the effect of stations with large values overwhelming stations with low values, percentage differences were used instead of raw numbers. For example, a station that averages 50 days with 0.05" from 1951-2013 has a 10% increase if a year recorded 5 extra days with 0.05". A station that average 20 days with 0.05" from 1951-2013 has a 25% increase if a year recorded 5 extra days with 0.05". If you combine the raw numbers from those two stations, they would sow a 15% increase in the number of days with 0.05". However, comparing the percentages yields an increase of 17.5%. Therefore, comparing the annual percentage deviation is more meaningful since stations with larger averages would ordinarily drown out stations with low averages.

The number of days with >= 0.05" and >= 0.50" are noticeably increasing at a statistically significant rate (95% level) in Alaska. The >= 1.00" and >= 2.00" give mixed signals and neither trend is statistically significant. This is due in large part to small numbers and a relatively few stations responsible for most of the deviations. 

Therefore, I feel comfortable stating that the number of small precipitation events and the number of moderately-sized precipitation events have definitely increased over the last 60 years here in Alaska. This is not so surprising given the fact that warmer air can hold more moisture and warmer air at the surface with constant temperature aloft (not analyzed) would lead to lapse rate instability. As for the frequency of 1" and 2" precipitation events, they are too infrequent to make judgments on.

Figure 3. Statewide average of percentage change from 1951-2013 average annual number of days with at least 0.05" of precipitation.

Figure 4. Statewide average of percentage change from 1951-2013 average annual number of days with at least 0.50" of precipitation.

Figure 5. Statewide average of percentage change from 1951-2013 average annual number of days with at least 1.00" of precipitation.

Figure 6. Statewide average of percentage change from 1951-2013 average annual number of days with at least 2.00" of precipitation.

Hourly Temperature / Rainfall Numbers

One of the great data sets that NCDC archives is the hourly ASOS observations. These are particularly useful for developing climate descriptions and analyses on relatively short timescales. Much has been made of this summer's cool temperatures and excessive rains but little has been noted on these shorter time-scales.

I decided to compare last year's hourly observations with this year's hourly observations for the June 1 to August 10 time period. Instead of using the DS 3505 ISH data, I pulled the METAR observations directly. There are certain advantages to using the METARs instead of the DS 3505 data; e.g., the distinction between moderate and heavy rain.

From a temperature perspective, 2014 has been substantially cooler than 2013 in Fairbanks. Figure 1 shows the average hourly temperatures during the June 1 to August 10 time period for 2013 (orange) and 2014 (purple). The 25th percentile and 75th percentile lines are also shown. Interestingly, the warmest 25% of this summer's observations are about the same as the mean of last summer.

Figure 1. Average, 25th percentile, and 75th percentile temperatures for every hour of the day during the June 1 to August 10 time period for 2013 and 2014.

Of course this has been an exceptionally wet summer in Fairbanks. As we noted last week, the average day with precipitation has been quite wet. Looking at the hourly data, what we see is that not only have there been many more wet days this summer, but when it has rained, many more daily observations have indicated rain. Figure 2 shows some summary statistics for the number of rainfall observations. The last column on Figure 2 shows that days with rain have more than twice as many daily rainfall observations as last summer. In fact, 10 of the 71 days this summer have recorded rain for 12 or more of the 24 hourly observations. Last year, there were no such days.

Figure 2. Count of the number of rain observations during the June 1 to August 10 time period for 2013 and 2014.

Wind Direction and Precipitation

Readers Eric and Gary have commented recently on the dependence of Fairbanks precipitation on wind direction.  It's widely understood (at least among weather enthusiasts) that westerly or southwesterly flow aloft tends to bring moisture to Fairbanks-land, but to what extent is this relationship borne out in the historical data?  This is a pretty straightforward analysis: I calculated the vector average wind speed at 700 mb (about 3 km MSL) from balloon soundings each day since 1948, and then I categorized the data into 30-degree direction windows, e.g. 0-30°, 10-40°, and so on.  For each direction window, and requiring a minimum wind speed of 10 knots, I then extracted the frequency of measurable precipitation and the average daily precipitation; the results are shown below.

As expected, the highest frequency of measurable precipitation is found for near-westerly flow at 700 mb; for summer the peak is west-southwesterly (230-260°), but for the other seasons, it's close to westerly.  All seasons also show a secondary peak in precipitation frequency; again the summer is distinct, with a frequency peak for easterly flow, but for the other seasons the secondary peak occurs for southeasterly flow.

The second chart, showing average daily precipitation amount for all days (not just non-zero precip days), also indicates a peak in precipitation amounts for westerly or west-southwesterly flow.  However, in summer the average amounts are nearly as high for northwesterly flow (310-340°) and for north-northeasterly flow.  The other seasons show much lower amounts in non-westerly flow regimes, although there is still a secondary peak for southeasterly flow in spring.  It's interesting to observe the extreme dryness of northerly and northeasterly flow in winter: there's no moisture to be had in that situation.

Finally, it's interesting to see the total contribution of each flow direction to the total precipitation at Fairbanks - see below.  The peak is pronounced in all seasons for flow just south of westerly (240-270°), because the preferred wind direction is out of the southwest; so even though other flow regimes can also be favorable for precipitation, they are less common and so contribute less to the total.  (The most common wind direction is 200-230° in autumn and winter, 190-220° in spring, and 230-260° in summer.)

Fairbanks Precipitation Classes

Readers of the this blog do not need to be told that this has been an extraordinarily wet summer. This is already the second wettest June through August on record in Fairbanks. Are we nearing the wettest summer on record because is has rained often or because when it does rain, it rains a lot. To answer this question, let us look at all rainy days in the Fairbanks historical record. Figure 1 shows a series of lines representing the number of days with A) any precipitation, B) measurable precipitation, C) >= 0.10" precipitation, and D) >= 0.50" precipitation for all years during the June 1 to Aug 5 time period.

On average, there are 24 days during this 66-day window with measurable precipitation. In 2014, there have been 29 days between June 1 and August 5 with measurable precipitation (range: 10 to 53). If you include Trace amounts, the long-term average is 38 days and the 2014 value is 47 (range: 14 to 58). In both instances, 2014 is above the long-term average but quite far from the largest values. However, 2014 does lead in several important categories – days with >= 0.25", >=0.33", >=0.50", and >=1.00".

Figure 1. Number of days with A) any precipitation, B) measurable precipitation, C) over 0.10" precipitation, and D) over 0.50" precipitation for all years during the June 1 to Aug 5 time period.

This leads to the conclusion that when it rains, it pours. Figure 2 shows the June 1 to August 5 total precipitation (green line) and the per rainfall event amount (purple line). As you can see, 2014 has reported approximately 0.37" of rain per day with measurable rainfall. Only one other year (1962) even comes close to this year's per rainy day average. That year had 10 fewer days with measurable precipitation through August 5.

Figure 2. Total precipitation and average precipitation per rainy day for all years during the June 1 to Aug 5 time period.

Nine times since June 1st the Fairbanks daily precipitation has exceeded the 95th percentile for the date. In theory, during any 66-day period, the 95th percentile should be exceeded 3.3 times. Figure 3 shows the Fairbanks precipitation exceedance probabilities with 2014 precipitation events overlaid.

Figure 3. Daily precipitation exceedance probabilities with 2014 precipitation events overlaid. Note: The probability lines only take into account days with 0.01" or greater.

Barrow-Area Temperatures

The Barrow Climate Reference Network (CRN) monitoring site has been in operation for 12 years now, and I thought it would be interesting to look at the observed temperature differences between the CRN location and the airport ASOS location.  The CRN station is located about 4.5 miles northeast of the airport station, closer to Point Barrow; the red stars mark the locations on the map below.

To begin with, we know that there is a pronounced urban heat island effect in winter in Barrow (see the 2003 study here), so we expect to see warmer winter temperatures at the airport location.  The 2002-present CRN data confirm this, but also show that the temperature difference between these two locations persists year-round on average.  The charts below compare the monthly means of the daily maximum and minimum temperatures:

The maximum and minimum temperature differences show substantial seasonal variations; June and July show warmer maximum temperatures at the airport (more than 2 °F warmer on average), but minimum temperature differences are largest in winter, especially late winter.  Interestingly, the Hinkel et al study linked above reported cooler temperatures in the urban area in summer compared to their rural measurements, but their rural zone was well to the southeast where the maritime influence was less.  Both the Barrow CRN and Barrow ASOS are close to the coast and so the urban heat island effect remains evident in summer.

The frequency distribution of temperature differences is illustrated in the following two charts, which show that daily maximum temperatures are lower at the airport less than 10 percent of the time year-round, while daily minimum temperatures are lower about 15 percent of the time.  Note that the daily maximum and minimum temperatures are defined for the same midnight-to-midnight period (standard time) at both stations.

The propensity for much higher summer maximum temperatures at the airport, and much higher winter minimum temperatures, is also clearly seen in the charts.  For example, the airport is 5 °F or more warmer by day on 16 percent of summer days, while minimum temperatures are 5 °F or more warmer in Dec-Feb on 10 percent of days.  I haven't looked at the dependence on wind speed, but it's likely that the temperature differences are much larger on relatively calm days, regardless of season (as found by Hinkel et al).

Finally, it's interesting to look at the annual mean values over the 11 complete years of overlapping data - see below.  The blue bars show the airport annual mean maximum and minimum temperatures, and the red bars show the CRN data.  Over this short period there is an upward trend in the annual mean temperature difference between the stations, and further investigation of this might be warranted.  An increase in the urban heat island effect seems a bit unlikely, as the population of Barrow dropped by 10 percent between 2000 and 2010 according to the U.S. census data.  It's possible that the weather pattern has favored less windy conditions in the most recent years, or perhaps the change is related to a minor relocation of the airport observing equipment in April 2008 (according to NCDC metadata records).  This latter possibility illustrates a major part of the rationale for the CRN program - with the CRN data, we don't have to worry about local changes to the environment, equipment upgrades, or faulty sensors.  It is a wonderful source of climate data and will only get better as more stations are added and as the years go by.

June-July Anomalies

Here's a graphical representation of the temperature and precipitation anomalies in the June-July period for 17 first order observing stations around Alaska.  The area of each colored circle is proportional to the anomaly in standard deviations (for temperature) or the 1981-2010 percentile rank (for precipitation).  If the June-July value was near the 1981-2010 normal, then the colored circle is small or non-existent.

The wide extent of the unusual wetness is remarkable; it was the wettest June-July period on record in Bettles, Fairbanks, and Juneau; and Anchorage was only slightly behind its record.  Barrow continues to see much-above normal precipitation, as it has done for many months.

The only dry area in Alaska this summer has been the southwest, which has also been very warm relative to normal.  The magnitude of the unusual warmth at Cold Bay is very exceptional; July was the warmest calendar month on record there, by some margin (55.8 °F compared to 55.2 °F in August 1998).  July also exceeded the 1981-2010 mean for July by an astonishing 3.8 standard deviations.  The lowest daily maximum temperature for the month was 55 °F, which is very close to the average daily high temperature in July.

The chart below shows the monthly mean temperature anomalies since 2004 at Cold Bay, in terms of standard deviations.  After a fairly lengthy spell of mostly below-normal temperatures from 2006 to 2012, the turn-around has been very dramatic, with 7 of the last 13 months being 2 standard deviations or more above normal.  Sea surface temperatures are now well above normal throughout the North Pacific, which is both cause and effect of the persistently warm weather pattern for a broad area including southwest Alaska.

July Rainfall Around Fairbanks

July ended up as the second wettest July on record for Fairbanks (1915-present). Rick compiled a list of monthly rainfall values and I put them on a map. The map below is the result of that compilation. The full list is shown below the map. As you can see, there is a north-south gradient of precipitation in the immediate Fairbanks area. 7"+ in the hills north of town and 5"-6" in Fairbanks proper.

Chatanika-Chena-Salcha Basins
Munson Ridge SNOTEL: 7.79"
Wickersham Dome HADS: 7.42"
Upper Nome Creek: SNOTEL: 7.23"
Little Chena Ridge SNOTEL: 7.15"
Fairbanks 11NE CRN: 6.86"
Stuart Creek RAWS: 6.75"
Manchu RAWS: 6.14"
Mt. Ryan SNOTEL: 6.00"
Little Chena River HADS: 5.91"
Upper Chena Dome SNOTEL: 5.26"
Upper Chena River HADS: 5.22" (Granite Tors Campground)
Chatanika RAWS: 5.16"
Monument Creek SNOTEL: 4.84"
Fort Wainwright RAWS: 4.82"
Teuchet Creek SNOTEL: 4.48"
Small Arms Range RAWS: 4.46"
Eagle Summit SNOTEL: 4.44"
Salcha River RAWS: 3.14"

Tanana River Drainage
Bonanza Creek LTR: 5.68"
Gold King RAWS: 5.15"
Blair Lakes RAWS: 3.05"
Livengood RAWS: 2.83"

ASOS/Coops:
Gilmore Creek: 7.82"
Fort Knox Mine: 7.68"
​Keystone Ridge: 6.77"
Goldstream Creek: 5.80"
Fairbanks IA: 5.78"
East Farmers Loop: 5.76"
Woodsmoke: 5.74"
Eielson AFB: 5.70"
College Observatory: 5.67"
North Pole: 5.66"
Goldstream Valley Bottom: 5.65"
University Experiment Station: 5.44"
Aurora: 5.​05"
Nenana: 4.93"
Tanana: 3.40"
Fort Greely: 1.66"

Warming Trend

The recent two-week spell of unseasonable chill has ended in Fairbanks, with temperatures finally getting back above 70 °F the past three days.  As reader Gary pointed out, the Climate Prediction Center is expecting a warmer than normal August, which I'm sure would be most welcome for residents of the Interior.  I thought it would be interesting to look at the statistical chance of a warm August based on the observed wetter than normal conditions in June and July.  We went through a similar exercise last month based on having a wet June, and suggested then that "unusual warmth appears to be a more likely outcome for the late summer".

The scatterplot below is the same as the first figure in last month's post, but now I've colored the points based on the August mean temperature; the colors correspond to the four quartiles of the 1949-2013 distribution for August temperature.  The slight correlation between June and July precipitation was noted last month.  The most notable feature of the color distribution seems to be that a cool August is favored when a dry June gives way to a wet July (upper left quadrant).  This year we fall in the upper right quadrant, and here we see a slight tendency for warmer than normal conditions in August; 10 of 16 years in the quadrant had a warmer than median August, and 5 of 16 were in the top quartile.  The two exceptions with high June rainfall were 1949 and 1955, but these were negative PDO summers.  This fact suggests that we should divide out the negative and positive PDO years - see the next two scatterplots for this breakdown.

The scatterplot for the positive PDO phase (as we are seeing this year) shows a possibly more robust indication of warmth in August, with 6 of 8 years seeing a warm August after a wet June and July.  It's also interesting that the aforementioned flip from dry June to wet July seems to be more common in negative PDO years.

In summary, wet June and July conditions are, perhaps counter-intuitively, associated with a higher than normal chance of a warm August in Fairbanks, especially when a positive PDO phase is observed.  This analysis agrees with the CPC outlook.

Fairbanks Precipitation Ranking

The forecast for the remaining two days of July in Fairbanks does not include any mention of rain. Therefore, I feel (reasonably) comfortable adding a preliminary rainfall ranking table.

Through July 29th, Fairbanks is approaching their annual normal precipitation of 10.81". When comparing similar monthly intervals from different years, only one January to July period was wetter (1929). In fact, every monthly grouping (ending in July) is ranked in the top 3. The May to July and June to July are far and away the wettest such periods on record in Fairbanks.

Should these numbers change in the next two days, this post will be updated.

Arctic Chill

Cool weather has continued lately in Barrow (see chart below), and it now looks likely that the June-July period there will end up as the coolest in more than 30 years.  The unusual atmospheric circulation is responsible, with persistent troughing over the Chukchi Sea.

Based on the NWS forecast for the remainder of July, the mean June-July temperature in Barrow should end up near 36.0 °F, which would be the coolest since 1982 - and about equal to the 1951-1980 normal.

 Here's the mean 500 mb height from June 1 to July 24:

And the 500 mb height anomaly; with this pattern, a cool, damp summer in interior and northern Alaska is inevitable.