Inversion Busting Winds

After diminishing for about 12 hours late Thursday night and Friday morning, winds picked back up Friday afternoon, and in spite of clear skies, winds overnight broke through the inversion, producing dramatic temperature swings in valley locations. Here's a high frequncyplot of temperatures from a suite of sensors near Smith Lake, off the west end of UAF West Ridge, showing a temperature rise of more than 10C in just a few minutes:

Courtesy UAF/IARC

Below is a plot of the hourly temperatures from Keystone Ridge, Goldstream Creek and Fairbanks Airport. Keystone Ridge, where winds have been northeast 15 to 30 mph since late Friday afternoon,  shows steady gradual cooling.The Goldstream Creek site shows, like Smith Lake, temperatures rising dramatically Friday evening, with gradual cooling since then. This well mixed boundary layer reflects the turbulent mixing produced by the winds. The situation at the Airport is more complex. The temperature did not pop-up until just before midnight, and a pool of cold air sloshed back over the airport between 5 and 7am. This cold pool is now being eroded away.

A Bright and Sunny Morn

Courtesy of Alaska Climate Research Center

It's a lovely day in Fairbanks-land, with blazing sunshine and temperatures to warm the hearts of any Alaskan. Lows this morning include:

Woodsmoke PWS: -30F (near North Pole)
Goldstream Creek: -29F
Eielson AFB: -28F
Two Rivers PWS: -27F
Fairbanks Airport: -26F
UAF West Ridge: -20F
College Hills PWS: -13F (near top of Balaine Hill)
Gilmore Creek CRN: -5F
Wickersham Dome: -2F
Keystone Ridge: -1F
Clearly Summit: +1F

Barrow Still Hot

Here's an update of the analysis of the ongoing ultra-warm autumn at Barrow, now that there is some sea ice in the area. Through the first 13 days of November the average temperature at Barrow is 9 degrees above normal (compare to Fairbanks, which is more than 8 degrees below normal for the same period). The plot shows the daily temperature departure from normal since September 1. Since September 11th, only two days have had an average temperature even slightly below normal. It is entirely possible that this will be the warmest autumn (September-November) of record in Barrow (current record is 25.8F set in 1998). 

Strong Inversion Monday Morning

Here's a plot of the low level temperatures from the Monday morning sounding at Fairbanks. This isn't, overall, an especially strong inversion by Interior Alaska standards, but the steep temperature increase of 23 degrees in just 76 meters is quite impressive. Clouds moved in Monday morning and weakened the inversion in by the afternoon.

40 below on the Flats

Fort Yukon 940am Monday, courtesy of the FAA

The Chalkyitsik RAWS (which is half way between fort Yukon and Chalkyitsik) hit 40 below Monday morning. I believe that this is the first 40 below of the season. The Beaver Creek RAWS has been down to 36 below the Fort Yukon AWOS to 33 below. 

Blogging to Resume

I had to leave Alaska on a family emergency last and had limited internet access. I'll get to questions and have new posts soon. Rick

October Summary for Fairbanks

Here's the summary for October

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
1104 AM AKDT FRI NOV 2 2012

...OCTOBER 2012 WEATHER SUMMARY FOR FAIRBANKS ALASKA...

OCTOBER WEATHER IN FAIRBANKS STARTED OUT WARM AND WET BUT
PROGRESSED INTO A FAIRLY COOL AND DRY PATTERN TOWARD THE MIDDLE OF
THE MONTH. CHINOOK WINDS CREATED UNSEASONABLY WARM TEMPERATURES IN
PARTS OF THE INTERIOR ON THE 4TH UNTIL A WIND SHIFT TO WESTERLIES
BROKE DOWN THE CHINOOK AND PUSHED A NOTABLE AMOUNT OF LATE SEASON
RAIN INTO TOWN ON THE 7TH AND 8TH. ON THE 7TH...0.21 INCHES OF
PRECIPITATION CLAIMED A NEW DAILY RECORD PRECIPITATION FOR
FAIRBANKS AND ON THE 8TH...0.55 INCHES WAS JUST SHY OF THE DAILY
RECORD OF 0.59 INCHES SET IN 1916. THE HIGHEST DAILY PRECIPITATION
OF THE MONTH WAS THE 0.55 INCHES WHICH FELL ON THE 8TH IN THE FORM OF
RAIN. THIS WAS THE HEAVIEST RAIN IN OCTOBER IN FAIRBANKS SINCE
1986.

AFTER THREE MONTHS OF BELOW NORMAL PRECIPITATION...OCTOBER MADE A
COMEBACK WITH A TOTAL OF 1.38 INCHES OF PRECIPITATION...WHICH IS
0.55 INCHES ABOVE NORMAL FOR THE MONTH. DESPITE THE ABOVE NORMAL
PRECIPITATION AMOUNTS...THE SNOWFALL AT FAIRBANKS INTERNATIONAL
AIRPORT THE TOTAL OCTOBER SNOWFALL OF 7.1 INCHES WAS 3.7 INCHES
BELOW NORMAL. UNLIKE MOST YEARS IN FAIRBANKS...THE FIRST MEASURABLE
SNOW ON THE 14TH REMAINED ON THE GROUND TO ADD TO THE DEVELOPMENT
OF THE WINTER SNOW PACK (1 INCH OR GREATER) ON OCTOBER
15TH...RATHER THAN MELTING. IT IS COMMON FOR THE FIRST MEASURABLE
SNOWFALL TO MELT...AND THE SNOW PACK TO DEVELOP WITH LATER SNOWS.

THE FIRST TRACE OF SNOWFALL OCCURRED ON SEPTEMBER 30TH THIS
YEAR...A WEEK LATER THAN THE AVERAGE OF SEPTEMBER 21ST. THIS YEARS
FIRST MEASURABLE SNOWFALL (GREATER THAN OR EQUAL TO 0.1 INCH) WAS
NEARLY TWO WEEKS LATER THAN NORMAL ON OCTOBER 14TH AS COMPARED TO
THE AVERAGE FIRST MEASURABLE SNOWFALL DATE WHICH IS OCTOBER 1ST.
THE GREATEST SNOWFALL OF THE MONTH WAS 2.9 INCHES WHICH FELL ON
THE 29TH.

DURING THE INDIAN SUMMER EARLY IN THE MONTH...ON OCTOBER 4TH...
FAIRBANKS AIRPORT REACHED 61 DEGREES...JUST SHORT OF THE RECORD
HIGH FOR THE DAY OF 62 DEGREES SET IN 1923. ON THE 4TH...COLLEGE
OBSERVATORY COOPERATIVE WEATHER STATION REPORTED A NEW RECORD HIGH
OF 59 DEGREES WHICH EXCEEDED THE PREVIOUS RECORD OF 58 DEGREES SET
IN 2001. THE LOW TEMPERATURE OF THE MONTH AT THE AIRPORT WAS 11
BELOW ON THE 24TH...FAR FROM THE RECORD DAILY LOW OF 22 BELOW SET
IN 1935.

OVERALL...THE AVERAGE HIGH TEMPERATURE AT THE FAIRBANKS AIRPORT
WAS 30.3 DEGREES AND THE AVERAGE LOW TEMPERATURE WAS 14.7 DEGREES.
THE AVERAGE TEMPERATURE OF 22.5 DEGREES FOR THE MONTH OF OCTOBER
WAS 1.7 DEGREES BELOW NORMAL...AND THE COOLEST OCTOBER SINCE 2008.

LOOKING AHEAD TO NOVEMBER...THE WANING DAYLIGHT IS ARGUABLY THE
MOST NOTICEABLE FEATURE OF NOVEMBER. FAIRBANKS LOSES NEARLY 3
HOURS OF DAYLIGHT IN THE MONTH OF NOVEMBER FROM 7 HOURS AND 46
MINUTES OF DAYLIGHT ON THE 1ST WITH A NOON SUN ANGLE OF 10
DEGREES...TO 4 HOURS AND 44 MINUTES OF DAYLIGHT ON THE 30TH WITH A
NOON SUN ANGLE OF 3 DEGREES. THE AVERAGE HIGH AND LOW ON THE 1ST
IS 18 ABOVE AND 3 ABOVE RESPECTIVELY...AND ON THE 30TH IS 7 ABOVE
AND 11 BELOW RESPECTIVELY. THE RECORD HIGH TEMPERATURE IN NOVEMBER
IS 54 DEGREES SET IN 1936 AND THE RECORD LOW IS 54 BELOW SET IN
1909.

Snow Drought

Courtesy of the FAA

Here in Fairbanks snowfall is only about 60% of normal for the season thus far, but it could be worse. Here is a Friday afternoon webcam photo from Kaltag, in the western Interior. Kaltag, on the east side of the Nulato Hills, is one of the snowiest low elevation places in Interior Alaska, with an mean annual snowfall of something around 120 inches. However, as you can see, thanks to the big aloft aloft that has been place for more than two weeks now, there is no snow on the ground at all.

Record Warm October in Barrow

We knew this was coming, but it’s now in the books: Barrow recorded the warmest October in more than nine decades of unbroken climate observations. The first plot shows the daily high and low temperatures this past month (the 1981-2010 normals are shaded for comparison). The high temperature was above normal every single day: the low temperature dipped below normal on just two days.

The mean temperature for the month was 27.5ºF, which is 2.0 degrees higher than the previous warmest October (set in 2006) and 10.3 degrees warmer than the 1981-2010 normal.

How does this compare to the historical data? Although this past October set a new record, it is obviously in keeping with a now decade long pattern of very warm Octobers, as illustrated in the plot below. The black line is simply the average temperature for the five Octobers up to and including any given year. It's noisy, but obviously the later 1930s and 1940s were mild and the 1970s and 80s were cool. After the mid-1990s there was a steep rise that has flattened out now at a level far higher than any five year period in the 1930s or 40s. The orange line really tells the tale:  this is the five year running standard deviation of mean October temperatures. Even during the warm 1930s and 40s there was roughly the same year-to-year variability as in the cold 1980s and 90s. However, that variability has collapsed in the past decade: October temperatures are not varying by very much at all these days.

It’s not just that some Octobers have been warm recently, it’s every October for the past decade has far above normal, and six of the ten warmest Octobers have occurred since 2002. The next plot shows the deviation in the mean temperature each October from the 1920-2001 mean. There is nothing special about the 1920-2001 period except that it ends right before the current streak of warm Octobers starts. Choosing a different long term average simply moves the zero line up or down. The patterns remains the same: the past decade of warm Octobers at Barrow is unprecedented: there is nothing like this streak in the past nine decades.

There’s no mystery why Barrow has become so warm in October: lack of near-shore sea ice. Prior to the late 1990s, the Arctic sea ice was typically either at Barrow or not far to the north and northwest by mid-October; in some years the ice was largely in place early in the month (an in rare occasions ice was in place in September). This allowed cold air to move from the high Arctic onto Alaska’s North Slope with little warming. Air over sea ice, which quickly becomes snow covered, can become (or remain) much colder than over the open ocean. The freezing point of sea water is 29F (lower than fresh water due to dissolved salts in sea water), so the temperature of air that had cooled to much lower temperatures over ice but then moves over water will fairly quickly approach that of the water. This is an important point: it’s not just whether the sea ice is at Barrow or not. The distance to the ice edge matters a lot. A fetch of 400 miles over open water (which is about what it was at the beginning of the October) will have a much bigger impact on air temperature than an ice edge 40 miles away, which will have a bigger impact than the ice edge four miles away. This of course is the same everywhere over open oceans: air temperature is close to the ocean surface temperature.

Below is the sea ice analysis for Halloween from the NWS Anchorage Sea Ice Desk. There is still 50 to 250 miles of open water between Barrow and the sea ice, depending on direction.

Once the ice closes in, the strong forcing to much warmer than normal temperatures caused by open ocean will be gone, and overwinter and spring temperatures are Barrow will depend more on prevailing atmospheric patterns.

Variable Winds Modulating Temperatures

1200 UTC Surface Analysis courtesy of Environment Canada

An interesting wind situation has prevailed in the past day over the Fairbanks area, with widespread northeast winds right down to the valley floor. The average wind at the Fairbanks Airport on Wednesday was 14.1 mph. This is most unusual this time of year for a northeast wind event: persistent winds this strong in winter typically occur with southwest flow following a frontal passage. The surface analysis for 4am ADT Thursday from Environment Canada shows the 1039bm high over the Brooks Range, with a decent, though not extreme pressure gradient over Interior Alaska.  The winds Thursday morning have slacked in some valley areas, allowing temperatures to fall smartly: down to 11 below at Woodsmoke near North Pole and 4 below at Fort Wainwright and Fairbanks International. However, one of the usual cold spots, Goldstream Creek, had puffs of wind all night. The temperature dipped to 2 below about 3am, then was back up to 7 above by 730am.

Barrow will have Warmest October of Record

Barrow looking north, Sunday 1030am. Courtesy of UAF Sea Ice Group

The mean temperature for the first 27 days of October at Barrow has been 28.0F. The warmest October was 2006 with an average temperature of 25.5F. This means Barrow would have to have an average temperature of 8.6F the last four days of the month NOT to set a new record for the entire month. Since winds remain west to northwest, there is no chance at all of that happening and it is a certainty that Barrow will have the warmest October of record. 

October Temperature Departures

Dawn Saturday at Lake Minchumina, courtesy of the FAA

For the first 26 days of October, here are the average temperature departures from normal (1981-2010 normals) for some NWS locations:

Juneau: -2.9F
Anchorage: -1.2F
Fairbanks: -2.1F
McGrath: +1.1F
Bethel: +1.2F
Nome: +2.1F
Kotzebue: +3.7F
Barrow: +9.1F

Find the outlier.

Freeze-Up Nearly Complete

Courtesy of Pro Music

Here's a view from Friday afternoon from the Pro Music webcam looking south across the Chena River in downtown Fairbanks. As you can see, freeze-up is nearly complete.

Wimpy No More

If Tuesday morning's inversion was lackluster by Interior Alaska standards, Wednesday morning's sounding looks a lot more like what we expect in winter. Temperatures above the valley floor have been rising since early Tuesday evening, and overnight the winds picked up. Nothing extreme, but enough to "mix it up". With clear skies under the big high aloft, the valley floor continues to cool, and the resulting inversion becomes self-reinforcing, isolating the valley surface from winds generated by the moderate pressure gradient. The result of all this are temperatures in the teens below in the usual cool areas on the valley floor (-15F at Goldstream Creek at 8am) to the teens above well up in the hills (+16F at Keystone Ridge at 8am). Fairbanks Airport has been down to 9 below thus far, the lowest of the season to date.

A Little Inversion

The surface based temperature inversion was fairly underwhelming at 3am Tuesday, as shown in the plot on the left: only about 9ºC in 1000 meters. After balloon launch time surface temperatures cooled some more before fairly widespread fog developed. Fairbanks Airport got to 6 below, Woodsmoke PWS 14 below and Goldstream Creek 16 below. Here on Keystone Ridge as of 9 am it's been down to 1 above; as I write this I'm looking at lovely dawn colors in the eastern sky, with the tops of the fog in the valley well below.

First Sub-Zero in Fairbanks

Arctic Village Monday afternoon. Courtesy of the FAA

Fairbanks Airport reported a low of 5 below Monday morning, the first sub-zero temperature of the season, and about a week earlier than average. For comparison, the record low for Oct 22nd is 16 below set in 1956.

Chicken reported 21 below and Arctic Village 18 below for lows Monday morning. Just like winter. Only warmer…

Sub-Zero Around Fairbanks

Courtesy of UAF's Alaska Climate Research Center

Friday evening a few of the normally cold spots nicked just below zero, but this sunny Sunday morning subzero temperatures are more widespread. Through 10am lows include:

Woodsmoke PWS -7F  (near North Pole)
Chena Hot Springs: -6F
Goldstream Creek: -5F
Eielson AFB: -5F
Fort Wainwright: +2F
Fairbanks Airport: +3
UAF West Ridge: +4F

Keystone Ridge: +10F

Putting Down the Winter Snowpack

The Fairbanks area received three to five inches of snow over the course of several days early this week, with the result that everywhere in the area now has a solid snow cover. In spite of the mild weather early in the month, this is right on schedule: the long term median date for establishment of the permanent winter snow cover is October 18th. It is possible, but high unlikely, that the current snow cover could be reduced to a trace. Since 1929, twice has there been two inches of snow on the ground (the current snow depth at the Airport) on October 20th, only to have it melt back to a trace later in the month. Snow cover is defined here to be a snow depth on one inch or more at the standard time of day for snow depth reporting (traces do not count) and each day thereafter also has one inch or more on the ground through March 31st.

A couple of things stand out on the chart. First, in the past twenty years there has been much less variability in when the winter snow pack was established compared to previous decades (only one year more than 10 days from the median). Also note that it's a lot more common to have very late establishment of snow pack than very early. Only two autumns has the snow pack been established more than 15 days early (1956 and 1992), but seven times has the snow cover been more than 15 days late (though none since 1982). This includes the remarkable autumn of 1934, when the thin snow cover of November was obliterated by the super Chinook of December 3-8, 1934 and then there was no measurable precipitation until after the day after Christmas, resulting in the only "brown Christmas" in Fairbanks weather history.

Fairbanks Temperature Update

After a mild start, October temperatures having been running below normal mid-month. Here's the 2012 plot of daily standardized temperature anomalies for Fairbanks through Thursday, October 18th.

Freeze-Up Underway

Here's a webcam photo taken Saturday morning from Pro Music looking south across the Chena River in downtown Fairbanks. As you can see, there is some ice showing up now. With sub-freezing weather now in place, the rivers will freeze quickly over the next few days.