Impact of Clouds on Temperatures

The last 24 hours have featured a textbook example of the impact of clouds on valley temperatures in Interior Alaska in winter. Here is a plot of the hourly temperature at the Fairbanks Airport. Variations in temperature are completely related to changes in clouds cover: clears out for a few hours, the temperature drops 20 degrees. Clouds return, and the temperature pops right back up. In contrast, here on Keystone Ridge, the temperature has varied by 5 degrees in the same time, -1F to -5F

Inversion Collapses: Cold Snap Ends

Temperatures aloft warmed dramatically over the past 36 hours, and persistent cloud cover and a moderate pressure gradient have taken their toll on the inversion. Here is a plot of the lowest 1000 meters from the morning sounding from today and Monday.


At 2am today (Nov 23) the temperature at the Fairbanks Airport rose to 2 above. This effectively ends the cold snap. The numerical models have not distinguished themselves in glory with the end of this event, and that is directly related to the inability of the models to effectively resolve the processes in the very near surface (boundary layer). That said, the airmass remains chilly and if and when clouds break temperatures will again fall in the valley. However, the unprecedented nature of this cold snap is over. I'll have a wrap-up in the next couple days.

Fairbanks Cold Snap Update

For the week ending Nov 21, the average temperature at Fairbanks was -30.1F. This is, by far, the coldest 7-day average temperature so early in the season and the coldest week in November in the WB/NWS era (since 1930). In the early years, when observations were done by cooperative observers, the week ending on Nov 30th in 1909 and 1927 were colder.

Clouds and some light snow have arrived and overnight temperatures have been mostly in the 20s below in the valleys. On exposed hillsides and channeled valleys a breeze picked up too. Here at Keystone ridge at 6am, -10F with northeast winds about 15mph with gusts to about 25 mph. Air quality is good!

Solar Noon in Barrow

Here's the FAA webcam shot looking south from the Barrow airport. The photo was taken at 116pm AST, which is very close to solar transit.

Updated Records

Here's am update showing the record lows that have been set this month at Fairbanks. The low of -38F this morning breaks the previous record of -35 set in 1904.

Dramatic Cooling

Here are plots of the temperatures in the lowest 1000 meters from the upper air sounding at Fairbanks from 3am AST Sunday and 3am AST Monday. While the surface temperature was only about 3C cooler Monday morning that Sunday morning, temperatures aloft fell much more: over 10C at 100 meters above the ground; the temperatures aloft are now as cold or colder than last week.

The NOAA-19 Polar orbiter infrared image from 5am AST Monday shows lots of cloud scraps across the interior but not much organized yet.

Coldest Early Season Week of Record at Fairbanks

The airmass cooled dramatically during the day Sunday but few clouds showed up, allowing for another very cold day. At the Fairbanks Airport, the morning low of 34 below, but the temperature fell to 37 below during evening, breaking the previous record of 36 below set in 1993.

For the week of Nov 14-20, the average temperature at the Fairbanks Airport was -27.6F. This is the lowest weekly average temperature of record so early in the season. The previous record was -26.5F set Nov 7-13, 1989. It is also very close to the coldest week anytime in November since 1930, when the Weather Bureau began observations: currently that record is -27.9F set November 21-27, 1948. That record will likely be broken after today. Prior to 1930, there are a couple of end-of-November cold snaps that far exceed what we've had thus far: In 1927, the average temperature Nov 24-30 was -36.6F and the same week in 1909 had an average temperature of -34.3F

Cold Moving East

The eastern Interior hung on to clouds a couple days longer that central and western sections, but skies have cleared now and temperatures fallen. The low of 46 below at Northway ties the record low for November 20th. Other low temperatures include 46 below at the Tok PWS, 45 below at Chicken and 43 below at Eagle before the wind picked up.

This morning's photo is the 11am view from Lake Minchumina, looking southeast toward Denali and the sunshine.

How Unusual is this Cold Snap?

An interesting, and increasingly asked question is: "how unusual is this cold snap?"

First some more numbers, just looking at Fairbanks (1904-2010):

Saturday (Nov 19) was the fifth day (in a row) with the daily minimum temperature 35 below or lower. Only four other Novembers have had five or more days with low temperatures of 35 below or lower.

Thus far, three days have had maximum temperatures of -20F or lower (Saturday will likely be the fourth). Eleven other Novembers have had three or more such days and six have had four or more.

The lowest temperature (thus far) has been -41F; this been exceeded in nine other Novembers.

However, this event is occurring not toward end of November, but around the middle of the month.

At the close of Saturday, the 7-day average temperature will be about -22F; there have been five other years that had a 7-day average temperature of -20F or lower ending November 20th or earlier. The coldest 7-day average temperature ending on or before November 20th is -26.5F, which occurred on the week ending November 13, 1989. In second place is Nov 11-17, 1956 at -23.9F.

Another way to look at this, though probably of dubious value, is to ask when the last time a cold snap set four daily record lows? Answer: September 1992, a "black swan" event if ever there was one in Interior Alaska. I say dubious because three of the four records broken were what are sometimes called "low hanging fruit", as can be seen in this plot of November daily record lows for Fairbanks:



Disclaimer: While I have doubts about the veracity of some of the pre-1930 data, it's what the NWS uses for daily records, so I include it here.

The three record lows of 33 below were the only records that high after November 4th. From this point onward only one day has a record lower warmer than -36F.

So, is this event unprecedented; no. Unusual? You bet; similar cold snaps at this time of year have occurred only a handful times in the past 106 years, and this may approach the coldest early season prolonged cold snap (before late November), though I'd guess at this point the 7-day record low mean of -26.5F set in 1989 will stand.

Strong Inversion

Back home now, so more useful posts, and I can comment too!!

Here's a plot of the lowest 500 meters of the upper air sounding from Fairbanks this (Saturday) morning. A fairly typical "strong inversion" situation, worth 30+ degrees F. Readily reflected in the surface observations.

At 8am…

Fairbanks Airport -35F
Eielson AFB -37F
Woodsmoke PWS -41F (near North Pole)

Cleary Summit -3F
Keystone Ridge -5F
Parks Highway RWIS -8F (at FNSB border)

Looks like this will change early next week as a tight cold low drops south from the high Arctic into the western Interior. I expect the inversion will largely break with clouds and light snow. There is a good chance that the hills will have somewhat lower temperatures than earlier this week while the lowlands will be substantially warmer than it has been.

Cold Continues

Summary from my colleague Corey B. with a nice summary of where this cold snap stands for so early in the season:

Public information Statement
National Weather Service Fairbanks AK
304 Am AKST Sat Nov 19 2011


…The Records Continue to Fall at Fairbanks...

The early winter November cold snap continues to re-write the
record books at Fairbanks. The current cold snap will go down in
the record Books as one Of the most severe early season cold snaps
at Fairbanks.

The high temperature yesterday at the Fairbanks International
Airport was 21 below. This breaks the previous record low maximum
temperature Of 19 below Which was established in 1969. The low
temperature yesterday Of 36 below breaks the previous record low
For the date Of 33 below also set in 1969.

At 213 Am this Morning...the temperature at the Airport dropped to
36 below. This breaks the old record low For November 19th of 33
below in 1969.

Today (Saturday) marks the 5th consecutive day with a low
temperature Of 30 below or colder at the Airport. This Ties with
1956...1969 and 1989 For the most consecutive days with a
temperature of 30 below or colder so early in the winter season.

The low temperature has now been 35 below or colder each Of the
last 5 days. This has never happened before so early in the
winter season at Fairbanks. The old record was only 2 days...and
was Last recorded in 1989.

The high temperature has now been 20 below or colder each Of the
last 3 days. This ties with 1989 For the most consecutive days
with a high temperature Of 20 below or colder so early in the
winter season.

Temperatures Over the Next Week Are Expected to Remain Well below
normal. A Cold low will drop out Of the Arctic and into the
western Interior early next week. The Airmass aloft will be colder
than the airmass currently across the Interior. However...there is
fairly high confidence that this next push Of cold air will be
accompanied by clouds and flurries. The clouds will act as an
insulator and keep temperatures somewhat warmer than this past
week. Temperatures much of next week Are expected to be in a range
of 10 to 25 below. There will likely be little difference in the
temperatures next week between the hills and valleys as the clouds
and depth of the cold air will prevent a low level inversion.

$$

CB

Record Low Friday

Update:

Another record so far early Friday, thanks to the record lows being significantly warmer. Fairbanks Airport 39 below breaks the previous record of 33 below set in 1969.

Low temperatures for Friday will be completely dependent on end time of the climate day, as temperatures are rising. For example, the low of 39 below at UAF West Ridge is a record; that was the temperature at 9am Thursday, and at 9am Friday it was up to 23 below. Temperatures in the hills are approaching zero, so about a 30 degree inversion this morning.

Few more record lows

A few more record lows were set Thursday in the Interior.

Fairbanks Airport: -41F old record -39F in 1969
North Pole: -49F old record -46F n 1969
Eielson: -43F old record -40F in 1969
UAF West Ridge: -40F old record -35 in 1969

The reported low in the Interior of -54F at Manley Hot Springs looks suspect, as this is seven degrees colder than the 9am temperature, when there was ice fog and no wind. Manley does not usually run so much colder than Tanana (low -42F) in these situations. Not impossible, but suspect.

Why are North Pole and Eielson Colder than Fairbanks?

While the North Pole and Eielson areas aren't always colder than Fairbanks, that is often then case in the winter (when there is not a Chinook) and for summertime low temperatures.

First, even more so than Fairbanks, North Pole is a flat land with lots of old sloughs and channels of the Chena and Tanana Rivers that provide good places for cold air to pool.

Second, there hardly any human development to the east and northeast of North Pole, while to the northeast of the Fairbanks Airport is, well, Fairbanks City. This is important in winter because the prevailing drainage flow of air is from higher to lower elevations, which in both cases is (north)east to (south)west.

Third, the North Pole is in "collection" area for cold air draining down the Chena River valley and far from any significant ridges. This helps keep wind speeds in North Pole very low in winter. The Fairbanks airport, in part influenced by nearby Chena Ridge, sometimes gets more wind in the winter than North Pole, which allows for more mixing of air, which keeps it from being quite as cold as North Pole.

More Record Lows

Here's the NOAA-19 Polar orbiter infrared image from 2pm AST Wednesday, showing cold air pooled in the valleys and clouds south and east of Fairbanks.

A few more record lows have been registered in the Fairbanks area, including 37 below at UAF West Ridge and 46 below at North Pole. This is not the coldest weather so early in the season. In 1989 a similar cold snap produced a low temperature of 46 below to North Pole and 44 below at Eielson AFB on November 13th.

Record Low at Fairbanks and Eielson AFB

The low temperature Tuesday at Fairbanks International reached 35 below at 1114pm. This is a new record for November 15th, breaking the previous record of 33 below set in 1969. Eielson AFB has already set a record low for Wednesday, November 16th. At 4am AST the temperature at Eielson was 38 below, breaking the previous record for 37 below set in 1956. North Pole had a low of 39 below on Tuesday, one degree shy of the record low of 40 below also set in 1969.

The inversion is slowly growing, with temperatures in the hills steady in the teens below.

Cold is Here

Not much of an inversion on this afternoon's RAOB from Fairbanks. Here's the plot from the University of Wyoming. At least a few record lows are likely to fall over the next 24 hours. Fairbanks is 28 below at 6pm, and the record is 33 below. The record for Wednesday at Bettles is only 42 below, which cold also be broken.

First 40 Below

The first 40 below temperatures of the season occurred overnight in the northern Interior. Some low temperatures through 5am Tuesday include 44 below at Arctic Village, 43 below at the Coldfoot SNOTEL and 40 below at Chalkyitsik RAWS (half way bewteen Chalkyitsik and Fort Yukon)

November Chill Starts

Updated:

Temperatures are falling smartly now over most of the Interior as the airmass cools and cloud cover begins to break. Here is the NOAA-19 infrared image from 5am AST Monday. Some lows through 10am AST temperatures include 38 below at Arctic Village, 36 below at Norutak Lake, west of Bettles, 33 below at the Beaver Creek RAWS southwest of Fort Yukon and 32 below at the Coldfoot SNOTEL and the Jim River DOT camp at Mile 136 Dalton Highway.

Record lows at Fairbanks are 33 below on Tuesday (in serious jeopardy) and 41 below on Wednesday, which also might go down.

We are now close enough to winter solstice that there will be very little solar based diurnal trend.

Cold Weather on the Way

Unusually cold weather is on the way for Interior Alaska for the upcoming weak. Here is the 12Z ECMWF valid at 3am AST Wednesday 500mb heights and 850mb temperatures (the color field). I've flipped the image so that the view is "Alaska-centric". The purple color over the eastern Interior and the western Yukon is -24C, and there is a core of colder than -28C over east of Northway. This is easily cold enough to support valley temperatures of 40 to 50 below in places the go clear and calm for a couple of days. This is pretty cold for mid November. With the airmass this cold inversions will not start off especially strong, but by late in the week inversions may become stronger.