Elevated Inversion

Here's the Fairbanks sounding from Wednesday afternoon, showing a nice elevated inversion. Temperatures were up into the upper teens to around 20 degrees above 2200' MSL, while zero to 10 above at lower elevations.

Sunny...But not Much Warming

Courtesy of Alaska Climate Research Center

The sun is getting higher each day but still is not  high enough to do much to break the surface inversion. The webcam photo from the Alaska Climate Research Center on UAF West Ridge was taken at exactly solar noon. 2pm temperatures are in the 20s and 30s below in the lowest areas, including 30 below at Woodsmoke, 27 below at Goldstream Creek and 23 below at Fairbanks International. In contrast, higher elevation temperatures at 2pm include 6 below at Keystone Ridge and 4 below at Wickersham Dome and Clearly Summit.

Still Warm…Aloft at Least

Fairbanks-land inversions continue to grow early Monday evening: at 6pm, it was above zero in the warmest higher elevations and still in the 40s below on the valley bottoms

Warming Aloft

Temperatures have started to rise above the valley floor in Fairbanks-land. On the right are plots of the temperature in the lowest 1000 meters from Sunday morning and Monday morning soundings. Above about 25 meters above the ground the sounding is warm Monday morning than Sunday morning, with the most dramatic warming between 200 and 400 meters AGL. Since then temperatures have continued to rise: at 10am temperatures are up to 11 below on Cleary Summit, 14 below at Wickersham Dome and 16 below on Keystone Ridge.

Daytime High Temperatures

Weather the past several weeks over Interior Alaska has been dominated by surface high pressure, with clear skies much of the time. Also, during the past couple weeks winds have not been able to break through the inversion. As a result, temperatures have remained strong elevationally stratified. Here is a plot of daytime (7am-7pm) daily high temperatures (based on hourly data) since Thanksgiving Day at eight weather stations in the greater Fairbanks area. The stations are:

WODA2=Woodsmoke PWS (near North Pole), elevation 500' MSL
GCSA2=Goldstream Creek CWOP elevation 577' MSL
PAFA= Fairbanks Airport, elevation 435' MSL
FAOA2=UAF West Ridge, elevation 597' MSL
CLGA2=College Hills PWS (near the top of Baline Hill) elevation 751' MSL
NHPA2=Nenana Hills RWIS (Parks Highway between Fairbanks and Nenana), elevation 1398' MSL
KERA2= Keystone Ridge, elevation 1600' MSL
WICA2=Wickersham Dome, elevation 2230' MSL

The comparative gap in the middle is a function of the narrow elevational band that is intermediate between "valley" and "hill" and there happens to be few weather stations in that band (there is at least one other PWS, that is in the intermediate band at 1100' MSL, CW6333, but it has reported only a few days in the past two weeks). That is too bad because many of the residences in the "hills" are only a few hundred feet above the valley floor. 

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.

The Way Cold Snaps End

Furiously warming aloft since mid-day Tuesday. The morning sounding tells the story. At 6am Wednesday, Cleary Summit+3F, Fairbanks Airport -34F

Normalcy Departs

Steep inversions are the rule this time of year in Interior Alaska, but this is not one of those times. The afternoon sounding reveals a more than 20C inversion, but it's quite gradual by Interior standards. Temperatures at typical residential hillside elevations are back down to around -30F this evening; it's only above about 2000' MSL that temperatures are near -10F.

One interesting feature of this sounding is in the lowest 100 meters, where the temperature is constant (jargon=isothermal). This is typical in ice fog.

Inverion Holds

Here's an updated plot of the inversion, with the Saturday afternoon sounding plotted along with the morning data.

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

Slow Cooling

Today's RAOBS series show only a little bit of cooling at the surface between 3am and 3pm, but more substantial cooling above about 200 meters above the valley floor. Winds here at Keystone Ridge have diminished quite a bit; my neighbor recorded a peak wind of 35 mph Tuesday evening, just before 8pm. Models are forecasting quite a bit of cooling aloft over the next couple of days. I'd guess that Fairbanks International may see the first 40 below of the season sometime late Thursday night or more likely on Friday.