Interestingly, however, the month was not more cloudy than usual in the Fairbanks area - in fact the mean cloud cover at the airport was lower than any other recent year except 2013 (when June was very hot and sunny). The CRN site located 11 miles NE of town recorded 18.6 MJ/m2 of solar radiation, which is slightly below the 2003-2015 average of 19.3 (standard deviation=2.1), so at that site it was somewhat cloudier. The high rainfall total combined with only modest cloud cover is consistent with the rainfall being unusually convective; thunder was observed on 12 days, which is the highest number of days in June since 2010.
Compare this pattern to what happened two years ago, when June was the wettest on record. In that month cloud cover was far above normal and thunder was observed on only 2 days. The maps below show the 500mb height anomalies in the two months. Back in 2014 there was a low pressure anomaly over the state, but this year there was a ridge to the southwest and a trough over the Arctic Ocean. Not all wet Junes are created equal in Fairbanks.
The maps below show the anomalies for June at 16 stations across the state. Except for Annette Island last month, the below-normal temperatures at Fairbanks and Bettles are the first cool anomalies to show up at any of these stations since December.
Interesting, because I'd thought for some time now that the recent weather pattern of warmer than normal winters and the cooler summers might largely be due to increased cloud cover. This would of course have an inverse result for the seasons, clouds generally keep it warmer in the winter but cooler in the summer. Perhaps what's different this year are the storms are smaller in size, so that it can be raining hard one minute and the sun be out the next. That has certainly been the pattern for the last few days out here east of Fairbanks.
ReplyDeleteBJ, your hypothesis is plausible, but previous work suggests that cloud cover is not always the primary modulator of temperatures in winter - see here:
Deletehttp://ak-wx.blogspot.com/2015/04/winter-2014-2015-cloud-cover.html
On the other hand we have this:
http://ak-wx.blogspot.com/2014/04/fairbanks-cloud-cover-vs-temperature.html
A more in-depth look at the topic for different times of year would be most interesting.
The Fairbanks airport is somewhat unique as periodically on cloudy days with broken to scattered layers the sky is devoid of clouds directly overhead the obs station. They mainly form over the hills SW>N>SE (and sometimes South) and move over the site depending on air flow.
ReplyDeleteThe Ester Dome webcam west of Fairbanks (http://avcams.faa.gov) will show this and is often obscured by clouds at that elevation about 2000' above town. Why there's no camera at the airport remains a mystery.
Gary
Interesting Gary. It makes sense that local subsidence caused by nearby terrain will sometimes affect cloud conditions over town.
DeleteIt's not absolute as few natural phenomena are and seems to occur when the nearby clouds are few>broken. Broken>overcast covers all.
DeleteToday it was mainly sunny at the airport from 12-4pm yet clouds surrounded the location primarily over nearby hills I assume due to heating and lifting as that terrain is prone to do. There is some packing effect of clouds based upon horizontal distance I realize.
During those conditions the Ester Dome webcam's loop function can be watched for intermittent ground shadowing of the airport runway as seen in the Southeast view.
All I know is it's a rare occasion when there are clouds forming over the airport and the air above the hills or valley to the south is devoid of condensation.
Gary