The disappearing cloud south of Thompson, MB of November 27, 2005

What happened

A slow moving stratiform cloud deck was observed covering a large portion of northern Manitoba on the morning of November 27, 2005. The region was under a light northwesterly flow with little or no thermal advection. Observations from the Thompson airport indicated overcast stratocumulus with morning ceilings as low as 2300 feet ASL lifting to 3000 feet in the afternoon; however, most observations averaged around 2600 feet. Pilot reports during the daytime hours indicated overcast cloud with bases ranging from 2400 to 3000 feet ASL and tops around 3600 feet. There were three pilot reports which included both bases and tops, and these indicated a cloud thickness of 800 feet, 700 feet, and 900 feet respectively. Very light snow with visibilities ranging from 6 to 10 miles was reported under this deck of stratiform cloud, mainly at Thompson, but also at Lynn Lake and Norway House when they were under the cloud deck.

Also evident on satellite imagery throughout the day within the stratiform cloud deck was an area downstream of Thompson with little or no cloud. This null area appeared to originate at a point immediately downwind of Thompson, then widened out towards the south.

Speculation is that a tall smokestack provided nuclei around which cloud particles could coalesce, and the result was a scouring out of the moisture from the cloud by the cloud condensation nuclei downwind of the smokestack.

Satellite images

Here is the high-resolution visible satellite animation

Prog tephigrams

Here is the prog tephi from 18Z from the GEM model, for Thompson
Here is a closeup of the tephigram shown above

Email the webmaster