A band of lake effect rain has developed off Lake Manitoba this morning and is currently affecting parts of west Winnipeg. Cool air (0c at 850 mb) flowing over the warm open waters of the MB lakes (16-18c) has created these bands of lake effect precipitation which should persist this afternoon into tonight. Currently low level winds are from a 300 degree orientation which is advecting the band into west Winnipeg and areas northwest. Rosser has picked up 4 mm of rain this morning underneath the band. Outside the band, the sun is shining in parts of Winnipeg!
For this afternoon and evening, models indicate low level steering winds should become more northerly, with a 330-350 orientation which should push the Lake Manitoba bands westward through Elie and Sanford and areas west. A 330-340 band off Lake Winnipeg would affect the Patricia Beach and Beausejour areas. (see example of 330 degree squalls from last October) I expect the bands to intensify this evening and tonight off both Lake Manitoba and Lake Winnipeg as a cold pool of -5C air at 850 mb moves over southern MB. This will give a 20C temperature differential between the lake water and 850 mb temperatures, which is getting extreme for lake effect precipitation (you need a minimum differential of 13c for lake effect initiation). There's even a chance that the precipitation could mix with or change to wet snow tonight into Friday morning, although I suspect the warm lake waters should maintain the precipitation mainly as rain.
The good news is that we should see a moderating trend this weekend with dry conditions and warmer temperatures as this cold pocket of air moves east.
Lake effect update.. Interesting to see squalls starting to re-orient themsleves this afternoon as low level winds become more northerly. The 300 degree rainbands off Lake Manitoba which had been affecting Winnipeg are now weakening, while a new 330-340 band sets up further west between Elie and Portage. See attached Doppler radar image from 12:20 pm showing this lake effect transition in progress. Note also lake effect bands starting to develop off Lake Winnipeg.