Flash Flood Threat and the Long Range Update

Conditions look very ripe for heavy, drenching thunderstorms over the eastern Prairies and into parts of northwestern Ontario through Saturday evening.

Unusually moist air surging up from the south will feed the thunderstorms, leading to the possibility of widespread flash flooding from southeastern Saskatchewan, through southern Manitoba and into northwestern Ontario the next 36 hours.

The main threat area through this evening will be southeastern Saskatchewan and into southwestern Manitoba. For Saturday, the highest threat is from south-central Manitoba into northwestern Ontario.

The two images below show the ECMWF model forecast for precipitable water early this evening and again Saturday evening. Precipitable water is the depth of water in a column of the atmosphere if all the water in that column were precipitated as rain.

When you see amounts in excess of 1.6 inches this far to the north you have to be concerned about flash flooding.

The ECMWF 48-hour rainfall forecast in inches through Saturday night is shown below.

You can see that the model is concentrating the heaviest rainfall over Manitoba with amounts as high as 50 mm (2 inches). Obviously, with any slow-moving storms or training storms there could easily be twice that amount in some localized areas.

In addition to the flash flood threat, some of these thunderstorms could produce damaging winds and hail with the potential for an isolated tornado.

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This is my latest interpretation of the ECMWF model bi-weekly long range update that goes through the week of July 21-27......

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