A trough line anchored to an upper low in central Saskatchewan will move across the Red River Valley tonight, bringing with it strong to severe thunderstorms.
As an upper low tracks eastward through Saskatchewan, an associated surface trough will slowly progress with it towards the SK/MB border. By late this afternoon, the trough line will be positioned from about Nipawin in central SK south towards Estevan, SK. Along with this feature, an upper wave will be moving into the area as well, with a 850mb cold front stacked on top of the surface trough by 21Z.
With the surface trough/upper cold front triggers in place, any storms that develop will have ample instability (SBCAPES of 1500 J/kg to 2000 J/kg alongside LIs of -6 to -9) as well as favorable wind profiles, with south to southeasterly surface winds veering to westerlies aloft. As well, a 40kt west-southwest jet will be poking into southern SK by late this afternoon.
Thunderstorm Outlook for August 7th, 2010 valid until 00Z
What does this all add up to? Likely several strong storms with the outside chance of a severe storm in the Kamsack, Yorkton, Moosomin, Carlyle, Swan River, Dauphin, Minnedosa, Virden and Melita areas. These areas will likely see a series of strong thunderstorms develop this afternoon, with a slight risk of severe thunderstorms. The biggest risk from these will probably be large hail (maybe loonie to golf ball sized) and heavy rain. Should a storm develop supercell characteristics with a good southeasterly inflow, there is a slight chance that a tornado may develop.
As the sun sets, a 25kt 850mb jet will override the warm front in North Dakota and help develop a MCS that will move eastwards into the RRV late this evening into the overnight period. The biggest risk from these storms will be heavy rain.
After this noisy evening, Winnipeg and the RRV should be in for a nice day for the next couple of days with highs approaching or reaching the low 30’s before the weather cools off a bit mid-week with the upper ridge flattening out as a strong impulse enters the northern Prairies bringing some cloud and showers/thunderstorms into the southern Praries. There is a slight chance of an isolated thundershower on Sunday along the remnant trough line in the RRV.