A comparatively stagnant upper-level pattern will remain in place through the medium range, featuring troughs in the Pacific and GL with an ongoing ridge anchored in the central/western USA which will bulge northward into the Prairies.

Troughiness in the east will face some resistance downstream as Atlantic Canada continues to be affected by periods of milder SW flow, although a series of cooling fronts moving in from the west will lead to bouts of unsettled weather and some modest cooling.

Rounds of active weather and variability look likely for ON & QC as well. Each frontal passage could spark rounds of showers and thunderstorms but also mark some refreshingly pleasant high pressure areas moving into the region behind them.

00z EPS 500mb height anomalies, days 1-5:


Days 6-10:


Despite some degradation in the amplitude of the pattern the extended range displays little notable alteration via the GFS ensembles as the continental H5 ridge remains oriented near the Four Corners in the USA. As usual this timeframe suffers from an increased level of uncertainty and bears additional scrutiny moving forward.

00z GEFS 500mb height anomalies, days 11-15:


00z NAEFS temp probabilities, days 8-14:


WPC total precip, days 1-7:


Tropical Depression Four has formed in the Atlantic, developing from a disturbance previously designated as Invest 94L.

TD4 looks to struggle with dry air and wind shear so the NHC has tempered expectations for any notable strengthening through day 5. Still, it represents another early system for the MDR in the vein of Bret in June.

Visisble satellite view of TD4:


NHC 5-day track:


July 4th 2017 SST profile in the Atlantic basin:


July 4th 2016 SST profile for comparison:


Severe thunderstorms impacted parts of SK and MB yesterday. There were multiple reports of large hail and a confirmed tornado (of currently undetermined strength) near Alida.

This is the latest summary from EC.