Tomorrow, we are looking at a large, deepening GLC carving through the north-central lakes into central Quebec. It should deepen to about 990 mb, anomalously low pressure for southern Canada in August.

98fndfd_init_2017082100

Within its warm sector, extreme dynamics are anticipated:

  • 12 hour surface pressure falls are expected to exceed 12 mb ahead of the cold front in E ON and QC
  • E ON, central and southern QC will be in the entrance region of a coupled H25 jetNAMUS_250_spd_033
  • H5 heights fall by 90 dm in 12 hours in E ON and QC
  • A strong 850 mb jet will form in E ON and QC, to the tune of 50+ kt in the afternoon hours, contributing to 0-1 km and 0-3 km helicity values in excess of 200 and 300 m2/s2 respectivelyNAMNE_850_spd_030

The dynamics are off the charts for eastern Canadian standards.

As for instability, ongoing convection in S ON will result in a lack of instability in that region although E ON, SC, and SE QC should enjoy a sunny morning and early afternoon, allowing for temperatures to flirt with the 30 C mark and CAPE values to exceed 2000 j/kg.

This lethal combination of CAPE and shear seeks to create an ideal environment for a mixed storm mode of HP supercells and squall lines with bow echoes in the afternoon hours on Tuesday. Supercells could produce large hail and potentially strong (EF2) tornadoes, whilst bow echoes could produce large swathes of damaging winds, simply because of the presence of the 90-105+ km/h low-level jet that could be mixed down to the surface in the torrential downpours associated with PWATs near 50 mm as expected tomorrow. People in the region should also watch for bookend vortices and semi-discrete cells in squall lines that could produce tornadoes.

In the meantime, enjoy the eclipse!

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