Our best chance for a nighttime lightning show so far this summer is tonight. Everything seems to be lining up for lots of flashing, rumbling, and downpours SOMEWHERE between Eugene and Seattle; and the Portland Metro Area is right in the middle.
A cool upper-level low pressure center has been sitting off the southern Oregon coastline for two days spinning moisture and occasional showers/thunder to it’s north. This afternoon we’ve already seen surface-based (from the heating of the day) storms fire over the Cascades. One briefly turned severe with large hail detected just west of Timothy Lake but it’s weakened now.
The setup is very good for a widespread thunderstorm outbreak from northwest Oregon through southwest Washington. The upper low makes it’s move to the north right over us late tonight and early Friday morning. The combination of ample moisture, lifted index down around -4 (5pm-2am), CAPE values up above 500, and good divergence aloft (for lifting) all screams “ACTION” to me. Plus a nice SSE upper level flow.
So when? That’s a tough call. Our RPM model shows storms coming down off the Cascades around 8-10pm, then another surge with the actual upper level low right around sunrise. The WRF-GFS has more generalized storms firing at times overnight. Both models show better conditions with the low slightly farther west than what was forecast 24 hours ago.
So now we just sit back and keep a close eye on the radar and satellite imagery…more updates later most likely.
Chief Meteorologist Mark Nelsen