Surprise Thunderstorm & Evening Thoughts

July 27, 2009

Thunderstorm just east of Mt. St. Helens this evening

Thunderstorm just east of Mt. St. Helens this evening

Wow…quite an impressive thunderstorm going crazy at this hour.  Check out the cloud to ground strikes…I estimate about 30 in just 15 minutes over the “Dark Divide” area between Mt. St. Helens and Mt. Adams.  That is the divide between the Lewis and Cowlitz river drainages that runs roughly west-east between the two mountains.   You can click on the image to bring up a larger version.  Does anyone think this MIGHT cause a problem tomorrow when the thunderstorm is gone and temps in that area approach 90 degrees?  I don’t remember any significant fires in this area in the last 15 years.

Here are my thoughts at 11pm:

Amazing that we made it to 103 (all airports in the PDX area hit the same temp!) with essentially a flat gradient, or just slightly easterly.  I rode my bike past Crown Pt. around 9am there was just a light easterly breeze.  So with a slightly warmer atmosphere tomorrow, but just a flat/light easterly flow, I figure about 2 degrees warming.    That’s how I ended up with the 105.  As for tonight…whew!  This will probably be the only time I’ll hop into the kids swimming pool when I get home.  At 10pm it’s 90 degrees.  I think even during the bizarre cloudy night during the 2006 heat wave we had dropped to 88 at 10pm.    Looks like a low around 70 will probably be reasonable.

Wednesday and Thursday’s temp forecast is a bit problematic.  It’ll be scorching hot…that much is for sure.  But we get much stronger offshore flow, more like September easterly wind due to a surface high coming down into the northern Rockies.  I think it may actually turn breezy through at least the eastern half of the metro area.  With better mixing one would think it could turn even hotter than that 105.  But the upper-level heights and 850 mb temps drop a bit at the same time.  So do we turn cooler or warmer?  I’m not sure, so I just left it at 105.  I could see a situation where we don’t get much, or any,  atmospheric cooling and then the easterly breezes pick up in the afternoon.  Maybe we’ll get a surprise 107?  This could be fun (and brutal).  Even with an east wind blowing, Thursday’s atmosphere is slightly cooler again, so maybe right around 100 or just under.  Holy cow…we’re talking 4 days at/above 100 degrees if that’s the case.

Beyond Thursday:  I see the 00z GFS has backed off on the trough approaching the Coast, pretty much eliminating the thunderstorm threat and keeping us pretty warm (85 at least) through the weekend and early next week.  Now to give some of you hope, I’m headed into Eastern Oregon starting Friday for a week-long vacation.  So that’s probably when the low will make it’s move, giving us a severe thunderstorm outbreak west of the Cascades.  Stay cool!

Chief Meteorologist – Mark Nelsen


The Heat Wave is Here

July 27, 2009

It’s an early day today;  I went on KXL this morning at 7:02am (early for me) to talk heat wave numbers.  I have to admit though that I actually like heat waves.  You get some meteorological excitement, such as some offshore flow, extreme temps…etc.  But honestly, it’s sunny for the next 3-5 days…how tough of a weather forecasting day could that be?  Heat waves in the Pacific Northwest are generally just a numbers game.  So let’s talk numbers.

Looking at the 7am obs. it’s obvious the airmass is significantly warmer this morning.  I only hit 63 for a low at my home at 1,000′ in a bit of a canyon.  It feels like a Hawaiian morning.  I see it only dipped into the upper 60s in the city.  But unfortunately it’s going to get a lot hotter than Hawaii this afternoon.  I’ll have to break down use the air conditioning today.  Generally I don’t unless it gets above 95 in Portland.  Even when it gets hot in the house (86 yesterday), by dark there is a 70 degree or cooler breeze blowing down the canyon into the wide open windows and doors…very efficient and quick cooling. 

Highs:  We hit 93 yesterday with weak onshore flow, but now I see the PDX-DLS gradient has switched to slightly easterly.  So I figure about 7 degrees of warming takes us up to right around 100 degrees.   Slightly more offshore flow and a warmer atmosphere awaits for Tuesday and Wednesday, so somewhere between 100 and 105 degrees for the next 3 afternoons should be a safe bet.  Now I haven’t looked at any 12z model data yet (it’s ONLY 7:30am), but I did notice on the 00z data that we supposedly don’t get really significant surface easterly flow over us in this heat wave.  I doubt we’ll even get east wind much out of the Gorge, let alone to I-205.  Due to that I think the 105 number is high.  IF we could get a sharper thermal trough west of the Cascades, then we could sure get close (or over) to the 107 degree record. 

Lows:  This part of the forecast is probably the biggest story.  Looks like PDX might have dropped to about 67 this morning?  MOS forecasts say the city only briefly drops below 70 the next few nights as well.  Considering how warm it stayed this morning, and a hotter atmosphere/highs on the way, seems like those numbers are a bit low.  More disturbing is our RPM which has done pretty well with heat wave temps recently.  It shows lows only in the 70s the next two nights.  Since we don’t have a dry east wind coming down into the city to get rid of the low level moisture (high dewpoints), it’ll be easier to keep the nighttime temps up.  Remember that PDX’s all-time warm low is 74 degrees.  I think we’ll be in the 70-74 degree range these next two nights…yuck!  By the way, there were STILL air conditioners at a “big boxy store that sells tons of toilet paper” as of yesterday when I was there.  So I would highly recommend putting out the $125 to get yourself one.

Okay, off to a morning bike ride…not a good day for an evening “between show” ride today!

Chief Meteorologist – Mark Nelsen