July 20, 2006
So after all the excitement the last 4 days or so, the heat wave has finally arrived. Looks like 93 was the high today at PDX. A collection of models, including our own RPM model here and the brand new 00z ETA, show a jump of about 10-12 degrees tomorrow. PLUS, the pressure gradient through the Gorge just switched to easterly. East wind is also blowing now at Timberline Lodge too. That plus a forecast of thermal trough in the Willamette Valley tomorrow makes me feel good about my warmest Day 1 forecast I’ve ever made for PDX. 104 for tomorrow. If so, that will be the warmest temp at PDX since the 105 in September of 1988…18 years ago!
Our RPM model also shows much warmer temperature tomorrow night, around 70 or above in the metro area. That would be interesting, since we haven’t stayed above 70 at night for years at PDX.
There’s no reason for any cooling Saturday, except our little model here (RPM) shows moisture working around the western edge of the upper-level ridge Saturday for lots of high clouds from thunderstorms. If that happens of course it’ll be cooler Saturday.
A very slow cooling trend next week as the ridge weakens somewhat, but summer temps continue. Try to stay cool…Mark
July 19, 2006
So we play the heat game again this afternoon, roll the weather dice and find…
Not much different since 24 hours ago. It’s a little boring but always nice when models really have a good handle on an approaching significant weather event. Last night I mentioned the models (mainly GFS) had cooled the temps just slightly in the Friday-Sunday period. That has now stopped and temperatures on each run (they come out very 6 hours) have stayed about the same.
I did notice the 18z GFS was slightly warmer and holds on to the heat a bit longer through. A peak of +26-27 C is shown Saturday afternoon on the GFS, but the only offshore flow is on Friday, then it’s flat through the rest of the weekend before onshore kicks in early next week. The ECMWF has been uncharacteristically warm the last 2 runs as well. It shows a +28 for Sunday AND Monday morning! Hmm, hopefully it’s not right with the 18z GFS just starting to "catch up". If so, I’d have to bring the 105-107 idea back in again. But for now I’m leaving the forecast as it was last night. Both GFS/ETA/MM5 do show a quicker warmup tomorrow than originally expected. They all show +12 to +16 degF from today’s high. Of course that would mean at least 95. So that sounds like a good number to me…Stay Cool! Mark
11:30pm Addition: 00z ETA & GFS were slightly warmer, especially the ETA, so I bumped Friday up to 104. The GFS surface temps appear to be inhibited by cloud cover of some sort. Hopefully not the monsoonal moisture sitting to our south. ETA doesn’t show any working north. And play nice guys…no need to argue over a forecast until AFTER the event actually occurs!
July 18, 2006
So here we go with "how hot" talk again.
First, looks like last night’s marine push has pushed itself out since onshore gradients are much weaker this evening. Probably no low clouds inland in the morning…that will be the last cloud cover we see until at least next Tuesday.
So you may have noticed I raised Friday 2 degrees, dropped Saturday 1, and Sunday 5. All models have really come together on the large scale details from Friday-Sunday now, so we get to argue (I know you folks do) over the small details.
I’ve noticed the trend over the last 24 hours of models is a slightly weaker upper-level high, and much more significant…it’s over or slightly east of us Saturday-Sunday. The 1981 & 1965 heat waves that gave us 105+ had the upper level ridge slightly west of the coastline, which drags the thermal trough west to the Coast too. In our forecast weekend pattern it doesn’t give us as sharp of a thermal trough west of the Cascades and saves the Coast from extreme heat too. I REALLY doubt we’ll see 105 at PDX in this pattern. Plus onshore flow late Saturday & Sunday should be enough to drop us into the 90’s Sunday, but I left the 100 on for Sunday for now. I may drop it tomorrow, or the Drew/Andy forecasting duo may do that in the morning.
So as I mentioned at 10pm, it looks like a really good heat wave, comparable to 1994, but not 1981. We would need the ridge to stick around through Tuesday for that. Okay boys and girls, discuss in detail…Mark
July 17, 2006
The big story this week of course will be the heat wave at the end of the week.
First, a pretty good onshore push is in progress this evening. Portland to The Dalles pressure gradient is up from 3.2 mb. yesterday evening to 5.7 now. Looks like wind on the river from Hood RIver to The Dalles are probably gusting over 50 mph, since DLS airport gusted to 48 mph at 5pm. It has a lighter west wind than the big windsurfing spots downriver (Rowena/Doug’s Beach/Swell City). It is a northwesterly push (as opposed to the strong pushes that come up from the SW), which usually doesn’t give us a ton of marine clouds.
Thinner marine clouds Wednesday allow temps to rise back into the lower 80’s…that should be the last day below 90 for many days.
12z/18z GFS, 12z ECMWF & Extended MM5 from UW all show a very strong 595 dm 500mb ridge developing directly over or just north of Oregon Friday-Sunday. Then it weakens, but summer warmth continues Monday and beyond. So the question is how hot? You’ve all discussed your theories (and will for the next 4 days I suppose), so here are my thoughts.
I checked the 1981 & 1965 heat wave maps (Surface, 500mb heights, 850mb temps) and found that the pattern is very similar to the forecast pattern.
– 500mb heights are the same.
– To get above 101 or so we need some easterly flow through the Gorge, maybe briefly making it to PDX (as in June). Both of those old heat waves had it and that’s in the works for Friday-Saturday. Sunday is the calm wind day before we turn onshore for Monday.
– 850mb forecast temps are the same as in the other two heat waves. ECMWF has a crazy 28 deg. C on Saturday afternoon!
So technically there is no reason we can’t get to 105 or higher. I went for 105 both weekend days on tonight’s forecast, which I’ve never forecast. I’ll revise upward the next few days if the maps remain the same.
Ever since I started my career here in 1991, I’ve wondered when/if we would see a repeat the 1981 heat wave, so maybe this is the year?
July 15, 2006
I was reading some of the comments in Mark’s previous blog posting… and some of you can guess what I’m about to discuss.
When commenting on topics, please avoid making any statements that are personally directed towards another poster. Sure… you can can refer to someone else’s post and respond to it — but it is not appropriate to make mean-spirited or overly personal comments towards another poster who has a different opinion.
This weather blog has some loyal comment posters and even more loyal readers. It is not OK to lose any of them because of personal comments. Mark (and I) have the ability to enable a program on this blog that prevents comments from being posted until he (or I) read them first. We’ve enabled that program before and we will again if the comments venture into a territory that they shouldn’t travel towards. We like giving you the freedom to post comments in real time… we feel this blog is superior when that is the case. But the comment posters will determine their own level of freedom based on behavior.
So… behave yourselves… be nice and polite… and then and all is good.
And… while I encourage you to keep you comments relative to the blog posting, I understand that the discussion can easily get sidetracked. And that’s OK… to a reasonable extent.
– Drew J
PS – I believe that the GFS and ECMWF are on to something for the end of the week… it does indeed look like the Northwest will heat up again. How hot? Stay tuned…
July 14, 2006
As several of you have noted, the GFS has again been trying to constantly warm us up with ridging the last week or so. And then later runs back off on the ridging. Remember back in May-June we saw the same thing in the 5-10 day forecast range. Hard to believe that at one point earlier this week I had 90’s in the forecast for Sunday? Instead we continue with moderate onshore flow for the foreseeable future. That DOES keep us from really heating up, so a perfect summer weather pattern continues into at least early next week.
Onshore flow should be a bit stronger tomorrow, so I’ve chopped about 5 degrees off the high temperature forecast. I could easily be wrong, so anywhere from 78-82 is possible tomorrow at PDX…Mark
July 13, 2006
Just about perfect July weather for the next few days. The chance for hot weather is gone for now since weak ridging is forecast overhead instead of a strong ridge. So expect light onshore flow through early next week. Of course the ebb & flow of marine air regulates the amount of morning cloud cover too.
You may be wondering why we get the onshore flow to start with? In the warm season the continent (North America) is much warmer than the ocean. Rising air produces lower pressure at the surface inland, which creates a flow of air from ocean to inland or "onshore flow". But it’s a bit more complicated than that. Upper level disturbances moving by can increase the onshore flow, such as yesterday’s cold front. If we get a strong ridge overhead, rising surface pressure inland can even briefly turn the flow offshore for awhile. That’s our hot easterly wind…very rare in the summer. So it all comes down to the wind always trying to move cool air inland, and occasional ridging slowing down the onshore flow, letting us warm up. It’s a constant battle between the two from June-September…Mark