The ‘endless’ summer heat has…ended; Cooler fall weather arriving early this year

7pm…

What a change today!

A thick marine layer surged inland overnight and never left west of the Cascades. In the “before” times (pre-2013 summers), this happened at least once every week or two in July and August. Nowadays an all-day marine layer is rare as warm/hot weather is far more consistent most summers in a warming climate. At 6pm you can see the thick cloud cover west of the Cascades and over Portland (yellow dot), clear sky but thin smoke at Hood River (2nd yellow dot), then a hellscape of fire smoke arriving in Bend (3rd yellow dot). AQI over there is 200-400 right now!

(kptv)

We only hit 71 in Portland today, the coolest day in over 2 months. In fact just two weeks ago we had a LOW temperature warmer than today’s HIGH

(kptv)

Our 5th (and likely final) heat wave of 2023 ended up being 3 consecutive days at 94 in Portland; yesterday the marine air started to push inland and that kept us below 90

(kptv)

At this moment, August is still running the warmest on record in Portland at 76.1 degrees. The average HIGH temperature is in the upper 80s. I remember early in my career (25-30 years ago) it was assumed that as summers warm, Portland would have temperatures more like Roseburg or Medford experience (in the 1990s). Sure enough, our average high has been in the upper 80s this month. Assuming our 7 day forecast is accurate, August 2023 will probably still go down as the hottest month on record in Portland, just slightly ahead of LAST August!

(kptv)

Other stations in the region aren’t quite as hot; Portland’s nighttime urban heat island is becoming more and more pronounced as the decades go on. Regardless, another blazing hot summer month for all of us inland from the coastline.

WHY SUMMER IS SORTA “OVER”

The big thing that sticks out to me today is the lack of heat on models the next 10 days. Sure, it’s possible we slip in a 85-90 degree day sometime before the first week of September is up. But more likely it’s going to be feeling like September through the foreseeable future.

Here’s a forecast of 500 millibar height anomaly for the next 7 days (GFS model ensemble average). Upper level troughing wants to sit along the West Coast most of the time. This is a one week average. No hot ridging nearby to keep us in the 80s/90s. You can get a nice/warm/sunny day(s) in this pattern. But in general, west of the Cascades we’ll see showers from time to time in this setup.

(kptv)

Then check out days 7-14; looks similar doesn’t it?

(kptv)

What about rain? I see several upper-level “shortwaves” (smaller disturbances) moving through this big trough. One tomorrow, Thursday, early Friday, and another Sunday. Models are suggesting THIS THURSDAY COULD BE A SOAKER. Check out the 10 day rain forecast from the Euro ensembles. 1/2″ to 1″ in the western valleys, and 1-2″ in the Cascades. This will put a serious dent in fires over/west of the Cascades, especially combined with cool temps and higher humidity.

(kptv)

Looking at it another way, you see many chances for showers from the different ensemble members over the next two weeks. It appears the wettest period IS the first 7 days.

(kptv)

Then check out the forecast temperatures from just one model, the GFS ensemble average; quite pleasant don’t you think?

(kptv)

SUMMARY

• The endless stream of warm/hot/sunny days is over for the season
• Yes, but we’ll still see lots of warm weather (just not hot) the next 10 days
• Showers will dampen things at times, but I don’t see heavy rain for now
• This is NOT the beginning of the fall rains, that’s more typical later in September
• If you are tired of the blazing hot weather, enjoy the next 7-10 days!

One practical effect; my cheap above-ground pool may not get used again this season. The water temp peaked at 89 degrees during the heat wave and now it’s down to around 80 degrees. After the first week of September the low sun angle and long nights mean it just doesn’t warm up anymore. That’s even with a 90 degree day! Summer will be fading the next 2 weeks…

5th heat wave of summer will be more reasonable, plus some overnight lightning on the way

9pm Wednesday…

The past few days have been very nice, although high level wildfire smoke from Canada brought us quite a bit of haze this afternoon. Don’t worry, I don’t see thick low level smoke again the next few days. Sunday wasn’t fun with AQI values up into the UNHEALTHY category for many of us.

WHAT’S AHEAD

1) Hot weather returns tomorrow afternoon and continues through Sunday. This time the airmass will be about 10-12 degrees cooler which keeps us in the 90s; luckily in the low-mid 90s too.

2) Overnight thunderstorms! A nearly perfect setup for nocturnal thunderstorms is in place for 5-8 hours. Many of us may wake up to lightning or thunder at some point tomorrow night.

3) Widespread showers are possible Tuesday/Wednesday next week, although at this point they don’t look like real soakers. But we haven’t seen anything more than sprinkles or light showers in over two months!

HOT WEATHER

One reason the heat wave won’t be too hot this time? We don’t have a big upper level ridge building overhead. Instead, a cool trough sits offshore, staying just far enough west to allow a warm/hot airmass to move into the Pacific Northwest. For the meteorologists and geeks, 850mb temperatures will be climbing up to around +20 this time around. Remember we peaked at +26 during last week’s heat wave. Here’s the view up around 18,000′ for Friday. Doesn’t look like a big heat wave does it?

(kptv)

The reason we’re able to get above 90 in this pattern is the offshore flow down at the surface. The surface map for Thursday afternoon shows a nice “thermal trough” of low pressure west of the Cascades. Maybe 2-3 millibars easterly flow through the Gorge for gusts 25-35 mph at Vista House tomorrow. After this time, we bounce between weak offshore and weak onshore flow through Sunday. This tells me we won’t see wide variations in high temperatures these next four days.

(kptv)

The setup is about the same in the upper atmosphere by Sunday afternoon, maybe a little stronger ridging to our east.

(kptv)

Then that entire trough shifts “kicks out” and reenters the main westerly flow Tuesday and Wednesday. A big cooldown will be the result along with at least a few showers.

(kptv)

So it appears we’ll pick up another 4 days at/above 90 for the season, boosting our total way up to 24.

(kptv)

And with increasing humidity Saturday and Sunday, we’re assured of more warm/sweaty nights. So far this month we’ve seen 6 record warm lows at PDX.

(kptv)

THUNDERSTORMS THURSDAY NIGHT

Sometimes we go an entire summer without seeing nighttime lightning west of the Cascades. When that DOES happen, it’s always a little treat for the weather geeks like me. Maybe some of you too. Well it appears we might see some thunderstorm action Thursday night. A weak upper level wave moves north across the Pacific Northwest tomorrow night through Friday morning.

(kptv)

Notice in the middle of the night the flow is southerly or even southeast. That is a CLASSIC setup for us west of the Cascades. The flow is “diffluent”, which means ahead of that wave the flow is “diverging” a bit (opposite of converging). When that happens, low level air must move upward to replace the higher level airmass. Upward moving air in a moist airmass leads to showers and thunderstorms. In the setup tomorrow night ANYONE can get a thunderstorm, even over the cold coastal low level airmass. Lightning can occur over a 50 degree fog; unrelated to surface heating. These will be “high-based” thunderstorms. They often produce abundant lightning (a great light show!) but sometimes don’t produce much rain. Regardless, cover anything that shouldn’t get wet before you go to bed Thursday night. And let’s hope we don’t get many fire starts because it’s right back to hot weather Friday behind the system. You can see the 3km NAM model producing the popup storms early Friday morning

(kptv)

These storms will be scattered, which means you might get knocked out of bed (not literally) by loud thunder at 3am, but your friend 15 miles away says “what thunderstorm???”.

(kptv)

That’s it for this evening, we’ll see how many of us are tired and cranky at work Friday after a rough night of sleep.

Quick Saturday evening update: blazing hot weather ahead next 3 days

9pm Saturday…

I’m working late this Saturday evening and just wanted to give you a quick update on what we’re seeing. Technically the heat wave started today; Portland “overachieved” with a 91 degree high. That now means we’ve reached our typical # of 90 degree days for the season

(kptv)

HEAT WAVE KEY POINTS

• We’re calling Sunday, Monday, and Tuesday FIRST ALERT WEATHER DAYS. That’s to draw your attention to those specific days due to extremely hot daytime temperatures along with unusually warm nights
• Check on your elderly friends/family the next 3-4 days! Most of us younger folks will be just fine if not annoyed/hot, and this sure isn’t like the deadly June 2021 event. But an older person without air conditioning is at risk with these temps. Make sure they are staying cool.
• Tomorrow through Tuesday we’ll likely be at/above 100 in the western valleys (including metro). Hottest will be Monday/Tuesday with low-mid 100s each afternoon.
• Wednesday/Thursday should be a BIT more reasonable, but still hot.
• Finally, a dramatic cooldown arrives Friday into next weekend. Normal temperatures return
• Fire danger will be very high the next few days. Tomorrow and Monday feature a gusty northerly wind in the I-5 corridor, quick moving grass fires can spread easily in the flat lowlands. Wind won’t be as gusty in the mountains, but fire danger will be very high up there.

DETAILS

What has changed in the last day or so? Nothing dramatic, but all models agree 850mb temps (temp at 4,000′ or so in Celsius) will be around +23 tomorrow over Salem, then peak at +25 to +26 Monday/Tuesday. That +26 is at the upper end of what we see in our area. Up until the 2021 heat wave the all-time high was around +27 to +28. Now this is under a building upper level high pressure area with heights at 500mb around 595dm tomorrow afternoon through Tuesday. That squashes the marine layer down to almost nothing, giving coastal area high temps in the 80s even without easterly offshore wind. Westerly wind in the Gorge shuts down tomorrow through Tuesday, with just a slight easterly drift the next two days. By Wednesday the usual westerlies will resume. Luckily we don’t have a dangerous period of gusty east wind on tap with this heat wave.

Our “cool” IBM GRAF model this summer is spitting out highs of 100 and 103 for Sunday/Monday in Portland. It also thought PDX would only make it to 86 today. That (along with other data) gives me confidence to raise the Monday forecast to 105 degrees.

(kptv)

IF we hit 105, that will be a rare event, especially this late in the season. In fact we’ve only hit 103 or higher TWICE (after this date) in the 80+ weather record history at PDX!

(kptv)

Notice the extremely warm overnight low temperatures. We’re going to see some spots stay above 70 degrees starting SUNDAY NIGHT (not tonight). Really tough sleeping weather if you don’t have air conditioning. One more reason to check up on older friends.

Even without the dry/dangerous east wind we tend to see in late summer and early fall, a gusty northerly wind can allow a small fire to quickly grow. It’s fair to say we’ll see a bunch of barkdust/grass/brush fires in the next two days. Those existing fires in the central Oregon Cascades will become much more active too.

(kptv)

To wrap it up, heat waves in our region are relatively easy to forecast because it’s just sunshine with bigger numbers. With 850mb temps dropping back to around 20 or so Wednesday/Thursday, we should be able to stay under 100 degrees those days. Still, this will likely be a 5 day stretch with daytime highs above 95 degrees. A long and grinding period of heat is ahead.

(kptv)

ALL models agree that the hot ridge falls apart by next weekend and temperatures should go way down. Maybe even some partly cloudy days with highs in the 70s ahead? We will see. I’ll be on vacation this next week finding a cooler spot with water so I probably won’t be posting until it ends. Meanwhile, don’t forget to download our weather app since we put lots of content on there each day that may not make it into this blog or on-air. Just this evening I recorded a quick video about coastal weather and water temps (not as cold as normal). Another video covered local river/lake temperatures.

(kptv)

Hottest weather of Summer 2023; First Alert Weather Days early next week

I was hoping we’d avoid one more heat wave this year but apparently I was being too optimistic. Next week is going to be the hottest week of the summer west of the Cascades. For that reason, we’re calling Monday-Wednesday First Alert Weather Days to grab your attention. The National Weather Service has issued an Excessive Heat Watch for the Portland metro area starting Monday too.

(kptv)

HIGHLIGHTS

• Enjoy the next 2 days with high temperatures in the 80s, hot weather arrives Sunday afternoon
• Expect at least 4 days at/above 95 degrees in the I-5 corridor starting Sunday. The most intense heat should be Monday and Tuesday.
• There’s a very good chance we see temperatures in the 100-105 range between Monday and Wednesday.
• Cooling should arrive Thursday/Friday next week. Typically late season (mid-late August) heat waves are shorter than the midsummer events.
• This will be 10-15 degrees “cooler” than the historic event in June 2021 (116 at PDX). Still, I’d call it a moderate to major heat wave for our area.

A few questions answered…

(kptv)

What has changed?

In my last post earlier this week I mentioned models were in some disagreement. One primary model (the American GFS) was saying “what heat wave?”. Well, it has now seen the light and agrees. Here’s a good graphic. This shows the GFS ensemble average 6 hourly maximum temperature. Each horizontal line is one model run. Most recent run on the bottom, the run from 2.5 days back is at the top. I’ve pointed at the “Monday afternoon” column. You can see the model has warmed dramatically the past 24 hours as you go from top to bottom between those arrows

(kptv)

Compare that to the last 5 days of the ECMWF ensemble average. Again, oldest on the top, most recent run at the bottom. Temps have been more consistently hot, but have even trended slightly hotter. When we see run after run consistently hot, it’s time to call for a heat wave.

(kptv)

How hot? Take a look at my forecast sheet. I know, it’s antiquated and a mess, but it works for me. The circled 850mb temps are ensemble averages from the GFS, ECMWF, and GEM (Canadian). 22-26 average with the GFS still lowest of the models. When we get to +25 to +26, that’s really hot stuff. The = symbol on Sunday, Monday, and Tuesday means flat pressure gradient across the Cascades; on those days all cooling breezes from the Pacific Ocean are confined west of the Coast Range. In fact it’s a light easterly gradient Sunday morning and midday. Notice the 596 on Monday. That’s 500mb height on the ECMWF operational model. A bit extreme, but anything above 592 or so is really hot.

(kptv)

This all adds up to a scorcher Monday through Wednesday. The reason models have warmed a bit is that they now have the upper level high a little closer to us. This is Sunday afternoon

(kptv)

The ridge reaches maximum strength Monday night and Tuesday

(kptv)

Then weakens and shifts west a little by Thursday = cooling

(kptv)

Put this all together and here are the numbers we are forecasting

(kptv)

And a 7 day forecast. We are one of the only Portland TV stations that puts the on-air 7 Day forecast online. You can always find it here: https://www.kptv.com/weather/7day/

(kptv)

Of course we may tweak the numbers a little bit over the next few days, but confidence is very high that the heat is on the way! I bumped up overnight temperatures a bit too based on recent unusually warm nights, possibly due to warmer than normal water temperatures offshore.

Enjoy the next two days!