Rain ahead, but October starts warm & dry

Well this is exciting…we’re going to see some widespread (light) rain for much of the region tomorrow.

It’s been very dry; in the past 3 months Portland has only picked up about 1/4″ of rain! That’s very stressful for our native vegetation, even with that huge soaking all through the spring months. And this September has been something else…warmest on record in Portland and Salem, and one of the warmest in other areas.

(kptv)

Right now September in Portland is running about like an average July 10-20 years ago! High 81, low 58.

(kptv)

So what’s ahead? Light showers both tomorrow and early Thursday, then we’re heading back to unusually warm and dry weather for the first few days of October. A weakening front is approaching the coast. Technically it’s an “occluded” front, but for TV purposes I left it as a cold front. One surge of rain arrives around sunrise, then the surface low with it’s attendant showers arrives tomorrow evening and night. There should be a brief dry period DURING THE DAYTIME tomorrow.

(kptv)

That surface low dies and is replaced by building high pressure late Thursday and on into the weekend. What about rain? Just perusing many different models gives somewhere between .10″ and .50″ for the metro area

(kptv)

Areas NOT showing color means less than .10″ rain forecast. Here’s the 18z ECMWF model’s precipitation forecast

(kptv)

You can see many areas east of the Cascades will just get a few showers. The Cedar Creek Fire in the central Cascades should get a soaking once again. Smoke from that fire drifted into the Willamette Valley today; I could smell it a couple of times while running errands.

We’re headed back to dry weather Friday through at least early next week, and even later NEXT week doesn’t look very wet. That’s because upper-level heights will remain higher than normal the next 8-12 days. Take a look at the 500 millibar anomaly for days 2 to 12 from the ECMWF model ensembles. Above normal heights through October’s first week (or longer).

(kptv)

GFS model ensembles are quite similar

(kptv)

Clearly the “wet season” isn’t going to arrive in the next 1-2 weeks. You can expect a very warm first weekend of October, then drier than normal through much (or all?) of that first week of the month.

Enjoy the showers, and a warm/dry weekend. I’ll be off on vacation through Sunday the 9th; hopefully we don’t get any surprises while I’m gone this time. Time for a 25th anniversary trip with my wife!

Chief Meteorologist Mark Nelsen

It’s late September and still no sign of a soaking rain ahead; but how unusual is that?

The sunshine and warm (not hot!) temperatures have been nice this month.

Blog Almanac(kptv)

But now it’s getting a bit weird. Where’s the rain? So far only .05″ rain in Portland, but take a look at how wet our recent Septembers have been

(kptv)

Most of the region has been relatively dry, but the southern half of Oregon HAS seen a nice soaking the past 3-4 days due to an upper level low sending clouds/rain through California and a bit farther north. Look at the areas that have picked up at least 1/2″ the last 3 days

72 hour rain totals(NOAA)

Now in most years the bulk of our first soaking falls in the 2nd half of the month. Take a look at the increase in rain chances as we go from August to November. A bump up in mid-September with about a 30% chance that any one day at mid-month will give us measurable rain. Then you see a 2nd jump in late October. By November we are IN the rainy season with a peak occurring in late November and early December. During that time about 70% of days (on average) will feature measurable rain; a drastic change from that 5-6% chance in early August!

(kptv)

Another way to look at this is: WHEN DO WE GET OUR FIRST “SOAKING” OF THE SEASON?

Let’s consider 1/2″ rain our first soaking at PDX. Notice in the graphic below that in many years it happens in mid-September. For some reason September 17th/18th has been popular lately! Not this year of course. Back in 2012 and 2011 (not on the graphic) there was no soaking until early October. In fact in just under 1 in 5 years that happens. So although it’s not unheard of to wait until October for real rain, it IS not a common occurrence. Then, every couple of decades, the rains REALLY hold off. By that I mean in 4 years (since 1940), Portland didn’t pick up 1/2″ rain until the 2nd half of October. I remember 1987…no soaking until Halloween and the days following. So I suppose the good news is that the rain ALWAYS arrives at some point; it always has by Halloween at the latest.

(kptv)

WHAT’S AHEAD?

The big message I’m seeing on all our modeling is that there’s no soaking in sight; at least through the end of September. Looking at the big picture, this loop of 500mb heights goes from now through the first day or so of October. It’s the 5 day average anomaly…warm colors are higher than normal and cool colors show below normal heights. Notice ridging is dominant along the West Coast through the 5 day period ending around the 3rd of October. That’s about 12 days out in time

(kptv)

If we just take a look at 3 different ensemble forecasts (many runs of the same model), the GFS, GEM, & ECMWF models all have a similar theme…much drier than normal through October 1st. The ensemble averages all give us 1/2″ or less rain through the rest of September (a week from Friday)

THE BIG MESSAGE?

This is one of those unusual years where you need to keep watering through all of September. Many years you can stop earlier in the month, but not this year. Luckily, even in drier years, plants/lawns stop using much water in October as temperatures cool. In much of the region the official irrigation season ends October 1st too.

Was this weekend’s east wind event unusual? No, but we ARE lucky no large fires emerged in NW Oregon & SW Washington

9pm Sunday…

YOU SHOULD BOOKMARK THIS PAGE FOR FUTURE BLOG POSTS. IT’S A LOT BUSIER AT WORK NOWADAYS. I WILL ALWAYS POST TO THAT KPTV SITE FIRST, THEN HOPEFULLY HAVE TIME TO RE-POST TO THIS LEGACY WORDPRESS SITE.

THIS SITE WILL BECOME MORE OF AN “ARCHIVE” FOR ME (AND YOU?). MOST DAYS, POSTS WILL MAKE IT OVER HERE, BUT DURING VERY BUSY WEATHER A FRESH POST MAY NOT APPEAR HERE FOR AWHILE

The forecast played out very well these past three days…

1. Dry easterly wind showed up and left right on schedule (Friday morning to Saturday evening)
2. The wind was not too strong, note no wind advisories or high wind warnings across the region. That was expected
3. Relative humidity bottomed out around 10-15% in the lowlands and foothills both afternoons as temperatures peaked.
4. Onshore flow with higher humidity, cloud cover, and light wind arrived overnight. That ended this dangerous east wind episode.

As mentioned in previous posts…this was going to be (and ended up as) a relatively typical late summer/early fall east wind episode. The same wind speeds and temperatures in the 80s/90s just two weeks from now would be far less of a problem because (it’s assumed) rain will likely have moistened vegetation/forests. This time was a problem due to extremely dry fuels. Most of us west of the Cascades in the valleys haven’t seen measurable rain since July 6th…66 days.

KPTV Weather Blog(kptv)

That is probably coming to an end tonight because at least SOME measurable rain should fall.

If you want to take a look at an extensive recap of the September 2020 windstorm and fires, you can find it here: https://fox12weather.wordpress.com/historic-september-2020-fires-labor-day-windstorm/

How did this weekend compare? Not even close. At my home in the Cascade foothills a strong easterly wind never really surfaced. I think my peak gust was only around 25 mph. Last time was 49 mph. Some other locations

Weather Station	2020 Peak Gust	Peak Gust Friday/Saturday
Portland Airport	52 mph	40 mph
Glenn Jackson (I-205) Bridge	60	35
Timberline Magic Mile Lift (7,000′)	106	58
Fremont Bridge	53	38
Horse Creek Raws (in Cascade foothills)	66	36
Hillsboro Airport	44	37
Mt. Hebo (3,000′ in Tillamook County)	92	47

Again, this isn’t a surprise; that Labor Day 2020 windstorm was a historic event! One other difference was the dewpoint & relative humidity. That airmass 2 years ago was much drier. Dewpoints down around 20 degrees; this time PDX bottomed out between 30-35 degrees. Still plenty dry to allow a fire to blow up quickly in the wind, but not as extreme.

So I’d say this event was a little stronger than a typical fall event, but nothing TOO unusual.

What made this event far different was the PSPS. Public Safety Power Shutoffs. Approximately 30,000 PGE and 12,000 Pacific Power customers had power cut at some point Friday through at least midday Saturday. Pacific Power had everyone back online yesterday evening, PGE has almost everyone back on as of 9pm this evening. Mine was off for about 55 hours. This is the first time power companies in Oregon have done a widespread shutdown. I don’t have any great insight into the reasoning, other than the obvious…tree branches can fall onto a powerline and start a fire. This has happened the past few years in California and during the Labor Day 2020 windstorm in Oregon.

I’ve never seen power shut off in the western Gorge with this strength of wind in the past, even when it’s extremely dry in September. For example the power was ON the night the Eagle Creek fire was racing through the Gorge 5 years ago (although wind not quite as strong). Something clearly has changed but that’s beyond my expertise…I’d better just stick to weather!

Good Fire Season News!

The very good news is that this episode was likely the peak of fire season and things die down from this point forward. It’s turning cooler, a few showers are moving through the region tonight and tomorrow, and there’s no sign of hot weather or dry easterly wind in the next 7-10 days.

(kptv)

There’s a very good chance that was our only “dangerous east wind fire weather event” of 2022. Last year we had showers before the easterlies showed up, so no big fire issue in September…it won’t happen every year. There are 2 huge fires (Cedar Creek & Double Creek) burning now that are consuming the most acreage…but even these should slow to a crawl the next few days. Growth this afternoon was far less under cloud cover and cooler temps down around Oakridge & Willamette Pass

(kptv)

That’s it for now…enjoy the nice early fall weather this week!

Dry & dangerous easterly wind arriving this morning as planned power outages begin

10am Friday…

The forecast is turning out as expected this morning. Cool Canadian air (cool by early September standards) has surged south into Eastern Washington and Oregon. That’s dense, heavier air = higher pressure. That air is surging over the Cascades and through the Columbia River Gorge; the dreaded late summer “east wind pattern”. This is always a problem over/west of the Cascades if fuels are dry and that’s the case this year…no rain for most of us in two months. If we would have seen showers a few days ago this pattern would not be a big issue; each early fall is different. Last year wasn’t a problem.

Portland General Electric has 10 Public Safety Power Shutoff areas and several of those have been turned off as of 10am. Yellow = no power right now.

(KPTV)

My power was shut off around 5:15 this morning, so this is one of the few weather blog posts written under the power of my trusty portable generator.

KEY POINTS

• We do NOT have a windstorm on the way…this is nothing like Labor Day 2020
• This is a relatively normal early fall season easterly wind episode, which still means plenty of wind
• BUT, this is the first time that power companies have decided to implement widespread power shut offs, thus the big news story.
• These shutoffs only affect 3-4% of all PGE customers! These are mainly very rural/forested areas.
• Easterly wind will pick up in the hills/mountains the rest of today and peak tonight/Saturday morning in those areas. Gusts could reach 30-45 mph at times in exposed foothill locations
• Easterly wind will be strongest this afternoon in the lowlands, die down tonight, then be gusty again through Saturday morning. Gusts 25-35 mph are likely in most populated areas during this time.
• All easterly wind (and extreme fire danger) ends around sunset or so Saturday evening. THIS EVENT WILL BE OVER IN 36 HOURS
• Expect to smell smoke at times along with a hazy/yellow/orange sky through tomorrow

I can smell smoke this morning at home, due to Canadian and Eastern Washington wildfires. That northeast wind is sending their “smell” our way. Please don’t call 911 because you smell smoke. There is a lot of smoke now moving around the region due to numerous fires..this will be with us through tomorrow

(KPTV)

Smoke forecasts show not just high-level smoke (yellow sky), but it’ll be getting mixed into the lower levels the next 36 hours. Air quality is headed downhill. Note lots of smoke from Idaho and NE Oregon fires making it west of the Cascades on Saturday

(KPTV)

Smoke modeling loops/imagery is available all summer/fall long on our FOX12WEATHER app…make sure you have that on your phone or device.

(kptv)

As mentioned above, so far PGE hasn’t activated all the power shutoff areas. That’s likely due to the relatively weak wind so far. I see Pacific Power has NOT shutdown any areas at this point. That’s good…no need to shut things down until a gusty/dry wind shows up. Check out Niagara weather station (in the North Santiam Canyon). East wind has arrived, but not too strong. Humidity IS way down…in the teens. Notice this is one of dozens of new weather stations installed in forested/foothill locations by the utility companies. Great information for meteorologists AND the public

(KPTV)

That’s it for now. We have a wide choice of newscasts to watch either on your TV or online https://www.kptv.com/livestream/

You can catch me there all late afternoon and evening long!

First east wind event of the fall season means high fire danger plus power shutoffs

9:45pm Wednesday…

Most Septembers in the Pacific Northwest feature a transition from hot/dry weather to cool/wet/cloudier conditions. Every few years it happens in late August, but usually September is the transition month. Fall in our areas also features a return to occasional dry easterly wind periods when dry Canadian air moves south and west into the Pacific Northwest. It does that because cool & dense air begins developing over the continental areas = high pressure. Higher pressure to the east means wind blows from land toward the sea…easterly wind. That setup is generally not a problem fire-wise October through May because some rain falls from time to time (or regularly) and forests are moist/wet.

IF one (or more) of these dry east wind events shows up BEFORE our first fall rain? We’re talking very high fire danger because fuels are totally dry from 2 months of heat and no rain. For this reason, mid-August to mid-September is the most dangerous time of the year for fires west of the Cascades. Almost all of our major fires have occurred during this time. We have one of these dangerous periods on the way for two days…Friday and Saturday. Luckily this event will be nothing like the wind storm that struck on Labor Day 2020. That one fueled 5 megafires (>100,000 acres) on the west slopes of the Cascades and the worst firestorms seen in our area the past 80+ years.

First a quick summary…

1) Friday and Saturday will feature very high fire danger from the Cascades west to the coastline

2) Fire danger goes back to “normal” Saturday evening as east wind disappears

3) Easterly wind gusts will be far less intense than what occurred at Labor Day 2020. 25-35 mph in lowlands and 35-50 mph on mountain ridges.

4) Hot temperatures accompany the wind, around 90 for a high Friday and well into the 90s Saturday

5) The coastline will reach well into the 80s Friday, with a few spots even reaching 90 for one day!

6) 40,000+ PGE and Pacific Power customers may have power cut at some point Friday through Sunday through planned shutoffs. I am one of those customers.

Technical info…

A weak upper-level system is sliding by tonight, bringing cooler air through southern Canada and putting a “dent” in the huge heat dome over the SW USA

(kptv)

But then a new hot area of high pressure (in the upper atmosphere) pops up over the Pacific Northwest Friday and Saturday

(kptv)

At the surface, easterly wind arrives early Friday morning in the hills and spreads down into the urban areas and I-5 corridor during the daytime. Notice the highest fire risk areas are in the foothills, mountains, and Gorge…where the wind will really be blowing hard at times. The numbers here represent a “Fire Weather Index”. I don’t think I’ve seen it above a 4 west of the Cascades all summer.

(kptv)

Now let’s go hardcore…time for a WRF-GFS model “cross-section”. I apologize for the 1st grade style annotations. It was a quick snipping tool job…

(kptv)

Time goes from right to left and you’re looking at the lowest 10,000′ of the atmosphere over Portland. The “850″ horizontal line is around the 5,000′ elevation. Each little “wind barb” has one flag for each 10kts. A thick flag = 50kts. What do I see? Wind overhead will be northerly through about midnight Thursday night. Then easterly wind develops overhead the rest of the night. By Friday midday the wind is surfacing in the metro area. I’ve highlighted the strongest period of wind…Friday evening through sunrise Saturday. 50-60 mph wind over Portland around 2-3,000′. Labor Day 2020 speeds were forecast (and ended up being) quite a bit stronger. Note that the wind goes calm in the lowest elevations Friday night before returning Saturday. It’ll keep blowing through the night on hills and in mountains/foothills. Some of you in the hills will be having a 70 degree windy night! By the way, the red lines represent temperature in Celsius. Up to about +24 at 850(mb) Saturday afternoon. That’s about the hottest it can get on the 10th of September. The record for September 10th in Portland is 98. In fact we’ve never been at/above 97 after that date. So most likely we’ll be in the 94-97 degree range late Saturday afternoon.

Fire smoke may show up during this hot & windy weather too. Canadian fire smoke could drift south over us Friday. Here’s the high-level smoke forecast for Friday morning

(kptv)

Since the low level wind will also be coming in from the northeast, we might actually see some smoke in the air Friday/Saturday too. The low-level smoke forecast.

(kptv)

If we can get through Friday and Saturday, a cooler weather pattern, more typical for mid-September, is on the way. Check out the Euro ensemble temperatures for the next 15 days…an obvious downturn after Saturday

(kptv)

That’s it for this evening…stay safe and cool later this week!