Stormy Weekend Ahead; 3 Storms

September 26, 2013

Is it November or is it the last weekend of September?  The weather maps say November!   We have one wet front coming through the Pacific Northwest tomorrow, then a much stronger (wetter and windier) storm forecast to move through the Pacific Northwest Saturday afternoon through Sunday morning.  A possible 3rd system could arrive Sunday evening.

Forecast models have come into very good agreement on what the ECMWF model started showing 2 or 3 days ago…an unusually wet and windy system for the last few days of September.

The Highlights

  1. Rain arrives by noon at the latest Friday…then it’ll be wet from that point through the weekend.  It’s an “indoor weekend”.
  2. Heaviest rain falls overnight Saturday night into Sunday morning.  There may be localized flooding (roads and creeks) during that time.  I expect 1.5 to 3″ of rain in the lowlands and 4-6″ in the foothills/mountains.  A few of the usual wet spots will likely see 6-10″!
  3. Large rivers probably won’t flood since the heaviest rain will last less than 24 hours and they are starting at their early Fall low levels.  Ground is also still (somewhat) dry and can absorb the first couple inches of rain.
  4. Strongest wind is Saturday evening and overnight Saturday night
  5. Wind gusts will be STRONGER than what we saw last weekend…60-70 mph on the Coast and 40-50 mph here in the valley.
  6. That is unusually strong for this time of year, especially since leaves are still on the trees to catch the wind; there will definitely be more power outages this weekend.
  7. No snow in Cascades, this is a warm fall system with snow levels up around 8-9,000′.


The Details:

Good to see all the models coming into nice agreement on timing and intensity of frontal features this evening.  I’m not too wound up about flooding for the reasons mentioned above and that this isn’t a perfect “atmospheric river” or “pineapple express” event.  Most of those go on for 2 days or so.  The real heavy rain really appears to be later Saturday through very early Sunday.  Check out our RPM for 1am Sunday.  The peak of the rain and wind action appears to be around midnight Saturday night on most models:


What an intense line of rainfall with the front!  This will move down into the Albany-Roseburg area Sunday morning.    Now here is the wind gust forecast:


Also surprisingly strong.  If it was December I’d think it was a very impressive wind field.  But it’s only September 28th.  Wow.  Note the 60+ mph gusts just ahead of frontal passage Saturday evening.  The strong wind will back off dramatically after the front moves to the south later in the night.  So if you want to see strong wind at the Coast…try 5pm-Midnight.  Here in the valley, we had some gusts in the 35-40 mph range with the system early this week with just a 7 millibar OLM-EUG gradient.  This time it looks more like 11 millibars.  With such a warm air mass it’s easier for the stronger wind to mix down this time of year, thus 40+ mph gusts are likely Saturday evening/night.  Get your generators ready if you live in an outlying area and have another 10 episodes of The Walking Dead to get through over the weekend (me).

After adding more rain during the day Sunday (not as intense), this is what our RPM shows for accumulation.  It includes Friday’s rain too…a 72 hour total:


Note the 10″ spots showing up in the Cascades…the WRF-GFS shows the same thing.  I think 3″ might be a little high here in the valleys, maybe 2″ or so.  So far we’ve seen 2.24″ rain in Portland this month…if we add another 2″, that’ll put us up to 4.24″.  The all-time September record is 4.30″ in Portland.  Even at the wetter downtown location, where records go back to into the 1800s, we’ve never seen 6″.  But let’s not count the “rain eggs” before they hatch.  It will definitely be the wettest September in years here.  Look at the last 10 years:


It’s make up time!  The title refers to when I used the graphic LAST September.


What happens after Sunday morning?  An interesting wrinkle provided by both the 12z ECMWF and now the 00z GFS.  They both are strongly hinting that another low pressure area develops and moves somewhere into Cascadia (BC to S. Oregon) later Sunday or Sunday night.  The 12z ECMWF looks like this with a 988 low moving into the Olympic Mtns:


The 00z GFS goes nuts with a 985mb low moving right onto the Long Beach Peninsula!


That could be a big windstorm for September 29th; one should assume that solution will change though.  More fun ahead…

Chief Meteorologist Mark Nelsen



Funnel Cloud Pictures

September 25, 2013

We’ve received two different reports of funnel clouds this afternoon. From Albany and North Plains. You may remember from last spring that these are somewhat common when we have a cool and showery air mass. And that’s what we have today. No other thoughts for now since I’m sitting in a parking lot.

Chief Meteorologist Mark Nelsen



A Stormy Afternoon; Wetter 7 Day Forecast Too

September 24, 2013

3:45pm Tuesday…

Action is picking up with some real heavy downpours, even some hail reported here and there.  You can see from the latest radar image that we are inbetween two intense lines of showers here in the metro area.


The line coming over the Coast Range will be here for the evening commute…expect some very heavy downpours and possible hail or thunder too.

Wednesday will be much calmer with just lighter pop-up showers, especially the 2nd half of the day and especially south of the metro area.

BIG change to the 7 Day forecast today.  It started with the ECMWF last night forecasting a far weaker upper-level ridge over us and farther east for the weekend.  Then the 12z ECMWF reaffirmed a good soaking beginning Friday evening and continuing through Tuesday:


The 12z/18z NAM agree, but the GFS is much slower moving precipitation in, keeping just about all the rain for Sunday and beyond.  We’ll see which one ends up correct, but the screaming message is that dry weather will only be in our area for 1-2 days (Thursday-Friday), maybe 3 days max, before wet weather returns.

Enjoy the downpours and weather action the rest of the afternoon & evening!

Chief Meteorologist Mark Nelsen



Cold Front Approaching: Wind/Rain Peaks Next 2 Hours

September 22, 2013

1pm Sunday…

As expected, quite a strong cold front moving in this afternoon, and timing is impeccable as well.  You can clearly see the cold front, which is embedded in the back edge of the heavy rainfall, moving across the northern Oregon coastline.  This is from the Ocean Shores radar on the Washington coast.  Portland radar is blocked by the Coast Range a bit in this area.


So the heaviest rain and strongest wind is just ahead and with the cold front, after it passes the rain will pretty much stop and wind will back off dramatically.  Thus the buik of this early fall storm will be in the metro area for the next 2 hours.  As a result, after 3pm it should be pretty much done.   In fact there will be sunbreaks popping out by dinnertime.

Here in the valley peak gusts will be in the 30-40 mph range.  I see Salem had a gust to 39 mph at noon and PDX just had a gust to 37 mph at 1pm, quite impressive for September!   Higher up, a 43 mph gust up on Chehalem Mtn. north of Newberg.  There will definitely be some power outages since leaves are still on the trees.  That makes for better wind resistance since the leaves catch more wind;  a better chance for limbs to break off…a little natural pruning.

Peak wind gusts at the Coast were about what we expected…45-60 mph.  I see a gust over 60 mph at Megler Hill north of Astoria but that’s up at 1,200′.   In the next hour the wind will back of dramatically there as the cold front passes.  In fact quite a bit of sunshine too!

No other storms in the forecast, just cool and showery for a few days and then maybe warmer and drier towards next weekend.  Details on that definitely up in the air.

Chief Meteorologist Mark Nelsen

Rain Moving In This Evening; Stormy Sunday Afternoon

September 20, 2013

Friday 5pm…

Right on schedule, rain is arriving in the western valleys of Oregon and Washington this evening.  It’s not real impressive, but a nice line of moderate rain running right up I-5 right now.  No thunder so far and at best we’ll just see an embedded flash of lightning or rumble.

Some good news for the weekend, models have backed off on the showers a bit for tomorrow.  It probably won’t be a dry day, but showers might take a while (after noon) to get going and may not be too heavy even then.  So there IS a chance for some dry weather tomorrow.

No change for Sunday

Quite a stormy day for late September, especially at the Coast.  A strong cold front moves inland during the afternoon.  Plenty of moderate to heavy rain for at least 3-5 hours means a very wet afternoon west of the Cascades (and in the Cascades too I suppose).  Gradients and models suggest wind gusts to 60+ mph out at the Coast  midday and early afternoon.  Here in the valley strongest wind should be south of the Portland metro area and westside…30-35 mph is possible in the afternoon.

Beyond Sunday, mainly cool/cold showers Monday through Wednesday as a chilly October-like upper level trough sits overhead.  Snow level should fall to around 5,000′, maybe even a bit lower both Tuesday and Wednesday mornings.  Check out the ECMWF ensemble chart…note how far below normal temps are from Monday through Thursday.  Also note hints of more seasonal (warmer) weather returning in the last day or two of the month.


Chief Meteorologist Mark Nelsen

ECMWF Weekly Maps

September 19, 2013

Last night’s run of the ECMWF…500mb height anomaly for the next 4 weeks:  Big negative anomaly all of next week, then a bit weaker.  After week two the negative spot shifts farther east.





Summer Wrap Up: Record Number of Warm Nights

September 17, 2013

An overwhelming number of Pacific Northwesterners agree it was the best summer in years.  That’s based on a poll I took on this blog from August 16th to 25th

74%  gave it an A or A+

19%  gave it a B

But a few of you didn’t like it…7% gave it either a C or D.  I’m guessing these are people who would prefer to live elsewhere in a cooler climate, OR, maybe very annoyed by the warm nights.  In fact this summer WE HAD MORE 60 DEGREE OR WARMER NIGHTS THAN ANY OTHER IN PORTLAND’S HISTORY:


People probably liked this summer for these reasons:

1. Some early warm weather in May and above average June temps, but still plenty of rain to finish up spring and avoid drought issues.

2. Lots of sunshine throughout the summer, not many thick marine layer days.

3. But enough marine layer to keep the extreme heat away.  We only had ONE record high temp at PDX this year, yet 11 record warm lows.  Two of those were ties.


The oddities this summer:

1. Several very humid periods around July 1st (the most humid stretch), and 3 more times in August and early September.  There was no single reason, but we did have several upper-level troughs inject moisture into our air a few times while at the same time no big onshore flow to cool us off or offshore flow to dry us out.  Basically there was nothing to “clear the air” each time.

2. Larger than average spread of high temps in the Willamette Valley vs. Portland Metro Area.  This was most noticeable in July.  Salem had 8 90 degree (or warmer) days, but Portland only had 4.  By the end of the season the difference wasn’t quite as extreme, but Portland still ended up with slightly below the normal “allotment” of 90 degree days.  That’s 12.9  If you don’t like 90 degree days, be thankful you don’t live in Ontario!!! Note the chart below.

3. Some good lightning at times in late August and early September.  Until that time it was pretty dead in Western Oregon…although that’s not so unusual.


Fall is here though and it looks wet over the next 7-10 days.

Okay, now you can all argue about why it was such a horrible summer, how I have a “warm bias”, or what you loved about the summer so much…

Chief Meteorologist Mark Nelsen