Flood Watch This Weekend

December 19, 2014

This weekend is going to be a wet one and with lots of tweets and press releases are flying around.  I want to clear up some confusion about who may or may not see flooding.

HIGHLIGHTS

If you live in the lowlands AWAY FROM RIVERS (80% of us do), flooding is unlikely.  It appears there just won’t be that much rain in the lowlands.

If you live in the lowlands near a river that comes out of the Cascades or Coast Range…flooding is far more likely.  If you live along the Sandy, Clackamas, or Molalla rivers I think significant or major flooding is possible.

If you live in the foothills of the Coast Range/Cascades, western Gorge, or mountains themselves, be on the lookout for mud/landslides late Saturday through late Sunday.

Today’s social media world has made communicating clear weather information a bit tougher.  Of course I’m adding to it just by posting this…sorry!

I see two trends this afternoon:

1.  Precipitation is looking even lighter in the lowlands with very little Saturday evening through late Saturday night.

2.  We dry out in the lowlands by midday Sunday…probably dry Sunday afternoon north of Salem.

Take a look at our RPM forecast for rain in the Portland area…just an inch or so.  If this happens you can totally forget about flooding in the metro area.  Notice no rain after 8am Sunday as the main rain band slips south:

MarkRain_RPM_NEXT24HOURS

But take a look at Welches…same model:

MarkRain_RPM_NEXT24HOURS_Welches

continuous rain the whole period…that’s why those mountain rivers will be flooding by Sunday

Chief Meteorologist Mark Nelsen


Warm Weekend Rain Still On The Way

December 18, 2014

11pm Thursday…

Models are still wet this evening, although not quite as extreme as 24 hours ago.  Our RPM shows 1-2″ rain Saturday/Sunday in the lowlands and 5-9″ in the Cascades

RPM_12KM_Precip_NWOR

The valley numbers sure wouldn’t give us any sort of widespread flooding, but I can see mudslides/landslides in the mountains east and west of us with those much higher numbers up there.  I checked the Willamette flood control reservoirs (Detroit Lake, Green Peter, Hills Creek etc…) and they are all at their winter low levels.  That means plenty of room for storing the rain; we won’t be seeing any flooding on the Willamette or Columbia.  More likely rivers like the Wilson, Nehalem, Sandy, & Clackamas will see at least some sort of flooding.  The NWS will probably issue a flood watch tomorrow.

Bad new for the Cascades of course.  Really depressing is the tree lighting on Saturday evening in Gov’t Camp.  This will be the 2nd consecutive year in which it’ll be pouring rain for this event instead of dumping piles of snow.  MarkSnow_MtHoodFcst_2013

There will likely be some snow next Wednesday, but the big picture shows no chance of any widespread ski area openings through at least Friday the 26th.  Some models produce some snow the weekend after Christmas, so maybe that will help.

By the way, there are two places in Oregon to ski with at least several lifts open…Mt. Bachelor and Anthony Lakes (near Baker City).


Weekend Washout Ahead: Some Flooding Possible

December 17, 2014

Do you need to build an Ark in the next 3 days?  No, but some local rivers COULD see flooding late in the weekend or early next week if models are correct.

Between now and Friday night not a whole lot to talk about, although Thursday night’s system will bring some snow to the Cascades down to pass elevations.

Then the jet stream will punch directly into Oregon and the southern half of Washington.  Take a look at the forecast for Sunday morning

gfs_300

…speeds approaching 200 mph surging northeast out of the tropics and aimed right at the Pacific Northwest.  The precipitable water forecast from the GFS model shows the “atmospheric river” of moisture very clearly.  Precipitable water is a measure of the total column of moisture through the atmosphere at any one location.

pcpwater_4aSun

You can see how an event like this got the name “atmospheric river”; it’s a narrow, but massive, transport of moisture-laden air from the tropics into the middle latitudes.  In this case it’s transported over us.  Pineapple Express or Java Jet works too because the source region is in the tropics.

That is only part of the reason we have a huge soaking ahead.  The other is our mountain ranges.  Both the Coast Range and Cascade Range are oriented directly perpendicular to this flow of air.  In the case of Saturday and Sunday, the flow of air will be strong from the west…around 70 mph at 5,000′.  That air suddenly has to rise, cooling the airmass.  When that happens it has to dump it’s load of moisture in the form of heavy rain.  You’d be amazed at how efficient this can be.  I’ve seen just a few sprinkles in the valley all day in an event yet a full inch falls in the mountains.

In the case of this weekend, our models are painting a very dramatic picture with unusually heavy rain over our mountains from Saturday through Tuesday morning.  Almost all of it is done by Monday morning.  The “drier” ECMWF shows maybe 4-8″ on the west slopes of the Cascades.  Note Oregon is under the gun and it isn’t very heavy north of St. Helens or Mt. Adams:

ecmwf_precip

The GFS is crazy wet, one of the wettest runs I’ve seen, 12-15″!  That’s serious flooding of rivers draining the Cascades (Sandy, Clackamas, Molalla, Santiam) if that were to occur:

gfs_tuesam

The WRF-GFS, which is based on the GFS, is showing slightly more tame numbers…but still over 10″ in some areas:

wrf_tuesam

Can you see the rain shadow in the western valleys too?  Only 2-3″ in the valleys but 3 times as much in the Cascades!  That’s perfectly normal in a strong westerly flow.  Also notice the 1/4″ for places like Maupin or Warm Springs.

So do we have a bunch of flooding coming?  We don’t know yet because models could easily shift the rain north or south in the next few runs.  But it’s definitely something we are keeping a very close eye on.

You probably already figured this out, but almost all of the precipitation will be in the form of rain in the Cascades; I think by Monday morning there will be nothing more than a patch or two of snow below 7,000′.

Chief Meteorologist Mark Nelsen


Worst Start To Ski Season in 30+ Years: What’s Ahead?

December 15, 2014

I never thought we’d see 2 consecutive Christmas Breaks with little to no skiing in Oregon…but it appears that may be about to happen, at least to start the two-week period.  It’s heartbreaking looking at the maps/models and knowing so many people’s paychecks, stores, & life dreams are wrapped up in what happens over the next three weeks.  I know last winter must have been a huge financial hit, especially for Oregon’s smaller ski areas and I fear what a repeat could do.  Hang in there!

This is what we have right now; about 25% of normal snowpack (for this date) on the ground in the Cascades.  It’s especially bad in the Mt. Hood area with only 8% of normal!  Dec15_SnowWaterBad

The Mt. Hood Test Site, at 5,400′ within the Timberline Ski Area, has been in operation since around 1980.  There has never been less than 2.7″ Snow Water Equivalent (water in the snowpack if you melt it all down).  That low was in 2002. Right now that location has 6″ of snow on the ground and 2.5″ SWE which means it’s the lowest ever recorded on that sensor on this date.

It’s probably safe to say this is the worst snowpack at this location in mid-December since the great 1976-’77 drought year.  It’s really bad…at this point in time.  No ski area other than Mt. Bachelor has more than 11″ of snow on the ground.  Bachelor got lucky because they are higher up (start at 6,000′) and some of the warmer storms gave them snow when others had rain.

Even last year (which was bad through January) was slightly better.  Here’s a quote from my blog posting last year on this date: “Timberline is reporting 27″ of snow, which is the least of any December 15th since 1989!  Most of you skiers probably remember the winter of 2004-2005…really bad.  That year was a skiing disaster with Skibowl only able to open for a few weeks and I think even Meadows was closed at times mid-winter.  That year we had 47″ on the ground in mid-December at Timberline.  BUT, there were 3 pineapple express events the following couple of months that kept destroying the fresh snow.  We’ll hope that’s not the case this time around.”

To borrow a bit more from last year, with last year itself added in:

This is one of just 5 times that Timberline has seen 30″ or less on the ground on December 15th.  So what happened in the other 5 years?  The following includes snow depth on the 15th and the results:

2013-2014  
27″,   25″+ by January 1st, 1 two foot storm in mid-January otherwise drought continued through first week of February. Big snow finally returned after first week of February

2002-2003  

30″,   80″+ by January 1st, but then not a very good ski season, poor conditions

1989-1990
15″,   18″ by January 1st, then 105″ by February 1st, massive snowstorms commenced in mid-January

1979-1980
30″,   41″ by January 1st, 85″ by February 1st, ski season limped along…not too bad

1976-1977
2″,  8″  by January 1st,   10″ on February 1st.  Worst drought and ski season (or no skiing) in years.  Hasn’t happened since, hopefully won’t occur again!

So you can see what we’ve had so far is no guarantee of what will come for the rest of the winter.  Although only 2 of the 5 really bad years recovered to a reasonable ski season.

LOOKING AHEAD

Why do I think there isn’t much hope starting this weekend, the start of the Christmas Break?  Because we have weak systems the rest of this week that will produce less than 1 foot of snow and then…another round of warm rain at the ski areas.  First, the WRF-GFS model’s snow forecast from now through Friday morning…just 2-5″ on Mt. Hood:

or_snow_Friam

Then the following three days look how much precipitation is forecast…2-5″ liquid.  If it were snow it would be 20-50″ snow depth!

or_pcp72.156.0000

But the snow forecast tells the story from Friday through Monday morning:

or_snow72.156.0000

Little to nothing.  That’s because a strong warm front arrives Saturday along with several days of warm weather and freezing levels around 7,000-8,000′.  It’ll all be rain from later Saturday through Monday.  What little snow we get this week would wash away and we’d have little or no snow on the ground at the Mt. Hood Ski Resorts by Tuesday the 23rd.  Wow…it doesn’t get any worse than this.  To top it off, the pattern looks relatively dry after that point with upper-level ridging along the West Coast.

To sum it up, I don’t see a pattern or sequence of weather events that could get a bunch of lifts open at ski areas for the next 7-10 days.

Of course I could be wrong.   But all models, through at least the next 7 days, agree with the general scenario above.

Chief Meteorologist Mark Nelsen


The REAL ECMWF Maps

December 15, 2014

Geez, can’t believe I posted 4 DAY OLD MAPS in the previous post!  Here are the real ECMWF monthly maps for the next 4 weeks:

500za_week1_bg_NA

500za_week2_bg_NA

500za_week3_bg_NA

500za_week4_bg_NA

Those first 3 weeks definitely have the ridging well to the west…could be a very cold pattern for us from around Christmas onward.  Drier than what the previous maps showed.

Chief Meteorologist Mark Nelsen


Monthly ECMWF Maps

December 15, 2014

Just saw the weekly 500mb height maps from last night’s monthly run of the ECMWF.  Ridging wants to hang around the West Coast much of the 2nd half of December.  Here is the first week showing the troughs impacting us at times.  They are weak and splitty, evidenced by the highest anomaly to our south.  This is bad for skiing, no significant snow (2 feet or more) on the way:

500za_week1_bg_NA

Then Christmas Week a change back to the November pattern we saw with ridging hanging right over us or trying to shift back a little to the west.  We turn very dry, although the ECMWF today has warm rain in the Cascades as the ridging is getting established Sunday through Tuesday next week:

500za_week2_bg_NA

It’s interesting to note the ensemble average seemed to be farther west yesterday, putting us on the edge of “backdoor” arctic air invasion.  Even the 12z ensemble average that just came out midday looks like that.  Slightly under two weeks from now:

500_Sun_28th

Back to the monthly run…Week 3:

500za_week3_bg_NA

A bit more north with the ridging, this could let some systems through underneath it…into mainly California.  We saw this in November a bit.  Mild West Coast and cold eastern USA.

And the final week which takes us almost to mid January…looks a classic “El Nino” setup again with a strong jet into California and the ridge has moved farther north.  This could be wet at times over us, similar to what we’ve seen early in December.

500za_week4_bg_NA

Remember this is just one run, although it is many different ensembles averaged together too.  The main message I take away from this is the ECMWF shows no cool/snowy westerly-flow pattern for the Cascades in at least the next 2-3 weeks.  That was totally absent last winter as well.  At least until the floodgates opened the 2nd half of February!

I’ll probably blog more on the pitiful (and possibly record-setting) state of the snowpack in the Cascades late today.

Chief Meteorologist Mark Nelsen


Windstorm Wrap Up

December 11, 2014

Now TODAY was a fun weather day for the meteorologists!  But it’ll be nice to relax after work now that the storm has moved on to the north.

First, a bit of a buried headline is the “heat”.  You just enjoyed the warmest December day since…the 1995 windstorm day!

MarkRecordHighTempsMetro

Notice Vancouver was just as warm.

On to the wind gusts.  Here are the numbers:

PLOT_Wind_Metro_PeakGusts_MANUAL2 PLOT_Wind_Metro_PeakGusts_MANUAL

Hillsboro, Aurora, & McMinnville reported those numbers and then went offline due to a power outage.  So it’s possible the numbers were higher.

Let’s talk about what went right and what didn’t turn out as well:

HIGHLIGHTS:

TIMING:  Wow, models were right on!  Peak wind gusts were right about the time we expected.  The winds picked up and dropped off quickly as expected.

DEPTH OF LOW:  Looks like low pressure center bottomed out somewhere near 973 millibars according to NWS.  That’s close enough to model forecasts, quite similar to WRF-GFS for sure.

TRACK:  It took until 24 hours ahead of time for models to pull it together, but they all showed a reasonably accurate path. The low just scraped by the NW tip of Washington and is running into Vancouver Island right now.

MODEL FORECAST WIND:  The WRF-GFS did really well, showing the higher speeds on this morning’s run.

WHAT DID WE MISS OR COULD IMPROVE ON?

MODELS:  GFS was the first to latch onto the correct track…there, I said it.  The ECMWF played catch-up until about 48 hours ahead of time.  The NAM was terrible until the last 12 hours…reminder to ignore it in the future.  GEM kept shoving the storm inland and didn’t correct itself even 24 hours ahead of time.

COAST FORECAST:  A total miss here.  It was nothing more than an average winter storm at the beaches, and definitely not a major storm as was advertised.  Peak gusts were almost all below 70 mph.  I saw a 79 at Newport Jetty and 89 at Sea Lion Caves, but that 2nd one was even out of our viewing area.  Astoria only hit 56!  Anyone on the coastline north of Lincoln City is thinking “that was it???”

INLAND WIND FORECAST:  I first said 45-60 mph, then yesterday said 45-55 mph for metro area airport locations (official sites).  Then this morning leaned more to 50-55 mph on my 10am posting.  For much of the area that forecast was fine, but obviously we had some gusts around 60 mph.  PDX airport seems to be a bit of an outlier at 67 mph, similar to that extra strong 55 mph gust last February when everyone else was much lower.    The NWS first had gusts 55-65 mph yesterday (a good call!) then lowered it to around 50 (local gusts to 60) for the metro area in this morning’s forecast and tweets.  Close enough.

SOCIAL MEDIA:  It’s a scary medium!  One where a bad fact can spread across the globe in minutes.  One bit of info that went out said PDX’s peak gust was the strongest since 1971.  Within minutes that was all over Twitter, and I saw a Weather Channel tweet about it!  The 1981 storm had a stronger gust.

How did this windstorm rank?

For the Portland metro area ON AVERAGE I would say it was similar to the December 2006 storm when you compare damage and power outages.  Looks like in some locations (PDX) it was stronger, but in 2006 we had far more power outages.  I noticed today that Multnomah county had far fewer outages than Washington county.  For whatever reason there was more impact central/westside than eastside and Clackamas county.  Clark county was hit hard too.  January 2000 was a similar storm to what we saw this afternoon.

The December 1995 was far stronger in our area.  Several reports of 70-80 mph gusts in parts of the West Hills.  Here’s a chart showing peak gusts at PDX compared to PGE outages.  You can see how much more widespread the 2006 & 1995 events were:

MarkWind_CompareWindstorms

It’s tough to compare these windstorms speed-wise because three different instruments have been used at PDX since the 1980s.  Up until 1994, the sensor at PDX was an instantaneous gust measurement, but when ASOS units were installed in 1995, the gust had to register for 5 seconds!  So recorded wind speeds went down for 11 years.  Basically it was harder to get high wind speeds.  All three storms on that chart above used the 5 second gust.  Then right after the 2006 storm new sonic anemometers replaced those units and now it’s a 3 second gust.  See how comparing the speeds is a bit of apples vs. oranges?  Wolf Read has an excellent piece of work about this issue on his webpage.

During the December 1995 storm, BOTH units were operating at PDX.  The new “official” gust was the 62 mph you see above.  But the old unit read 74 mph with instantaneous gust.  You can see the difference!

What are YOUR thoughts about the storm?

Chief Meteorologist Mark Nelsen