9pm Update: Freezing Rain Stays South of Salem

November 30, 2014

FREEZING RAIN SHOULD BE A NO-SHOW IN THE PORTLAND METRO AREA AND SALEM ON MONDAY

Almost all evening models (except the ECMWF) are in and show rain staying SOUTH OF SALEM tomorrow morning so that’s what we’ll go with.  The are all remarkably similar on the rain band sitting between Salem and Roseburg most of the day.  Note the WRF-GFS shows a big soaking around Eugene, but nothing north of about Albany:

wrf_4pmprecip

There are hints of a few sprinkles far eastside metro area between 4-8am, but at this point (if it occurs at all) it appears to be too little to even produce ice on roads.  Something to keep an eye on for the morning commute out there though.  By far eastside I mean east of Gresham/Damascus/Estacada.  This showed up on the 00z MM5-NAM, HRRR, and our RPM model. Note the colored areas start at .10″

RPM_12KM_Precip_NWOR

Then after 8am or so it’ll should be dry from Salem northward with quite a bit of late afternoon sun.  Actually all day tomorrow looks mainly sunny at Tillamook, Astoria, and Longview!

To reflect the changing forecast, I updated the CHANCE OF FREEZING RAIN graphic for the 10pm show:

MarkFreezingRain_IceDetails2

Chief Meteorologist Mark Nelsen


Freezing Rain Update

November 30, 2014

If you live south of Salem in the Willamette Valley, expect some areas of ice on roads tomorrow morning.  That’s because rain will arrive around daybreak, especially from Albany to Eugene.  It will be cold enough in some spots (not all areas) to allow the liquid rain to freeze into a glaze.

Here are my latest thoughts as of 5pm Sunday…

  1. Most of our models are dry in the Portland Metro area all day Monday, keeping all (or almost all) of the rain even south of Salem.
  2. A couple generate very light sprinkles overhead in the morning hours for us.  It may or may not be below freezing at that time.
  3. Much better chance for brief freezing rain from Albany through Corvallis/Eugene around daybreak.

As a result, the NWS has a Freezing Rain advisory for only the central/southern Willamette Valley, not the metro area, for Monday morning.  Even down there it’s possible the freezing on roadways will be real spotty.

MarkWarnings_FreezingRain_Snow

Right now I’d assign these chances to Freezing Rain (ice glazing on roads) affecting the morning commute:

MarkFreezingRain_IceDetails

There is one more evening run of the models which should help us either totally eliminate any precipitation in the metro area or not.

Chief Meteorologist Mark Nelsen


Cold Air Is Here…Freezing Rain Threat Decreases

November 29, 2014

The chilly air has moved in…we are 31 at 9pm in Portland compared to 46 just 24 hours ago! East wind is just starting up in the Gorge and that wind will arrive after sunrise for most of us.

As a result of clear skies, low relative humidity, and light wind, temperatures are dropping quickly. We’ll end up around 20 in the coldest parts of the metro area and 20s everywhere else. Not quite as cold as two weeks ago, but close.
FCST_Tonight_Metro

No changes in tomorrow’s forecast with sunshine, a gusty east wind, and chilly temps.

But Monday is sure looking different as of this evening’s model runs.  The last three model runs have been suppressing the precipitation farther south, decreasing the intensity, and slowing it down.   If current runs are correct, much of the day could be dry in the metro area and/or rain will fall with temperatures above freezing.  Take a look at our RPM 7am Monday:

MarkRPM_Cloud_Snow_Fcst and 11am with precipitation just arriving.MarkRPM_Cloud_Snow_Fcst2 That’s too late to get freezing rain with marginal temps and a dying east wind.  The reason the east wind dies off more quickly this time around is because the northern stream of the jet is sending a weather disturbance east across southern British Columbia and Washington.  Flow from the WNW up at 700mb and higher tends to form lee-side troughing on the east side of the Cascades.  This always happens and in this case high pressure weakens quickly over the Columbia Basin on Monday.  Pressure gradient is down to just 2-4 millibars easterly by Monday evening through the Gorge.  So one more reason it won’t be too hard to warm it up above freezing Monday morning.

So does this mean no freezing rain Monday?  No, but the chance of it occurring has dropped quite a bit.  Of course tomorrow’s model runs could bring the rain farther north again, but the trend is usually your friend and the trend since 12z has been to keep it farther south.

By the way, the last 24 hours was a little bit of a disappointment up on the mountain.  At least to me.  I was hoping we could over-achieve and get a foot or more.  Timberline and Meadows had 8-10″ and Skibowl 6″,  But we need a lot more and I don’t see that coming.  Mt. Bachelor is the only ski area in the state that has been able to offer several lifts for Thanksgiving Weekend skiing.  You can see why; they have more than two feet on the ground.  I don’t see a significant snow storm for Mt. Hood in the next 3-4 days at least so next weekend MAY not be much better.

MarkSnow_MtHood_Totals

Chief Meteorologist Mark Nelsen


No Snow Saturday, but Ice/Snow Storm Gorge For Monday

November 28, 2014

10:30pm Friday…

First, don’t get too excited about snow anywhere close to the metro area tomorrow.  Sticking snow level drops to around 1,500′ in the morning and stays there all day.  We’ll just see scattered showers the first half of the day so it’s possible anyone could see a snowflake mixed in with the showers but that’s it.  Those of you above 1,000′ in the Cascade foothills have a better chance of a dusting early in the day since it’ll be wetter up against the mountains.  Same thing in the Coast Range. More obvious will be the change from highs in the upper 50s to afternoon temps just above 40…that winter feeling in the air is back!

Tomorrow night and Sunday we have some modified arctic air working down out of Canada and into the Pacific Northwest.  It’s not as cold as the last event two weeks ago and sure isn’t an “arctic blast” with 850mb temps only around -7/-8 and high temps in sunshine around 40 Sunday.  But quite a chill again and this time it’s straight from the north instead of coming at us from the northeast.  That said, the effect is the same.  Easterly gradient through the Gorge builds quickly and by Sunday morning it’s in the 8-10 millibar range from The Dalles to Portland.  Sunday will be a sunny, but very cold and windy day across the entire metro area.  Windchill temps will likely only be in the 20s and lower 30s all day!

Things get REALLY INTERESTING late Sunday night and Monday…Moisture moves north from the upper-level low off the California coast and forms a sort of deformation band directly over northern Oregon and the extreme southern part of Washington.  This sits overhead for more than 24 hours.  You can see the convergence of the northern part of the jet and the flow from the south midday Monday… wrf_36kmMon

 

As of this evening, all models are on board with this general idea, which brings up three questions:

1. How cold will the airmass be?  Cold enough for anything in the Gorge to be frozen through all of Monday.  PROBABLY not cold enough in the metro area for frozen, although the timing of precip arrival (at sunrise or soon after) would increase the chance for something frozen.

2. How much moisture?  This is a tough one because the placement of the precipitation is farther north on some than others.  Some models are far wetter than others too.  The ECMWF is a real soaker, but keeps the heaviest stuff just south of us, like what happened a couple of weeks ago.  It shows 1/2″ liquid over PDX, but 2″ around Albany by early Tuesday!  The GFS is a little wetter and farther north showing around 1″ over PDX.

3. What precipitation type?  This is the easier one!  Hopefully all the forecasters can agree this time that whatever falls west of the Gorge will be in liquid form.  The atmosphere 2-4,000′ up is forecast to be even warmer than two weeks ago with forecast soundings showing temperatures as high as 40 degrees 2,000′ or so overhead.  It’ll be either rain or freezing rain Monday morning in our area.  In the Gorge, freezing rain at the west end and a wintry mix central/east end.  Could start as snow and then change to freezing rain.

If heavier precipitation forecasts pan out…the potential exists for a very disruptive snow/ice storm in the Gorge again…That’ll be twice so far this season by December 1st!

I work Saturday and Sunday…actually every day through next Friday…so I’ll update again as we get closer.

Chief Meteorologist Mark Nelsen

 


Back to Normal: Wintry Weather Returns

November 28, 2014

Our freakish late November “heat wave” has ended.  After spending 4 days above our NORMAL HIGH TEMPERATURE (49-50), we just dropped to 48 degrees as a cold front moved overhead and the wind switched around to gusty northwesterly instead of the constant/warm south wind.

Let’s recap the 5 warm temperature records tied or broken at PDX:

TUESDAY:  Tied record high temp (63), new record warm low temp (54)
WEDNESDAY: New record high temp (62), new record warm low temp (54)
THURSDAY: New record warm low temp (54)

This has totally decimated what little Cascade snowpack we had.  Both Timberline and Meadows went from about a 2 foot base to just patches of snow on the ground with lots of bare spots.  The official SNOTEL sensor at 5400′ just below Timberline went from 19″ to 4″ depth.  During that time 4.80″ of rain fell.

Good news though!  Looks like up to a foot could fall in the next 18 hours.  Here’s the plan:

MarkHeadlines_SpringBreak

If you are traveling the next 2 days, this means bad news in the mountains…

MarkRoadConditions_I84_5_Passes

I’ll blog later (after evening models come in) about the possibility for lower elevation snow and/or freezing rain.

Chief Meteorologist Mark Nelsen


Quick Look Towards Early Next Week

November 25, 2014

We tied a record high today, broke a warm record low this morning, and will probably break a record high again tomorrow:

MarkWarm_PortlandRecords

Because of the warm weather, travelling conditions are excellent this weekend

MarkRoadConditions_I84_5_Passes

Enjoy the warmth because it’ll end quickly this coming weekend.

Maps/models have been interesting the past few days; fraught with forecasting peril.  The reason?  A split flow with most jet energy going to our south the next week but some northerly flow in the upper atmosphere too.  Over the past two days the emphasis has been on a shot of colder air Saturday-Monday moving down from the north and into the Pacific Northwest.  It doesn’t last long, because it appears the milder southern portion of the jet will take over again early next week.

There are two reasons the forecast is uncertain in this situation:

1. The interaction between moisture to the south and colder air to the north always raises the possibility of frozen precipitation, mainly in the Gorge, but at times models have shown it almost cold enough in the metro area.

2. Placement and timing of precipitation changes with model runs depending on how much energy from each part of the jet stream affects us most.

As of this evening, it looks like we’ll see a shot of the cold air arrive on Saturday.  This will be drier air so not much rain Saturday.  Then dry offshore flow kicks in for two days (Sunday and Monday).  Get ready for a couple of days of cold east wind.  High temps around 40 instead of 60!  On Sunday we’ll probably be dry, but then models are bringing moisture over the top of the cold air Monday.

Monday is the day I see a good chance for freezing rain and/or snow in the Gorge.  Here in the metro area it remains to be seen if it would be cold enough for freezing rain.  Definitely a marginal event, more so than what we saw a couple of weeks ago.  Plus we’ll see when/where the moisture shows up.  The evening ECMWF doesn’t even give us precipitation Monday!

Another reason to just relax and enjoy Thanksgiving!

I’m working Friday-Sunday and I’ll have a lot more time to see how things are shaping up.

Chief Meteorologist Mark Nelsen


Cascade Meltdown: Bad News in The Mountains

November 25, 2014

As I mentioned in a post late last week, the brand new snowpack was going to have to endure several days of warm temps and rain this week before we get back to cooler weather.

It’s not doing well.  In just 24 hours or so, we’ve seen the nearly 2 feet of snow compress/melt down to 10″ or less.

MarkSnowPack_MeltingQuickly

That’s due to unusually warm weather (45-50 degrees at Gov’t Camp) and heavy rain.  It appears at least 2″ has fallen on Mt. Hood, possibly 3-4″ in spots too.  A 5 foot deep snowpack in midwinter could absorb that much rain and not lose too much depth.  But this rain is falling on fresh snow which can’t handle a deluge.

We have one more warm (but dry) day in the mountains, then another warm/rainy system for Thursday.  So most of the last 10″ will be gone by the time sunrise hits Friday.  At that point all three ski areas on Mt. Hood should only see patches here/there along with any snow harvested from parking lots or created through snow making during that cold weather.  Skibowl tells me they made 3 feet of snow on the tubing run during the cold weather, so that should survive.  Meadows has some new toys that allow them to move all the parking lot snow onto the slopes…that’s pretty clever.  This is not all that unusual to see a miniscule snowpack in late November…check out the numbers for the past 8 years:

MarkSnowPack_MeltingQuickly2

So when DO we get new snow up there?  Possibly some on Friday…maybe.  Then forecast models are all over the place Saturday and beyond.  For now, you can assume there won’t be any big ski area openings through this weekend.  By that I mean 30% or more of the runs open.

Chief Meteorologist Mark Nelsen