Third Coldest February In Seattle History (And Snow Showers Later Today!)

Knowing the highs and lows for the first 26 days of February, and with reliable forecasts for the next two, it is now evident how February temperatures will rank at Sea-Tac Airport on an historical basis:

It will be the third coldest February in a record going back to the late 1940s.

The average temperature this month at Sea-Tac I calculated was 36.46 F.

The coldest Februaries at Sea Tac were 35.64F in 1956 and 35.88F in 1989.

2019 is next in line, followed by 37.3F in 1949.  I can't imagine this rank changing no matter what the temperature is the next two days.

This February is particularly cold considering all the construction (and thus warming) in the area around Sea-Tac Airport since 1989.   So meteorologically we really we in a league with the top two.

A plot of Sea-Tac Airport temperatures, with the normal highs and lows, is, well, chilling. We had a week where the average high barely hit the average low, and in no day since Feb 4th has the our high temperature even approached the normal high.  The last few days have even cooled. 

An interesting question is whether there are been much of a trend in February temperatures over Puget Sound. 

Using the wonderful NOAA ESRL website, here is a plot of the February mean temperatures over the Puget Sound lowlands from 1950 to 2018.  A lot of variability but little trend over the past 70 years.  Interestingly, there is a big cold spell in February roughly every 30 years:   1956, 1989, and 2019 (not shown, but there will be another major spike down this year).  

The whole state?   Pretty much the same story (see below).  Little evidence of long-term warming, but several degrees of variability (up and down excursions).  Later in the century, we would expect some warming due to increasing greenhouse gases, but warming is slowed here in the Northwest by the slow to warm eastern Pacific.

Finally, there is a chance of snow showers later today, particularly east and north of Seattle.  A weak disturbance is moving through and temperatures are marginal here in Seattle for snow.  The total precipitation forecast through 11 PM is shown below...very light over the lowlands, but heavier towards the Cascades.

The expected snowfall in that period is essentially zero near the water, but ramps up towards the Cascades.   Portland gets some light snow.  Nothing to rush to the food store for.  But more good news for the Cascade snowpack.

from Cliff Mass Weather and Climate Blog https://ift.tt/2Egw50H

Third Coldest February In Seattle History (And Snow Showers Later Today!)

Knowing the highs and lows for the first 26 days of February, and with reliable forecasts for the next two, it is now evident how February temperatures will rank at Sea-Tac Airport on an historical basis:

It will be the third coldest February in a record going back to the late 1940s.

The average temperature this month at Sea-Tac I calculated was 36.46 F.

The coldest Februaries at Sea Tac were 35.64F in 1956 and 35.88F in 1989.

2019 is next in line, followed by 37.3F in 1949.  I can't imagine this rank changing no matter what the temperature is the next two days.

This February is particularly cold considering all the construction (and thus warming) in the area around Sea-Tac Airport since 1989.   So meteorologically we really we in a league with the top two.

A plot of Sea-Tac Airport temperatures, with the normal highs and lows, is, well, chilling. We had a week where the average high barely hit the average low, and in no day since Feb 4th has the our high temperature even approached the normal high.  The last few days have even cooled. 

An interesting question is whether there are been much of a trend in February temperatures over Puget Sound. 

Using the wonderful NOAA ESRL website, here is a plot of the February mean temperatures over the Puget Sound lowlands from 1950 to 2018.  A lot of variability but little trend over the past 70 years.  Interestingly, there is a big cold spell in February roughly every 30 years:   1956, 1989, and 2019 (not shown, but there will be another major spike down this year).  

The whole state?   Pretty much the same story (see below).  Little evidence of long-term warming, but several degrees of variability (up and down excursions).  Later in the century, we would expect some warming due to increasing greenhouse gases, but warming is slowed here in the Northwest by the slow to warm eastern Pacific.

Finally, there is a chance of snow showers later today, particularly east and north of Seattle.  A weak disturbance is moving through and temperatures are marginal here in Seattle for snow.  The total precipitation forecast through 11 PM is shown below...very light over the lowlands, but heavier towards the Cascades.

The expected snowfall in that period is essentially zero near the water, but ramps up towards the Cascades.   Portland gets some light snow.  Nothing to rush to the food store for.  But more good news for the Cascade snowpack.

from Cliff Mass Weather and Climate Blog https://ift.tt/2Egw50H

Snow Heads to Oregon, While Western WA Enjoys Cold/Dry/Windy Conditions

It is now snowing from Vancouver, Washington down to southern Oregon, as a low center moves across the southern part of the state.    The infrared satellite picture around 7 AM Monday shows the situation, with a plume of moisture moving northeastward across Oregon and then into southeast Washington.

The latest weather radar imagery shows the snow, but this is probably not an accurate rendition of the true state of affairs. 

Why?   First, snow does not show on radar as well as rain (ice does not scatter microwave radiation as readily as liquid water).   But more important, Oregon has terrible radar coverage.   I mean bad. They don't have a weather radar on the coast and much of eastern Oregon has zero radar coverage in the lower atmosphere.  The eastern slopes of the WA Cascades are not much better.

The folks in Oregon should be up in arms about this--and they need someone like our Senator Cantwell, who pushed for the Langley Hill radar on our coast.

A six-hour forecast of sea level pressure and low-level (2500 ft) temperatures for 10 AM today predicts the low center will be over the southern Oregon Cascades at 10 AM ( see below).  Very cold air is over BC and eastern WA, with simply cold air over western WA and NW Oregon. Extremely cold air is found over central and eastern Montana, illustrating how the Rockies protects us from the really primo cold stuff.

Snow will not get near Puget Sound, but central Oregon will be buried.  Here is last nights UW WRF model forecast for total snowfall for the 48 h ending 4 PM Tuesday. In Washington, Walla Walla will get a piece of it, but the real action will be south of Salem.   You will not want to go to Eugene, which will resemble Siberia before this over.

This snowfall is really a gift from the weather gods for Oregon.  A month ago, there was substantially below-normal snow pack over the Oregon Cascades.  By the time it is over, Oregon will have a normal snowpack.  Very good news for water resources, fish, and the ski industry..

Here in western WA the weather story the next few days will be dry, cold and windy.  Cold, dry northeasterly flow is now pushing through the Fraser River valley into NW WA, with gusts to 30 mph and more as I write this (see surface map below).     With a strong pressure difference across the Cascades,  gusty easterly flow is now descending into the Cascade foothills from Enumclaw to North Bend.

A high-resolution model prediction for the surface (10-m) wind gusts at 4 AM this morning shows the wind action, including the acceleration of easterly winds down the Strait of Juan de Fuca.

A dry, partly sunny, but cool week is ahead.    Will we end up with the coldest February on record at Sea-Tac?  It will be soon time to run the numbers!

from Cliff Mass Weather and Climate Blog https://ift.tt/2E8wxOu

Snow Heads to Oregon, While Western WA Enjoys Cold/Dry/Windy Conditions

It is now snowing from Vancouver, Washington down to southern Oregon, as a low center moves across the southern part of the state.    The infrared satellite picture around 7 AM Monday shows the situation, with a plume of moisture moving northeastward across Oregon and then into southeast Washington.

The latest weather radar imagery shows the snow, but this is probably not an accurate rendition of the true state of affairs. 

Why?   First, snow does not show on radar as well as rain (ice does not scatter microwave radiation as readily as liquid water).   But more important, Oregon has terrible radar coverage.   I mean bad. They don't have a weather radar on the coast and much of eastern Oregon has zero radar coverage in the lower atmosphere.  The eastern slopes of the WA Cascades are not much better.

The folks in Oregon should be up in arms about this--and they need someone like our Senator Cantwell, who pushed for the Langley Hill radar on our coast.

A six-hour forecast of sea level pressure and low-level (2500 ft) temperatures for 10 AM today predicts the low center will be over the southern Oregon Cascades at 10 AM ( see below).  Very cold air is over BC and eastern WA, with simply cold air over western WA and NW Oregon. Extremely cold air is found over central and eastern Montana, illustrating how the Rockies protects us from the really primo cold stuff.

Snow will not get near Puget Sound, but central Oregon will be buried.  Here is last nights UW WRF model forecast for total snowfall for the 48 h ending 4 PM Tuesday. In Washington, Walla Walla will get a piece of it, but the real action will be south of Salem.   You will not want to go to Eugene, which will resemble Siberia before this over.

This snowfall is really a gift from the weather gods for Oregon.  A month ago, there was substantially below-normal snow pack over the Oregon Cascades.  By the time it is over, Oregon will have a normal snowpack.  Very good news for water resources, fish, and the ski industry..

Here in western WA the weather story the next few days will be dry, cold and windy.  Cold, dry northeasterly flow is now pushing through the Fraser River valley into NW WA, with gusts to 30 mph and more as I write this (see surface map below).     With a strong pressure difference across the Cascades,  gusty easterly flow is now descending into the Cascade foothills from Enumclaw to North Bend.

A high-resolution model prediction for the surface (10-m) wind gusts at 4 AM this morning shows the wind action, including the acceleration of easterly winds down the Strait of Juan de Fuca.

A dry, partly sunny, but cool week is ahead.    Will we end up with the coldest February on record at Sea-Tac?  It will be soon time to run the numbers!

from Cliff Mass Weather and Climate Blog https://ift.tt/2E8wxOu

A Very Difficult Snow Forecast

The ingredients for lowland snow, somewhere in the region, are now evident:  cold air will be moving in aloft during the next days, an upper level trough is approaching, and a low pressure center will be approaching the Northwest coast.

How these pieces will come together is the issue and I will give you may take based on the latest forecast models.   Either Portland or Seattle is going to get a lot of snow, and I suspect it will be the former.

This will be a performance in three acts.

First Act:  Showers Coming Today

There is a band of showers moving in this morning and afternoon, as illustrated by the radar image at 10:40 AM

But at this point, the freezing level is relatively high (around 1400 ft), which means the snow level (the level where all the snow is melted), is around 400 ft (see observed temperatures below, from the Seattle SnowWatch website).  So most lowland residents will only see rain, perfects with a few flakes mixed in during the heavy showers). 

There will be snow showers in the mountains, near the Hood Canal, and for those of you living at higher elevations.  The UW forecast snow totals ending 4 AM Sunday, tells the story.

Act 2:  Cold Air Moves in As an Upper Trough Approaches

As in any good play, some of the protagonists reveal themselves in the second act.   An upper level trough will be building and moving south into our region (see upper level-500hPa-- map for Sunday at 4 AM).   Such a trough results in upward motion (which can produce clouds and precipitation) and can push cold air southward at low levels.

 In fact, the forecast surface chart at 10 AM Sunday shows cool air moving into our region (blue colors) and a weak low center of SW Washington.

The predicted configuration is close but not quite right to give a substantial snow event over western Washington.   The trough is extending too far offshore, the upward motions over us is weak, and the low center is not very strong.  But small differences in the trough position and shape could make a huge difference.  So let's try to tease out the uncertainty by looking at the total accumulated snowfall at Sea Tac Airport using the NWS GEFS multi-run ensemble.  There is some variability, but the average is about .5 inches.  Accumulation on the ground would be less.  And remember this is at Sea-Tac, which is relatively high (452 ft). (Note...time is in UTC, with 12Z/24 being 4 AM Sunday)

 The UW has another, and higher resolution ensemble (run by my group).  There is a lot of uncertainty, but the average is about .8 inches.

So the bottom line of the second act, is that some light snow is possible tomorrow, but it won't add up to much.  Perhaps .5-.75 inches falling out of the sky, with relatively little accumulation.

Third Act:  The Real Threat Emerges

In my plays, the real action occurs in the third act, and this weather situation is no different.  The tension is palpable.  The villain (or whatever you want to call it), will be modest low pressure system that will approach our coast from off the Pacific.  The U.S. GFS model and the UW model that is driven by it, takes the low center into southern Oregon (see below), leaving Puget Sound in dry, cold conditions (4 AM Monday is shown).

As shown by the 48-hr snowfall totals ending 4 AM Tuesday, this forecast produces little snow north of Olympia, but Portland gets several inches, and central/southern Oregon gets huge amounts of the white stuff.   

The vaunted European Center models brings the system a bit further northward--see below.

And the resulting 48-hr snow total from the European Model brings very light snow to Puget Sound and notably more to Portland (6 inches or more).  Salem and Eugene would be snowbound.

There is substantial uncertainty for Puget Sound snowfall, but it looks like we will get little, with Portland "enjoying' the brunt of the action in the third act.

Fourth Act:   More Snow Later This Week?

In a typical fourth act, there is a denouement, where all the plot twists are resolved.  But not in this play.   The European Center Ensemble prediction of accumulated snowfall, shows the potential next week on Tuesday and later.    But this blog is long enough, and this dramatist has to go outside and clean up debris in his yard.

from Cliff Mass Weather and Climate Blog https://ift.tt/2GGb8jl

A Very Difficult Snow Forecast

The ingredients for lowland snow, somewhere in the region, are now evident:  cold air will be moving in aloft during the next days, an upper level trough is approaching, and a low pressure center will be approaching the Northwest coast.

How these pieces will come together is the issue and I will give you may take based on the latest forecast models.   Either Portland or Seattle is going to get a lot of snow, and I suspect it will be the former.

This will be a performance in three acts.

First Act:  Showers Coming Today

There is a band of showers moving in this morning and afternoon, as illustrated by the radar image at 10:40 AM

But at this point, the freezing level is relatively high (around 1400 ft), which means the snow level (the level where all the snow is melted), is around 400 ft (see observed temperatures below, from the Seattle SnowWatch website).  So most lowland residents will only see rain, perfects with a few flakes mixed in during the heavy showers). 

There will be snow showers in the mountains, near the Hood Canal, and for those of you living at higher elevations.  The UW forecast snow totals ending 4 AM Sunday, tells the story.

Act 2:  Cold Air Moves in As an Upper Trough Approaches

As in any good play, some of the protagonists reveal themselves in the second act.   An upper level trough will be building and moving south into our region (see upper level-500hPa-- map for Sunday at 4 AM).   Such a trough results in upward motion (which can produce clouds and precipitation) and can push cold air southward at low levels.

 In fact, the forecast surface chart at 10 AM Sunday shows cool air moving into our region (blue colors) and a weak low center of SW Washington.

The predicted configuration is close but not quite right to give a substantial snow event over western Washington.   The trough is extending too far offshore, the upward motions over us is weak, and the low center is not very strong.  But small differences in the trough position and shape could make a huge difference.  So let's try to tease out the uncertainty by looking at the total accumulated snowfall at Sea Tac Airport using the NWS GEFS multi-run ensemble.  There is some variability, but the average is about .5 inches.  Accumulation on the ground would be less.  And remember this is at Sea-Tac, which is relatively high (452 ft). (Note...time is in UTC, with 12Z/24 being 4 AM Sunday)

 The UW has another, and higher resolution ensemble (run by my group).  There is a lot of uncertainty, but the average is about .8 inches.

So the bottom line of the second act, is that some light snow is possible tomorrow, but it won't add up to much.  Perhaps .5-.75 inches falling out of the sky, with relatively little accumulation.

Third Act:  The Real Threat Emerges

In my plays, the real action occurs in the third act, and this weather situation is no different.  The tension is palpable.  The villain (or whatever you want to call it), will be modest low pressure system that will approach our coast from off the Pacific.  The U.S. GFS model and the UW model that is driven by it, takes the low center into southern Oregon (see below), leaving Puget Sound in dry, cold conditions (4 AM Monday is shown).

As shown by the 48-hr snowfall totals ending 4 AM Tuesday, this forecast produces little snow north of Olympia, but Portland gets several inches, and central/southern Oregon gets huge amounts of the white stuff.   

The vaunted European Center models brings the system a bit further northward--see below.

And the resulting 48-hr snow total from the European Model brings very light snow to Puget Sound and notably more to Portland (6 inches or more).  Salem and Eugene would be snowbound.

There is substantial uncertainty for Puget Sound snowfall, but it looks like we will get little, with Portland "enjoying' the brunt of the action in the third act.

Fourth Act:   More Snow Later This Week?

In a typical fourth act, there is a denouement, where all the plot twists are resolved.  But not in this play.   The European Center Ensemble prediction of accumulated snowfall, shows the potential next week on Tuesday and later.    But this blog is long enough, and this dramatist has to go outside and clean up debris in his yard.

from Cliff Mass Weather and Climate Blog https://ift.tt/2GGb8jl