February Weather in the Pacific Northwest

[Deweydog]

Snowflakes nucleate around mineral or organic particles in moisture-saturated, subfreezing air masses. They grow by net accretion to the incipient crystals in hexagonal formations. The cohesive forces are primarily electrostatic.

 

Nucleus Edit

In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. The particles that make ice nuclei are very rare compared to nuclei upon which liquid cloud droplets form; however, it is not understood what makes them efficient. Clays, desert dust and biological particles may be effective,[6] although to what extent is unclear. Artificial nuclei include particles of silver iodide and dry ice, and these are used to stimulate precipitation in cloud seeding.[7] Experiments show that "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than −35 °C (−31 °F).[8]

 

Growth Edit

Once a droplet has frozen, it grows in the supersaturated environment, which is one where air is saturated with respect to ice when the temperature is below the freezing point. The droplet then grows by deposition of water molecules in the air (vapor) onto the ice crystal surface where they are collected. Because water droplets are so much more numerous than the ice crystals due to their sheer abundance, the crystals are able to grow to hundreds of micrometers or millimeters in size at the expense of the water droplets. This process is known as the Wegener–Bergeron–Findeisen process. The corresponding depletion of water vapor causes the droplets to evaporate, meaning that the ice crystals grow at the droplets' expense. These large crystals are an efficient source of precipitation, since they fall through the atmosphere due to their mass, and may collide and stick together in clusters, or aggregates. These aggregates are usually the type of ice particle that falls to the ground.[9] Guinness World Records lists the world's largest (aggregate) snowflakes as those of January 1887 at Fort Keogh, Montana; allegedly one measured 15 inches (38 cm) wide. Although this report by a farmer is doubtful, aggregates of three or four inches width have been observed. Single crystals the size of a dime (17.91 mm in diameter) have been observed.[3] Snowflakes encapsulated in rime form balls known as graupel.

 

The exact details of the mechanism underlying the tendency of ice particles to stick together and form aggregates remain unresolved. Proposed mechanisms include mechanical interlocking, sintering, electrostatic attraction as well as the existence of a "sticky" liquid-like layer on the crystal surface.

 

Appearance Edit

Color Edit

Although ice by itself is clear, snow usually appears white in color due to diffuse reflection of the whole spectrum of light by the scattering of light by the small crystal facets of the snowflakes of which it is comprised.[4]

 

Shape Edit

The shape of the snowflake is determined broadly by the temperature and humidity at which it is formed.[9] Rarely, at a temperature of around −2 °C (28 °F), snowflakes can form in threefold symmetry — triangular snowflakes.[10] The most common snow particles are visibly irregular, although near-perfect snowflakes may be more common in pictures because they are more visually appealing. It is unlikely that any two snowflakes are alike due to the estimated 1019 (10 quintillion) water molecules which make up a typical snowflake,[11] which grow at different rates and in different patterns depending on the changing temperature and humidity within the atmosphere that the snowflake falls through on its way to the ground.[12] Snowflakes that look identical, but may vary at the molecular level, have been grown under controlled conditions.[13]

 

Although snowflakes are never completely symmetrical, a non-aggregated snowflake often grows so as to exhibit an approximation of six-fold radial symmetry. The symmetry gets started[14] due to the hexagonal crystalline structure of ice. At that stage, the snowflake has the shape of a minute hexagon. The six "arms" of the snowflake, or dendrites, then grow independently from each of the corners of the hexagon, while either side of each arm grows independently. The micro-environment in which the snowflake grows changes dynamically as the snowflake falls through the cloud, and tiny changes in temperature and humidity affect the way in which water molecules attach to the snowflake. Since the micro-environment (and its changes) are very nearly identical around the snowflake, each arm tends to grow in nearly the same way. However, being in the same micro-environment does not guarantee that each arm grow the same; indeed, for some crystal forms it does not because the underlying crystal growth mechanism also affects how fast each surface region of a crystal grows.[15] Empirical studies suggest less than 0.1% of snowflakes exhibit the ideal six-fold symmetric shape.[16] Very occasionally twelve branched snowflakes are observed; they maintain the six-fold symmetry.[17]

[Blizzard777]

In Texas enjoying temps in 70,s. Will miss the action Sunday but back in Seattle Monday for freeze.

I get to go there again in March! Hoping for some good Thunderstorms action.

[Geos]

PDX NWS Discussion, this was before the 12z suite

 

 

Now for the million dollar question... Will it snow in the lowlands

Sunday? The answer is probably yes for most, though accumulating snow

is less likely. Snow levels crash from near/above the Cascade Passes

Sat morning to near the valley floor by Sunday morning behind the

front. Beginning Sunday morning, or perhaps even late Sat night, snow

may begin to mix in with the rain down to the valley floor in any

showers. By Sunday afternoon, thermal profiles become favorable for

snow levels near the valley floors despite onshore flow, as 850 mb

temps fall to -8 deg C. However, low-level onshore flow will keep

temps well above freezing during the day Sunday at the lowest

elevations. Though there will probably be a few exceptions due to

heavier showers bringing down the snow level, and these types of

showers will be widespread given the low-level lapse rates, we held

the general snow level at 500 to 1000 feet due to surface heating.

00z suite of guidance trended a bit further west with the broad upper

trough developing over the Pac NW Sunday, with some potential of a

deformation band developing somewhere over the area as the

westernmost of a pair upper low centers tracks southward through

western WA/OR. 00z NAM frontogenesis and omega fields suggest this

potential, with some QPF lingering well behind the front into Sunday

evening. By then, it will be cold enough for accumulating snow down

to the lowest elevations. Also...by Sunday, the air mass over the

coastal waters will be very unstable in the low-levels, almost like a

lake effect snow situation back East. This could surprise coastal

areas with several quick shots of snow as showers move onshore.

Lightning is not out of the question either along the coast, but not

likely enough to mention in the forecast.

 

The bottom line of this dissertation-length discussion is that while

we have a good idea of the major players affecting our weather

through the upcoming weekend, the details are very complex and it is

likely that there will be changes to the forecast over the coming

days. However, it is very likely that the high Cascades will see

their best snow event in quite some time, and it is likely that just

about everyone in our forecast area sees at least a snowflake or two

in the air by the end of the weekend. The potential is there for

significant impacts to the lowlands, but at this point it does not

look like the ingredients come together for widespread significant

accumulations in the lowlands.Weagle

 

I like the part about the ocean effect snow and lightning!

[ShawniganLake]

You should quote the other two then post it.

I read something about a snowflake or two.

[Blizzard777]

Tim is a badass, posting weather maps at 30000ft. 

 

I’m going to need a taller ladder

[Geos]

Interesting the GEM shows some snow showers into Monday.

 

 

[Front Ranger]

Looks very dry in CA over the next 10 days... run the precip loop. All the precip is still focused on WA and OR where its not needed compared to other places.

 

Although OR mountains need snow.

 

Like I said, I think CA will eventually do alright. 

 

Looking at the West as a whole, this pattern is so much better than anything else in forever.

[TT-SEA]

Hopefully not being charged an exorbitant amount to use their wi-fi.

 

$2.99 for the entire flight

[seattleweatherguy]

Wow cheaper than Alaska

[Front Ranger]

$2.99 for the entire flight

 

So like a cent/minute. Not bad.

[Blizzard777]

$2.99 for the entire flight

What is the current temp at 36,000 feet over the Pacific? Have a great time!

[MR.SNOWMIZER]

Snowflakes nucleate around mineral or organic particles in moisture-saturated, subfreezing air masses. They grow by net accretion to the incipient crystals in hexagonal formations. The cohesive forces are primarily electrostatic.

 

Nucleus Edit

In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. The particles that make ice nuclei are very rare compared to nuclei upon which liquid cloud droplets form; however, it is not understood what makes them efficient. Clays, desert dust and biological particles may be effective,[6] although to what extent is unclear. Artificial nuclei include particles of silver iodide and dry ice, and these are used to stimulate precipitation in cloud seeding.[7] Experiments show that "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than −35 °C (−31 °F).[8]

 

Growth Edit

Once a droplet has frozen, it grows in the supersaturated environment, which is one where air is saturated with respect to ice when the temperature is below the freezing point. The droplet then grows by deposition of water molecules in the air (vapor) onto the ice crystal surface where they are collected. Because water droplets are so much more numerous than the ice crystals due to their sheer abundance, the crystals are able to grow to hundreds of micrometers or millimeters in size at the expense of the water droplets. This process is known as the Wegener–Bergeron–Findeisen process. The corresponding depletion of water vapor causes the droplets to evaporate, meaning that the ice crystals grow at the droplets' expense. These large crystals are an efficient source of precipitation, since they fall through the atmosphere due to their mass, and may collide and stick together in clusters, or aggregates. These aggregates are usually the type of ice particle that falls to the ground.[9] Guinness World Records lists the world's largest (aggregate) snowflakes as those of January 1887 at Fort Keogh, Montana; allegedly one measured 15 inches (38 cm) wide. Although this report by a farmer is doubtful, aggregates of three or four inches width have been observed. Single crystals the size of a dime (17.91 mm in diameter) have been observed.[3] Snowflakes encapsulated in rime form balls known as graupel.

 

The exact details of the mechanism underlying the tendency of ice particles to stick together and form aggregates remain unresolved. Proposed mechanisms include mechanical interlocking, sintering, electrostatic attraction as well as the existence of a "sticky" liquid-like layer on the crystal surface.

 

Appearance Edit

Color Edit

Although ice by itself is clear, snow usually appears white in color due to diffuse reflection of the whole spectrum of light by the scattering of light by the small crystal facets of the snowflakes of which it is comprised.[4]

 

Shape Edit

The shape of the snowflake is determined broadly by the temperature and humidity at which it is formed.[9] Rarely, at a temperature of around −2 °C (28 °F), snowflakes can form in threefold symmetry — triangular snowflakes.[10] The most common snow particles are visibly irregular, although near-perfect snowflakes may be more common in pictures because they are more visually appealing. It is unlikely that any two snowflakes are alike due to the estimated 1019 (10 quintillion) water molecules which make up a typical snowflake,[11] which grow at different rates and in different patterns depending on the changing temperature and humidity within the atmosphere that the snowflake falls through on its way to the ground.[12] Snowflakes that look identical, but may vary at the molecular level, have been grown under controlled conditions.[13]

 

Although snowflakes are never completely symmetrical, a non-aggregated snowflake often grows so as to exhibit an approximation of six-fold radial symmetry. The symmetry gets started[14] due to the hexagonal crystalline structure of ice. At that stage, the snowflake has the shape of a minute hexagon. The six "arms" of the snowflake, or dendrites, then grow independently from each of the corners of the hexagon, while either side of each arm grows independently. The micro-environment in which the snowflake grows changes dynamically as the snowflake falls through the cloud, and tiny changes in temperature and humidity affect the way in which water molecules attach to the snowflake. Since the micro-environment (and its changes) are very nearly identical around the snowflake, each arm tends to grow in nearly the same way. However, being in the same micro-environment does not guarantee that each arm grow the same; indeed, for some crystal forms it does not because the underlying crystal growth mechanism also affects how fast each surface region of a crystal grows.[15] Empirical studies suggest less than 0.1% of snowflakes exhibit the ideal six-fold symmetric shape.[16] Very occasionally twelve branched snowflakes are observed; they maintain the six-fold symmetry.[17]

What about time travel? can you explain in great detail?

[Geos]

RGEM starts to show the convergence zone turning to snow in Snohomish County at like hour 46.

 

[Deweydog]

What about time travel? can you explain in great detail?

[MikeInEverett]

Maybe I’ll finally score some decent c-zone snow. Something that hasn’t happened in forever, which is surprising given my location.

[DareDuck]

Where's Tim?

Jeez he doesn’t post for an hour and you miss him?

[TigerWoodsLibido]

$2.99 for the entire flight

Wow thats a great deal!

[Geos]

Maybe I’ll finally score some decent c-zone snow. Something that hasn’t happened in forever, which is surprising given my location.

 

Wondering if the NW flow might orientate the band in such a way that stretches from Edmonds area ESE or SE towards central King County for a bit. 

 

Nice for you.

 

[seattleweatherguy]

Wondering if the NW flow might orientate the band in such a way that stretches from Edmonds area ESE or SE towards central King County for a bit.

 

Nice for you.

 

Big hole over king county on that map

[Frontal Snowsquall]

Certainly looks like the best shot at a real snow event but temps look suspect.

 

us_model-en-087-0_modez_2018021612_129_1256_241.png

us_model-en_modez_2018021612_129_494_155.png

us_model-en-087-0_modez_2018021612_129_494_488.png

Looking great! Still about 5 days away to iron out the exact details but this has lots of potential. These BC sliders seem to stall as they head inland and can produce bigger accumulations then forecasted.

[wxmet]

Euro 00z looks horrible for the central Sound. Dry slot, warm temps, little in the way of snow. The mid week system looks more interesting. 

[Geos]

Not overly impressed with the NAM right now. Hoping some moisture can sneak around into northern King Sunday morning about the time the cold arrives. 

 

[FroYoBro]

Euro 00z looks horrible for the central Sound. Dry slot, warm temps, little in the way of snow. The mid week system looks more interesting. 

 

So are you a professional meteorologist? 

[Blizzard777]

44 out with blustery south winds

[wxmet]

So are you a professional meteorologist? 

 

I don't work as one but I do have a degree in meteorology. 

[ShawniganLake]

[Deweydog]

So are you a professional meteorologist?

I doubt frozen yogurt is your brother.

 

I am not a dog.

[Esquimalt]

A1B4E402-9989-4CDF-8254-180DFD106AE5.png

Wow.  Amounts are even higher than on the 12Z.  Weird.  Do you think this model is going to be right?  How well does it usually perform in these situations?  

[seattleweatherguy]

I don't work as one but I do have a degree in meteorology.

Nice how long does it take to get one of those.

[TigerWoodsLibido]

50 with light winds and sprinkles on the radar.

[MR.SNOWMIZER]

Nice how long does it take to get one of those.

Amazon. About 2 days.

[Jesse]

Nice how long does it take to get one of those.

Accuweather has a program where you can listen to a two week course of Joe Bastardi podcasts and they mail you one after completing the open note quiz at the end.

[SilverFallsAndrew]

. American charges like $14.99 for the flight...

 

The EURO rapes me with 6" of snow on Wednesday.

[HighlandExperience]

Accuweather has a program where you can listen to a two week course of Joe Bastardi podcasts and they mail you one after completing the open note quiz at the end.

Truth or try khan academy

[Jesse]

Truth or try khan academy

You get a complementary Orphan Annie decoder pin if you score 70% or higher.

[Perturbed Member]

s**t. American charges like $14.99 for the flight...

 

The EURO rapes me with 6" of snow on Wednesday.

 

Average length, did the Euro tell you what the girth will be?

[ShawniganLake]

Wow. Amounts are even higher than on the 12Z. Weird. Do you think this model is going to be right? How well does it usually perform in these situations?

If it has the surface features correct it could be close, but that’s still a bit of a guess. It’s usually high on totals during marginal temps, as to be expected when it’s using 10:1 ratios. As with most models, I’ve seen it do really well and not so good.

[Jesse]

Here it comes. I always like looking at this loop:

 

https://atmos.washington.edu/~ovens/loops/wxloop.cgi?sat_500+9

 

Our upcoming cold pattern will be ushered in by the shortwave trough currently over Kodiak Island, AK digging down and retrograding the ridge.

[Geos]

Total 3km NAM snow. No well define CZ though.

 

 

Look closely enough and you can see 2" totals from Shoreline through Everett and Marysville.

[seattleweatherguy]

Total 3km NAM snow. No well define CZ though.

 

 

Look closely enough and you can see 2" totals from Shoreline through Everett and Marysville.

Fine with me if that works out. I'd be in that area