The Epic Thundersnow of December 18, 2008

The Epic Thundersnow of December 18, 2008

My favorite forecast of all-time was my forecast on the evening of December 17, 2008, when I was a sophomore in high school. It had all the things you could want in a forecast – it was a lowland snow forecast, it had a ton of uncertainty, and above all, it was EXTREMELY high stakes. You see, I had started my daily Facebook weather forecasts the previous spring, and I was the person my classmates and teachers turned to when snow was in the forecast. With December 18, 2008 being a Thursday, I was in the spotlight. And for a day, I became the hero of Garfield High School.

I believed we would see snow as a strong Puget Sound Convergence Zone developed over the area, giving Seattle its highest-impact snow event since the “Monday Night Football Ice Rink of 2006” (see Scott Sistek’s wonderful article on the insane weather during November 2006, this event occurred on the 27th). This convergence zone wasn’t quite your classic convergence zone; it was more of a stationary arctic front, with southwest flow through the Chehalis Gap providing moisture and cold northerly winds from the Strait of Georgia/Fraser River Valley converging right over Seattle and forming a thin band of heavy precipitation. Most of all, both of the mesoscale models from the University of Washington – the MM5-NAM and WRF-GFS – showed a band of snow slipping south through Seattle and strengthening in the wee hours of the 18th, giving me even greater confidence that we’d see a memorable snowstorm.

But not everybody was on board. Some other, higher-profile TV folk believed there’d be less than an inch of snow. The National Weather Service was going for 1-3 inches, and I was highest of all, going for 1-5 inches. My forecasts ended up being low, and we even had some insane thundersnow to boot. It was a truly unforgettable event.

4 am PST Infrared Satellite and 500 hPa heights
4 am PST Infrared Satellite and 500 hPa heights
Credit: UW Atmospheric Sciences Archive Tool

The synoptic (large-scale) setup was perfect for lowland snow. We had a giant ridge in the Northern Pacific and a giant trough over us, allowing modified arctic air to seep into the Pacific Northwest. Some arctic air seeped over the coastal mountains of British Columbia into the Pacific Ocean, picking up moisture and taking a turn eastward into Western Washington. Meanwhile, downright frigid air funneled through the Fraser River Valley into Western Washington, blasting Bellingham and the San Juans with a cold, northerly gale. When this moist, unstable and cool air came into Western Washington and collided with these cold, northerly winds, we experienced an extraordinary event.

Here’s a snippet from the Seattle NWS Forecast Office from their 4:10 PM forecast discussion on 12/17/2008.


Here’s the visible satellite imagery during noon on December 17. You can clearly see the cold, arctic air picking up moisture over the Pacific and taking a more eastward trajectory in the process.

Visible Satellite Imagery at noon PST, 12/17/2008
Visible Satellite Imagery at noon PST, 12/17/2008
Credit: UW Atmospheric Sciences Archive Page

Finally, here’s my forecast on the eve of December 17, 2008. The first paragraph refers to the infamous “no-snow-snow-day,” where the schools closed school due to an “uncertain forecast” even though there was little chance of snow in the first place.

December 17, 2008

So… as soon as the new weather models came out last night, I really wanted to write a new forecast. I was really tired though, so I didn’t. The new models showed two things: first, they showed an even stronger snow shadow over Seattle. A snow shadow is where air sinks and dries off of a mountain range (in this case the Olympics), leaving little moisture for areas downwind of them). Second, they showed warmer temperatures as the low pressure system moved further north than expected, bringing southerly winds with them. I had that “sinking feeling” that A.) There was going to be school tomorrow B.) I would end up with an egg on my face before the week was through and C.) I was going to have to suddenly do a lot of homework.

Luckily for me, the school districts don’t know about the UW atmospheric sciences page! (I highly suggest you check it out, just google it and look at the forecasts)

Really though, I wasn’t that off. Snow totals were an inch less than I expected, and I expected an inch.
I can’t stress this enough though. DON’T GIVE UP HOPE!!! I EXPECT to see snow tonight, especially in north Seattle. A convergence-zone thing will occur, expect it’s not really a classic convergence zone. It is more akin to a deformation band, (edit – it wasn’t a deformation band, and my explanation of one is extremely oversimplified. The thing that made it unusual was that it had a northerly component from the Fraser River Valley/Strait of Georgia.) which is diverging air aloft and converging air at the surface. Main point is… at around 7 P.M. tonight, temperatures will cool back below freezing and snow will begin. The band of snow will be centered in N. King/S. Snohomish counties, but it will slowly drift south.

Convergence zone snow amounts are extremely hard to predict. I actually believe that the worst case scenario would leave a foot in Seattle (best case for me). Anywhere from 1-5 inches looks more likely.

Alright I’m gonna go bench 5 Billion tons of weight right now, but I’ll make another update when I’m done. Just wanted to explain what is going on, and that snow is still in the forecast.

Alright, it’s 6:04 (pm), and I’m back. Tonight, I am much more confident that we will get snow. And here’s why…


This nightmare for forecasters but hero for kids forms when a NW wind hits the Olympics and splits. One part goes into the Strait on Juan de Fuca, and another part goes through the Chehalis Gap. They meet in Western Washington, and when they meet, there is often precipitation (and often snow). The most often place for the PSCZ to meet is right on the Snohomish/King county line. Take a look at the radar right now. You will see a stationary band of snow from about Lake Forest Park north. This is the convergence zone. Over the course of this night, the convergence zone will shift down south, dropping anywhere from 1-5 inches of snow with it. This is a pretty wide range, and it is really hard to predict where the convergence zone will go. We could even get over 5 inches. And, of course, there is always that possibility that we could get none. But all in all, I am MUCH more confident that we will get snow tonight with this convergence zone. The only things that could really mess us up are if the convergence zone stays north and the air mass doesn’t cool off as much. All models are in agreement that those things will not happen though.

Here’s my time frame:

7-11 P.M. The convergence zone will be in full force, especially over northern king and southern Snohomish counties. Some places to the south will see light snow or mixed snow and rain showers, but these will increase in intensity and snow percentage due to the convergence zone sliding south and temperatures cooling.

11 PM-4 AM: The zone will shift south and stall over the Seattle area, bringing some snow with it.

4 AM-7 AM The zone may shift even further south, towards Sea-Tac or so, before finally fizzing out.

I hope I am right. If I’m not, I am going to be SCREWED tomorrow.

Do a snow dance… for me =)

No extended forecast tonight… do you really care what the weather is going to be like in a couple days? I’ll continually update this page as new information comes in.

(update later that evening)

So the new weather models came in. And they brought some news with them. Drumroll…
roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll roll

The snow still looks on track! A few details have changed though. The snow looks like it will arrive much later in the evening (well technically tomorrow morning). One model, the GFS, says the snow will arrive in Seattle at 3-4 AM and last for a couple hours, dropping approximately 1-2 inches of snow here. Another model, the NAM, says that the snow will arrive in Seattle at 6 AM and last a little longer with some higher snow totals… anywhere from 1-4 inches. I can’t stress this enough. Don’t freak out that it isn’t snowing now.

In the event that there is school tomorrow, bring eggs. Throw them at me. Or bring something to make fun of me. It would be hilarious. Especially people in band class. That would be AWESOME!!! However, if I’m right, ya’ll gonna respect my authority. And I still think I’m we are gonna get snow tomorrow. As for which model to go with, I am going with the NAM. This could complicate matters again because of timing… so again I don’t know what the school district is going to do. In any event… snow will stick to the roads. Charlie Phillips thinks there will be snow, and Charlie Phillips thinks that there will be a complex decision to make by the school district. If all goes well though, there should be no school on Thursday. Thank you God.

Updated at 10:17 P.M. Wednesday

I forgot to mention that even if we don’t see a convergence zone, we could see a few pop-up showers that could drop some zone. In fact, the radar shows some headed towards us right now, but they also look to be fizzling out.

Talk about high stakes. Hope to not see most of you tomorrow…

Needless to say, this was a very nerve-wracking forecast. I would either be immortalized in the eyes of my classmates as “that one kid who forecast the snow correctly even when everybody was doubting him,” or I would potentially end up with many, many eggs on my face.

Thankfully, I ended up having a stellar forecast! The radar image below shows an animation from 4 pm 12/17 to 3 pm 12/18. As you can see, a thin but very, very intense band of snow began to form just before 13 UTC (5 am). There were thunderstorms embedded in this band, and sure enough, Seattle was treated to two very, very memorable flashes of lightning.

Camano Island (KATX) radar loop from approximately 4 pm 12/17/2008 to 3 pm 12/18/2008. Most of the precipitation was falling as snow. Note the intense band of snow that forms over Puget Sound at approximately 5 AM 12/18/2008. This band brought peak snowfall rates of well over an inch per hour and had two booming lightning strikes, one of which was blindingly white from my house in the Madrona neighborhood of Seattle and scared the living daylights out of me!
Camano Island (KATX) radar loop from approximately 4 pm 12/17/2008 to 3 pm 12/18/2008. Most of the precipitation was falling as snow. Note the intense band of snow that forms over Puget Sound at approximately 5 AM 12/18/2008. This band brought peak snowfall rates of well over an inch per hour and had two booming lightning strikes, one of which was blindingly white from my house in the Madrona neighborhood of Seattle and scared the living daylights out of me! All precipitation after this was snow.
Images from the UW Atmospheric Sciences Radar Archive, gif created with

Here’s a smaller and slower loop showing the formation of the band. Note the high reflectivities associated with the band – you can see yellows in there!

Radar imagery from KATX showing formation of convergence zone. Loop from 2:42 am to 6:57 AM PST 12/18/2017
Radar imagery from KATX showing formation of convergence zone. Loop from 2:42 am to 6:57 AM PST 12/18/2017

Finally, here’s a zoomed-in image of the area of heaviest precipitation at the approximate time of the lightning strikes. I thought they (especially the first one) were right over me since the thunder and lightning were simultaneous, but apparently everybody in Seattle thought that. There’s no way the strike was in Georgetown, which is where the pixel with the highest reflectivity is located.

The heavy snow shower that brought lightning to the Seattle metro area. This image shows the shower centered over Georgetown, but I swear the flash from the lightning at my house some 10 miles to the north was blinding and the thunder as instantaneous and deafening. Perhaps the strike reached out from the center of the storm.
The heavy snow shower that brought lightning to the Seattle metro area. This image shows the shower centered over Georgetown, but the lightning/thunder at my house 10 miles to the north were simultaneous and blinding/deafening. The strike must have occurred outside of the shower core.
Created using the NOAA Weather and Climate Toolkit.

As you can see, there was a stark contrast in the tone of comments on the wall of the “Charlie’s Weather Forecasts” Facebook group before and after the storm.



Of course, it’s natural to be ecstatic when you wake up to this!

And when it came to the lightning, I wasn’t the only one who was shocked by the blast.

Here’s my post-storm analysis and reflection during the following day. I talk about the famous “no-snow snow day” that I mentioned in my previous post.  After reviewing the storm that brought me so much fame, I look ahead to another storm that brought even more snow to the Seattle area, with some freezing rain to top it all off.

December 19, 2008
Predicted: 27 18
Actual: 27 20

I really needed a breather yesterday. That’s why I didn’t write a forecast. Of course, the forecast for the next few days is as challenging as the last, maybe even more. We will have a very warm Pacific system overrunning frigid air, and this could have a variety of effects for Seattle. First, let me give my opinion on the weather events over the past couple of days, including what I did well and what I could have done better.

For Wednesday, the schools should have never canceled. The lack of snow was expected. We were supposed to see an inch at most, probably less. The problem is that the media ALWAYS overhypes snow events. When there is a CHANCE of snow, the media makes it seem like snow is CERTAIN. Of course, meteorologists have to do some things too. And I learned some lessons from that storm.

I should have emphasized the fact that we probably wouldn’t see snow more. People were surpirsed that we didn’t see snow but I wasn’t. I thought I had made that clear. But looking back at my forecast, I realized that I really hadn’t. So in the future, I will emphasize the FACTS about snow more, cause the media usually only acts to screw things up (cause that is how they make money, right? By having names like “Storm of the Century” and captivating the audience so they get more viewers). Next time, I will try to make this more clear.

Also, this storm reinforced my belief about convergence zones. You can often predict that they are going to happen, but it is hard to predict WHAT will happen. Wednesday night, while I was forecasting 1-5 inches of snow, (Q13) Fox was forcasting 1/10. We were both wrong. Totals were more like 3-8 inches. The funny thing is my initial forecast was the most accurate… 3-6 inches. Funny how that works. People paint an intial forecast, then freak out as details change, but if they stayed with the initial forecast, they would have been more correct. I’m not saying that longer range forecasts are more accurate, in fact they never really are because model errors are magnified over the long run. Still, that’s how it worked yesterday, even if it was by chance. That’s called irony.

Remember how I was saying it wasn’t really a convergence zone? That was exactly what happened. Instead of two winds colliding, the warmer southerly wind, since it was less dense than the colder northerly one, lifted over it. This lift created snow showers. This zone stayed over us for quite some time, dropping anywhere from 3-8 inches of snow over the Seattle area. I did a better job then most of forecasting this, but still, the NIGHT before, all models were saying we would get about 2 inches at the most. I got kinda lucky, and although there is definitely some skill, I just chose the right side. In reality, just cause I forecasted this event better than the NWS or tv stations doesn’t mean I’m somehow more skilled than them. I most certainly am not. I’m a kid, and they are professionals. Except for Q13 Fox. (2017 edit: I’ve have gotten to know their forecast team very well and they are wonderful people!!!!)

Looking at the snow totals, it looks like the snow lottery winners in the Seattle area were Beacon Hill, with Amie Szeto from Beacon Hill reporting a little over 8 inches before it was all said and done. Of course, we had an accidental report of 4 feet from Sammy Lesnick, and Jamie Daudon posted a grand total of 60 feet from the Arctic circle, but these reports are questionable at best. Generally, the highes snow totals appeared to be right around Beacon Hill and Mt. Baker. Places further north, like Wallingford and Magnolia, only got 3-4 inches. Since the temperatures were below freezing all day, there wasn’t that much of a variation in snow amounts with elevation (for once)

I was up all night of course waiting for snow… I woke up at 3 A.M., too excited to fall asleep again. I looked at the radar and saw a convergence zone (an actual one) forming right over my house. As it got stronger, it got wider, and the snow intensity increased. One common misconception that I have seen is that we received hail. We recieved something similar, but not the same. We received snow pellets, which are extremely common with convergence zones, actually more common than snow itself with narrow, intense ones.

At around 5 A.M., a HUGE lightning flash struck extremely close to my house… probably 40-100 yards away. There was no pause at all between the lightning and thunder, and the flash was nearly blinding. At first, I thought it was a huge power surge. It then began to snow very heavily. Shaken but not stirred, I continued checking the radar and chatting on facebook (which in retrospect was probably not smart at all). A minute later, another lightning flash struck very close to my house. This one was a little further away, but still extremely loud. At that point, I shut off my computer and all electronic appliences. I didn’t want a power surge to ruin my computer, and I didn’t want to get indirectly struck because I was holding an AC/DC appliance. I walked outside real quick (boy I am full of dumb ideas) to see if I could feel the charge in the air. I could, and my hair started to stand up. I actually think I explain somewhere in the discussion topics another experience with static electricity in which I almost get struck by lightning. It should be under “unusual weather experiences” or something. If it’s not or you want to hear more, just write on the wall and I’ll tell the story. 
Alright… so let’s get to the forecast… oh man… just remember that if I get this oen wrong, the fact that I got yesterday cancels out any egging opportunity. Sorry Max Elvis David and Christopher Swanson, but you may have to be eating omelets for the next 6 months.
So… the forecasting models show three possible major weather events here. First… a major windstorm could be on tap for the foothills of Western Washington. Models have slacked off a little on this one, but some are still adamant (the GFS) in bringing SUSTAINED winds of over 60 mph to some foothill locations (most notably, North Bend) with gusts approaching 100 mph. This would be an extraordinary wind event. Meanwhile, winds in Seattle would be much less, with gusts maybe over 45 mph. I’ll talk about timing later, but the winds appear like they will be the worst late Saturday night and early Sunday morning, as the low pressure system approaches from the west and high pressure remains centered in Eastern Washington. This event has some serious potential, and you bet that I will be up in North Bend to capture some footage if we do indeed have the high winds that some models are forecasting.

Next… snow
We could see a much more widespread snow event. Seattle proper could see 1-6 inches of snow, and places like Hood Canal could see as much as 2 feet! Places like West Seattle will see much more snow than places like Bellevue. The further east you go, the lower the amounts will be.

Why, you may ask?
When air flows down, it warms and dries. It should still be very cold (since the air in Eastern Washington is so cold) but it should be VERY dry. This dry air will limit snowfall in those areas. Of course, Seattle is right between the areas where little snow is expected and where a ton is expected. So expect a steep gradient.

These overrunning events are extremely hard to forecast. Be on the lookout for meteorologists pushing back the start times for precipitation. This usually signals that the total snow accumulation will be rather limited. We really don’t know how much snow we will get until the storm is actually on top of us and we can see how this storm interacts with the local terrain.

Third, we could see freezing rain…
And I just heard on the radio that Paris Hilton’s house got broken and 2 million dollars worth of jewelery got stolen. Tell me why Paris Hilton has 2 million dollars worth of jewelery and people who actually do stuff, even if it’s flipping burgers, live in poverty? Oh well…

Sorry. Back to the freezing rain, this will be a classic overrunning event, where warm Pacific air overruns cold, arctic air. What you can get is rain forming because the air aloft is warm, but then freezing as it hits the ground because the ground is still below freezing. Too early to go into depth about that… but it could happen.

These overrunning events are extremely difficult to forecast… but I have confidence that we will at least see some snow before it is all over. I may do an extended forecast later, but I’ve spent about 45 minutes writing this, and I’m ready for a break. The extended looks cool, but not cold, although we may see some colder air filling in after Sunday, which would again freeze snow to the roads, although not a hard freeze.

And finally, here are some snow totals my friends gave me from around the Seattle area. With the notable exceptions of the Arctic Circle and Sunset Hill, the highest amounts were between Madrona (my neighborhood) and Rainier Beach, primarily due to the epic thundersnow that began that fateful Thursday with a bang.

Arctic Circle: 60 feet, 11:22 am
Sunset Hill: 4 feet, 2:09 pm
Between Rainier Beach and Beacon Hill: At 12:10 pm, 6 inches and “still snowing!”. At 1:54 pm, 7.5 inches and “still going.” At 4:38 pm, “finally 8 inches!” and “still snowing a bit, from time to time.” At 9:20 pm, 8.1 inches and “stopped snow :(”
South Beacon Hill: 7.25 inches and “still pounding,” with a Safeway truck stuck on a road going uphill and hitting powerlines. 1:20 pm
Seward Park/Columbia City: 7 inches, end of day
View Ridge: 6.5 inches and “cloudy” at 6:24 pm
North Leschi/Madrona: 6.5 inches at 6:15 pm
Rainier Beach: 6.125 inches and “still snowing hard,” 12:45 pm
Top of Mt. Baker Hill: >6 inches, “still snowing,” 2:12 pm
West Seattle: 6 inches and “still going,” 12:57 pm
Central District: 6 “incheroos,” 1:20 pm
West Seattle: 6 inches, 2:05 pm
West Seattle (Genessee Hill): 6 inches, 4:25 pm
Beacon Hill: 5.75 inches at 12:11 pm
Rainier Beach (lake level): 5.5 inches, 5 pm
West Seattle: 5.5 INCHES! and “Still snowing,” 12:06 pm
Madrona, close to water and 40″ elevation (me): 5.25 inches at 12:10 pm. I didn’t measure at the end of the day but I likely had  ~6.5″ based on the North Leschi/Madrona report
Mt. Baker (neighborhood, not mountain): 5.2 inches, 11:42 am
North Beacon Hill: 5 inches, 11:15 am
Beacon Hill: 5 inches “AND STILL SNOWING!”, 11:47 am
Seward Park: 5 inches and “still coming,” 12:27 pm
Central District: 4.5 inches at 11:48 am
Upper Rainier Beach: 4.5 inches, 1 pm
West Seattle: 4-5 inches at 12:20 pm
Beacon Hill: 4 inches and “Still snowing!”, 11:56 am
Madison Park: 4 inches and “still lightly falling,” 1:00 pm
Capitol Hill: 4 inches and “still coming down,” 1:25 pm
Woodland Park: 4 inches, 4:07 pm
View Ridge: 3.5 inches and “snowing pretty hard,” 12:17 pm
Montlake Community Center: 3.2 inches, 11:45 am
Queen Anne Hill: 3 inches and “still dumping,”  11:42 am
Unknown Location (I think North Seattle): 3.5 inches, end of day
Wallingford: 3+ inches, 11:54 am
Arbor Heights (West Seattle): 3 inches and “coming down hard,” 12:32 pm
Auburn: 3 inches and “still snowing,” 12:39 pm
Greenwood: 3 inches, 4:07 pm
Bryant: 2.5 inches, “First time all day it’s not snowing,” 3:54 pm
Wedgewood: 2 1/8 inches, 1:15 pm

And that’s it for the snow totals from this storm! The storm I mentioned above in my post reviewing “Thundersnowmageddon 2008” did come to fruition, and I got some reports from that as well. All these were taken on December 21st.

Auburn: 11.5 inches, 10:18 pm
Maple Leaf:
11″ inches but the snow is being blown around a lot. 5:53 pm.
Capitol Hill: 6 inches and “it’s still snowing..ahh!” at 1:59 pm. At 9:30 pm, 11 inches.
Between Rainier Beach and Beacon Hill: 8.9-9 inches, 11:21 pm
Alki Beach: “at least 7 inches… AT LEAST. IT NEVER SNOWS ON ALKI!!!!!!!!!!!!!” 2:45 pm
Ft. Lauderdale, Florida: 0 inches, 5:05 (EST)

Finally, we had a couple reporters from out of town who gave us their findings a little later.
Portland: Between 1-2 feet, 12/24/2008
Germany: “No snow at all,” 12/23/2008

I can’t find any images of this storm right now, but I’ll be sure to look for some later. There was footage of me skiing down a blackberry-clad hill that had some snow on it – I’ll see if I can dig that up too. For now, you’ll have to put up with a shaky video I took skiing on 12/22/2008 after our second big snowstorm from the top of Alder Hill down to Lake Washington Blvd. Boy oh boy was that fun.

All-in-all, this was by far my favorite weather event in my life thus far. With the hefty snow totals, the atomic lightning blast, and the euphoria of all my classmates, this memory is one I will cherish for the rest of my life.