November Hurricanes in the Northwest

Often over looked by major media outlets, fall and winter storms in the Northwest often pack a one-two punch of wind and rain in the lowlands (3 punches if you count snow in the mountains). Well this coming week, we have the potential for 4 storms in a 7 day span, all of which would bring breezy conditions (slightly less than windy conditions) and a large dose of rain for lowland locations. Here are a couple images I have taken off the University of Washington weather models that show the evolution of these low pressure systems

This first frontal system will move in Sunday night bringing gusty conditions to the coast and some breezy conditions inland. The black lines in the image are called isobars, lines of constant pressure. The closer those lines are, the stronger the winds. You can see the lines are packed close together along the coast which is where the strongest winds will be. The next storm....

Appears to be a bit stronger with a central pressure near 970mb by the Northern tip of Vancouver Island. This system moves in Monday evening and would bring winds between 15-30mph for the lowlands and gusts maybe to 45mph. Any remaining leaves on your trees would sure to be down by now. The next system moves in a few days later...

Thursday afternoon and evening. This low center is weaker than the previous one, 985 milibars, but would certainly bring a good amount of rain. Winds would be strongest along the coast during this scenario as well.

This final system of the week may be the most dynamical of the 4. What sets this one apart is the strong high pressure down south towards the central coast of California, just barely visible in this image. It's at about 1027 milibars and the low pressure center, in the Northwest corner of the image is around 970 milibars. Such a large difference in pressure, over a relatively small area can great a large pressure difference field, and since air tends to move from high to low pressure, the winds would accelerate very quickly between the high and low. This is why the isobars in this image span a very large area and are very packed together. Once this system moves in, it could be the windiest of the 4 system for the week.

In comparison, lets look at some images of hurricanes and these storms, known as mid-latitude cyclones.

Here is Hurricane Katrina

Yes, it's quite large and probably has very strong winds (I will get to that in a second).

Here is the Hanukkah Eve Storm that hit the Northwest in December of 2006,

I would beg that this storm is even larger, and has a much larger area of impact.

The best way to compare these systems is the central pressure though. The Saffir-Simpson Hurricane Scale details this

Now, Hurricane Katrina had a minimum central pressure of 902mb...we don't see those pressures with mid-latitude cyclones, it's even rare for tropical cyclones. But what I want you all to see is that NW storms can get into the 970's, even 960's on occasion. That would be on par with a Category 2 or 3 hurricane, but on a much larger scale (the larger scale also prevents MLC's to have stronger winds like Hurricanes have).

As you can see, we are in for a bumpy ride this coming week as these systems approach. I'll leave you with a couple images of the rainfall that will hit us.

This the 24hr accumulated precip ending Tuesday afternoon. The black is between 2.5 and 5" of rain...yikes. The red is between 5 and 10", localized over the central cascades near Oregon. Here is the snowfall at the same time...

Climbing up above 2 feet in some areas!!

This the rainfall ending Saturday afternoon...5-10" possible for the Olympics.

More snowfall for the Northern Cascades.

Flooding will be a major concern this week with lots of rain and rising rivers that won't have a lot of time to recede.

Meteorologically Yours,

Aaron

"S" Word Update

I have already encountered some questions about whether we will see some snow this week. For an update, the models have not favored a scenario for snow around the Pac NW. Over the past 3 model runs, specifically the UW WRF (Weather Research Forecasting) model has 'warmed' temperatures up just enough on Thursday and Friday that any moisture around would probably fall as rain first...and maybe a heavier shower could see some wet snow mixed in.

First off, there is no terrifically organized system moving in with the cold so the moisture maker is limited. Pockets of showers could be expected but once again, those would be limited and sparse. Not to mention, hard to predict exact locations. One brighter side to this is that a Puget Sound Convergence Zone could set up once the upper level trough moves through which could enhance precip and bring down the snow level in localized locations.

Will continue updates through the week as more information can be gathered.

Inkling for Some Fluffy Stuff?

Around the Northwest, the mere mention of the "s" word can bring about a panic only one can experience to understand. Well this time of year, snow becomes a popular topic around communities as people become anxious for cooler weather and just the possibility of not having to go to the mountains to play in the terrific white fluff. In addition, snow becomes a popular topic among meteorologists because weather models begin to turn from the summer time calmness (around the Pacific Northwest) to the stormy fall weather and the hint of colder winter temperatures. Sometimes, the two even come together. ;)

The issue with predicting snow around the Northwest, is that it's hard to get snow. The Pacific Ocean strongly mediates the air temperature here near the coast so it takes VERY cold air temperatures to overcome that heating and get snow.

The next hardest part about forecasting snow, arguably the hardest part, is that forecast models ARE NOT PERFECT! As meteorologists we learn about the atmosphere and it's motions, and these models predict those motions. Well that's a pretty tall task to ask of the models. I learned from my professor at the University of Washington, Cliff Mass, a good picture of how to understand model variability. It looks something like this:

Imagine a ski resort. You have 5 runs that all start at the top of the mountain and go down the mountain in different directions. Now think of each run as a forecast and going down the mountain as going farther out in time for the forecast (this will stretch your thinking a little). Here is a rough picture of my illustration

Now at the bottom of the mountain, the forecasts (runs) are all at different spots. As you go farther up the mountain, closer to the forecast time, the forecasts become closer and closer together until you get to the top, where they become relatively similar and agreeable.

Well in forecasting snow, sometimes models will paint a snow forecast 7 days out, lets say the Green line. You notice how the green line doesn't start and end at the same point along a vertical axis, so it may say snow 7 days out and rain the day before the forecast time. It's a very risky business to trust models 7 days out from a forecast time.

Models have gotten better over the years though. 2 decades these models were just getting started and you might not have been able to trust a forecast 2 or 3 days out. Now, 5 days is reasonable for trusting, although exact details (amount of snow, rain, winds, etc.) shouldn't be taken from a 5 day forecast.

Now to what I really wanted to talk about, but I felt I should give some grounds for my feelings about this. The model run by UW this morning painted a "favorable" picture for snow next Thursday and Friday. It would be a classic Pac NW scenario for snow, which I will get back to in a minute. Here are a couple images that the model outputs

I'll start with the upper level pattern of the atmosphere, at 500hpa pressure. Those pink colors, those are very cold temperatures associated with a trough of low pressure digging south from the Canadian continent. This is an important factor because air coming off the ocean is not very cold, but from the Canadian land, it would be VERY cold.

The next thing that is needed is a low pressure developing at the surface, which is clearly visible here. The low is centered right off Vancouver Island, bringing moisture and "pulling" the cold air at the surface towards it. Air tends to accelerate from High to Low pressure. This forecast is for 147hrs (from this morning at 4am). Here is the forecast for 171 hrs.

The low is centered right over Washington, pulling cold air right into Western Washington. The white color indicates temperatures near 0 degrees celsius.

Here is estimated snowfall for a 3 hour period ending Friday afternoon. This shows some snowfall around South Puget sound and the Eastside. Another 3 hours later...

 Some snow in Northern Western Washington. And here is the 24hr accumulated snowfall totals...

As expected the Eastern foothills would see more accumulation, and only a slight amount around the lowlands.

However, all of this forecast for the end of next week should be taken as a grain of salt, as I noted previously. It's just TOO EARLY to tell.

I felt this would be a good opportunity to explain this aspect of forecasting too far out, while also arousing your interest in some possible snow :) Because I'm sure excited

You can follow me on twitter for even more up to date information regarding Pac NW weather and even weather throughout the nation: @huskyAaron
OR visit my Facebook page: Aaron Hill Weather

I will post updates to this story as I get them :)

Cheers!

Fall is Upon Us

What reminds you of fall? The leaves changing colors...school begins...days begin to get darker earlier. Well for me, it's superb low pressure systems coming in off the pacific. Yes, I'm a nerd. Latest Infrared Satellite imagery shows a well defined low off the Washington coast, which will push in a front overnight tonight with associated rain. 

The latest radar image from the Langley Hill radar (yes, that's the new one on the coast) shows the rain has already begun advancing inland. Just a quick note, the Camano Island radar is still down for the new Dual Pol radar update. Should be back up and running in a week or so.

The general atmospheric circulation pattern is set up to allow some strong lows to move by the coast tonight and Tuesday night. Below is an image of the large trough extending down the West Coast.

The trough will persist through Wednesday...
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As we see a new system move in Tuesday night. Here is the forecast for 3hr precipitation Tuesday night around 8pm. Plenty of moisture down the West Coast, with Southern Oregon getting hammered with rain.

You can also see a nice cut off low over the area which will enhance the Southerly flow and keep things fairly mild. By Friday, a ridge builds in which should dry us off quite nicely.

Fall is here so expect the rain to continue for the next....well 3 months. :) Normal high temperatures around this time of the year are the mid 60s. Tuesday and Wednesday highs will be in the upper 50s, and temps will climb to the mid 60s by Friday.

Coastal Radar

The new coastal radar is here! AND IT'S OPERATIONAL! Beginning yesterday the data from the new coastal radar, just north of Hoquiam, was being streamed to the outside world. You can see the long range images at the
National Weather Service Seattle office site,

National Weather Service

You can see the radar picks up on echoes well out over the Pacific and stretching out towards Vancouver Island (frontal band that will break down by today). This is an incredible day for Western Washington weather technology as state legislature and Professors from the University of Washington have been fighting for this radar for over a decade. This radar will be a crucial piece of understanding the structure of storms coming in from the Pacific. It is equipped with the new Dual Polarization technology that will help detect the types of particles (ice, snow, rain, heavy rain, hail, etc.) that are in the clouds. The Camano Island radar will now be shut down for 10-14 days as it also will receive this new technology. Washington will be the first state in the US will all of their radars fully operational with Dual Pol technology.

Have a great day! Will have a brief post soon about some actual weather :)

Top 50 Amateur Blogs

Recently I received an email regarding some of the best amateur meteorology blogs out on the web. Somehow, by some miracle, I made the top 50. I feel it is my duty to not only make you aware of the recognition but also share with you some of the other weather blogs out there that are in my opinion, quite fantastic. I have not looked at all of these, and I don't think I know any of the authors but I have followed a few and these guys sure do know what they are talking about. Here is the website so you can take a look at the top 50 Amateur Meteorology Blogs

http://www.associatedegreeonline.net/amateur-meteorology

Oh and by the way, I will be heading back up to the Northwest in the next week so expect some upcoming blogs about the weather. Seeing as I've been in Southern California for the summer, It has been a bit difficult to keep up on Northwest Weather. I will certainly get back to it once school kicks back up :)

Tropical Cyclones!

In the wake of Hurricane Irene, we have two new developments in the tropics. The National Hurricane Center has indicated an area of interest just east of the Yucatan Peninsula, noted here with the orange hashing

 They indicate it has a 30% chance of becoming a tropical cyclone but both the European model and GFS model that i have looked at indicate it's development into a tropical depression or a tropical storm over the next couple of days.

The reason I would favor this idea is because of the gulf of mexico. Tropical cyclones feed off of warm ocean waters and the gulf is a prime location for storms for this reason. This tropical wave depicted above is projected to move into the gulf where i suspect it to feed into those waters and develop. It may not become a hurricane but it will certainly produce rain for the upcoming weekend so people making plans for Labor Day around the gulf need to heed to warnings or watches about this storm.


2ND STORM: Tropical Storm Katia is now in the Central Atlantic with 60knots sustained winds. Conditions are favorable for Katia to develop into a strong Hurricane but it's threat to land is still uncertain. Models at the moment have trended for Katia to continue towards the east coast but then turn Northwest and Northward over the next week or so.

The reasoning for Katia to turn like that is the upper level patters of the atmosphere. The mid latitude jetstream can have a profound impact on these tropical storms, almost "steering" them northward. It looks like a trough that moves over the east coast kind of pulls the storm northward and it joins into the mid latitudes. This would be good thing for the east coast after they got pounded with heavy rains and subsequent flooding from Irene.

I'll have another update on the tropics in a day or so, I hope

On a side note, I was shown an article by FOX news the other day about how the US doesn't need a National Weather Service anymore and that private forecasting companies and media like The Weather Channel are far better at forecasting than the NWS. This is preposterous on so many levels, most importantly, where do those private companies and the media get their information? Oh yeah, the NWS, who runs the models and talks about conditions hourly. I can't believe FOX even allowed this opinion article to be published. Pathetic

http://www.foxnews.com/opinion/2011/08/27/do-really-need-national-weather-service/

Have a great work week!

Will a La Nina Winter Return?

La Nina La Nina, oh where art thou La Nina. While many people would have hoped La Nina was in our rear view mirror, after experiencing a dismal winter and an even worse Spring, it looks like we won't be able to drive fast enough away from her. The Climate Prediction Center is the major government body in the US that predicts our ENSO cycle (El Nino Southern Oscillation) and they have just recently posted a La Nina watch for this upcoming winter. So if you didn't enjoy this past winter or Spring, you may consider taking a nice long trip to Mexico for a break or two.

For those of you who would like to know a little more about La Nina, read on

La Nina is declared when the Sea Surface Temperature in the Central and Eastern Pacific averages .5 degrees Celcius below normal for 3 consecutive 3 month intervals. Here is a graphic that I hope explains this more.

This graphic shows the last La Nina we went through this Winter and Spring. The declaration of a La Nina occurs with temperatures taken from the 3.4 region shown in the 2nd box above. I'm not sure why it has to be this region but I know it is.

These are the regions here with the 1+2 box nearest the South American Continent.

You can see in June and into July we we starting to just average positive sea temperatures and now in August we have retreated back to negative anomalies. Model projections that are run by the Climate Prediction Center as well as many other agencies around the world are beginning to show the return of La Nina this winter or we enter into a Neutral phase, between El Nino and La Nina.

The average of these model runs is shows to hover near neutral conditions and not "double-dip" to La Nina. But if current conditions continue, I wouldn't be surprised to see the average of these models continue to inch closer to La Nina conditions. The CPC's own model is also run numerous times.

Their's clearly shows a double-dip La Nina scenario predicted.

While this last winter wasn't the Snowmaggedon projected by many media outlets, La Nina winters do typically give Washington cooler and wetter weather patterns. I will be anxious to see what the next outlook says.

(How La Nina forms: Trade winds in the tropics move from the east to the west, contrary to here in the mid latitude areas where the winds move from West to East. During a La Nina episode these trade winds are strong and move warm ocean waters on the surface of the Pacific to the West. This brings upwelling to the eastern Pacific (cool, deep ocean water moves up) and this is why we register colder sea surface temperatures. The atmosphere and it's circulations are affected by this surface temperature movement in a variety of different ways and current research is still being done today on how these changes affect weather in Washington and all along the West Coast. It is a challenging research area since the period of oscillations are so large and we have only approximately 60 years of La Nina/El Nino records)

Summer Rain

I just took a look at the Global Forecast Model that the National Center for Environmental Prediction runs and it doesn't look too good for the Northwest over the coming week. Two upper level lows, associated with clouds, rain, and cooler weather will be making their way into the Northwest, with their eyes set on Washington.

It looks like clouds will dominate Wednesday and Thursday and there is a decent chance of rain for the beginning part of next week.

Just a short quick forecast tonight

Summer in the Northwest!

For the past two weeks or so, it seems as if the Northwest has grown out of it's cool Spring and jumped right into a decent summer. Being down here in Southern California I haven't checked out any of the weather up there lately but I did this morning.

It looks like the upper levels of the atmosphere over the next couple of days will be "weak". What I mean by that is the airflow will not be as strong at the 500mb pressure level and  there doesn't appear to be any trough (cooler and wetter) or ridge (warm and sunny) that parks itself over the area.

This is a typical summertime phenomenon as it means there is a weak onshore push in the mornings and the afternoon heating of the atmosphere will clear out the clouds for a partly sunny or mostly sunny afternoon.

That's why the forecast for the next week calls for highs in the mid to upper 70s for almost 7 days straight. Almost unheard of for the Northwest. I haven't looked at longer range models (out 15 days) but I wouldn't be surprised to see this pattern continue.

Enjoy the sunny weather up there Pacific Northwesterns! And remember, If it's sunny there, it's always a little more sunny down here in So Cal. ;)

I'll have another blog in a few days detailing some local California weather and what I'm learning at the National Weather Service

Next Tropical Storm?

UPDATED AUGUST 4th 10:00 AM PST

TS Emily is now located just South of the Dominican Republic moving WNW at 5mph, quite slow. The updated projected path still takes it just East of Florida but with now direct impact on the state. Still, rain and wind will most likely affect the peninsula and the Keys with Tropical Storm force.



UPDATED AUGUST 3rd 2:00PM PST

I have just looked at some of the more recent forecasts and it looks like Florida will be glanced by the storm. It is now officially Tropical Storm Emily and is located just Southwest of Puerto Rico. A recent radar image from Puerto Rico shows just part of the storm

Heavy rain, wind, and possible flooding will accompany the storm as it is crossing over the Caribbean islands. It's current forecasted track will take it just east of Florida but will still likely impact the state with rain and wind.

It appears likely that it will not intensify into a Hurricane by morning Saturday, where it is just east of the Florida coast. Will update on any more notices

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Current satellite images show a tropical "wave" in the western Atlantic near the Northern Windward Islands and Leeward Islands.

The National Hurricane Center has given it a 90% chance for tropical cyclone development over the next 48 hours. This could mean very short notice for Tropical Storm warnings in the Caribbean group of islands. GFS model runs done last night bring the low pressure system just East of Florida by August 6th, 6 days out

 But another model run, the ECMWF (dont worry about what the letters mean) showed almost no development by day 6 and the storm dissapating. There is plenty of uncertainty with the storm as the model run done around midnight PST last night (06Z) showed this

With the low WELL off the coast and not a threat to the US coastline.

At the moment, with no surface circulation, the tropical wave is not a depression but is likely to form into one with favorable atmospheric conditions over the next 48 hours. Air Force Hurricane Hunters will monitor the progression of the storm for the next several days.

Updates to Follow

Tropical Storm Don

The first major storm threatening the US coast is upon us as Tropical Storm Don is nearing the Texas Southeast coastline. In about 36 hours it will make landfall as most likely a tropical storm, strengthening just slightly from its current state. Continued vertical shear and interaction with some dry air will prevent the storm from intensifying much further. Here is the projected path of the storm

You can see there are tropical storm warnings up for the Texas coastline and also a tropical storm WATCH for the extreme southern tip of the TX coast.

Wind speeds right now of tropical storm force encompass a small circular area in the gulf and projected wind speeds for the storm are as follows

Probability of tropical storm force winds are shown here with the light brown indicating 60 to 70 percent and the darker brown (hitting the coastline) 50-60%.

With a strong ridge set up over the middle of the country, and models projecting it to be stationary for the next 36-48 hours, I would expect the storm to follow this Northwesterly path up until landfall and just a little afterward before shifting Northward and Northeast a few days from now.

With the big drought occuring right now in Texas, this rain will be welcomed by many. I will post updates on Twitter as needed. @huskyAaron

Unusual...Year?

Well after a very cool Spring in the Northwest, it appears the pattern that brought the low pressure right over the Pac NW has not dissapated. The average July temperature in Seattle is 75.3 and it has been a full degree below normal through the first half of the month (74.1).

So what is this "pattern" you ask?? Well in meteorology an often used term for cooler and wetter weather is what we call a trough. The atmospheric flow in the upper levels of the atmosphere roughly follows a wavelike pattern with a bulge upward (to the North) being a ridge and a bulge downward (to the South) being a trough. The trough is associated with low pressure and the ridge is associated with high pressure. As many of you know, High pressure brings us the warm and sunny weather. The low pressure brings us showers and clouds. Here is an example of a forecast map with the ridge and trough.

Clicking on the image you can see the ridge over the central pacific and the trough over the west coast. Well this pattern has not changed much over the past few months and it looks like it won't change for the next week either.

It's unfortunate because this is the driest time of the year for the Northwest (and warmest).

The climate prediction center produces forecasts out to 14 days and here is what they have predicted

This is for the 6-10 day

 And here is the 8-14 day stretch. As you can see, the west coast remains cooler than normal and the central/eastern parts of the country remain well above normal temperatures.


Now I want to take some time and talk about Oxnard, CA weather. I have learned a few things about the local weather here that make me very excited about the next couple of weeks. No, there won't be any major weather occurences, in fact, it is just the opposite. It is going to get nicer :)

Around this time of year the weather is quite temperate. Mornings start off with a marine push that moves a large layer of clouds overheard. By about midday the clouds start to burn off and a cool seabreeze starts that helps temperatures to not exceed the low 70s. With a higher humidity it feels like 80, very pleasant for myself.

In a few weeks the monsoon season for Arizona begins to break down and higher pressure moves in to the four corners area of the US and this brings warm, desert air over the coastal mountains, preventing that morning marine push. What that means?? Clear and sunny all day long. And that continues for weeks into September and October when the Santa Ana winds pick up.

I'll have another post next week as I begin my volunteer internship at the National Weather Service!!

Summer Update

Sorry about the lack of posts lately, since school is out I've been quite busy getting ready to go to California and start volunteering at the National Weather Service. So here is a quick synopsis of what is to come:

After the past couple of beautiful days with highs in the 80s, we will have a pattern chance for the next couple of days. A low pressure system to drag Southeastward from the Gulf of Alaska tonight into Friday. This will mean onshore flow returns tonight bringing marine air and moisture. Tomorrow morning most will wake up to low clouds and cooler temperatures. A few areas of drizzle cannot be ruled out either.

Onshore flow remains through tomorrow so only a few areas in the afternoon will burn through the clouds. Expect partly cloudy skies and a chance of showers Thursday afternoon. Highs will be in the low 70s.

Similar for Friday with partly sunny skies and a chance of showers, although the shower chance will be less. A little cooler than Thursday as the low passes over the Northwest so highs will only be in the upper 60s.

A return to drier conditions for the weekend but the onshore flow continues so I would expect morning clouds burning off to partly sunny skies in the afternoon.

Make it a great week!

Forecast for the Coming Week

Well I don't think anyone can argue the past couple of days has been "remarkable" by our standards here in the NW. With a sub-par Spring including a record setting cold April and above normal rainfall, I would take a gander that 100% of Seattle was very excited to see upper 60s and low 70 degree temperatures by the end of the work week. Unfortunately, we could not carry over those warm temps into the weekend as most people woke up to cloudy skies and some drizzle around Saturday morning. The clouds should stay around for most of the weekend and a shower chance cannot be ruled out for the rest of Saturday and Sunday.

I've talked about weather "models" on this blog many times. I wanted to explain them a little more in depth today and give you a "sneak peek" into what us weather people do. These models consist of some very long and complicated algorithms that take data from a variety of sources and compile them into equations and formulas that spit out a FORECAST for potential weather in the coming days. These models are run at different resolutions to capture fine scale details. For example, here in the Northwest we have a convergence zone that can range from 3-20 miles wide and much longer than that in length. In computer models, you need a detailed resolution to pick up on the convergence zone. If you don't have good enough resolution (higher resolution), you won't pick up on the zone. The University of Washington runs models at 36km, 12km and 4km resolution, with a 1.3km model in the more or less testing phase. With the higher resolution models though, you need even more detailed physical parameters and physical equations to detail weather phenomenon. These models can be crucial in determining where the heaviest snowfall will be in a winter storm, where the strongest winds will be in a storm, or where the highest temps will be during a heat wave. The skills of forecasting have improved ten fold over the last decade and surely will continue to improve. This is a growing field as weather becomes more dangerous to growing populated areas.

Now on to this week. Here are some of the model projections of the 500mb pattern for the coming days. 500mb is a pressure level and it marks about halfway in the atmosphere in terms of mass. Half of the mass of the atmosphere is below 500mb, the other half above.

What we see here in this picture is an upper level low, centered over the Northwest. A low is associated with showers and cooler temperatures. This is the forecast for Monday, so I would say a chance of showers is a good bet.

Tuesday looks dry and Wednesday looks like a transition day and we see above that Thursday looks very similar to Monday. Showers and cooler. Many of you might not know this, but this pattern has DOMINATED our spring. These lows have brought very cool temperatures around here and it has depressed us to no end (BRING ON SUMMER!!!).

Friday looks much of the same.....

As does Saturday....

Oh and Sunday. Looks like our brief stint of "summer" will have to suffice for at least the next week.

Tuesday looks fairly nice with temperatures climbing a bit again into the upper 60s so schedule your outdoor activities or work meetings accordingly :)

La Nina and What That Means for Summer In Pac NW

I have received a few questions regarding our La Nina situation and what that entails for summer. Well to be completely honest with you, in the Northwest, it means nothing. In general, a La Nina winter (that continues into the summer OR that transitions to a "neutral" summer, more on that in a minute) has practically no effect for our summer weather.

You can see here in this schematic that during the Northern Hemisphere winter, a "cold episode" (aka La Nina) brings a cooler and wetter pattern here to the Northwest. And if you have lived through this Spring, you can surely attest to this being true. But in the summer, there is nothing out of the ordinary. So if I was to make a prediction for this summer I would say it would be climatoligically normal. 70s and somewhat dry. Now that isn't to say we won't see a heat wave (for our standards that's reaching the 90s) or get a little wet for a couple days, but according to the research we have on La Nina summers, there would be nothing out of the ordinary.

So what about an El Nino summer you ask? Practically the same.

The real impact is in the winter, not summer.

As you can see, the variations on climate are only clearly visible during the winter.

So what is the forecast for this summer?? Well the models run by the Climate Prediction Center have not narrowed down on one particular idea. Here is a plot of all the different models and how they are projecting our transition from La Nina.

The models (on average) are trending for us to reach a neutral winter for 2011-2012. Now I don't want to really "scare" anyone but our neutral winters here in the NW typically bring our strongest storms (I have not done a lot of research on this but maybe I shall). The December 08 snow storm was a neutral winter. Plenty of wind storms come through in neutral winters also.

We shall see how this plays out but for now, enjoy our NEAR 70 DEGREE FRIDAY!!

-Aaron

Recent National Weather

With a strong La Nina in place, a large scale pattern has arisen to some very cold temperatures here on the west coast and very violent and extreme weather in portions of the Midwest and Southeast. What happens is an upper level trough will set up over the west coast or Northwest and that means a ridge builds up over the Midwest or East coast. Fronts and mid latitude cyclones like to develop in between the trough and ridge where short impulses move along this wavelike pattern. Think about a rope that you move up and down. The up wave is the ridge and the down wave is the trough. If your moving the rope up and down but every once in a while jerk the rope, you’ll generate a shorter wave that moves faster than the big ones. It works the same way in the atmosphere in simple terms. These shortwave impulses move along the long-waves and they produce the low pressure systems in between the trough and ridge. Usually that location is just east of the Rockies and in the Midwest.

Another feature of this pattern is that winds tend to follow this large scale pattern higher up in the atmosphere, not near the ground. I don’t want to get into the physics of supercells, tornadoes, and clouds but you need plenty of moisture, wind, and heating for these things to take off. Well with the ridge over the Midwest, it allows a stream of moisture coming up from the Gulf of Mexico to collide with winds coming down off of the Rockies and central plains. In short, it is a breeding ground for these strong storms. It is also the time of year where the sun it getting stronger and the upper atmosphere layers have not quite warmed up. This leads to more buoyant air in lower levels and that air will rise as the cooler air sinks. This is another ingredient for storms called mixing, it helps create those towering cumulonimbus clouds (thunderstorms, also known as anvil clouds).

  Recently, since we have been stuck in this pattern, there have been a series of storms producing EF-3 tornadoes (out of a scale of 6). There will certainly be more to come as well. I'll talk about the physics and thermodynamics of these storms in another blog.

Intense Rain

If any of your were around downtown (Or U District as I was) you might have noticed that downpour of rain around 12 o'clock that even drenched the ducks at Drumheller fountain. It was a very sudden onset of very intense rain and the radar picture is a classic image of a typical Midwest front (yes, Mid-West, not Northwest).

The yellows are some very noticeable (intense) rainfall and the red is raining cats and dogs, very very heavy rain and probably hail. That "line" of heavy rain there is a classic representation of a front and actually, that back edge where there is no rain, the boundary between the rain and lack of it is where the front lies. It's pretty neat to see it in radar around here because it is typically quite hard to see it.

Now that wasn't the only rain from yesterday that bumped up the total rain in the guage yesterday. In fact, we broke a record at Sea-Tac yesterday with 1.47" of rain, a daily record. Today's record (the 10th) is only .87" and were are up to .48" already this morning at 8:54 as i'm writing this. I think it is possible we break another record today. But last night another round of rain moved in that I found quite impressive.

I happened to be going to bed around this time and lets just say I was awakened a few times during the night. This is probably the rain that pushed us over the record yesterday and bumped up our total rainfall for today just this morning.

We can expect a brief lull in between systems this afternoon as most of the rain is done, but the wind will continue through this afternoon. It will be breezy around the sound and some stronger winds in the Northwest Interior and the San Juans. That was Storm #3 last night in a series of 10 STORMS that are aimed at us over the next 2 weeks. Friday looks like the calmest day of the week with just scattered showers and some sun-breaks. Friday night is when Storm #4 moves in and #5 is expected Sunday. Scattered showers Saturday and Monday and #7 is aimed for Tuesday. Now the 10 Storm scenario was made with some longer range forecast that I'll call "unreliable" at that length (15 days). Not that the data is wrong, but it is extremely hard right now to forecast that far out (In a decade, maybe it won't be that hard to do). But for now #8 may scoot south. It still looks quite wet though