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