What a change a month makes! Back on the 10th and 13th of March, we had two powerful windstorms roll through the area, with the one on the 10th causing lots of damage to the Northern Interior and creating a lot of coastal flooding and the one on the 13th making my last day of teaching ski lessons to kindergartners up at Alpental an adventure for the ages. Now, here we are, less than a month later, and we’re expected to hit the 80s throughout the area today. Springtime isn’t known for dramatic shifts in weather, but we can get these big ridges of high pressure that bring us exceptionally warm days, and after all the rain we’ve had, the change has never felt so dramatic.
One of my favorite tools for predicting the temperature on these warm days is the ProbCast tool developed by the Applied Physics Laboratory at University of Washington. As we obtain more and more computer power, ensemble forecasting (where we run a whole bunch of models with slightly perturbed initial conditions) is going to take over our more traditional, “deterministic” forecasting, where we run one model and base our forecasts off of that. The ProbCast tool gives the estimated high temperature based on multiple models, and also lists the 10% probability of the observed temperature exceeding or not reaching a certain temperature. My most memorable ProbCast experience was during our record heat wave of 2009, when Seattle hit 103 degrees, which was exactly what the Probcast was predicting.
Many news outlets are predicting the high temperature to be around 80 degrees or so. Let’s see what the ProbCast says!
85! Yikes! And there is a 10% chance that the temperature could exceed 89, meaning there is an outside chance the temperature could exceed 90! I personally think this is a little bullish and I don’t think we’ll hit 85, but low 80s is a good bet.
Here’s the ProbCast map throughout all of the Pacific Northwest for today. As you can see, many places west of the Cascades are forecast to be in the 80s – not just in Washington but in Oregon as well. If you want to escape the heat, go to Wyoming.
A big ridge of high pressure over our area is enough to make us warm and sunny, but the key to our record warmth is the offshore winds that are forecast to come down the Cascades into our area. As air sinks, it warms, and even though the air in the upper atmosphere is generally cooler than the air in the lower atmosphere, it warms at such a rate that by the time it reaches the lower atmosphere, it is often warmer than the air that was previously in place. The key to having offshore flow is to have higher pressure in Eastern Washington and lower pressure in Western Washington, and as the map below shows, we will have that today. It isn’t the biggest pressure difference, so winds won’t be too strong, but it is enough to bring us that warm, offshore flow while preventing the cooler, maritime, onshore flow from cooling off our neck of the woods.
On Friday, we’ll start to cool down in Western Washington, but we’ll still be pretty darn nice. Eastern Washington will see it’s warmest weather of the year. By Saturday, stronger onshore flow returns, cooling us off dramatically back into the 60s.
Enjoy the sun!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Charlie
