Tuesday, April 5, 2016

Another Beautiful Week On Tap

Wow, what a change in weather we have had! From the wettest winter on record to two consecutive weeks with temperatures above 70 degrees! Our transition from autumn to winter is swift, but our transition from winter to spring usually takes a little bit more time. It certainly hasn't taken much time so far!

Last week, many places around Western Washington, including Sea-Tac, got into the 70s on Thursday and Friday. Although some morning clouds prevented us from reaching those same temperatures in the lowlands on Saturdays - temperatures were extremely warm in the mountains. I was skiing up at Alpental and was absolutely boiling. It was stunningly beautiful though, and I had a lot of fun.

The reason last week was so nice was because we had a large, persistent "Omega Block" right over our area, giving us clear skies, warm temperatures, and for some people (including myself), terrible allergies. We will also be warm and sunny later this week, but the warmth won't last for an extended period of time. However, Thursday in particular will be much warmer than any day last week.

Let's take a look at the WRF-GFS 1000-500 hPa thickness chart. I love this chart because it does a great job of quickly showing which areas are expected to be warm and which areas are expected to be cool. This is because "thickness" between two pressure levels is a function of density, and the less dense the air, the higher the thickness.

Here's what the thicknesses are like over the West Coast around 11 am this morning. As you can see, we have a ridge to our south with relatively high thicknesses over the area, but in order to get into the 70s, you'd want that ridge to become stronger and you'd want thicknesses to be in the 560s or higher.

Valid 11:00 am PDT, Tue 05 Apr 2016 - 6hr Fcst
 Credit: University of Washington Atmospheric Sciences

Wednesday morning, we look a little better. Right now, I think that Sea-Tac will stay below 70 on Wednesday, but I would not be surprised if they got all the way into the low 70s.

Valid 08:00 am PDT, Wed 06 Apr 2016 - 27hr Fcst
Credit: University of Washington Atmospheric Sciences

But wow, look at Thursday afternoon! Thursday is expected to be our warmest day of the week, with temperatures in the upper 70s for many locations. Sea-Tac's record high for that date was 78, set back in 1996. I think we are going to break it!!!

Valid 05:00 pm PDT, Thu 07 Apr 2016 - 72 Fcst
Credit: University of Washington Atmospheric Sciences

Another thing to look at is what the actual temperatures are like in the upper levels of the atmosphere. The Storm Prediction Center has a really cool tool where you can see the average and record values for a given parameter throughout the entire year. These parameters were measured using radiosondes - those big weather balloons with instruments that travel up to 100,000 feet through the atmosphere, taking measurements along the way.

850 hPa temperature climatology at Quillayute (UIL)
Credit: Storm Prediction Center

The 850 mb temperatures at 5 pm Thursday are forecast to be 16-17 degrees Celsius, which would set a new record not only for April 4th but for all of February and March as well, and possibly even January and April. Needless to say, it will be extremely warm in the upper atmosphere, and that warmth will make its way down to the surface.

Valid 05:00 pm PDT, Thu 07 Apr 2016 - 60 Fcst
Credit: University of Washington Atmospheric Sciences

A key factor for making temperatures really toasty here in the lowlands is the existence of offshore winds. We should have offshore flow on Thursday, with the foothills getting the strongest offshore flow and thus warming up the most. This will hold true for the coast as well - places like Forks (and, to a lesser extent, Quillayute) get a warming, offshore flow from the Olympics. I suspect that most places on the coast will set new record highs on Thursday.

On Friday, the ridge moves east of the area, but we should still have enough residual warmth to squeak out another day in the 70s. We cool off for the weekend, and beyond that, we look seasonable, with highs in the upper 50s to lower 60s with periods of light rain at times. Definitely a far cry from the intense windstorm we saw less than a month ago!


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