April 2020 Recap and Stormy Weekend Potential

April 2020 is now in the books, and what a month it was (obviously not just relating to weather). We started the month with drier than normal conditions (you can read more about that here), and ended with slightly wetter than normal conditions. The graph below clearly supports that the total precipitation for the last 10 days of April was above normal at Paine Field.

Figure 1: Rain accumulation data for 4.21.20 to 4.30.20

In total, however, we were still unable to make up for the deficit at the start of the month, and we still ended up below average for the whole month (see Figure 3 below).

Here is a graphic that shows an overview of the temperatures for the month at Paine Field. No records were broken in terms of highs or lows, as illustrated by each blue bar staying within the bounds of the shaded red and blue areas. However, the average high temperature was just slightly above average.

Figure 2: Temperatures at Paine Field for April 2020

To summarize the month, take a look at the following graphic. It is important to note here that in the temperature category, the first column of data (“average”) refers to what actually happened in April 2020, while the second column is the average over several years of data.

Figure 3: April 2020 Summary at Paine Field

Shifting gears here, it is officially May, and after a great start to the month today, things start to get a little bit exciting.

After a weak system moves in overnight, a stronger one moves in Saturday, which brings with it rain and the potential for thunderstorms. The Storm Prediction Center (SPC) has included the area in the general thunderstorm category. Parts of Eastern Washington are even included in the “marginal” category of severe storms.

CAPE (Convective Available Potential Energy) values are forecast to be quite decent for our standards. Take a look at 21z tomorrow (which is 2 PM local time):

Figure 4: CAPE values according to the NAM for 2 PM Saturday

This run of the NAM puts 649 J/kg of CAPE at Paine Field, which is decent for our neck of the woods. NE Oregon and SE Washington looks to be a great setup for thunderstorms, some of which could be severe.

As a side note, in order for a thunderstorm to be considered “severe,” it must “contain one or more of the following: hail one inch or greater, winds gusting in excess of 50 knots (57.5 mph), or a tornado” (according to NOAA).

The primary threat for our neck of the woods should be wind gusts, so make sure to secure loose objects that could get potentially carried by strong gusts. The following graphic is for 3 PM tomorrow, showing wind gusts according to the NAM. Gusts of 36 mph are shown for KPAE, but it easily could exceed that if a strong storm develops.

Figure 5: NAM wind gusts at 3 PM tomorrow

The strength of storms that we get is contingent on whether we get sun breaks. The sun greatly destabilizes the atmosphere through surface heating–which enhances upward motion and thus, storms. If we get enough of a sun break tomorrow, our chances of thunderstorms will go up.

The chance for thunderstorms should decrease as the sun goes down because of the lack of surface heating from the sun. However, the chance again returns on Sunday. Although, the risk seems to be greater on Saturday.

If you see anything exciting, send it to me by posting it on my Facebook page or tagging me on Twitter!

I’m hoping that we get some action tomorrow, and I know I’m not the only one…here’s to some exciting weather to start out the month of May!

Abnormally Dry April About to Turn Wet

water droplets on clear glass

Much of this month has been the taste of Spring that many of us has needed as a sort of mood-booster during these uncertain times. There has been plenty of dry weather and sun to go around.

In fact, this mostly dry start is abnormal. Take a look at these charts showing the minimum 20 day precipitation total at both KSEA and KPAE:

Table 1
Table 2

These tables show the driest starts to the month of April on record for both Sea-Tac and Paine Field, respectively. Since records began in 1948, this has been the second driest start to the month of April at Sea-Tac…the driest since 1951! Paine Field isn’t quite as impressive, but it still sits at number 7 (although most of that total fell on April 18th).

This has been great to go outside for some walks or bike rides as we all continue to do social distancing. I know I’ve taken advantage of it by going on many bike rides!

Unfortunately (or fortunately, depending on who you are), our weather pattern is about to shift.

The first system is on deck by tomorrow, packing quite a punch for this April’s standards. You can see it on visible satellite imagery, lurking in the eastern Pacific.

Figure 1: Satellite image taken around 3:30 PM on 4.21.20

Take a look at the following GIFs, showing the 3-hour precipitation totals as the system moves into the area:

Figure 2: 12z Euro run of 3 hour precipitation for 4.22.20
Figure 3: 12z GFS run of 3 hour precipitation for 4.22.20

Much of the state looks to take a hit, with even Eastern Washington getting in on the action.

Figure 4: Euro Ensemble showing 24 hour QPF (accumulated rainfall) for KPAE

Figure 4 above suggests that this system could be one of the wetter ones on tap for the area in the next week or so. But it also shows that it’s not the only system on its way.

Showers decrease gradually throughout the day Thursday, with a mini ridge of high pressure taking shape. This should help keep Friday mostly dry, with the exception of some scattered showers. Yet, another system arrives late Friday into Saturday, with potentially a third following it (things could certainly change a week out from now). You can see the three spikes in the 24-hour QPF in Figure 4 corresponding to each system. The GFS shows similar spikes, as shown below.

Figure 5: GFS Ensemble showing 24 hour QPF for KPAE

By next week, both models are suggesting we could add an additional 2 inches of rainfall to our April total at Paine Field. The Euro and the GFS don’t agree as much at Sea-Tac, with the GFS showing just over an inch while the Euro is near the 2 inch mark.

If those totals came into fruition, our April rainfall deficit could be completely erased. To give some perspective, the normal rainfall for the month of April is 2.58 inches at Paine Field and 2.71 inches at Sea-Tac.

During this time, high temperatures should be close to normal.

This month has given all the sun-lovers something to rejoice over…but now it’s the rain-lovers’ turn!

They Say “April Showers Bring May Flowers”… So Where Are The Showers?

The majority of this month has been quite pleasant weather-wise. The sun and dry weather has served as a mood-booster for so many people in the midst of the COVID-19 pandemic. But it still begs the question…where is the rain?

Here is the Paine Field precipitation accumulation graph so far for the month of April.

Figure 1: Accumulated precipitation for KPAE, via NOAA

With the exception of some trace rainfall on April 11, all the rainfall has occurred in the first few days of the month, amounting to just 0.35 inches. The normal amount for this period is 1.48 inches.

When looking at the same graphic for Sea-Tac, we get a similar story.

Figure 2: Accumulated precipitation for KSEA, via NOAA

Except here, there has only been 0.01 inches of accumulated rainfall. You can hardly even see the green line on the graphic.

To put this into perspective, take a look at this tweet.

Much of California has been getting hammered by storms and rainfall and has significantly more than us here in western Washington. Even areas of Arizona have more than Sea-Tac! Wow.

So why has our weather been so nice recently? It has been the result of a ridge of high pressure that has been acting as a block, preventing storms from making it to our region. (You can read more about this in Cliff Mass’ blog, found here.)

And, spoiler alert, this nice weather is likely to continue through the rest of the week.

Highs today should be in the mid-to-upper 60s for most of us.

Overnight tonight, clouds begin to increase as onshore flow (i.e. from west to east) develops. As a result, Wednesday morning has a chance to start cloudy. But as the figure shows below, clouds should burn off by the afternoon. Because of the cloudy start, Wednesday’s highs could be slightly lower than today’s.

Figure 3: Cloud cover percentage (darks = less clouds, lights = more clouds)

Thursday and Friday look to be the warmest and nicest days of the week, with highs in the low 70s possible!

Figure 4: GFS high/low temperatures for KPAE
Figure 5: GFS high/low temperatures for KSEA

It should be perfect to go outside and go on bike rides, walks, and the like… of course maintaining social distancing 🙂

Some models/ensemble members of models show a chance for light showers on Saturday, but if anything falls, it likely won’t amount to much. Models are also suggesting the chance of some rainier weather next week, but it’s too far in advance to know for sure.

In the meantime, enjoy the sunny weather!