The Unusual: Normal Weather

Weather is like one's children:  for most of the time you think of it as being exceptional.

And to be honest, I give short-shrift to normality in the blog, since I love to talk about the unusual, the extreme, and the interesting weather situations.

But today I am going to break the mold and tell you that for the last week the weather has been excruciatingly normal.  Boring to some, perhaps.

Take temperatures at Seattle Tacoma Airport for the past week (see chart below with normal highs and lows in red and blue, respectively).  Pretty typical stuff.

Sea-Tac precipitation?  The actual (red) is within .1 inches of normal during the same period.  You are probably starting to yawn.

Clouds...plenty of them, with a few breaks.   Totally normal in late April.

These normal conditions are found throughout the state.   For example, Pasco's temperatures during the same time are.....completely typical:

The famous U.S. Drought Monitor:  no drought in our State, except for some slight dryness over the far southeast.

The official Climate Prediction Center precipitation forecast for the next 3 months for Washington?  EC (equal chances if above or below normal)....which means a forecast of normal.

This is simply maddening.... normal is not good for the weather business.  

Destabilization

The air above us has cooled down substantially compared to a week ago, with temperatures near 5000 ft (850 hPa) on the WA coast at -1.1C this morning, compared to 16C in the middle of the heat wave last week.      But the sun is even stronger being a week later and it has the ability to substantially warm the surface.

So with cool temperatures aloft and strong warming at the surface, a large vertical temperature gradient (or lapse rate) developed, one that allows the lower atmosphere to destabilize and convect.

Yes, just like in your hot cereal, when you rev up the heat, the cereal starts to convect--some cereal moving up, some moving down.  Convection results when temperature in a fluid decreases rapidly in height.  In the case of a dry atmosphere, the temperature must decrease by at least 9.8C per kilometer.

In the atmosphere today, instead of upward and downward convection currents in the oatmeal, we have convecting air parcels, with clouds (cumulus) forming with the upward motion.   Today's satellite picture documented the convecting action. At 7:40 AM, there was a lot of layered (stratiform) low clouds over our region (see satellite picture).  These are generally stable clouds without much vertical development.

The the strong late-April sun did its magic over land during the morning and that warming, coupled with cool temperatures above, caused instability and convection over land.  The satellite image at 12:15 PM shows this clearly in the puff-ball looking clouds.  Over our coastal waters it was virtually clear....same with the Strait of Juan de Fuca.  The water surface did not heat up.

The shallow nature of the convection was evident in local weather cams, such as my favorite SkunkBay Weather cam on the north side of the Kitsap Peninsula (see below)

And for those of you who like to have plenty of water during the summer, there is very good news.  The Yakima River reservoir system, so critical for agriculture in the Yakima Valley, has now reached the typical full level, but nearly two months earlier than normal  (see image)

The same thing is true for the City of Seattle reservoirs (red line below).

 There is still plenty of snow to melt int the mountains, unlike last year, so things look very good regarding water for this summer.