Hotter & Drier Conditions Ahead

FastCast—Thursday, Sep. 14 to Sunday, Sep. 17:

A change is coming in the weather for the Pacific Northwest, with hotter and drier conditions likely through Saturday, beginning to cool on Sunday. In the lowlands, expect highs in the upper 70s to mid 80s, hottest on Friday and Saturday. Conditions will also be quite dry, with relative humidity in the lowlands dropping to 25-40%. There are still multiple burn bans in effect across Washington state, so be very mindful of any kind of burning before we get significant rain. Highs will drop to the mid to upper 70s on Sunday. Expect morning lows through Sunday in the upper 40s to low 50s across the region.

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Continue reading the full blog below!

With a significant high pressure ridge building over the region through Saturday, weather will get significantly warmer and drier. Let’s take a look at the forecast!

We’ll compare and contrast the European and GFS (American) forecasts for Thursday, Friday, and Saturday to see the differences in temperature possibilities.

First, let’s take a look at Thursday’s highs on the European model, seen below.

This forecast shows Thursday’s highs reaching the mid to upper 70s (isolated low 80s) in the lowlands, the mid 60s to mid 70s on the coast, and the mid to upper 80s (isolated low 90s) in the Willamette Valley. Eastern Washington will reach the upper 70s to upper 80s.

Next, we’ll compare this to the GFS forecast for Thursday, seen below.

The GFS Thursday forecast shows lowland highs in the low 70s to low 80s, hottest from Tacoma south. This forecast also shows the low to mid 70s on the coast, mid to upper 80s in the Willamette Valley, and upper 70s to upper 80s in Eastern Washington.

We’ll continue on to the European model forecast for Friday.

This forecast shows lowland highs in the mid 70s to low 80s (isolated mid 80s around Shelton & Olympia). Coastal highs will reach the mid 60s to mid 70s (except low to mid 60s at the beaches), and the Willamette Valley will increase to the upper 80s to low 90s. Eastern Washington will increase to the low 80s to low 90s.

Let’s compare this to the GFS forecast for Friday, seen below.

On Friday, the GFS shows lowland highs in the mid 70s to mid 80s, hottest from Seattle south. The coast will reach the mid 60s (low 60s at the beaches), and the Willamette Valley will reach the upper 80s to low 90s. Eastern Washington will increase to the low 80s to low 90s.

Finally, we’ll look at Saturday’s forecasts. Saturday has the most disagreement between the European and GFS forecasts. The European model forecast is below.

The European model shows cooling west of the Cascades on Saturday, with lowland highs in the upper 60s to mid 70s north of Seattle, and in the mid to upper 70s south of Seattle. This forecast shows the coast reaching the upper 50s to low 60s, the Willamette Valley reaching the low to mid 80s, and Eastern Washington increasing to the upper 80s to mid 90s.

The GFS forecast shows a completely different scenario for the lowlands, seen below.

The GFS forecast for Saturday shows lowland highs reaching the mid 70s to low 80s from Seattle northward, and the low to mid 80s from Seattle southward. This forecast shows the coast reaching the mid 60s to low 70s (except the low 60s on the beaches), the Willamette Valley reaching the upper 80s to low 90s, and Eastern Washington reaching the low 80s to low 90s (cooler than the European).

So, what is causing all this September “heat”? The answer is seen below, in the European model upper-air forecast.

This forecast shows a high pressure ridge over the Western US and British Columbia on Friday. This ridge will bring the heat. Also, note Hurricane Lee off the Eastern Seaboard, heading north toward New England and Nova Scotia.

One positive about this period of hotter temperatures is that morning lows will be quite pleasant, especially west of the Cascades. Below is the European model forecast for Friday morning’s lows.

Expect morning lows in Western Washington to reach the upper 40s to low 50s, with isolated areas remaining in the mid 50s. Eastern Washington (except Spokane and the North Cascades) will be warmer overnight, with lows in the upper 50s to upper 60s, and the Willamette Valley will have lows in the mid to upper 50s. 

This pattern of relatively “cool” morning lows for Western Washington will continue over the next few days.

Stay tuned for more updates about the weekend forecast and beyond!