A trof of low pressure swinging out of the Gulf of Alaska can be seen on satellite this morning, which will signal a major change in our weather pattern beginning on Thursday. Ahead of the approaching weather system, today we will see slight warming with highs near 90 and west winds 5-10 mph. As we go into the evening hours, a developing onshore flow will bring a shallow marine layer toward the Cascades and result in increasing west/northwest winds down the East Slopes of the Cascades. We will see winds tonight in the Wenatchee Valley 10-15 mph. This will lead to a bump in fire weather concerns as dry humidity values persist on the leeward side but the late timing and strength of winds should keep readings below critical thresholds for this first push. The trof will swing into Western Washington Thursday afternoon and across Eastern Washington overnight ushering a dry cold front through. Winds will become gusty into the afternoon and evening hours with a general west to southwest trajectory 10-15 mph during the day tomorrow with gusts up to 32 mph Thursday night. This will promote the next critical fire weather day for the combination of gusty winds and low humidity values. A fire weather watch is in place from 3:00 p.m. tomorrow to 8:00 p.m. tomorrow night. Temperatures on Thursday will cool a few degrees over Central Washington as well with highs tomorrow in the mid to upper 80’s. As those west winds pick up on Thursday we will also see improving air quality throughout the Wenatchee area.
Then on Friday and right through early next week we can expect cooler than average temperatures and a deep westerly flow that will continue to produce improved air quality across the Pacific Northwest especially by Friday and Saturday. Afternoon high temperatures in the extended period will drop below normal in the upper 70’s and low 80’s which should contribute to decreased fire activity. More importantly higher humidity (especially at night) should slow fire activity especially over the big fires in the north Cascades beginning Thursday night. British Columbia fires should also produce less smoke with the arrival of the cooler, higher humidity air mass. Areas of smoke may still be possible though across Okanogan, Ferry and Stevens counties Friday and Saturday.
By Sunday night and into Monday, the medium range weather models continue to provide hope that a significant rain event will occur. A vigorous area of low pressure will arrive from the north Sunday night into Monday. This provides a scenario that may produce more widespread rain than we have seen in many weeks. We have a 20-30% chance of showers both Sunday night and Monday.
On Tuesday, we can expect a dry and cool day with afternoon highs in the upper 70’s to lower 80’s.