Synopsis

Conditions will remain dry and unseasonably warm in the 70s and low 80s through Thursday. An incoming weather system Friday will bring chances for rain and mountain snow as well as cooler temperatures and gusty winds.

Discussion

Tuesday night through Thursday: A ridging pattern remains in place over the region, keeping mostly clear skies, light winds, and a subtle warming trend in the forecast through Thursday.

Looking at temperatures, afternoon highs will generally range throughout the 70s to around 80 degrees, around 10 to 15 degrees above climatological normals for early October. Despite the warm daytime temperatures, overnight/early morning lows will still be chilly as is typical during the autumn months as the nights get longer. Strong radiational cooling under clear skies and light winds will support low temperatures dropping into the mid to upper 30s for the sheltered northern valleys. Patchy fog and frost has been observed in these valleys the past several mornings and will likely recur each morning through Thursday. For most locations outside of the sheltered northern valleys, lows will be in the 40s. A few readings in the 50s are forecast at the foothills of the Cascades and Blue Mountains, where downsloping winds will keep nighttime temperatures warmer.

Friday through Monday: Confidence is increasing in the forecast for Friday into early next week. 70 percent of ensembles now show a trough dropping down the coast of British Columbia and over the Inland Northwest Friday afternoon into Saturday. As the trough begins moving in from the north and tightening the pressure gradient across the region, winds will pick up out of the west. Sustained speeds will range from 15 to 25 mph for most locations with the highest winds through the Cascade gaps and across the Columbia Basin eastward into the Spokane area and the Palouse. Wind gusts have trended stronger in latest model runs with widespread gusts of 35-40 mph in the forecast.

In addition to gusty winds, Friday's weather system will usher in significantly cooler temperatures. Afternoon highs on Friday will be in the upper 60s to upper 70s. By Saturday, highs will decrease by 10-20 degrees, topping out in the 50s for most areas. Highs remain in the 50s Sunday and Monday. Overnight/early morning lows will be noticeably cooler as well. Friday morning will see lows in the 40s to low 50s - similar to what we've been seeing the past few days. Saturday morning will feel much chillier in the 30s to low 40s.

Lastly, the system will bring returning chances for precipitation. Initially, strong westerly flow will result in a prominent rain shadow over much of Central and Eastern WA, keeping precipitation focused over the Cascade Crest and ID Panhandle mountains. As the system shifts further south, precipitation will wrap around the low, bringing precipitation chances to the northern mountains and east slopes of the Cascades Saturday into early Sunday. By late Saturday night, some of this precipitation could fall in the form of snow as snow levels drop to around 4000 feet.

Heading into Sunday, the trough continues its southward trek into Oregon and Northern California, shifting moisture and precip chances out of the region. Winds, however, will continue. High pressure to our north and low pressure to our south will create a north-to-south pressure gradient, resulting in another round of gusty winds out of the north Saturday night into Sunday. Strongest winds are expected down the Okanogan Valley onto the Waterville Plateau and into the Columbia Basin as well as down the Purcell Trench. Expect sustained speeds around 20 mph and gusts of 35-40 mph for the aforementioned areas.

Overall, we're about to enter a much more fall-like pattern. The seasons are changing! /Fewkes