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Aviation discussion updated

AVIATION...31/00Z TAFs

VFR levels under clear skies persist across northern California and southern Oregon. Gusty north winds along the coast will ease into the evening. MVFR/IFR ceilings are possible along the coast late tonight into early Monday morning, but a slight easterly component to winds may limit ceiling development. Any coastal ceilings that do develop look to clear out before Monday afternoon. Elsewhere, VFR will continue to prevail for at least the next 24 hours.

PREV DISCUSSION

/Issued 302 PM PDT Sun Aug 30 2026/

KEY MESSAGES...

* Dry and windy conditions are expected on Monday, bringing critical fire weather concerns to the Scott and Shasta Valleys as well as broad areas east of the Cascades. Other areas may not reach thresholds, but have elevated concerns for similar conditions.

* Tuesday marks a transition to active weather expected on Wednesday. A cold front will bring below seasonal temperatures across the area. Rainfall is expected west of the Cascades, with lighter showers possible to the east.

* Light scattered showers and cool conditions are expected for Thursday and Friday.

DISCUSSION...Zonal flow aloft behind a trough moving off to the northwest will bring summery weather across northern California and southern Oregon today. Coastal cities will see periods of gusty winds this afternoon as well as chances for marine stratus to develop overnight. North-northeast overnight winds may keep the skies clear or reduce development.

An upper ridge passing over the area on Monday looks to raise daytime highs about 5 degrees for most Oregon counties. Northern Lake County may see temperatures increase by up to 10 degrees, while Siskiyou and Modoc counties will see smaller fluctuations. In addition to those warm and dry conditions, southerly flow will bring gusty winds into the Scott and Shasta Valleys, northeast Siskiyou County, Modoc County, southeast Klamath County, and southwest Siskiyou Counties. A Red Flag Warning has been issued for these areas as gusty winds and dry conditions reach critical levels.

Tuesday will be a transition day ahead of midweek active weather, so forecasting may change as models get a better hold on that change. The overall pattern has not changed; A weak shortwave trough will swing over the area ahead of midweek activity. Temperatures look to cool by 5 to 15 degrees for most areas, depending on the timing and path of that shortwave. This trough may bring some initial activity to western Siskiyou County and along the Cascades. While slight thunderstorm chances (5-15%) remain in the forecast for these areas, CAPE values trending lower and moisture trending marginally upward might mean that some light showers be a part of any thunderstorms that do develop. Those chances do linger into Tuesday night, then ease on early Wednesday morning.

On Wednesday, a cold front from an approaching low pressure system will bring cool temperatures and rainfall across areas west of the Cascades as well as some rainfall to the east. The most rainfall is expected over Curry County, with 1.0 to 1.5 inches at lower elevations and over 2 inches possible over terrain. Coos and northern Douglas counties as well as the Illinois Valley could see 0.75 to 1 inch of rainfall. Roseburg and westernmost Siskiyou County could see around 0.5 inches, with 0.25 inches possible in the Rogue Valley and northern Klamath counties. Eastern Siskiyou, southern Klamath, and northern Lake counties may see a few hundreths of an inch. Overall, impactful rainfall is not expected. However, as this is the first substantial rainfall in a while, water accumulation is possible in areas where debris blocks drainage routes. Additionally, oils may rise to road surfaces and bring locally slick conditions. Extra caution while traveling is advised.

For Thursday and Friday, the low pressure system lingers to the west just off the Oregon coast and keeps a trough over the area. Cool temperatures will continue through the end of the week. Shower chances linger but decrease to 40-60% on Thursday and 20-40% through Friday. The higher chances tend to stay west of the Cascades, but southwest flow around the trough may help light showers reach Modoc and southern Lake counties late Thursday into Friday morning.

Forecasting for next weekend is somewhat erratic, as ensemble members show a variety of outcomes. Meteogram guidance shows light activity continuing through the weekend. Beyond that, rain signals are a minority (10-20% for the ECMWF ensemble, 5-10% for the GFS) and are fairly erratic but are definitely not absent. -TAD

MFR WATCHES/WARNINGS/ADVISORIES

OR...Red Flag Warning from noon to 8 PM PDT Monday for ORZ624.

CA...Red Flag Warning from noon to 8 PM PDT Monday for CAZ280-281-284- 285.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Monday for PZZ350-356-370-376.