Weather Lookup

Synopsis

Mostly clear skies and calm winds may bring frost and/or fog development across much of NW or and SW wa in the mornings through monday. Mostly dry conditions through monday. Low chances for scattered showers monday night, then precipitation chances increase later next week with limited weather impacts expected.

Discussion

Through friday...visible satellite imagery early saturday afternoon shows areas of fog/stratus across some inland valleys with mostly clear skies elsewhere. Afternoon temperatures are expected to warm into the mid- 50S, before quickly falling into the 40S after sunset this evening. The upper trough that has been spinning just offshore all week became elongated offshore overnight and is slowly pushing inland today through tonight. This will bring a 20-40% chance of showers to mainly the lane and linn county cascades and foothills this afternoon and evening, decreasing around midnight. Valley locations should remain dry with just some high clouds overhead.

Dry conditions continue sunday into monday as an upper level ridge of high pressure builds over the pacnw behind the trough passage. Skies are expected to clear after midnight tonight, which combined with calm winds is expected to lead to another round of widespread fog or low stratus across inland valleys sunday morning. Radiational cooling is also expected under these conditions, which will allow minimum temperatures outside of urban areas to cool into the mid to upper 30S. Fog/low stratus should dissipate by midday with sunny skies and high temperatures in the 50S. Expect a rinse and repeat of this forecast on monday.

Today's 12Z ensemble guidance has come into much better agreement on the overall weather pattern through midweek next week, though some uncertainty on specifics still exist. Guidance indicates a low pressure system will develop in the eastern pacific early next week as the high pressure moves inland over the pacnw. The majority of ensemble members indicate this low will move inland somewhere in northern ca or along the ca/or border late monday through tuesday. Currently the forecast has a 10-25% chance of scattered showers monday night into early tuesday with very limited rain amounts, though depending on the strength and north to south extent of this low, these chances could decrease in subsequent forecasts. Tuesday through most of wednesday look to dry out with temperatures warming to near 60 degrees for the interior lowlands. Then precipitation chances increase again late wednesday into friday as ensemble members indicate another front or two could bring a couple more rounds of moisture to the area. At this point, no significant precipitation impacts are expected with any of these weather systems, though there's a 25-50% chance of wind gusts increasing over 30 MPH along the coast (5-20% chance inland) with each frontal passage late in the week. -03

Aviation

Through 00Z sunday...satellite imagery and terminal observations as of early saturday afternoon depicts predominately VFR conditions for most terminals except for the central and southern willamette valley, where there is a mix of MVFR/IFR/LIFR cigs. The further south in the valley you go, the lower the cigs. Satellite imagery shows stratus slowly dissipating across the valley, so expect remaining stratus to persist through about 21-23Z sat.

Tonight, will see another around of LIFR conditions due to fog and low stratus across valley terminals as high pressure builds aloft and brings increasing cloud breaks. Guidance suggests a 30-60% chance for vis < 1/2sm across the valley at any given hour between 12-17Z sun. However, typical foggy spots such as khio and keug could see fog as early as 06-07Z sun based on what we saw last night. Fog/stratus development is favored across the rest of the valley by 11-13Z sun. Light north/northwest winds around 5 KT or less across the valley this afternoon, becoming calm overnight. Light easterly winds continue at the coast which will support VFR conditions at kast/konp through the taf period.

Kpdx and approaches...IFR cigs through 19-20Z sat, improving to VFR afterwards with high clouds. Tomorrow morning, there is a 20-40% chance for LIFR vis due to fog at any given hour between 12-17Z sun. Northwesterly winds around 5 KT or less today, becoming variable overnight. -10

Marine

Weak low pressure offshore gradually dissipates today as winds decrease below 10 KT. Seas around 4 to 5 ft continue to subside to 3 to 4 ft into sunday morning. Offshore winds develop late sunday night and persist into early next week. A long period west-northwest swell also arrives sunday evening, building seas to around 7 to 9 ft at 16-19 seconds on monday. Chances for seas over 10 ft on monday remain at around 30-50% across the outer waters. This long period swell will result in a moderate threat for sneaker waves at the coast sunday evening through tuesday. Caution should be used at beaches when in or near the water.

A weak low pressure system approaches the waters mid next week, returning light southerly winds. By the end of the week, model guidance hints at a stronger system entering the waters, resulting in a 60-80% chance for maximum wind gusts exceeding 21 KT on friday with a 30-50% chance for seas exceeding 15 ft. -10/dh