textproduct: Portland

SYNOPSIS

A weak cold front will progress eastward over the Cascades this evening, bringing an end to any lingering rain showers for most locations. Chances for light showers increase slightly on Saturday, however most locations will stay dry through the day with noticeably cooler temperatures. Cool nights will bring chances for morning frost in rural valleys away from urban cores this weekend into early next week. Dry conditions are expected Sunday through at least Monday, with chances for light rain increasing slightly late Tuesday. Temperatures trend a bit warmer late in the week with dry weather as upper-level ridging amplifies over the region.

SHORT TERM...Now through Sunday night

Radar, satellite, and surface weather observations from early Friday afternoon depicted a narrow band of rain occurring along a southwest-northeast oriented cold front draped over the northern Willamette Valley, Portland-Vancouver metro, Columbia River Gorge, and south WA/north OR Cascades. Behind this weak front, isolated light showers and sprinkles were being observed. As this front continues progressing eastwards over the Cascades this evening, rain will quickly come to an end aside from a few stray showers. Observed rain totals are generally topping out between a trace and 0.10 inches, except for slightly higher amounts at the coast and over higher terrain. While this isn't very much rain, it at least breaks our impressive 13-day dry streak.

Observed wind gusts with this frontal passage have generally peaked between 15-30 mph, resulting in little to no impacts. However, westerly winds in the central Columbia River Gorge and on exposed ridgetops adjacent to the Gorge are not expected to peak until later this evening immediately behind the frontal passage. These areas can expect max gusts between 25-45 mph, strongest on exposed ridgetops. Even then, wind impacts should be minor.

Although rain will quickly end this evening in the wake of the cold front, chances for rain will increase again late tonight into Saturday. This is in response to a closed upper-level low that is set to move southward over the region on Saturday, bringing wrap-around moisture on the relatively cooler backside of the low over western WA/OR. Given the light and showery nature of precipitation on Saturday, rain totals will be even lighter than Friday for most locations (70-90% chance rain amounts will be less than 0.10"). In fact, many locations will see little to no rain at all on Saturday, especially downwind of higher terrain where rain-shadowing will be most pronounced.

It is also worth noting that clearing skies over the Upper Hood River Valley tonight may support lows dipping into the 30s depending on how quickly westerly winds come to an end. If winds become calm early in the night, lows could easily drop to 33-36 degrees. If winds hang on until sunrise, lows would struggle to fall below 40 degrees. The current forecast suggests winds will become lighter by 4-5 AM, which would allow temperatures to quickly plummet thereafter until sunrise, with areas of frost likely forming shortly before sunrise in wind-sheltered areas where lows below 37 degrees are possible. Dee and Parkdale have the best chance for frost development by sunrise on Saturday (80-90% chance), and these areas have a Frost Advisory in effect to cover this threat. Odell may see patchy frost as well, however chances are relatively lower at around 35-45%.

Chances for more widespread and impactful morning frost increase considerably Saturday night into Sunday morning given clear skies and calm winds will be in place through the night. There is high confidence for frost and morning lows between 33-36 degrees over the Upper Hood River Valley, Cascade foothills, north Oregon Coast Range valleys, Battle Ground/Brush Prairie area, and portions of the central/southern Willamette Valley to the east of the I-5 corridor near the foothills (e.g. Lebanon, Scio, Albany, Halsey, Brownsville, Sweet Home, Marcola, Mohawk, Jasper). Sub-freezing temperatures less than 32 degrees are likely in Dee and Parkdale (70-90% chance). Therefore, various Frost Advisories are currently in effect where confidence in frost formation is highest. Anyone growing outdoor plants that are susceptible to frost damage should cover plants or move plants indoors if possible. -23

LONG TERM...Monday through Thursday night

The long term forecast is highlighted by seasonable temperatures Monday through Wednesday with temperatures becoming warmer and above average late in the week as an upper-level ridge over the far northeast Pacific early in the week becomes more amplified and moves over the U.S. West Coast. This set-up will bring mainly dry conditions Monday through Thursday night, with one potential exception late Tuesday into Wednesday morning when chances for light rain increase to 10-30% as a weak cold front over the coastal waters attempts pushing inland. Even if this front is able to move inland, it would be decaying, which suggests rain amounts would likely be very light (a trace to 0.10 inches, if any at all). Currently around 50-70% of the total ensemble space from the 00Z/Oct. 9 iteration of the ENS/GEFS/GEPS shows no rain at all Tuesday into Wednesday, with rain most favored over southwest WA, coastal areas, and higher terrain. No impacts are expected with this front.

For temperatures, expect chilly morning lows to continue Monday morning and Tuesday morning, especially in rural areas and sheltered valleys where lows in the mid 30s will support frost. Locations that currently have Frost Advisories in effect for Saturday night/Sunday morning are the areas with the highest chances for continued frosty mornings with lows below 37 degrees on Monday and Tuesday (40-65% chance, except 80-90% in the Upper Hood River Valley). Afternoon temperatures will be much more mild, with highs in the mid to upper 60s over the lowlands Monday through Wednesday, warming into the upper 60s to mid 70s on Thursday. -23

AVIATION...Through 00Z Sunday

A mix on conditions continue to affect the airspace as a frontal system moves through the area. While coastal terminals have improved to VFR as of 21Z Fri, a mix of conditions from VFR to IFR continue at inland terminals as rain reduces CIGs and VIS. Expect these deteriorated conditions to mix out by 22Z Fri, resulting in VFR conditions throughout the airspace, of which will continue through at least 08Z Sat. Around 08-12Z Sat, chances for low stratus/fog increase at a few terminals, notably at KONP, KHIO, and KEUG with chances of LIFR conditions around 10-20%. As for other terminals, there is a 15-25% chance of MVFR CIGs. Any deteriorated conditions that occur will likely improve back to VFR by 18-20Z Sat.

Otherwise, west/northwesterly winds around 6-12 kt continue across the interior lowlands, then ease around 03Z Sat. Along the coast, 10-15 kt winds with gusts up to 21 kt will ease around 03-06Z Sat.

KPDX AND APPROACHES...VFR conditions through the period. West/northwesterly winds around 5-9 kt will ease after 03Z Fri. There is a 15-25% chance of MVFR CIGs between 12-19Z Sat. ~12

MARINE

A frontal system has moved through most of the waters today, with the remainder of the front moving through the waters south of Cape Foulweather as of 2 PM. Breezy northwesterly winds with gusts up to 25 kt continue tonight into Saturday morning over the waters north of Cape Falcon. With this frontal system bringing a northwesterly swell, seas will build to 9-12 ft at 9-10 seconds from north to south over most of the waters this evening through Saturday afternoon.

As a result of seas building and becoming steep and choppy, a Hazardous Seas Warning remains in effect for the outer waters north of Cape Falcon until 5 AM Saturday. Additionally, Small Craft Advisories remain in effect over all of the waters (including the Columbia Bar) except for the inner waters south of Cape Foulweather and outer waters north of Cape Falcon until 2 PM Saturday due to steep and choppy seas of 8-10 ft at 9-10 seconds. By Sunday, winds weaken and veer out of the north/northeast while seas fall back to 6-8 ft through early next week. ~12/10

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from midnight Saturday night to 9 AM PDT Sunday for ORZ104-106-113-117-121-123>125.

Frost Advisory from midnight tonight to 9 AM PDT Saturday for ORZ121.

WA...Frost Advisory from midnight Saturday night to 9 AM PDT Sunday for WAZ205-208.

PZ...Small Craft Advisory until 2 PM PDT Saturday for PZZ210-251.

Small Craft Advisory until 2 PM PDT Saturday for PZZ252-272-273.

Hazardous Seas Warning until 5 AM PDT Saturday for PZZ271.

Small Craft Advisory from 5 AM to 2 PM PDT Saturday for PZZ271.