textproduct: Portland

SYNOPSIS

A weak frontal system will move in today, returning cooler temperatures and light rain through Saturday. Cool nights will bring chances for morning frost in rural valleys away from urban cores this weekend into early next week. Dry conditions with seasonable temperatures are expected Sunday and Monday before chances for precipitation return mid-week.

SHORT TERM...Today through Sunday night

Upper-level troughing is entering British Columbia as of early Friday morning, and radar and satellite imagery depicts the associated surface front moving into the Olympic Peninsula with a band of light rain. This decaying front will continue to progress southeastward, bringing rain to the north Oregon and south Washington coasts by 5-8 AM, and the I-5 corridor by 8-11 AM. The best chances (60-90%) for rain totals exceeding 0.10 inch today are across the north Oregon Coast Range, Willapa Hills, and south Washington/north Oregon Cascades due to orographic enhancement. Meanwhile, areas along the central Oregon coast and within the Willamette Valley are more likely to stay drier given that this system is relatively weak and tracking further north. Chances for exceeding 0.10 inch across the Willamette Valley today remain around 20-40%.

When it comes to winds, will see breezy west/northwesterly winds peaking around 25-35 mph with the initial frontal passage across the south Washington coast, Willapa Hills, north Oregon Coast Range, Columbia River Gorge, and Upper Hood River Valley. Could see some locally higher gusts of 35-45 mph for higher peaks and exposed ridgetops. Can't rule out some isolated gusts up to 50 mph along the central Columbia River Gorge (5-10% chance). Everywhere else, winds generally remain light and non-impactful.

As the upper trough progressing eastward into the Canadian Rockies, a second shortwave impulse will move south on its western flank on Saturday. Will see the trough elongate and eventually pinch off into a closed upper low, which will settle south over California by early next week. This feature will produce a second chance of light rain later Friday night into Saturday as scattered showers develop within the cooler air aloft. The rain from this second shortwave will be even lighter, as chances for exceeding 0.10 inch of rain across northwest Oregon and southwest Washington fall to 10-30%, with even lower chances as you head south of Salem and Lincoln City.

As the core of cooler air aloft moves overhead behind this general system, temperatures will quickly fall back toward seasonal norms in the upper 50s and 60s today and Saturday. Overnight lows will similarly trend cooler, especially tonight. Tonight into early Saturday morning, there is high confidence that higher elevation portions of the Upper Hood River Valley near Dee and Parkdale will see temperatures in the mid 30s, resulting in an elevated potential for frost. A Frost Advisory is in effect for portions of the Upper Hood River Valley County late tonight into Saturday morning.

Conditions dry out by Sunday as low pressure exits the region and upper-level ridging builds aloft. Temperatures warm up a few degrees on Sunday but remain near seasonal norms. Sunday morning will feature a near-repeat of Saturday morning, if not colder under more clear skies and calm winds. This would favor increasing chances (20-40%) for frost in sheltered valleys away from urban areas and a freeze within the Upper Hood River Valley. -10/DH

LONG TERM...Monday through Thursday

Ensemble guidance remains in good agreement that the elongated upper trough will drop southward into California by early next week. Meanwhile, upper level ridging over the NE Pacific will nudge back over the region, leading to dry and more seasonably warm temperatures into the mid to upper 60s. By Tuesday-Wednesday, 45% of ensemble members are showing troughing dropping down from Canada, returning chances for precipitation. Meanwhile, the other 55% continue to show weak ridging over the region, maintaining drier conditions. However, by Thursday, the majority of ensemble members are hinting at more amplified ridging over the Pacific Northwest, suggesting a continuation of dry conditions with slightly warmer temperatures. -10/DH

AVIATION...Through 12Z Saturday

Satellite imagery and terminal observations as of early Friday morning depicts widespread marine stratus along the coast bringing IFR/MVFR CIGs, while stratus is beginning to develop across portions of the Willamette Valley. MVFR stratus is forming in the east Portland Metro and Salem, which is expected to expand early this morning. There is also LIFR fog at KEUG. A weak frontal system will move in later this morning, which will increase mixing across the Valley. Rain is already starting along the north Oregon coast and will spread into the Valley by 15- 18z Fri. Once the front moves through this morning and rain begins, increased mixing will help lift CIGs and dissipate any fog. This will be a quick-moving front, as rain will taper off behind the front after 21z Fri. From there, will see a return of predominately VFR conditions across all terminals tonight. Increasing west/northwesterly winds around 5-10 kt across the Valley, and 9-12 kt along the coast with gusts up to 21 kt at KAST. The more northern track of this system will favor stronger winds for northernmost terminals.

KPDX AND APPROACHES...MVFR CIGs through 18z Fri with rain beginning around 15-18z Fri. Increased mixing will support CIGs lifting to VFR after 18z Fri. Decreasing showers and increasing cloud breaks expected this afternoon/evening. West/northwesterly winds 5-8 kt. -10

MARINE

A frontal system will move through the waters today, bringing breezy northwesterly winds with gusts up to 25 kt. Given that the front will be coming out of the north, will see winds strengthen first over the waters north of Cape Falcon this morning, then gradually increase toward the south throughout the day. A northwesterly swell will also follow behind the front, resulting in seas building to 10-13 feet at 9-10 seconds by this evening. Small Craft Advisories go in effect this morning for the waters north of Cape Falcon, but due to steep and choppy seas near 12-13 ft, a Hazardous Seas Warning was also issued for the waters beyond 10 NM and north of Cape Falcon beginning this afternoon. Small Craft Advisories for the waters south of Cape Falcon begin this afternoon and last through early Saturday morning, mainly for 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. -10

PQR WATCHES/WARNINGS/ADVISORIES

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

WA...None.

PZ...Small Craft Advisory from 11 AM this morning to 5 AM PDT Saturday for PZZ210.

Small Craft Advisory from 8 AM this morning to 5 AM PDT Saturday for PZZ251.

Small Craft Advisory from 2 PM this afternoon to 2 AM PDT Saturday for PZZ252-272-273.

Small Craft Advisory until 2 PM PDT this afternoon for PZZ271.

Hazardous Seas Warning from 2 PM this afternoon to 5 AM PDT Saturday for PZZ271.