textproduct: Portland

SYNOPSIS

A cool and somewhat unsettled pattern will persist through the weekend as upper-level troughing remains over the Pacific Northwest. Periodic marine pushes will continue to bring morning cloud cover inland, while weak disturbances may produce occasional light precipitation along the coast and at higher terrain. Forecast uncertainty increases into early next week as ensemble solutions diverge on the pattern.

DISCUSSION...Now through Wednesday

Upper-level troughing remains the dominant feature over the northeast Pacific, maintaining a cool air mass and persistent onshore flow across the region. Another push of marine stratus is expected tonight into Friday morning, with clouds likely reaching well into the interior lowlands. Despite the cloud cover, precipitation chances remain low, with most locations staying dry. Temperatures Friday should remain in the upper 70s across the interior and 60s along the coast.

The broader trough will remain in place through Saturday, although another weak disturbance may enhance precipitation chances, particularly north of a line from McMinnville and Mollala. Ensemble guidance currently gives a 20-60% chance of measurable rainfall across these areas. Any precipitation that develops is expected to be light, with the coast, Coast Range, and Cascade foothills favored for the highest chances. Continued onshore flow will also maintain the potential for morning marine stratus across the interior. By Sunday, the upper-level low shifts east and a shortwave ridge forms, allowing temperatures to increase 1 to 3 degrees into the upper 70s across interior.

Looking into early next week, ensemble guidance continues to favor a cooler and potentially wetter pattern, but confidence remains limited. An increasing number of ensemble members support measurable precipitation across a larger portion of the forecast area, though there remains substantial spread in the timing, amplitude, and eventual position of the upper-level trough. Further refinement will be possible as the pattern becomes better resolved. Lastly, to give a rough approximation of expected precipitation early next week, probabilistic guidance suggests chances for at least 0.01 inches of rain over 48 hours from early Tuesday to late Wednesday ranges from 70-90%. As for chances of higher amounts of rain, there is a 40-70% chance for 0.25 inches, 25-50% chance for 0.50 inches, and a 5-30% chance for 1 inch. ~12

AVIATION...Through 06z Saturday

An upper-level trough extending over the Pacific Northwest will support continued onshore flow and increased nighttime chances for restricted cigs as marine stratus pushes inland. Cloud coverage will increase initially along the coast, with high confidence in MVFR cigs, but only moderate chances for IFR, highest along the central Oregon coast (70% at KONP) and decreasing to the north (30% at KAST). Inland, chances for MVFR cigs increase through the night, reaching 50-70% at KTTD and KEUG by 11-13z Fri and 30-50% at other inland terminals. Low clouds will erode through the morning, with a return to VFR conditions by 16-18z Fri inland and 18-21z Fri along the coast. North to northwest winds of 3 kt or less tonight will build to 5-10 kt inland and 8-12 kt along the coast by midday Friday.

KPDX AND APPROACHES...VFR conditions expected to prevail throughout the period, with moderate chances, 40-50%, for MVFR cigs from 13-17z Fri as marine stratus pushes inland. Low clouds will then tend to erode by midday Friday. Northwest winds ease to 3-5 kt tonight, then build to 5-8 kt by Friday afternoon. -36

MARINE

As low pressure near Vancouver Island weakens, high pressure continues to build in across the NE Pacific. Light southerly winds veer westerly later this afternoon, becoming north-northwesterly by early Friday. Winds are expected to remain around 10-15 kt or less. A weak front drops into the northern coastal waters late Friday into Saturday with little to no impact expected. Northerlies persist through the weekend while predominately wind driven seas remain at around 3 to 5 ft. The pattern may become a bit more active early to the middle of next week as there is potential for multiple frontal systems to move into the coastal waters. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.