textproduct: Portland

SYNOPSIS

A cool and increasingly unsettled pattern will continue through the end of the week as upper-level troughing settles over the Pacific Northwest. Periodic marine pushes and weak frontal passages will bring increasing cloud cover and low chances for precipitation, with the best opportunities along the coast and higher terrain. Temperatures may briefly rebound Sunday, although uncertainty increases into early next week.

DISCUSSION...Now through Tuesday

Upper-level troughing over the northeast Pacific continues to shift northeastward towards British Columbia, with cooler air gradually spreading into the Pacific Northwest. This onshore wind pattern resulted in marine stratus funneling into the interior lowlands early this morning, but has already burned off inland as of noon, leaving just broken stratus along the coast. Temperatures will remain near seasonal norms today, with highs in the low 80s inland and 60s along the coast.

Another surge of marine stratus is expected tonight into Thursday morning as onshore flow strengthens. A shortwave embedded within the broader trough will move across the region Thursday morning, accompanied by a weak frontal boundary. Precipitation chances remain highest along the coast and Coast Range, generally 10 to 30 percent, with locally higher chances of 30 to 40 percent across Pacific County. Elsewhere, measurable precipitation chances remain 5 percent or less. Cooler air accompanying the disturbance will lower interior highs into the mid to upper 70s Thursday, while coastal locations remain in the 60s. Little change is expected Friday as the upper trough remains in place. Continued onshore flow will favor another round of morning marine stratus, with afternoon temperatures remaining in the mid to upper 70s across the interior.

A reinforcing disturbance may bring a better opportunity for precipitation Saturday, particularly across areas north of Salem. Current ensemble probabilities for measurable rainfall are around 15 to 30 percent, although considerable uncertainty remains regarding the strength and track of this feature. Temperatures should remain on the cool side, with highs generally in the mid 70s.

The upper-level pattern begins to flatten during Sunday, which should allow temperatures to gradually recover toward the upper 70s to maybe 80. However, ensemble guidance continues to show considerable spread heading into early next week, with some solutions favoring renewed troughing and precipitation while others maintain a more progressive and drier pattern. Confidence therefore remains relatively low beyond the weekend, where high temperatures could reach anywhere between 70 and 80 degrees. ~12

AVIATION...Through 06z Friday

An upper-level low offshore will continue to bring onshore flow and support the inland penetration of low marine clouds through tonight. At the coast, MVFR/IFR cigs are favored through the morning, although there is only moderate confidence, 40-70%, in IFR occurrence, highest along the central Oregon coast and decreasing to the north. At inland terminals, the highest chances for MVFR cigs are along the Lower Columbia, in the Portland area, and in the southern Willamette Valley. MVFR chances reach 50-70% in the hours around sunrise, from 12-17z Thu. Widely scattered rain showers are possible near the upper low, with 30% chances for restricted vis within light rain at KAST from 16-22z Thu. Otherwise, conditions should tend to improve through the day Thursday to VFR inland and MVFR at coastal terminals. South to southwesterly winds around 5 kt overnight will build to 5-10 kt by midday Thursday, although gusts to 20 kt are expected closer to the low at KAST. Winds then veer through westerly to northwesterly by Thursday evening.

KPDX AND APPROACHES...VFR conditions likely to prevail into tonight, with increasing chances for MVFR cigs after 12z Thu, reaching 50-70% from 14-17z Thu before low clouds begin to mix out. Southerly winds around 3-5 kt through tonight steadily veer to southwesterly through Thursday morning to northwesterly by Thursday evening. -36

MARINE

Low pressure centered 300 miles west of the Washington coast will continue to track toward Vancouver Island through Thursday. Southerly winds will continue across the coastal waters, generally around 10-15 kt. A weak front will move across the waters Thursday morning briefly increasing southerlies up to 20 kt. Could see a brief period of isolated gusts up to 25 kt across the inner waters north of Cape Falcon and around the Columbia River Bar between 8 AM and 2 PM.

High pressure begins to rebuild over the waters later Thursday into Friday returning north to northwest winds across the coastal waters into the weekend. Predominately wind driven seas are expected to remain around 3 to 6 ft through the weekend. Somewhat more active pattern may return early next week. /DH

PQR WATCHES/WARNINGS/ADVISORIES

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