textproduct: Portland

SYNOPSIS

Persistent onshore flow will bring near-average temperatures with varying degrees of morning clouds and afternoon sunshine for much of the next week. A series of weak fronts will bring notable chances for light rain and drizzle to portions of the north Oregon and Washington coast Tuesday and Saturday.

DISCUSSION...Now through Saturday

The latest satellite and radar imagery depicts cloud cover along the coast and coast range, extending westward out over the Pacific. Conditions are mostly clear east of the coast range with a few fair weather cumulus developing. Southwest flow in the mid levels is expected to persist as an upper level trough sits over the far northeast Pacific. This is supporting a weak cold front that is moving over the area and bringing light rain and drizzle to the coast north of Tillamook and into Pacific county in Washington. Conditions dry out this evening and overnight lows drop into the 50s for most locations.

Marine stratus is expected to develop overnight, mainly impacting coastal locations but could see some low clouds in the Portland metro and southern Willamette Valley to start the day. Dry and seasonable conditions expected on Monday as upper level heights increase slightly, supporting temperatures in the low 80s for interior lowlands and 60s along the coast. By Tuesday, another shortwave will push the weak boundary back toward the coast, yielding light rain chances on the coast and within coastal terrain north of Tillamook, with the highest likelihood again in Pacific County, WA. Reinvigorated marine cloud cover associated with the boundary will also see temperatures cool a few degrees again on Tuesday, before heights again rebuild aloft, favoring a slow warming trend through the remainder of the workweek. Ensemble members continue to highlight another chance for a shortwave and weak surface front to support cooler temperatures and light rain chances along the north OR/southern WA coast late in the week, but uncertainty in the timing and placement of this feature remains high at this lead time. -19/36

AVIATION...Through 06z Tuesday

A dying frontal boundary will stall near the Oregon coast and across western Washington tonight. This will maintain southwesterly flow aloft across the region with a greater than 80% chance that conditions deteriorate into a mix of MVFR and IFR conditions along the coast while conditions primarily remain VFR for inland TAF sites. With that said, marine stratus is anticipated to develop over the Cascade foothills overnight and back build westward into the Willamette Valley. There is uncertainty whether ceilings will form around 4- 5kft or end up being lower if they develop. Around 30-40% of the high resolution models suggest MVFR ceilings will occur at most of our inland TAF sites during the 09-15z timeframe. With that said, our best statistical model suggests the probability for MVFR ceilings at any given hour only tops out around 10-20% for our inland TAF sites during that time. If MVFR ceilings do develop, they appear most likely to dissipate between 17-19z Monday.

KPDX AND APPROACHES...Onshore flow will maintain predominantly VFR conditions through 06z Tuesday with around a 20% chance for MVFR ceilings at any given hour between 12-18z Monday.

MARINE

A weak front continues to move east, bringing light showers to the waters off the south WA and north OR coasts through the evening. Southwest winds around 10 kt with gusts to 15 kt. Seas remain in the 4-6 foot range at 9-10 seconds through the middle of the week. Winds will shift to a more seasonable northerly pattern behind another passing frontal boundary on Tuesday. Strengthening northerly flow will see increasing chances (30-50%) for peak diurnal wind gusts to reach 20-25 kt Wednesday and Thursday afternoons, especially within 10 NM of the coast. Seas otherwise continue at 4-6 ft through the remainder of the week. -19/36

PQR WATCHES/WARNINGS/ADVISORIES

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