textproduct: Portland

DISCUSSION...Now through Saturday

High pressure near the surface continues to linger overhead as an upper-level trough of low pressure well off the coast transitions into a closed low and dives into California. This pattern supports continued calm conditions across the region albeit with some weak easterly/offshore flow today, turning a light onshore for Monday. High temperatures both today and Monday generally rise into the upper 60s to low 70s across the inland valleys which ends up falling just a degree or two short of our normal high temperatures for this time of year. Tonight into Monday morning clear skies and light winds, especially in sheltered valleys, will promote efficient cooling which may led to two potential impacts. The first is for isolated pockets of frost in some of our high mountain valleys, like the Upper Hood River Valley, as low temperatures could again fall into the mid to upper 30s. However, chances for temperatures to drop below 36 degrees are only around 15-20% come Monday morning. The second impact is patchy fog potential during the sunrise hours where low-level moisture, the aforementioned efficient cooling, and light winds overlap. The central and southern Willamette Valley, Coast Range valleys, and Cascade valleys are among the more favored locations for fog. Any fog should be localized and dissipate by late morning.

The next meaningful change arrives Tuesday as a upper-level trough and weakening frontal boundary move into the region. The highest confidence for measurable precipitation remains along the north Oregon coast and Coast Range into southwest Washington, where precipitation probabilities now sit around 60-90% during the day Tuesday before decreasing Tuesday night into Wednesday morning. Some precipitation may extend into the northern Oregon Cascades as well. Farther inland and lower in elevation, the signal for rainfall much weaker, with only around 10-30% of ensemble members indicating more than a trace of precipitation in the Portland metro and Willamette Valley Tuesday through Wednesday morning. Thus, inland valley locations likely end up mostly dry through this midweek period especially the further south you go.

Dry conditions are expected to return by midday Wednesday at the latest through Thursday. Ensemble guidance becomes increasingly spread out late next week but the larger-scale flow remains fairly progressive overall. Some solutions favor another weak trough and cooler conditions with a few light rain chances along the coast on Thursday, while others maintain zonal flow or weak ridging and generally dry weather. Specifically, the latest ensemble clusters are as such: 35% weak troughing, 35% weak ridging, and 30% roughly zonal. There is not yet enough agreement to favor a specific outcome, that said, the weather related impacts from any of these scenarios appear rather benign. -99/12

AVIATION...Through 12Z Monday

Primarily VFR conditions are expected through the TAF period. Early this morning a scattered to broken high level cloud deck AOA ~20,000ft continues to move across portions of the region however the central and southern Willamette Valley have begun to clear more noticeably while winds lighten. This may pave the way for patchy fog/low stratus development again between 12-16z with IFR/LIFR conditions. The best chances for degraded conditions (30-40%) appear to be at KEUG and to an extent KONP/KSLE (10-25%) with only a 5-10% chance elsewhere. Should any fog/low stratus occur it will quickly clear by 16-17z at the latest. North winds increase again along the coast to 15-20 kt by 19-21z today, though they remain generally less than 10 kts inland.

KPDX AND APPROACHES...VFR conditions are anticipated through the TAF period. Thanks to high clouds overnight into this morning and northerly winds keeping the atmosphere mixed, chances for morning fog/low stratus are very low, only ~5% locally at PDX. North to northwest winds around 5-10 kt through the period. -99

MARINE

Expect northerly winds to persist across the coastal waters today thanks to lingering high pressure near the surface helping to facilitate gusts up to 20-25 kts at times. There'll likely be a short lull in wind gusts this morning, mainly across the inner waters, before they increase again this afternoon into the evening. Small Craft Advisories remain in effect through 11 PM PT Sunday. Wave heights will remain around 4-6 ft at 8-10 seconds through tonight.

Then our focus shifts to a frontal boundary approaching the waters on Monday shifting winds more westerly during the daytime hours then eventually southerly Monday evening. This frontal feature finally moves through the waters the second half of Tuesday. There are high chances (70-90%) of wind gusts exceeding 21 kts(Small Craft Advisory criteria) late Monday into Tuesday for the coastal waters north of Cape Falcon, with gusts most likely peaking around 25-30 kts. Lighter northerly winds return Tuesday night. A longer period west to northwesterly swell of 5-8 ft at 12-16 seconds will also move into the coastal waters late Monday through Wednesday, resulting in a moderate sneaker wave threat and increasing significant wave heights into the 6-9ft range. While seas gradually fall into Thursday, models hint at the arrival of another WNW swell of similar magnitude around Friday. -99/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 5 AM PDT early this morning for PZZ210. Small Craft Advisory from 2 PM this afternoon to 8 PM PDT this evening for PZZ210. Small Craft Advisory until 11 PM PDT this evening for PZZ251>253-271>273.