textproduct: Portland

SYNOPSIS

Generally dry conditions prevail through the upcoming week as we progresses further into October. Clear skies and cool nights increase chances for frost across a good chunk of the region to start the week. Temperatures trend warmer late week as an upper-level ridge amplifies over the region. Ensembles hint at the potential return of some rainfall towards the end of the weekend.

LONG TERM.... Wednesday to Saturday

Come the middle of the week, the majority of ensemble members are in agreement with upper-level ridging remaining slightly offshore of the U.S. West Coast before the axis of this ridge slowly shifts overhead late week. This will maintain mostly dry and warm conditions on Wednesday, however, we could see some increasing cloud cover as a system rides the northern periphery of the ridge and heads into northern Washington/British Columbia. Ensembles have nudged the track of this system a touch further north compared to previous runs which has dropped precipitation chances along the south Washington coast below 10-15%. Will also note the increased cloud cover will help to trend our low temperatures slightly higher and reduce the threat for widespread frost development.

Thursday and Friday when the upper-level ridge moves directly overhead, daytime temperatures jump into the 70s across interior valleys. Offshore easterly flow likely develops across the Cascades and in the Columbia River Gorge during this late week time-period too. Heading into the weekend, the upper ridge gets pushed further east by upper-level troughing coming down from the Gulf of Alaska. There remains uncertainty with the timing, position, and magnitude of the troughing at this point, but what we can say with higher confidence is that this pattern would return cooler temperatures and chances for precipitation for the weekend into the following week. -99/10

AVIATION...Through 18Z Monday

VFR conditions with mostly clear skies expected across NW OR and SW WA through the TAF period due to building high pressure over the region. North/northeasterly winds today, strongest along the coast and central/southern Willamette Valley at 10-13 kt with gusts to 20-25 kt. Elsewhere, winds remain around 4-7 kt. Winds decrease after 02-04z Mon, becoming light and easterly along the coast and variable inland.

Between 07-15z Mon, clear skies and calm winds will support temperatures falling towards 33-36 degrees F across much of the area outside of the Portland metro and as low as 28-32 degrees F in the Upper Hood River Valley. Locations that are able to cool down to these temperatures may see frost development on metal surfaces.

KPDX AND APPROACHES...VFR conditions expected through the TAF period. Northwesterly winds 4-7 kt today, becoming light and variable by 03-06z Mon. -03

MARINE

As of Sunday afternoon, seas north of Cape Falcon are less than 6-7 feet and not forecast to increase into the evening hours. Additionally, the period is fluctuating between 9 seconds and 21 seconds at buoy 46029 as the incoming high period westerly swell takes over at times. Because seas are not as steep as expected, the Small Craft Advisory for zones PZZ271 and PZZ251 have been cancelled. Seas south of Cape Falcon are increasing to around 8 feet, though the periods are also fluctuating between 9 seconds and 21 seconds. However, since the seas are higher, the Small Craft Advisories remain in effect, though have been cut back to expire at 8 PM PDT when the high period swell is forecast to become the main swell. The Small Craft Advisory for the Columbia River Bar remains in effect until 8 PM PDT due to a strong ebb increasing seas to around 7 to 8 feet, with the ebb peaking around 550 PM PDT today. Winds remain northerly today with gusts mainly less than 15-20 kts, though there will be a few occasional gusts 21-25 kts south of Cape Foulweather through this evening.

Benign marine conditions expected for the rest of the week. Winds gradually weaken on Monday and remain northerly through early Tuesday morning. Tuesday to Wednesday, winds turn more southwesterly ahead of an approaching weak front, but return northerly by the end of the week. Seas subside to 4 to 6 ft at 12 to 15 seconds with winds remaining below 15 kt. -03

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from midnight tonight to 8 AM PDT Monday for ORZ104-107-109-112>119-123>125. Freeze Warning from midnight tonight to 8 AM PDT Monday for ORZ121. WA...Frost Advisory from midnight tonight to 8 AM PDT Monday for WAZ202-204>208. PZ...Small Craft Advisory until 8 PM PDT this evening for PZZ210- 252-253-272-273.