textproduct: Portland

SYNOPSIS

Conditions remain dry with well above average temperatures. Easterly winds will gradually weaken as a trough approaches. A weak cold front will bring chances for light rain late tonight into Saturday morning, before high pressure returns dry weather Saturday night into Sunday. The next chances for rain are Monday into early Tuesday with an approaching low pressure system, although guidance continues to trend drier.

LONG TERM...Sunday through Thursday

Dry weather expected on Sunday as flow aloft becomes more zonal with the passage of the shortwave trough. Highs very similar to Saturday peaking in the mid 60s for most interior lowlands and mid 50s to low 60s along the coast. Sunday night into Monday morning will bring another chance for frost in the Upper Hood River Valley and the southern Willamette Valley as lows could drop into the mid to upper 30s.

Cluster analysis continues to depict a trough impacting the region Monday and Tuesday but trends have the trough taking a more southeast trajectory and just glancing NW OR and SW WA. Approximately 40% of ensemble members have light QPF for the Portland area while 60% of members have light QPF around Newport. Models continue to track this trough more towards northern California, limiting any decent rainfall across the forecast area. Chances for 24-hour rainfall totals exceeding 0.25 inches between 5 AM Monday to 5 AM Tuesday have dropped to 10-15% along the coast and coast range, southern Willamette Valley, and the OR Cascade Foothills.

By Wednesday, ensembles show the upper trough swinging into central California, while weak high pressure shifts over the Pacific Northwest, favoring predominately dry conditions. At the same time, it does appear that another upper-level trough will begin to approach British Columbia and potentially make its way down into the Pacific Northwest late next week, returning chances for precipitation. -19/DH

AVIATION...Through 12Z Saturday

Mainly VFR conditions expected though a few patches of fog have developed under mostly clear skies. Intermittent fog has been reported by KONP and KEUG but may not stick around long. Marine stratus is expected to develop this afternoon as a trough approaches and winds turn more westerly. Conditions along the coast start to deteriorate with probabilities for MVFR/IFR CIGs increasing to around 50% at 20Z and further to 70-80% after 6Z Saturday. This disturbance will also bring light rain after 6Z, mainly around KAST. Easterly winds remain strong through the western Columbia River Gorge and into the eastern metro. KTTD is still registering wind gusts over 30 kt but should gradually trend lower through the day as the pressure gradient weakens. Winds elsewhere will become northwesterly around 5 kt this afternoon.

KPDX AND APPROACHES...VFR with clear skies through the TAF period. Light winds becoming northwesterly less than 5 kt. -19

MARINE

Benign marine conditions continue. Northwest winds turn southerly this afternoon into the evening as a weak front passes through. Winds turn back to the northwest on Saturday behind the front. Seas remain around 4-7 ft at 10-12 seconds through early Saturday morning.

A steeper northwesterly swell arrives this weekend, building seas to 7-9 ft by Saturday evening and 10-13 ft early next week. Uncertainty remains on how high seas will rise early next week due to uncertainty on the track of the low pressure system associated with the swell. There is a 15-30% chance for seas exceeding 15 ft on Monday, with the highest chances beyond 30-40 NM. Will also note that the long periods from the swells will result in a moderate sneaker wave threat Friday into early next week. Caution should be used when in or near the water. -19/03

PQR WATCHES/WARNINGS/ADVISORIES

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