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.

SHORT TERM...Now through Saturday Night

Upper level ridging will continue shifting east as troughing over the northeast Pacific and Alaska progresses eastward. Conditions remain dry across the region with another day of above normal temperatures. Highs in the mid to upper 70s across the interior lowlands, 10-15 degrees above the normal low to mid 60s. Highs along the coast will be much closer to normal as the offshore pressure gradient continues to weaken, allowing westerly onshore flow to return and marine stratus to push into the coast. Highs expected to top out in the low to mid 60s. High level clouds will also increase through the day as the upper level trough progresses. The offshore pressure gradient between Troutdale and the Dalles will continue to weaken through the day which will gradually decrease easterly winds to less than 10 mph by the afternoon.

An embedded shortwave trough passing to the north will glance the region, sending a cold front through the area tonight and into Saturday morning. This will bring moderate to low chances of light rain to northern portions of the forecast area for Saturday morning. Mean QPF values range from a trace to 0.10 inch, generally north of Lincoln City at the coast and from the Portland metro area northward, with highest chances for rain in the southwest WA Cascades. Conditions expected to dry out by the afternoon with northerly winds behind the front. Highs will be closer to normal, topping out in the mid to upper 60s across the interior valleys. Will need to keep an eye on Saturday night as clouds clear and temperatures drop into the 30s. Outside of the Cascades, the coolest temperatures are expected in the Upper Hood River Valley. -19/DH

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 18z Saturday

Largely VFR conditions expected through 00z Sat along the coast and through 12z Sat inland. High cloud coverage will tend to increase ahead of an approaching front. Marine stratus will see 70-90% chances for IFR cigs at coastal terminals after 00-03z Sat, before chances for rain increase after 06-09z Sat. Highest confidence in rain is along the north OR/south WA coast (KAST, KTMK). Inland, chances for MVFR cigs reach 60-70% after 12z Sat while the chances for rain peak at 30-60% from 12-15z Sat.

Gusty east winds continue through the western Columbia Gorge, supporting continued gusts to 20-30 kt at KTTD into this afternoon before the offshore pressure gradient eases as the frontal boundary approaches. Elsewhere, light winds inland and west to northwest winds along the coast will turn out of the south to southwest at around 5 kt ahead of the frontal passage.

KPDX AND APPROACHES...VFR conditions with increasing high cloud cover through this evening and into tonight. A passing front will bring chances for MVFR cigs and light rain from 12-15z Sat. Light east winds may reach the terminal this afternoon before turning southerly ahead of the frontal passage tonight. -36

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.