textproduct: Portland

SYNOPSIS

High pressure continues over the region today with mostly dry conditions expected through this evening. A weak front will bring chances for light rain tonight into Tuesday. Dry again on Wednesday. Active weather returns as a series of frontal systems bring increasing chances for rain later Thursday through the weekend. Seasonable temperatures continue through the week.

LONG TERM...Thursday through Sunday

Models and their ensembles are in good agreement that the upper level ridge remains over the northeast Pacific on Thursday. But, WPC cluster analysis does indicate high probability of the ridge breaking down and flattening out, allowing for more westerly flow into the Pacific NW Friday and into the weekend. This should allow for frontal systems to bring increased rainfall and more active weather to the area. Uncertainty in rainfall amounts remains moderately high, but extreme rainfall appears very unlikely. For example, the probability for IVT values > 250 kg/m/s from the coast to the foothills is quite high (greater than 80-90%) both Friday and Saturday, but the probability of IVT values greater than 500 kg/m/s is very low. Both the GEFS and ECMWF ensemble means suggest total precipitation amounts of around 2 inches near Astoria through Sunday. The NBM suggests similar amounts for Friday through Sunday (72-hour period), while the 90th percentile (10% chance of exceeding) suggests potential for total rainfall amounts nearing 3 to 4 inches. Still, more beneficial with minimal impacts expected. Will note that HEFS guidance does show increasing (but still low) chances for local rivers reaching action or minor flood stage, with the highest chances for coastal rivers (up to 5-15%) into early next week. /DH

AVIATION

An upper level ridge of high pressure will maintain predominately VFR conditions through at least 06z Tuesday. An exception to this is patchy stratus across parts of the southern Willamette Valley, as well as along the lower Columbia River near KKLS. MVFR CIGs are likely to linger near KEUG through 14-16z this morning, while LIFR CIGs should stay north of the Portland metro. Light and variable winds along with mostly clear skies this morning will allow for cooler temperatures into the lower 30s, which favors frost development.

By 06z Tuesday, probabilities for MVFR cigs around 3000 ft increase to near 50% at KAST as a weak front approaches the area. Light rain showers are likely to develop at KAST shortly after 06z Tuesday.

KPDX AND APPROACHES...VFR conditions expected through this evening beneath scattered high clouds. There is less than a 10% chance of IFR stratus approaching the terminal from the north early this morning. Expect temperatures this morning to drop into the lower 30s. Expect increasing clouds after 00z as a weak front approaches from the northwest. Chances for MVFR CIGs increase after 09z Tuesday. Light and variable winds expected today. /02

MARINE

With high pressure offshore today, will see north to northeast winds to around 10 kt, while seas remain around 4 to 6 ft. A weak front traversing the waters tonight into Tuesday will shift winds to northwest, increasing up to 15-20 kt, while a long period westerly swell builds seas to around 9 to 10 ft on Tuesday. Have issued a Small Craft Advisory for the outer coastal waters north of Cape Foulweather to cover this marginal threat.

Winds and seas ease midweek as high pressure returns. A more active weather pattern develops late in the week as a series of frontal systems is expected to moves across the waters from Thursday into the weekend. There remains a 20-40% chance of seas rising above 10 ft again Friday into Saturday. /DH

BEACH HAZARDS

A long-period westerly swell is expected along the northwestern Oregon and southwestern Washington coasts from late Monday through Wednesday next week. Wave heights increasing to 8 to 10 ft on Tuesday may not appear to present a safety risk to those on area beaches, but these energetic waves will present a moderate to high risk for sneaker waves, waves which can run significantly farther up a beach than normal, including over rocks and jetties. In addition, a period of perigean spring or "king" tides means these waves will have an even easier time reaching high up onto beaches, limiting the areas which may be safe from wave action.

A Beach Hazards Statement has therefore been issued from 7 AM Tuesday to 10 PM Wednesday. Sneaker waves can create potentially life-threatening conditions in the surf zone when beachgoers can be unexpectedly knocked off their feet and pulled out into cold ocean waters. Caution should be used when in or near the water, and those with children should be especially watchful. Never turn your back on the ocean, and be sure to keep an eye on the waves. Those participating in razor clam digs should additionally exercise caution. -36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 4 AM to 10 PM PST Tuesday for PZZ271- 272.