textproduct: Portland

SYNOPSIS

A broad low pressure system is spinning off of the Oregon and California border. This low is going to amplify high pressure over the region and promote gusty winds overnight into Saturday. Within the ridge, a weak shortwave will pass over late Saturday into Sunday bringing a quick shot of rain. Dry and cold conditions on Monday before additional rounds of rain on Tuesday through the remainder of the week.

LONG TERM...Monday night through Friday

After the cooler air mass, an inverted trough in the midlevels will bring in slightly warmer air. This warmer airmass is associated with an incoming warm front that arrives late Monday into Tuesday. A strengthening jet streak is present at 250 mb (35,000 ft) Tuesday morning and it is moving directly over the forecast area. This amplified lift combined with warm air mass and moisture will produce widespread rain. While initially it may not be heavy, it will intensify though the afternoon and evening. A concern that will have to be watched moving forward though is the presence of a low level jet at 500 mb. This jet is vertically oriented which could create breezy northerly winds along the coast into Wednesday morning.

Weather will maintain a typical fall pattern through the end of the week. -27

AVIATION

Flying conditions are expected to continue improving toward VFR across the region through this evening as high pressure begins to build inland. Areas of mist or lingering light rain showers with vis/cigs restricted to IFR have been observed early this afternoon, however the drying trend should see even these areas improve by 06z Sat. Elsewhere inland, there is only a 10-20% chance MVFR conditions continue beyond 02-03z Sat, with VFR cigs otherwise favored. Aforementioned high pressure building inland will see generally light winds turn offshore through tonight. Terminals downwind of terrain gaps will be the most likely to see stronger east flow, most notably at KTTD where sustained winds of 15-20 kt may gust over 30 kt tonight. Gusts in excess of 20 kt are expected to reach as far west as KPDX, and even coastal terminals including KAST/KONP may see east winds reach 10 kt. The only other potential for flight impacts through the period are low chances, 10% or less, for fog development within the central and southern Willamette Valley after 09-12z Sat. Persistent sky cover would act to limit these chances, as would enough clearing and cooling to support frost development. In either of these cases, chances for fog would be minimal.

KPDX AND APPROACHES...Building high pressure inland will see MVFR cigs continue improving to VFR in the next few hours while low cloud cover lessens and cloud bases lift to 4-5 kft. East winds will strengthen west of the Columbia River Gorge, reaching 10-15 kt with gusts of 20-25 kt at KPDX after 04-06z Sat and continuing through tonight. Gusts may not ease below 15 kt until 18z Sat. -36

MARINE

A weakening low pressure system continues to meander westward away from the coast of northwestern Oregon early this afternoon, yielding generally east winds at 5-15 kt to its north and southwesterly to southerly winds at 5-10 kt to its south. Winds will turn offshore across the waters tonight at around 10 kt, although areas immediately downwind of gaps in the coastal terrain, including west of the mouth of the Columbia River, may see locally stronger winds and gusts of 15-20 kt. Another weak low moving over the waters on Saturday will yield variable winds and seas of 4-7 ft before high pressure building offshore will see largely northerly flow late Sunday into next week. A long-period westerly swell will arrive late Monday into Tuesday, pushing seas toward 10 ft before easing back to 5-7 ft by Wednesday. -36

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...None.