textproduct: Portland

SYNOPSIS

Weak front with light showers shift eastward today. Onshore flow persists through the next week. High pressure begins to build through Friday with Friday expected to be the hottest day this week. Another system arrives on Saturday which will bring increasing probabilities of precipitation and westerly winds.

LONG TERM...Thursday Night through Tuesday

The trough in the northeast Pacific will remain through much of the weekend but on Thursday, a brief shortwave with an associated weak front will pass north of the area, but stratus may fill. On Friday, while onshore flow persists, a weak ridge forms which will usher in warmer air to the region. 850 mb temperatures will reach around 15 deg C in the afternoon and the 850-250 mb RH difference remains very dry. Therefore, Friday will likely be the hottest day of the week though not anywhere near record breaking. Within the Willamette Valley we will see temperatures in the mid to upper 80s with some areas, especially urban ones, reaching 90. The coast will be beautiful in the mid to upper 60s.

This warm up will be short lived though as the trough previously mentioned traverses eastward. A cooler frontal system will dip down over the region increasing precipitation chances, and bringing in cooler air. Temperatures will likely drop by around 10 degrees or so on Saturday with increasing chances for precipitation. Most models are keeping the bulk of the rain to the north, but there remains around a 30-40% chance of measurable rain over the terrain of southwest Washington and the coast north of Tillamook. Overall though, accumulations will be light. As is common with cold frontal passages, the environment will become convective however thunderstorms are not expected at this time. We are missing a bulk of the instability that we would need to see another thunderstorm outbreak. Another component is wind. In generally, wind will be temperature and pressure gradient driven with the highest wind speeds through the E-W aligned terrain like the Columbia River Gorge and the passes of the Cascades.

Onshore zonal flow remains through early next week with dry conditions expected. -27

AVIATION...Through 00z Thursday

VFR conditions were being observed at all terminals as of 2130Z Tuesday with ceilings generally above 5000-6000 ft, except near 3500 ft at KAST. Ongoing cloud cover is mainly associated with a decaying cold front that moved inland earlier today. Radar observations showed light rain showers occurring ahead of this front over the northern Coast Range, however these showers will not impact any of the TAF sites.

The main uncertainty with the aviation forecast is exact ceiling heights late tonight into tomorrow morning, as well as whether or not cloud cover will be predominately scattered or broken. The latest guidance currently suggests a broken cloud deck will attempt developing over the north Oregon Cascades and portions of the Willamette Valley and Portland metro between 06-12Z Wednesday. However, probabilities currently favor low-end VFR ceilings with this potential stratus deck. Probabilities for MVFR ceilings below 3000 ft peak between 10-16Z Wednesday between 15-35% at all TAF sites, except 45-55% at KAST.

KPDX AND APPROACHES...Scattered clouds with ceilings at or 7000 ft are expected today, resulting in VFR conditions. VFR conditions will most likely remain in place through 00Z Thursday, however there is a 15% chance for MVFR ceilings below 3000 ft between 10-16Z Wednesday. Light and variable winds around 5 kt are expected to become northwesterly late this afternoon, with gusts up to approximately 15 kt with an incoming sea breeze. -23

MARINE

Buoy observations from early to mid Tuesday afternoon showed seas remaining within the 4 to 6 foot range. These seas are expected to continue with a dominant west to northwest swell at 7-9 seconds and a secondary long-period south-southwesterly swell persisting through much of the week. Northwest winds will develop over the waters Tuesday evening in the wake of a cold frontal passage. North winds on Wednesday will become lighter and back to the south on Thursday with another weak frontal passage.

Yet another weak front looks to traverse the waters early this weekend, after which northwesterly flow will strengthen and veer out of north into early next week as high pressure builds offshore. Confidence in wind gusts of at least 20-25 kt is moderate to high on Sunday, increasing from around 60% west of the mouth of the Columbia to greater than 90% offshore of Florence. Those chances are even higher on Monday, some 90-95% or higher across the coastal waters. The chances for gale-force gusts on Monday are low but not negligible, generally 10-20% south of Cape Foulweather as well as within 10 NM of the coast from Cape Falcon to Cape Foulweather. -36/23

PQR WATCHES/WARNINGS/ADVISORIES

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