textproduct: Portland

SYNOPSIS

A weak front will bring chances for rain across southwest Washington and along the far north Oregon coast into Monday morning, while the Willamette Valley, Cascades, Cascade foothills stay dry. A very strong high pressure system will strengthen and remain anchored over the Pacific Northwest Tuesday through next weekend. This will result in long stretch of dry weather with abnormally mild temperatures and light winds. Expect at least 6 to 8 consecutive dry days in a row with generally clear skies at night and a lot of sunshine.

LONG TERM...Tuesday through Saturday

As the middle of the week approaches, a ridge of high pressure (mentioned in the short term discussion) will start to build over California and the entirety of the Pacific NW. This will result in warming conditions as well as clearing skies across the forecast area. High pressure aloft, will result in a thermally induced surface trough developing. This will support weak offshore flow to calm winds developing as well as a robust subsidence inversion. These conditions will bring degraded air quality/stagnation concerns back into the forecast, if the high pressure persists for an extended period of time. Diving into the models, 850 mb temperatures range from 11 C to 15 C and that means daytime highs in the mid 50s to low 60s through the end of the forecast period. Normal high temperatures for mid January are in the mid to upper 40s within the Willamette Valley and Portland metro.

Models and their ensembles, along with the WPC 500 mb clusters and the Climate Prediction center, are in very good to excellent agreement that an anomalous ridge of high pressure will persist over the Pacific NW, with climatology showing conditions within the 95th-99th percentile of normal. 500 mb heights look to peak around 580-590 dam. The next variable is the length of time that this high will remain anchored over the region. Leaning towards the more conservative time, models have this high remaining over the region for 6 to 8 days. However, some model solutions are suggesting an even longer time frame pushing past 10 to 12 days. Lastly, some model runs are showing the ridge briefly weakening Wednesday night/Thursday.

To put this in more digestible words: A strong upper level high, that is very rare for this time of year, is expected through the majority of the upcoming week and likely into next weekend. Overall, prepare for at least 6 to 8 days in a row with no precipitation at all across all of northwest Oregon and southwest Washington and temperatures remaining well above normal for this time of year. /42

AVIATION

Expect generally VFR conditions to persist through the evening hours as high pressure buckles overhead thanks to a frontal system passing just to our north. While the majority of the region remains dry, KAST will be the exception with light rain arriving 00-03z Sun. Otherwise, further inland, it's going to be another tricky fog/low stratus forecast tonight into Sunday morning across the Willamette and Tualatin valley since additional high cloud cover is slated to stream overhead limiting radiational cooling. KHIO, KUAO, KSLE and KEUG have the best chances (15-45%) to see surface visibilities drop below 1 SM 06-18z Sunday, with the highest relative chance at KHIO (45%). Have hinted at lowering visibilities where confidence is highest - largely a persistent forecast from what we saw this (Saturday) morning. VFR conditions likely continue at KPDX, KTTD, and KONP due to a combination of high clouds and light easterly flow.

KPDX AND APPROACHES...VFR conditions continue with CIGs AOA 10kft and winds around 5-10 kt or less through the TAF period. Currently probabilities for MVFR-IFR CIGs/VIS are only around ~10% between 14-20z Sunday. -99

BEACH HAZARDS

There is a high threat of sneaker waves at the coast through Monday due to a continued long-period southwesterly to westerly swell. Sneaker waves can create potentially life- threatening conditions as waves may run farther up the beach than expected. These waves can easily catch people off guard and cause beachgoers to be knocked off their feet and pulled out into cold ocean waters. Never turn your back to the ocean. Caution should be used when in or near the water, and those with children should be especially watchful. Sneaker waves can lift or roll large, heavy logs or rocks which can lead to serious death or injury. Keep off rocks, logs, and jetties near the waterline on beaches.